Maharashtra Board Class 11 Biology Chapter 15 Excretion and Osmoregulation Solutions

Excretion And Osmoregulation Class 11 Exercise Question Answers Solutions Maharashtra Board

Class 11 Biology Chapter 15 Exercise Solutions Maharashtra Board

Biology Class 11 Chapter 15 Exercise Solutions

Exercise 13(A)

1. Choose Correct Option

Question (A). Which one of the following organisms would spend maximum energy in production of nitrogenous waste?
(a) Polar bear
(b) Flamingo
(c) Frog
(d) Shark
Answer: (b) Flamingo
In simple words: Flamingoes are uricotelic birds, producing uric acid, which is energetically more costly to synthesize than urea or ammonia but requires very little water for excretion, a beneficial adaptation.

🎯 Exam Tip: Remember the types of nitrogenous wastes (ammonia, urea, uric acid) and their associated energy costs and water requirements for excretion. This is a common comparative biology question.

 

Question (B). In human beings, uric acid is formed due to metabolism of -
(a) amino acids
(b) fatty acids
(c) creatinine
(d) nucleic acids
Answer: (d) nucleic acids
In simple words: In humans, uric acid is a breakdown product primarily from purines, which are components of nucleic acids (DNA and RNA).

🎯 Exam Tip: Understand the metabolic pathways leading to different excretory products. Uric acid is distinct from urea and ammonia in its origin and toxicity.

 

Question (C). Visceral layer : Podocytes :: PCT : -
(a) Cilliated cells
(b) Squamous cells
(c) Columnar cells
(d) Cells with brush border
Answer: (d) Cells with brush border
In simple words: The proximal convoluted tubule (PCT) is lined with cells that have a brush border (microvilli), greatly increasing surface area for reabsorption, similar to how podocytes form the visceral layer of Bowman's capsule for filtration.

🎯 Exam Tip: Connect the structure of different parts of the nephron to their specific functions, especially regarding reabsorption and filtration mechanisms.

 

Question (D). Deproteinised plasma is found in -
(a) Bowman's capsule
(b) Descending limb
(c) Glomerular capillaries
(d) Ascending limb
Answer: (a) Bowman's capsule, (b) Descending limb, (d) Ascending limb
In simple words: Deproteinised plasma, also known as glomerular filtrate, is initially found in Bowman's capsule after filtration and then flows through the renal tubule, including the descending and ascending limbs of the Loop of Henle.

🎯 Exam Tip: Identify the fluid composition at various stages of urine formation within the nephron. Glomerular filtrate lacks large proteins but contains most other plasma components.

 

Question (E). Specific gravity of urine would - if level of ADH increases.
(a) remain unaffected
(b) increases
(c) decreases
(d) stabilise
Answer: (b) increases
In simple words: Increased ADH (Antidiuretic Hormone) causes more water to be reabsorbed from the urine, making the remaining urine more concentrated and thus increasing its specific gravity.

🎯 Exam Tip: Understand the role of ADH in water reabsorption and its direct impact on urine concentration and specific gravity. This is a key concept in osmoregulation.

 

Question (F). What is micturition?
(a) Urination
(b) Urine formation
(c) Uremia
(d) Urolithiasis
Answer: (a) Urination
In simple words: Micturition is the biological process of expelling urine from the urinary bladder through the urethra, commonly known as urination.

🎯 Exam Tip: Know the specific terminology for physiological processes in the excretory system. Distinguish micturition from urine formation or kidney-related diseases.

 

Question (G). Which one of the following organisms excrete waste through nephridia?
(a) Cockroach
(b) Earthworm
(c) Crab
(d) Liver Fluke
Answer: (c) Crab
In simple words: As per the provided text, crabs are listed as excreting waste through nephridia.

🎯 Exam Tip: Be precise about the excretory organs specific to different animal phyla, as there can be variations and specialized structures across species.

 

Question (H). Person suffering from kidney stone is advised not to have tomatoes as it has -
(a) seeds
(b) lycopene
(c) oxalic acid
(d) sour taste
Answer: (c) oxalic acid
In simple words: Tomatoes contain oxalic acid, which can combine with calcium to form calcium oxalate crystals, a common component of kidney stones, hence patients are advised to limit consumption.

🎯 Exam Tip: Relate dietary components to their physiological effects, especially in the context of kidney health and stone formation.

 

Question (I). Tubular secretion does not take place in -
(a) DCT
(b) PCT
(c) collecting duct
(d) Henle's loop
Answer: (b) PCT
In simple words: While significant reabsorption occurs in the PCT, tubular secretion, which involves actively transporting wastes from blood into the filtrate, primarily occurs in the DCT and collecting duct, not the PCT.

🎯 Exam Tip: Differentiate between the functions of different parts of the nephron, particularly between filtration, reabsorption, and secretion.

 

Question (J). The minor calyx -
(a) collects urine
(b) connects pelvis to ureter
(c) is present in the cortex
(d) receives column of Bertini
Answer: (a) collects urine
In simple words: The minor calyx is a cup-shaped structure in the kidney that directly collects urine from the renal papillae before it flows into the major calyces and then the renal pelvis.

🎯 Exam Tip: Familiarize yourself with the anatomical structures of the kidney and their specific roles in the urinary pathway.

 

Question (K). Which one of the followings is not a part of human kidney?
(a) Malpighian body
(b) Malpighian tubule
(c) Glomerulus
(d) Loop of Henle
Answer: (b) Malpighian tubule
In simple words: The human kidney contains Malpighian bodies (renal corpuscles), glomeruli, and Loops of Henle as parts of its nephrons; Malpighian tubule is an excretory organ found in insects, not humans.

🎯 Exam Tip: Accurately distinguish between excretory structures found in different organisms, particularly between human nephron components and insect excretory organs like Malpighian tubules.

 

Question (L). The yellow colour of the urine is due to presence of -
(a) uric acid
(b) cholesterol
(c) urochrome
(d) urea
Answer: (c) urochrome
In simple words: Urochrome is a pigment produced from the breakdown of hemoglobin, and its concentration primarily determines the yellow color of urine.

🎯 Exam Tip: Know the factors influencing urine characteristics, such as color, pH, and specific gravity, and the substances responsible for them.

 

Question (M). Hypotonic filtrate is formed in -
(a) PCT
(b) DCT
(c) LoH
(d) CT
Answer: (a) PCT
In simple words: After glomerular filtration, the filtrate in the Proximal Convoluted Tubule (PCT) is isotonic to plasma, not hypotonic. The question might imply a stage where the filtrate becomes hypotonic, which is typically in the ascending limb of the Loop of Henle due to solute removal without water, but if PCT is the given answer, we follow it.

🎯 Exam Tip: Understand the changes in tonicity (isotonic, hypotonic, hypertonic) of the filtrate as it moves through different parts of the nephron due to water and solute reabsorption and secretion.

 

Question (N). In reptiles, uric acid is stored in -
(a) cloaca
(b) fat bodies
(c) liver
(d) anus
Answer: (a) cloaca
In simple words: Reptiles excrete uric acid as a semi-solid paste to conserve water, and it is stored in the cloaca, a common opening for excretory, digestive, and reproductive systems, before elimination.

🎯 Exam Tip: Note species-specific excretory adaptations, especially water conservation strategies in arid-dwelling animals like reptiles that use uric acid excretion.

 

Question (O). The part of nephron which absorbs glucose and amino acid is -
(a) collecting tubule
(b) proximal tubule
(c) Henle's loop
(d) DCT
Answer: (b) proximal tubule
In simple words: The proximal tubule is primarily responsible for the reabsorption of essential nutrients like glucose and amino acids from the filtrate back into the bloodstream.

🎯 Exam Tip: Remember that the PCT is the primary site for the reabsorption of most solutes and water, playing a crucial role in conserving valuable substances.

 

Question (P). Bowman's capsule is located in kidney in the -
(a) cortex
(b) medulla
(c) pelvis
(d) pyramids
Answer: (a) cortex
In simple words: Bowman's capsule, which contains the glomerulus, is a key component of the renal corpuscle and is exclusively located in the renal cortex of the kidney.

🎯 Exam Tip: Distinguish between the renal cortex and medulla and the structures typically found in each region of the kidney. The Bowman's capsule is a cortical structure.

 

Question (Q). The snakes living in desert are mainly -
(a) aminotelic
(b) ureotelic
(c) ammonotelic
(d) uricotelic
Answer: (d) uricotelic
In simple words: Desert snakes are uricotelic, meaning they excrete nitrogenous waste as uric acid, which requires very little water for elimination, a critical adaptation for survival in arid environments.

🎯 Exam Tip: Relate the type of nitrogenous waste product (ammonia, urea, uric acid) to the habitat and water availability for different animal groups.

 

Question (R). Urea is a product of breakdown of -
(a) fatty acids
(b) amino acids
(c) glucose
(d) fats
Answer: (b) amino acids
In simple words: Urea is the primary nitrogenous waste in mammals, formed in the liver from the detoxification of ammonia, which is produced during the deamination (breakdown) of excess amino acids.

🎯 Exam Tip: Understand the origin of urea in the body, specifically its formation from amino acid metabolism through the urea cycle.

 

Question (S). Volume of the urine is regulated by -
(a) aldosterone
(b) ADH
(c) both a and b
(d) none
Answer:
In simple words: The volume of urine is primarily regulated by hormones like ADH, which controls water reabsorption, and aldosterone, which regulates sodium and subsequent water reabsorption, both influencing the final urine volume.

🎯 Exam Tip: Remember that multiple hormones, notably ADH and aldosterone, work together to precisely control fluid and electrolyte balance, thereby regulating urine volume and concentration.

 

Question 2. Answer the following questions

Question (A). Doctors say Mr. Shaikh is suffering from urolithiasis. How it could be explained in simple words?
Answer: Urolithiasis is the condition of having calculi in the urinary tract (which also includes the kidneys), which may pass into urinary bladder.
In simple words: Urolithiasis simply means the presence of stones (calculi) within the urinary system, which can include the kidneys, ureters, or bladder.

🎯 Exam Tip: Focus on clear, concise definitions for medical terms related to the excretory system, linking the term to its physical manifestation (e.g., stones).

 

Question (B). Anitaji needs to micturate several times and feels very thirsty. This is an indication of change in permeability of certain part of nephron. Which is this part?
Answer:
1. Need to micturate several times (polyuria) and feeling very thirsty (polydipsia) is a symptom of diabetes insipidus (imbalance of fluids in the body).
2. ADH prevents diuresis and due to absence of ADH, large amount of dilute urine is excreted.
3. ADH stimulates reabsorption of water from last part of DCT and entire collecting duct by increasing the permeability of cells.
4. If the permeability of these cells changes, it will result in increase in urine volume (frequent micturition) and increase in the osmolarity of blood. An imbalance in volume and osmolarity of body fluids increases thirst.
[Note: Water is reabsorbed by osmosis in PCT, DCT and descending limb of loop of Henle)
In simple words: Anitaji's symptoms point to an issue with ADH regulation affecting the permeability of the distal convoluted tubule (DCT) and collecting duct, leading to excessive water loss and thirst.

🎯 Exam Tip: When analyzing clinical scenarios, connect symptoms to underlying hormonal imbalances and the specific parts of the nephron involved in fluid regulation.

 

Question (C). Effective filtration pressure was calculated to be 20 mm Hg; where glomerular hydrostatic pressure was 70 mm of Hg. Which other pressure is affecting the filtration process? How much is it?
Answer: The other pressure affecting the filtration process is osmotic pressure of blood and filtrate hydrostatic pressure. Commonly effective filtration pressure (EFP) is represented as;
EFP = Glomerular Hydrostatic pressure in glomerulus - (Osmotic pressure of blood + Filtrate Hydrostatic pressure)
If EFP = 20 mmHg and Glomerular Hydrostatic pressure = 70 mmHg
20 = 70 - (Osmotic pressure of blood + Filtrate hydrostatic pressure)
. . (Osmotic pressure of blood + Filtrate hydrostatic pressure) = 70-20
Then (Osmotic pressure of blood + Filtrate Hydrostatic pressure) = 50 mmHg.
[Note: Given values are insufficient to calculate the exact osmotic pressure of blood and filtrate hydrostatic pressure. The sum of the two values can be calculated to be 50 mmHg ]
In simple words: The other pressures opposing filtration are the osmotic pressure of blood and the hydrostatic pressure of the filtrate in Bowman's capsule; their combined value, given the effective filtration pressure, is 50 mmHg.

🎯 Exam Tip: Remember the formula for Effective Filtration Pressure (EFP) and the three main pressures involved: Glomerular Hydrostatic Pressure (GHP), Blood Colloid Osmotic Pressure (BCOP), and Capsular Hydrostatic Pressure (CHP).

 

Question (D). Name any one guanotelic organism.
Answer: Spiders, scorpions and penguins are guanotelic organisms as they excrete guanine.
In simple words: Guanotelic organisms, like spiders and scorpions, excrete nitrogenous waste primarily in the form of guanine.

🎯 Exam Tip: Broaden your knowledge of excretory products beyond ammonia, urea, and uric acid to include less common ones like guanine, and their associated animal groups.

 

Question (E). Why are kidneys called 'retroperitoneal'?
Answer: Kidneys are located in abdomen. Kidneys are not surrounded by peritoneum instead they are located posterior to it. Thus, kidneys are called retroperitoneal.
In simple words: Kidneys are called retroperitoneal because they are situated behind the peritoneum, the membrane lining the abdominal cavity, rather than being enclosed within it.

🎯 Exam Tip: Understand the anatomical positioning of organs relative to the peritoneum; retroperitoneal placement is important for organs like kidneys and pancreas.

 

Question (F). State role of liver in urea production.
Answer:
1. Ammonia formed during the breakdown of amino acids is converted into urea in the liver of ureotelic animals.
2. This conversion takes place by the help of the ornithine / urea cycle.
3. 3 ATP molecules are used to produce one molecule of urea using the ornithine/ urea cycle. Since, the liver contains carrier molecules and enzymes necessary for urea cycle, it plays a major role in urea production.
In simple words: The liver plays a crucial role in urea production by converting highly toxic ammonia, derived from amino acid breakdown, into less toxic urea via the ornithine cycle, using ATP.

🎯 Exam Tip: Recognize the liver's central role in metabolism, including its critical function in detoxifying ammonia by converting it to urea for excretion.

 

Question (G). Why do we get bad breath after eating garlic or raw onion?
Answer:
1. Raw onion and garlic contain volatile sulphur-containing compounds.
2. Sulphur-containing compounds have a distinctive odour which remain in the mouth after consumption of onion and garlic.
3. Also, volatile compounds (like certain sulphur containing compounds) in foodstuffs are generally excreted through the lungs and may result in bad breath.
In simple words: Garlic and raw onion cause bad breath because they contain volatile sulfur compounds that are released into the mouth, absorbed into the bloodstream, and then expelled through the lungs.

🎯 Exam Tip: Understand that the lungs are secondary excretory organs, eliminating volatile substances, and this explains phenomena like "garlic breath".

 

3. Answer the following questions

Question (A). John has two options as treatment for his renal problem : Dialysis or kidney transplants. Which option should he choose? Why?
Answer:
1. If John has two options of dialysis and kidney transplant, readily available he must opt for kidney transplant.
2. A kidney transplant, if successful, can improve the quality of life of a patient and reduce the risk of death.
3. The patient would not have to endure frequent dialysis procedures. Repeated visits for dialysis takes time and may not allow the patient to perform normal activities or go to office regularly.
4. Dialysis is regarded as a holding measure until kidney transplant can be performed or a supportive measure in those for whom a transplant would be inappropriate. However, dialysis cannot replace all the functions of a normal kidney such as production of hormones like erythropoietin, calcitriol and renin. Hence, if John has an option of kidney transplant, he must opt for it.
In simple words: John should choose a kidney transplant over dialysis because a successful transplant offers a better quality of life, reduces mortality risk, and restores all kidney functions, unlike dialysis which is a temporary supportive measure.

🎯 Exam Tip: Compare and contrast the benefits and limitations of dialysis versus kidney transplant as treatments for renal failure, focusing on long-term health and quality of life.

 

Question (B). Amphibian tadpole can afford to be ammonotelic. Justify.
Answer:
1. Tadpole (larval stage of life cycle of amphibian) is aquatic. They are ammonotelic as they excrete nitrogenous waste in the form of ammonia.
2. Ammonia is very toxic and requires large amount of water for its elimination.
3. It is readily soluble in water and diffuses across the body surface and into the surrounding water.
4. Also, the water lost during excretion can be made up through the surrounding water in ammonotelic organisms.
Hence, amphibian tadpole can afford to be ammonotelic.
In simple words: Amphibian tadpoles are ammonotelic because, as aquatic larvae, they have constant access to water to dilute and excrete highly toxic ammonia, which readily diffuses into their environment.

🎯 Exam Tip: Link an animal's habitat and developmental stage to its mode of nitrogenous waste excretion, particularly the high water requirement for ammonia excretion.

 

Question (C). Birds are uricotelic in nature. Give reason.
Answer:
1. Birds are capable of converting ammonia into uric acid by 'inosinic acid pathway' in their liver.
2. Uric acid is least toxic and hence, it can be retained in the body for some time.
3. It is least soluble water hence, negligible amount of water is required for its elimination.
4. This mode of excretion can also help reduce body weight (an adaptation for flight) and those animals which
need to conserve more water follow uricotelism.
Hence, in order to conserve water as an adaptation for flight, birds are uricotelic in nature.
In simple words: Birds are uricotelic because excreting uric acid, which is nearly insoluble and non-toxic, allows them to conserve significant water and reduce body weight, both crucial adaptations for flight.

🎯 Exam Tip: Connect evolutionary adaptations, like flight and water conservation, to specific physiological mechanisms such as the type of nitrogenous waste excreted.

 

Question 4. Write the explanation in your word

Question (A). Nitya has been admitted to hospital after heavy blood loss. Till proper treatment could be given; how did Nitya's body must have tackled the situation?
Answer:
1. Heavy blood loss is called haemorrhage. In case of haemorrhage or severe dehydration, the osmoreceptors stimulate Antidiuretic hormone (ADH) secretion.
2. ADH is important in regulating water balance through the kidneys. For detailed mechanism of reabsorption by ADH:
Regulating water reabsorption through ADH:
Hypothalamus in the midbrain has special receptors called osmoreceptors which can detect change in osmolarity (measure of total number of dissolved particles per liter of solution) of blood.
If osmolarity of blood increases due to water loss from the body (after eating namkeen or due to sweating), osmoreceptors trigger release of Antidiuretic hormone (ADH) from neurohypophysis (posterior pituitary). ADH stimulates reabsorption of water from last part of DCT and entire collecting duct by increasing the permeability of cells.
This leads to reduction in urine volume and decrease in osmolarity of blood.
Once the osmolarity of blood comes to normal, activity of osmoreceptor cells decreases leading to decrease in ADH secretion. This is called negative feedback.
In case of hemorrhage or severe dehydration too, osmoreceptors stimulate ADH secretion. ADH is important in regulating water balance through kidneys.
In absence of ADH, diuresis (dilution of urine) takes place and person tends to excrete large amount of dilute urine. This condition called as diabetes insipidus.
[Note: Hypothalamus is a part of forebrain]
Another regulatory mechanism that must have been activated is RAAS. For detailed mechanism of electrolyte reabsorption:
Electrolyte reabsorption through RAAS:
Another regulatory mechanism is RAAS (Renin Angiotensin Aldosterone System) by Juxta Glomerular Apparatus (JGA).
Whenever blood supply (due to change in blood pressure or blood volume) to afferent arteriole decreases (e.g. low BP/dehydration), JGA cells release Renin.
Renin converts angiotensinogen secreted by hepatocytes in liver to Angiotensin I.
'Angiotensin-converting enzyme' further modifies Angiotensin I to Angiotensin II, the active form of hormone. It stimulates adrenal cortex to release another hormone called aldosterone that stimulates DCT and collecting ducts to reabsorb more Na⁺ and water, thereby increasing blood volume and pressure.
In simple words: Nitya's body would respond to heavy blood loss by activating ADH to increase water reabsorption, reducing urine volume, and initiating the RAAS system to increase blood volume and pressure, thereby attempting to restore homeostasis.

🎯 Exam Tip: Explain the integrated response of the body to hypovolemia (e.g., heavy blood loss), detailing the roles of ADH and the Renin-Angiotensin-Aldosterone System (RAAS) in maintaining blood pressure and fluid balance.

 

Question 5. Complete the diagram / chart with correct labels / information. Write the conceptual details regarding it
Answer:
ℹ️ चित्र व्याख्या (Diagram Explanation): यह आरेख एक फ्लोचार्ट है जो रेनिन-एंजियोटेंसिन-एल्डोस्टेरोन सिस्टम (RAAS) के माध्यम से रक्तचाप और रक्त आयतन के नियमन को दर्शाता है, जो होमियोस्टेसिस की बहाली की ओर ले जाता है। यह किडनी में धमनी दाब में कमी, ADH और एल्डोस्टेरोन के स्राव, और Na+ और पानी के पुनःअवशोषण को दर्शाता है जिससे रक्त आयतन और दाब बढ़ता है।
The composition of urine depends upon food and fluid consumed by an individual. There are two ways in which it the composition is regulated. They are as follows:
i. Regulating water reabsorption through ADH
ii. Electrolyte reabsorption though RAAS
iii. Atrial Natriuretic Peptide
i. Regulating water reabsorption through ADH:
Hypothalamus in the midbrain has special receptors called osmoreceptors which can detect change in osmolarity (measure of total number of dissolved particles per liter of solution) of blood.
If osmolarity of blood increases due to water loss from the body (after eating namkeen or due to sweating), osmoreceptors trigger release of Antidiuretic hormone (ADH) from neurohypophysis (posterior pituitary). ADH stimulates reabsorption of water from last part of DCT and entire collecting duct by increasing the permeability of cells.
This leads to reduction in urine volume and decrease in osmolarity of blood.
Once the osmolarity of blood comes to normal, activity of osmoreceptor cells decreases leading to decrease in ADH secretion. This is called negative feedback.
In case of hemorrhage or severe dehydration too, osmoreceptors stimulate ADH secretion. ADH is important in regulating water balance through kidneys.
In absence of ADH, diuresis (dilution of urine) takes place and person tends to excrete large amount of dilute urine. This condition called as diabetes insipidus.
[Note: Hypothalamus is a part of forebrain]
ii. Electrolyte reabsorption through RAAS:
Another regulatory mechanism is RAAS (Renin Angiotensin Aldosterone System) by Juxta Glomerular Apparatus (JGA).
Whenever blood supply (due to change in blood pressure or blood volume) to afferent arteriole decreases (e.g. low BP/dehydration), JGA cells release Renin.
Renin converts angiotensinogen secreted by hepatocytes in liver to Angiotensin I.
'Angiotensin converting enzyme' further modifies Angiotensin I to Angiotensin II, the active form of hormone. It stimulates adrenal cortex to release another hormone called aldosterone that stimulates DCT and collecting ducts to reabsorb more Na⁺ and water, thereby increasing blood volume and pressure.
iii. Atrial natriuretic peptide (ANP): A large increase in blood volume and pressure stimulates atrial wall to produce atrial natriuretic peptide (ANP). ANP inhibits Na+ and Cl- reabsorption from collecting ducts inhibits release of renin, reduces aldosterone and ADH release too. This leads to a condition called Natriuresis (increased excretion of Na⁺ in urine) and diuresis.
In simple words: Urine composition is regulated by ADH (controlling water reabsorption), RAAS (managing electrolyte and water reabsorption to increase blood pressure), and ANP (counteracting RAAS to reduce blood volume and pressure), ensuring fluid and electrolyte balance.

🎯 Exam Tip: For complex regulatory systems, clearly outline the individual roles of each hormone (ADH, aldosterone, ANP) and how they interact to achieve overall fluid and electrolyte homeostasis.

 

Question (B).
ℹ️ चित्र व्याख्या (Diagram Explanation): यह आरेख एक नेफ्रॉन की संरचना को दर्शाता है, जो गुर्दे की कार्यात्मक इकाई है। इसमें बोमन कैप्सूल, ग्लोमेरुलस, समीपस्थ कुंडलित नलिका (PCT), हेनले लूप का अवरोही और आरोही अंग, दूरस्थ कुंडलित नलिका (DCT) और संग्रह नलिका जैसे विभिन्न भाग शामिल हैं, जो मूत्र निर्माण प्रक्रिया में उनकी स्थिति को दर्शाते हैं।
1. Nephrons are structural and functional units of kidney.
2. Each nephron consists of a 4 - 6 cm long, thin-walled tube called the renal tubule and a bunch of capillaries known as the glomerulus.
3. The wall of the renal tubule is made up of a single layer of epithelial cells.
4. Its proximal end is wide, blind, cup-like and is called as Bowman's capsule, whereas the distal end is open.
In simple words: Nephrons are the kidney's basic filtration units, each comprising a renal tubule and glomerulus, designed to filter blood and process the filtrate into urine.

🎯 Exam Tip: Be able to identify and label all major parts of the nephron and understand their anatomical relationships and general functions in urine formation.

 

Question (C). Visceral layer : Podocytes :: PCT :
(a) Cilliated cells
(b) Squamous cells
(c) Columnar cells
(d) Cells with brush border
Answer: (d) Cells with brush border
In simple words: The cells lining the Proximal Convoluted Tubule (PCT) have a brush border of microvilli, which increases the surface area for reabsorption.

🎯 Exam Tip: Correctly identifying the specific cell types in different parts of the nephron is crucial for understanding their functional roles in filtration and reabsorption.

 

Question (D). Deproteinised plasma is found in _______
(a) Bowman's capsule
(b) Descending limb
(c) Glomerular capillaries
(d) Ascending limb
Answer: (a) Bowman's capsule, b. Descending limb, d. Ascending limb
In simple words: Deproteinised plasma, also known as glomerular filtrate, is initially formed in Bowman's capsule and then flows through the renal tubule, including the descending and ascending limbs of Henle.

🎯 Exam Tip: Understanding the path of filtrate through the nephron and what substances are present or absent at each stage is key for questions on kidney function.

 

Question (E). Specific gravity of urine would _______ if level of ADH increases.
(a) remain unaffected
(b) increases
(c) decreases
(d) stabilise
Answer: (b) increases
In simple words: Antidiuretic Hormone (ADH) promotes water reabsorption, leading to less water in the urine and thus a higher concentration of solutes, which increases the specific gravity of urine.

🎯 Exam Tip: Questions about hormone regulation in the kidney often test the effect of hormones like ADH on urine concentration and volume.

 

Question (F). What is micturition?
(a) Urination
(b) Urine formation
(c) Uremia
(d) Urolithiasis
Answer: (a) Urination
In simple words: Micturition is the physiological process of expelling urine from the urinary bladder through the urethra.

🎯 Exam Tip: Knowing the correct biological terms for kidney-related processes is fundamental for clear communication and answering definition-based questions.

 

Question (G). Which one of the following organisms excrete waste through nephridia?
(a) Cockroach
(b) Earthworm
(c) Crab
(d) Liver Fluke
Answer: (c) Crab
In simple words: Nephridia are excretory organs found in many invertebrate animals; among the given options, crabs use nephridia-like structures (antennal glands) for excretion.

🎯 Exam Tip: Understanding the diversity of excretory organs across different animal phyla helps in comparative biology questions.

 

Question (H). Person suffering from kidney stone is advised not to have tomatoes as it has _______
(a) seeds
(b) lycopene
(c) oxalic acid
(d) sour taste
Answer: (c) oxalic acid
In simple words: Tomatoes contain oxalic acid, which can combine with calcium to form calcium oxalate, a common component of kidney stones, hence patients with kidney stones are advised to limit their intake.

🎯 Exam Tip: Clinical applications of biological knowledge, like dietary advice for medical conditions, are common and require understanding the underlying physiological and chemical interactions.

 

Question (I). Tubular secretion does not take place in _______
(a) DCT
(b) PCT
(c) collecting duct
(d) Henle's loop
Answer: (b) PCT
In simple words: While significant reabsorption occurs in the Proximal Convoluted Tubule (PCT), tubular secretion, which involves actively transporting substances from blood into the filtrate, primarily occurs in the Distal Convoluted Tubule (DCT) and collecting duct, and to a lesser extent in some other parts, but not as a primary function in the loop of Henle.

🎯 Exam Tip: Differentiate the primary functions (filtration, reabsorption, secretion) in each part of the nephron for effective learning and answering specific questions.

 

Question (J). The minor calyx _______
(a) collects urine
(b) connects pelvis to ureter
(c) is present in the cortex
(d) receives column of Bertini
Answer: (a) collects urine
In simple words: The minor calyx is a cup-shaped structure in the kidney that collects urine from the renal papillae, which are the tips of the renal pyramids.

🎯 Exam Tip: Knowledge of kidney anatomy, including the roles of structures like calyces, pelvis, and ureter, is essential for understanding the path of urine flow.

 

Question (K). Which one of the followings is not a part of human kidney?
(a) Malpighian body
(b) Malpighian tubule
(c) Glomerulus
(d) Loop of Henle
Answer: (b) Malpighian tubule
In simple words: The Malpighian body (renal corpuscle), glomerulus, and Loop of Henle are all parts of the human kidney's nephron; however, 'Malpighian tubule' is a term typically used for excretory structures in insects, not humans.

🎯 Exam Tip: Be precise with anatomical terminology; similar-sounding terms can refer to different structures in different organisms.

 

Question (L). The yellow colour of the urine is due to presence of _______
(a) uric acid
(b) cholesterol
(c) urochrome
(d) urea
Answer: (c) urochrome
In simple words: The characteristic yellow color of urine comes from urochrome, a pigment resulting from the breakdown of hemoglobin.

🎯 Exam Tip: Understanding the components of urine, including pigments, helps explain its physical properties and can indicate underlying physiological states.

 

Question (M). Hypotonic filtrate is formed in _______
(a) PCT
(b) DCT
(c) LoH
(d) CT
Answer: (a) PCT
In simple words: Hypotonic filtrate, meaning a filtrate with a lower solute concentration than blood plasma, is formed in the Proximal Convoluted Tubule (PCT) after the initial reabsorption of a large amount of solutes and water.

🎯 Exam Tip: Knowing where the filtrate's tonicity changes within the nephron (e.g., isotonic in PCT, hypotonic in ascending loop, hypertonic in collecting duct) is important for understanding urine concentration.

 

Question (N). In reptiles, uric acid is stored in _______
(a) cloaca
(b) fat bodies
(c) liver
(d) anus
Answer: (a) cloaca
In simple words: Reptiles are uricotelic, meaning they excrete nitrogenous waste as uric acid, which is often released along with feces via the cloaca.

🎯 Exam Tip: Excretory mechanisms vary across species; understanding the primary waste products and their disposal methods in different animal groups is crucial.

 

Question (O). The part of nephron which absorbs glucose and amino acid is _______
(a) collecting tubule
(b) proximal tubule
(c) Henle's loop
(d) DCT
Answer: (b) proximal tubule
In simple words: The proximal tubule is primarily responsible for the reabsorption of essential nutrients like glucose and amino acids from the filtrate back into the bloodstream.

🎯 Exam Tip: The PCT is a major site of selective reabsorption, and knowing what substances are reabsorbed here is vital for understanding kidney function.

 

Question (P). Bowman's capsule is located in kidney in the _______
(a) cortex
(b) medulla
(c) pelvis
(d) pyramids
Answer: (a) cortex
In simple words: Bowman's capsule, which encloses the glomerulus, is found in the outer region of the kidney known as the cortex.

🎯 Exam Tip: An understanding of the anatomical organization of the kidney, specifically which parts of the nephron are located in the cortex versus the medulla, is key.

 

Question (Q). The snakes living in desert are mainly _______
(a) aminotelic
(b) ureotelic
(c) ammonotelic
(d) uricotelic
Answer: (d) uricotelic
In simple words: Desert snakes are uricotelic, meaning they excrete nitrogenous waste primarily as uric acid, which requires very little water for its elimination, conserving water in arid environments.

🎯 Exam Tip: The type of nitrogenous waste excreted (ammonia, urea, or uric acid) is often an adaptation to the availability of water in an organism's habitat.

 

Question (R). Urea is a product of breakdown of _______
(a) fatty acids
(b) amino acids
(c) glucose
(d) fats
Answer: (b) amino acids
In simple words: Urea is the main nitrogenous waste product in mammals, formed in the liver from the detoxification of ammonia, which is produced during the breakdown of amino acids.

🎯 Exam Tip: Recall the urea cycle and the metabolic pathways that lead to the production of nitrogenous wastes to answer questions about their origin.

 

Question (S). Volume of the urine is regulated by _______
(a) aldosterone
(b) ADH
(c) both a and b
(d) none
Answer:
In simple words: [Explain the core idea clearly in 1-3 highly simplified sentences for students.]

🎯 Exam Tip: [1-2 sentences highlighting scoring parameters or core evaluation criteria metrics.]

 

Question 2. Answer the following questions

Question (A). Doctors say Mr. Shaikh is suffering from urolithiasis. How it could be explained in simple words?
Answer: Urolithiasis is the condition of having calculi in the urinary tract (which also includes the kidneys), which may pass into urinary bladder.
In simple words: Urolithiasis means kidney stone disease, where hard deposits form in the kidneys or urinary tract, causing pain and potential blockage.

🎯 Exam Tip: Clinical terms and their simplified explanations are often tested to ensure basic comprehension of medical conditions.

 

Question (B). Anitaji needs to micturate several times and feels very thirsty. This is an indication of change in permeability of certain part of nephron. Which is this part?
Answer:
1. Need to micturate several times (polyuria) and feeling very thirsty (polydipsia) is a symptom of diabetes insipidus (imbalance of fluids in the body).
2. ADH prevents diuresis and due to absence of ADH, large amount of dilute urine is excreted.
3. ADH stimulates reabsorption of water from last part of DCT and entire collecting duct by increasing the permeability of cells.
4. If the permeability of these cells changes, it will result in increase in urine volume (frequent micturition) and increase in the osmolarity of blood. An imbalance in volume and osmolarity of body fluids increases thirst.
[Note: Water is reabsorbed by osmosis in PCT, DCT and descending limb of loop of Henle)
In simple words: Anitaji's symptoms point to issues with the distal convoluted tubule (DCT) and collecting duct, as these are the parts of the nephron whose water permeability is regulated by ADH, affecting urine concentration and thirst.

🎯 Exam Tip: Connecting specific physiological symptoms to the malfunction of particular parts of the nephron or hormonal regulation demonstrates a deeper understanding of kidney function.

 

Question (C). Effective filtration pressure was calculated to be 20 mm Hg; where glomerular hydrostatic pressure was 70 mm of Hg. Which other pressure is affecting the filtration process? How much is it?
Answer: The other pressure affecting the filtration process is osmotic pressure of blood and filtrate hydrostatic pressure. Commonly effective filtration pressure (EFP) is represented as;
EFP = Glomerular Hydrostatic pressure in glomerulus - (Osmotic pressure of blood + Filtrate Hydrostatic pressure)
If EFP = 20 mmHg and Glomerular Hydrostatic pressure = 70 mmHg
20 = 70 - (Osmotic pressure of blood + Filtrate hydrostatic pressure)

(Osmotic pressure of blood + Filtrate hydrostatic pressure) = 70-20
Then (Osmotic pressure of blood + Filtrate Hydrostatic pressure) = 50 mmHg.
[Note: Given values are insufficient to calculate the exact osmotic pressure of blood and filtrate hydrostatic pressure. The sum of the two values can be calculated to be 50 mmHg ]
In simple words: Besides glomerular hydrostatic pressure, the osmotic pressure of blood and the hydrostatic pressure of the filtrate within Bowman's capsule oppose filtration; their combined opposing pressure in this case is 50 mm Hg.

🎯 Exam Tip: Be prepared to apply formulas and perform simple calculations for concepts like effective filtration pressure, and understand the contributing and opposing forces.

 

Question (D). Name any one guanotelic organism.
Answer: Spiders, scorpions and penguins are guanotelic organisms as they excrete guanine.
In simple words: Guanotelic organisms, like spiders, excrete guanine as their primary nitrogenous waste.

🎯 Exam Tip: Knowing examples of different excretory types (ammonotelic, ureotelic, uricotelic, guanotelic) is important for classification and comparative biology questions.

 

Question (E). Why are kidneys called 'retroperitoneal'?
Answer: Kidneys are located in abdomen. Kidneys are not surrounded by peritoneum instead they are located posterior to it. Thus, kidneys are called retroperitoneal.
In simple words: Kidneys are called retroperitoneal because they lie behind the peritoneum, the membrane lining the abdominal cavity, rather than being suspended within it.

🎯 Exam Tip: Anatomical position and terminology are crucial; understanding terms like retroperitoneal helps in accurately describing organ location.

 

Question (F). State role of liver in urea production.
Answer:
1. Ammonia formed during the breakdown of amino acids is converted into urea in the liver of ureotelic animals.
2. This conversion takes place by the help of the ornithine / urea cycle.
3. 3 ATP molecules are used to produce one molecule of urea using the ornithine/ urea cycle. Since, the liver contains carrier molecules and enzymes necessary for urea cycle, it plays a major role in urea production.
In simple words: The liver plays a crucial role in urea production by converting highly toxic ammonia, generated from amino acid breakdown, into less toxic urea through the ornithine cycle, using ATP.

🎯 Exam Tip: The liver's role in detoxification and waste product synthesis (like urea) is a key concept that links metabolism to excretion.

 

Question (G). Why do we get bad breath after eating garlic or raw onion?
Answer:
1. Raw onion and garlic contain volatile sulphur-containing compounds.
2. Sulphur-containing compounds have a distinctive odour which remain in the mouth after consumption of onion and garlic.
3. Also, volatile compounds (like certain sulphur containing compounds) in foodstuffs are generally excreted through the lungs and may result in bad breath.
In simple words: Garlic and raw onion contain volatile sulfur compounds that, after consumption, are absorbed into the bloodstream and then partially excreted through the lungs, causing bad breath.

🎯 Exam Tip: Accessory excretory organs, such as lungs, play a role in eliminating volatile waste products, which is an often-overlooked aspect of excretion.

 

3. Answer the following questions

Question (A). John has two options as treatment for his renal problem: Dialysis or kidney transplants. Which option should he choose? Why?
Answer:
1. If John has two options of dialysis and kidney transplant, readily available he must opt for kidney transplant.
2. A kidney transplant, if successful, can improve the quality of life of a patient and reduce the risk of death.
3. The patient would not have to endure frequent dialysis procedures. Repeated visits for dialysis takes time and may not allow the patient to perform normal activities or go to office regularly.
4. Dialysis is regarded as a holding measure until kidney transplant can be performed or a supportive measure in those for whom a transplant would be inappropriate. However, dialysis cannot replace all the functions of a normal kidney such as production of hormones like erythropoietin, calcitriol and renin. Hence, if John has an option of kidney transplant, he must opt for it.
In simple words: John should choose a kidney transplant if possible because it offers a better quality of life and replaces all kidney functions, unlike dialysis which only filters blood and requires regular treatments.

🎯 Exam Tip: Comparing and contrasting medical treatments like dialysis and transplant requires an understanding of their mechanisms, benefits, and limitations.

 

Question (B). Amphibian tadpole can afford to be ammonotelic. Justify.
Answer:
1. Tadpole (larval stage of life cycle of amphibian) is aquatic. They are ammonotelic as they excrete nitrogenous waste in the form of ammonia.
2. Ammonia is very toxic and requires large amount of water for its elimination.
3. It is readily soluble in water and diffuses across the body surface and into the surrounding water.
4. Also, the water lost during excretion can be made up through the surrounding water in ammonotelic organisms.
Hence, amphibian tadpole can afford to be ammonotelic.
In simple words: Amphibian tadpoles are ammonotelic because they live in water, which provides the necessary large volume to dilute and excrete highly toxic ammonia safely through diffusion across their body surface.

🎯 Exam Tip: Relate the type of nitrogenous excretion (ammonotelism, ureotelism, uricotelism) to the animal's habitat and water availability, as this is a common concept in adaptations.

 

Question (C). Birds are uricotelic in nature. Give reason.
Answer:
1. Birds are capable of converting ammonia into uric acid by 'inosinic acid pathway' in their liver.
2. Uric acid is least toxic and hence, it can be retained in the body for some time.
3. It is least soluble water hence, negligible amount of water is required for its elimination.
4. This mode of excretion can also help reduce body weight (an adaptation for flight) and those animals which
need to conserve more water follow uricotelism.
Hence, in order to conserve water as an adaptation for flight, birds are uricotelic in nature.
In simple words: Birds are uricotelic because they excrete uric acid, which is nearly insoluble and requires minimal water for excretion, thereby conserving water and reducing body weight for flight.

🎯 Exam Tip: Understanding the adaptive advantages of different excretory strategies, particularly for flight or arid environments, is a key point in evolutionary biology.

 

Question 4. Write the explanation in your word

Question (A). Nitya has been admitted to hospital after heavy blood loss. Till proper treatment could be given; how did Nitya's body must have tackled the situation?
Answer:
1. Heavy blood loss is called haemorrhage. In case of haemorrhage or severe dehydration, the osmoreceptors stimulate Antidiuretic hormone (ADH) secretion.
2. ADH is important in regulating water balance through the kidneys. For detailed mechanism of reabsorption by ADH:
Regulating water reabsorption through ADH:
Hypothalamus in the midbrain has special receptors called osmoreceptors which can detect change in osmolarity (measure of total number of dissolved particles per liter of solution) of blood.
If osmolarity of blood increases due to water loss from the body (after eating namkeen or due to sweating), osmoreceptors trigger release of Antidiuretic hormone (ADH) from neurohypophysis (posterior pituitary). ADH stimulates reabsorption of water from last part of DCT and entire collecting duct by increasing the permeability of cells.
This leads to reduction in urine volume and decrease in osmolarity of blood.
Once the osmolarity of blood comes to normal, activity of osmoreceptor cells decreases leading to decrease in ADH secretion. This is called negative feedback.
In case of hemorrhage or severe dehydration too, osmoreceptors stimulate ADH secretion. ADH is important in regulating water balance through kidneys.
In absence of ADH, diuresis (dilution of urine) takes place and person tends to excrete large amount of dilute urine. This condition called as diabetes insipidus.
[Note: Hypothalamus is a part of forebrain]
Another regulatory mechanism that must have been activated is RAAS. For detailed mechanism of electrolyte reabsorption:
Electrolyte reabsorption through RAAS:
Another regulatory mechanism is RAAS (Renin Angiotensin Aldosterone System) by Juxta Glomerular Apparatus (JGA).
Whenever blood supply (due to change in blood pressure or blood volume) to afferent arteriole decreases (e.g. low BP/dehydration), JGA cells release Renin.
Renin converts angiotensinogen secreted by hepatocytes in liver to Angiotensin I. 'Angiotensin-converting enzyme' further modifies Angiotensin I to Angiotensin II, the active form of hormone. It stimulates adrenal cortex to release another hormone called aldosterone that stimulates DCT and collecting ducts to reabsorb more Na⁺ and water, thereby increasing blood volume and pressure.
In simple words: Nitya's body would respond to heavy blood loss by releasing Antidiuretic Hormone (ADH) to reabsorb water and activating the Renin-Angiotensin-Aldosterone System (RAAS) to increase blood volume and pressure, thereby trying to maintain fluid balance.

🎯 Exam Tip: Questions on homeostatic regulation, especially involving ADH and RAAS, require a detailed understanding of the hormonal cascade and its effects on kidney function and blood pressure.

 

Question 5. Complete the diagram / chart with correct labels / information. Write the conceptual details regarding it

Question (A).
ℹ️ चित्र व्याख्या (Diagram Explanation): यह आरेख RAAS (रेनिन-एंजियोटेंसिन-एल्डोस्टेरोन प्रणाली) के माध्यम से रक्तचाप और रक्त आयतन के नियमन को दर्शाता है। यह एक जटिल प्रतिक्रिया तंत्र है जो रक्तचाप कम होने पर सक्रिय होता है और इसे सामान्य स्थिति में बहाल करता है, जिसमें रेनिन, एंजियोटेंसिन और एल्डोस्टेरोन जैसे हार्मोन शामिल होते हैं।

Answer:
ℹ️ चित्र व्याख्या (Diagram Explanation): यह आरेख रेनिन-एंजियोटेंसिन-एल्डोस्टेरोन प्रणाली (RAAS) के माध्यम से रक्तचाप और रक्त आयतन के नियमन को दर्शाता है। यह दिखाता है कि कैसे कम रक्तचाप के जवाब में, रेनिन जारी होता है, जिससे एंजियोटेंसिन I और II बनता है, और अंततः एल्डोस्टेरोन का स्राव होता है, जो सोडियम और पानी के पुन:अवशोषण को बढ़ाता है और रक्तचाप को सामान्य करता है।

The composition of urine depends upon food and fluid consumed by an individual. There are two ways in which it the composition is regulated. They are as follows:
i. Regulating water reabsorption through ADH
ii. Electrolyte reabsorption though RAAS
iii. Atrial Natriuretic Peptide

i. Regulating water reabsorption through ADH:
Hypothalamus in the midbrain has special receptors called osmoreceptors which can detect change in osmolarity (measure of total number of dissolved particles per liter of solution) of blood.

If osmolarity of blood increases due to water loss from the body (after eating namkeen or due to sweating), osmoreceptors trigger release of Antidiuretic hormone (ADH) from neurohypophysis (posterior pituitary). ADH stimulates reabsorption of water from last part of DCT and entire collecting duct by increasing the permeability of cells.

This leads to reduction in urine volume and decrease in osmolarity of blood.

Once the osmolarity of blood comes to normal, activity of osmoreceptor cells decreases leading to decrease in ADH secretion. This is called negative feedback.
In case of hemorrhage or severe dehydration too, osmoreceptors stimulate ADH secretion. ADH is important in regulating water balance through kidneys.

In absence of ADH, diuresis (dilution of urine) takes place and person tends to excrete large amount of dilute urine. This condition called as diabetes insipidus.

[Note: Hypothalamus is a part of forebrain]

ii. Electrolyte reabsorption through RAAS:
Another regulatory mechanism is RAAS (Renin Angiotensin Aldosterone System) by Juxta Glomerular Apparatus (JGA).

Whenever blood supply (due to change in blood pressure or blood volume) to afferent arteriole decreases (e.g. low BP/dehydration), JGA cells release Renin.
Renin converts angiotensinogen secreted by hepatocytes in liver to Angiotensin I. 'Angiotensin converting enzyme' further modifies Angiotensin I to Angiotensin II, the active form of hormone. It stimulates adrenal cortex to release another hormone called aldosterone that stimulates DCT and collecting ducts to reabsorb more Na⁺ and water, thereby increasing blood volume and pressure.
In simple words: The regulation of urine composition involves hormones like ADH, which controls water reabsorption, and the RAAS and ANP systems, which adjust electrolyte and water balance to maintain blood pressure and volume.

🎯 Exam Tip: Flowchart-based questions require careful analysis of each step and its physiological consequence. Ensure you understand the sequence and roles of all hormones and structures involved in renal regulation.

 

iii. Atrial natriuretic peptide (ANP): A large increase in blood volume and pressure stimulates atrial wall to produce atrial natriuretic peptide (ANP). ANP inhibits Na⁺ and Cl- reabsorption from collecting ducts inhibits release of renin, reduces aldosterone and ADH release too. This leads to a condition called Natriuresis (increased excretion of Na⁺ in urine) and diuresis.

Question (B).
ℹ️ चित्र व्याख्या (Diagram Explanation): यह चित्र मानव नेफ्रॉन की संरचना को दर्शाता है, जिसमें बोमन कैप्सूल, ग्लोमेरुलस, समीपस्थ और दूरस्थ कुंडलित नलिकाएं, हेनले का लूप और संग्रह नलिका शामिल हैं। यह वृक्क की कार्यात्मक इकाई का विस्तृत दृश्य प्रस्तुत करता है।

Answer:
ℹ️ चित्र व्याख्या (Diagram Explanation): यह आरेख एक नेफ्रॉन की संरचना को लेबल के साथ प्रस्तुत करता है, जिसमें ग्लोमेरुलर कैप्सूल, ग्लोमेरुलस, समीपस्थ और दूरस्थ कुंडलित नलिका (PCT और DCT), हेनले का अवरोही लूप और संग्रह नलिका शामिल हैं। यह वृक्क के भीतर अल्ट्राफिल्ट्रेशन और पुन:अवशोषण के स्थलों को दर्शाता है।

1. Nephrons are structural and functional units of kidney.
2. Each nephron consists of a 4 - 6 cm long, thin-walled tube called the renal tubule and a bunch of capillaries known as the glomerulus.
3. The wall of the renal tubule is made up of a single layer of epithelial cells.
4. Its proximal end is wide, blind, cup-like and is called as Bowman's capsule, whereas the distal end is open.
In simple words: Nephrons are the tiny filtering units of the kidney, each composed of a renal corpuscle (Bowman's capsule and glomerulus) and a renal tubule, working together to filter blood and form urine.

🎯 Exam Tip: Understanding the basic structure of a nephron and the general function of each part (e.g., Bowman's capsule for filtration, tubules for reabsorption/secretion) is foundational.

 

5. The nephron is divisible into llowman's capsule, neck, proximal convoluted tubule (PCT), Loop of Henle (LoH), distal convoluted tubule (DCT) and collecting tubule (CT).
6. The glomerulus is present in the cup-like cavity of Bowman's capsule and both are collectively known as renal corpuscle or Malpighian body.

Question (C)
ℹ️ चित्र व्याख्या (Diagram Explanation): यह आरेख एक एकल नेफ्रॉन और उसके आसपास के पेरिटुबुलर केशिका नेटवर्क की विस्तृत संरचना को दर्शाता है। इसमें एफ़ेरेंट और इफ़ेरेंट धमनियाँ, ग्लोमेरुलस, बोमन कैप्सूल, समीपस्थ और दूरस्थ कुंडलित नलिकाएँ, हेनले का लूप (अवरोही और आरोही अंग) और संग्रह नलिका शामिल हैं, जो वृक्क की फ़िल्टरिंग इकाई का पूरा दृश्य प्रदान करता है।

Answer:
Nephron is the structural and functional unit of kidney.
Structure of nephron:
A nephron (uriniferous tubule) is a thin walled, coiled duct, lined by a single layer of epithelial cells. Each nephron is divided into two main parts:
i. Malpighian body
ii. Renal tubule
In simple words: Nephron is the fundamental unit of the kidney, responsible for filtering blood and producing urine, consisting of a Malpighian body for filtration and a renal tubule for processing the filtrate.

🎯 Exam Tip: Diagram-based questions often require labeling or describing the structures shown; a clear understanding of nephron anatomy is essential for this.

 

ℹ️ चित्र व्याख्या (Diagram Explanation): यह आरेख एक नेफ्रॉन की संरचना को और पेरिटुबुलर केशिका नेटवर्क को दर्शाता है। इसमें एफ़ेरेंट और इफ़ेरेंट धमनियाँ, ग्लोमेरुलस, बोमन कैप्सूल (ग्लोमेरुलर कैप्सूल), समीपस्थ और दूरस्थ कुंडलित नलिकाएँ, हेनले का लूप और संग्रह नलिका शामिल हैं। यह वृक्क की फ़िल्टरिंग इकाई का पूरा दृश्य प्रस्तुत करता है।

i. Malpighian body: Each Malpighian body is about 200pm in diameter and consists of a Bowman's capsule and glomerulus.
a. Glomerulus:
Glomerulus is a bunch of fine blood capillaries located in the cavity of Bowman's capsule.
A small terminal branch of the renal artery, called as afferent arteriole enters the cup cavity (Bowman capsule) and undergoes extensive fine branching to form network of several capillaries. This bunch is called as glomerulus.
The capillary wall is fenestrated (perforated).
All capillaries reunite and form an efferent arteriole that leaves the cup cavity.
The diameter of the afferent arteriole is greater than the efferent arteriole. This creates a high hydrostatic pressure essential for ultrafiltration, in the glomerulus.
b. Bowman's capsule:
It is a cup-like structure having double walls composed of squamous epithelium.
The outer wall is called as parietal wall and the inner wall is called as visceral wall.
The parietal wall is thin consisting of simple squamous epithelium.
There is a space called as capsular space / urinary space in between two walls.
Visceral wall consists of special type of squamous cells called podocytes having a foot-like pedicel. These podocytes are in close contact with the walls of capillaries of glomerulus.
There are small slits called as filtration slits in between adjacent podocytes.
ii. Renal tubule:
a. Neck:
The Bowman's capsule continues into the neck. The wall of neck is made up of ciliated epithelium. The lumen of the neck is called the urinary pole. The neck leads to proximal convoluted tubule.
b. Proximal Convoluted Tubule :
This is highly coiled part of nephron which is lined by cuboidal cells with brush border (microvilli) and surrounded by peritubular capillaries. Selective reabsorption occurs in PCT. Due to convolutions (coiling), filtrate flows slowly and remains in the PCT for longer duration, ensuring that maximum amount of useful molecules are reabsorbed.
c. Loop of Henle :
This is 'U' shaped tube consisting of descending and ascending limb.
The descending limb is thin walled and permeable to water and lined with simple squamous epithelium.
The ascending limb is thick walled and impermeable to water and is lined with simple cuboidal epithelium.
The LoH is surrounded by capillaries called vasa recta.
Its function is to operate counter current system - a mechanism for osmoregulation.
The ascending limb of Henle's loop leads to DCT.
d. Distal convoluted tubule:
This is another coiled part of the nephron.
Its wall consists of simple cuboidal epithelium.
DCT performs tubular secretion / augmentation / active secretion in which, wastes are taken up from surrounding capillaries and secreted into passing urine.
DCT helps in water reabsorption and regulation of pH of body fluids.
e. Collecting tubule:
This is a short, straight part of the DCT which reabsorbs water and secretes protons. The collecting tubule opens into the collecting duct.
In simple words: The Malpighian body (Bowman's capsule and glomerulus) filters blood, while the renal tubule (including PCT, Loop of Henle, DCT, and collecting tubule) selectively reabsorbs essential substances and secretes wastes to form urine.

🎯 Exam Tip: A thorough understanding of each part of the nephron, its cellular structure, and its specific role in the processes of filtration, reabsorption, and secretion is crucial for detailed questions.

 

ℹ️ चित्र व्याख्या (Diagram Explanation): यह आरेख बोमन कैप्सूल और ग्लोमेरुलस की विस्तृत संरचना को दर्शाता है, जिसे मैल्पीघियन बॉडी कहते हैं। यह केशिकाओं (ग्लोमेरुलस), पोडोसाइट्स (विसेरल दीवार), कैप्सुलर स्पेस और विभिन्न दबावों (रक्तचाप, कॉलोइडल ऑस्मोटिक दबाव, कैप्सुलर हाइड्रोस्टेटिक दबाव) को प्रदर्शित करता है जो अल्ट्राफिल्ट्रेशन की प्रक्रिया को नियंत्रित करते हैं।

Question (D).
ℹ️ चित्र व्याख्या (Diagram Explanation): यह आरेख ADH (एंटीडाययूरेटिक हार्मोन) और RAAS (रेनिन-एंजियोटेंसिन-एल्डोस्टेरोन प्रणाली) दोनों के माध्यम से जल और इलेक्ट्रोलाइट सांद्रता के नियमन को दर्शाने वाला एक विस्तृत प्रवाह चार्ट है। यह बताता है कि कैसे कम पानी की सांद्रता और रक्त में Na+ आयनों का परिवहन वृक्क द्वारा जल और आयन के पुन:अवशोषण को उत्तेजित करके समस्थापन को बहाल करता है।

Answer:
ℹ️ चित्र व्याख्या (Diagram Explanation): यह आरेख ADH (एंटीडाययूरेटिक हार्मोन) और RAAS (रेनिन-एंजियोटेंसिन-एल्डोस्टेरोन प्रणाली) दोनों के माध्यम से जल और इलेक्ट्रोलाइट सांद्रता के नियमन को दर्शाने वाला एक विस्तृत प्रवाह चार्ट है। यह दर्शाता है कि कैसे शरीर में पानी की कमी या रक्तचाप में गिरावट के जवाब में, ये प्रणालियाँ सक्रिय होती हैं, जिससे वृक्क द्वारा पानी और सोडियम का पुन:अवशोषण बढ़ जाता है, और रक्त में सामान्य पानी और सोडियम की सांद्रता बहाल हो जाती है।

The composition of urine depends upon food and fluid consumed by an individual. There are two ways in which it the composition is regulated. They are as follows:
i. Regulating water reabsorption through ADH
ii. Electrolyte reabsorption though RAAS
iii. Atrial Natriuretic Peptide

i. Regulating water reabsorption through ADH:
Hypothalamus in the midbrain has special receptors called osmoreceptors which can detect change in osmolarity (measure of total number of dissolved particles per liter of solution) of blood.

If osmolarity of blood increases due to water loss from the body (after eating namkeen or due to sweating), osmoreceptors trigger release of Antidiuretic hormone (ADH) from neurohypophysis (posterior pituitary). ADH stimulates reabsorption of water from last part of DCT and entire collecting duct by increasing the permeability of cells.

This leads to reduction in urine volume and decrease in osmolarity of blood.

Once the osmolarity of blood comes to normal, activity of osmoreceptor cells decreases leading to decrease in ADH secretion. This is called negative feedback.
In case of hemorrhage or severe dehydration too, osmoreceptors stimulate ADH secretion. ADH is important in regulating water balance through kidneys.

In absence of ADH, diuresis (dilution of urine) takes place and person tends to excrete large amount of dilute urine. This condition called as diabetes insipidus.

[Note: Hypothalamus is a part of forebrain]
ii. Electrolyte reabsorption through RAAS:
Another regulatory mechanism is RAAS (Renin Angiotensin Aldosterone System) by Juxta Glomerular Apparatus (JGA).

Whenever blood supply (due to change in blood pressure or blood volume) to afferent arteriole decreases (e.g. low BP/dehydration), JGA cells release Renin.
Renin converts angiotensinogen secreted by hepatocytes in liver to Angiotensin I. 'Angiotensin-converting enzyme' further modifies Angiotensin I to Angiotensin II, the active form of hormone. It stimulates adrenal cortex to release another hormone called aldosterone that stimulates DCT and collecting ducts to reabsorb more Na⁺ and water, thereby increasing blood volume and pressure.
iii. Atrial natriuretic peptide (ANP): A large increase in blood volume and pressure stimulates atrial wall to produce atrial natriuretic peptide (ANP). ANP inhibits Na⁺ and Cl- reabsorption from collecting ducts inhibits release of renin, reduces aldosterone and ADH release too. This leads to a condition called Natriuresis (increased excretion of Na⁺ in urine) and diuresis.
In simple words: Urine composition is regulated by ADH, which controls water reabsorption, and the RAAS system, which controls salt and water balance to maintain blood pressure, along with ANP, which counters these effects to reduce blood volume and pressure.

🎯 Exam Tip: Detailed knowledge of hormonal feedback loops, especially the interconnected roles of ADH, RAAS, and ANP in maintaining fluid and electrolyte balance, is crucial for high-scoring answers.

 

Question (E).
ℹ️ चित्र व्याख्या (Diagram Explanation): यह आरेख एक हीमोडायलिसिस मशीन के कार्य सिद्धांत को दर्शाता है, जिसे आमतौर पर कृत्रिम वृक्क के रूप में जाना जाता है। यह दिखाता है कि कैसे रोगी के रक्त को एक डायलूसिस यूनिट के माध्यम से फ़िल्टर किया जाता है, जहाँ अपशिष्ट उत्पाद डायलैसेट द्रव में फैल जाते हैं और साफ़ रक्त को वापस रोगी में भेज दिया जाता है।

Answer:
ℹ️ चित्र व्याख्या (Diagram Explanation): यह आरेख एक हीमोडायलिसिस मशीन की कार्यप्रणाली को दर्शाता है। यह दिखाता है कि कैसे रोगी के रक्त को एक सेलोफेन ट्यूब के माध्यम से निकाला जाता है, जिसे डायलैसेट द्रव में डुबोया जाता है। अपशिष्ट उत्पाद डायलैसेट में फैल जाते हैं, और साफ़, फ़िल्टर किए गए रक्त को वापस रोगी की नस में लौटा दिया जाता है, जिससे गुर्दे की विफलता में रक्त शोधन की प्रक्रिया को दर्शाया जाता है।

1. When renal function of a person falls below 5 - 7 %, accumulation of harmful substances in blood begins. In such a condition the person has to go for artificial means of filtration of blood i.e. haemodialysis.
2. In haemodialysis, a dialysis machine is used to filter blood. The blood is filtered outside the body using a dialysis unit.
3. In this procedure, the patients' blood is removed; generally from the radial artery and passed through a cellophane tube that acts as a semipermeable membrane.
4. The tube is immersed in a fluid called dialysate which is isosmotic to normal blood plasma. Hence, only excess salts if present in plasma pass through the cellophane tube into the dialysate.
5. Waste substances being absent in the dialysate, move from blood into the dialyzing fluid.
6. Filtered blood is returned to vein.
7. In this process it is essential that anticoagulant like heparin is added to the blood while it passing through the tube and before resending it into the circulation, adequate amount of anti-heparin is mixed.
8. Also, the blood has to move slowly through the tube and hence the process is slow.
In simple words: Hemodialysis is an artificial blood filtration process used when kidneys fail; the patient's blood is passed through a machine with a semipermeable membrane immersed in dialysate, allowing waste products to diffuse out before clean blood is returned to the body.

🎯 Exam Tip: Understanding the principles of diffusion and osmosis is essential for explaining how hemodialysis works, especially the role of the dialysate and the semipermeable membrane.

 

Question 6. Prove that mammalian urine contains urea.
Answer:
1. Urea is a nitrogenous waste formed by breakdown of protein (deamination of amino acids).
2. During this process, amino groups are removed from the amino acids present in the proteins and converted to highly toxic ammonia. The ammonia is finally converted to area through ornithine cycle. Thus, the urea formed is passed to kidneys and excreted out of the body through urine.
3. Reabsorption of urea (proximal tubule, collecting ducts) and active secretion of urea (Henle loop) leads to a urea circulation (urea recycling) between the lumen of the nephron and renal medulla, which is an important element of the renal urine concentration.
4. About 54 g of urea is filtered per day in the glomerular capsule, of which approximately 30 g is excreted in the urine and 24 g is reabsorbed into blood (assuming GFR is 180 litres/day).
5. Urinalysis can help detect the amount of urea in urine (Urine urea nitrogen test, urease test, etc.).
In simple words: Mammalian urine contains urea because urea is the end product of amino acid metabolism, formed in the liver via the ornithine cycle, filtered by the kidneys, and then partially reabsorbed while the rest is excreted in urine, which can be detected by various urine tests.

🎯 Exam Tip: To prove the presence of urea, refer to its metabolic origin, its journey through the kidney (filtration, reabsorption, excretion), and methods for its detection in urine.

 

Practical / Project : Visit to a nearby hospital or pathological laboratory and collect detailed information for different blood and urine tests.
Answer: Testing the urine is known as urinalysis. It generally has three parts:
1. Visual examination: Check sample colour and clearness.
2. Dipstick examination: Checks for abnormal amounts of glucose, protein, etc.
3. Microscopic examination: Check for presence of RBCs. WBCs, bacteria, crystals, etc.
4. Apart from routine urine examination, specific tests may also be done. They are as follows:
(i) BUN (Blood Urea Nitrogen) Test: It measures the amount of nitrogen in blood and evaluates kidney function.
(ii) Urease Test/ Urea Nitrogen Test: It is done to check the amount of urea in urine sample.
(iii) Urine albumin to creatine ratio (UACR) test: Estimates the amount of albumin in urine.
In simple words: Urinalysis, a common diagnostic tool, involves visual, dipstick, and microscopic examination of urine to check for color, clarity, presence of abnormal substances like glucose or protein, and cellular components, alongside specific tests like BUN and UACR to assess kidney health.

🎯 Exam Tip: Understanding common diagnostic tests, like urinalysis, and what each component indicates about physiological health, connects theoretical knowledge to practical applications.

 

12th Biology Digest Chapter 15 Excretion And Osmoregulation Intext Questions And Answers

Can you recall? (Textbook Page No. 174)

Question 1. Why are various waste products produced in the body of an organism?
Answer: Metabolism produces a variety of by-products, some of which need to be eliminated. Such by-products are called metabolic waste products.
In simple words: Waste products are produced in the body as a natural consequence of metabolism, which involves various chemical reactions essential for life that generate substances needing elimination.

🎯 Exam Tip: Focus on understanding that metabolic processes inevitably lead to waste generation, highlighting the fundamental need for excretory systems.

 

Question 2. How are these waste eliminated?
Answer: Depending on the type of waste product, they are eliminated through various organs of the body:
The various excretory products produced by the human body are as follows:
1. Fluids such as water; gaseous wastes like CO2 nitrogenous wastes like ammonia, urea and uric acid, creatinine; minerals; salts of sodium, potassium. calcium, etc. if present in body in excess are excreted through urine, faeces and sweat.
2. Pigments formed due to breakdown of haemoglobin like bilirubin (excreted through faeces) and urochrome (eliminated through urine).
3. The pigments present in consumed foodstuffs like beet root or excess of vitamins, hormones and drugs.
4. Volatile substances present in spices (eliminated through lungs).
In simple words: Waste products are eliminated through specialized organs like kidneys (urine), lungs (CO2, volatile substances), skin (sweat), and liver/intestines (bile pigments, feces), depending on the waste type.

🎯 Exam Tip: Differentiating the specific waste products eliminated by each excretory organ is crucial for comprehensive understanding.

 

Have you ever observed? (Textbook Page No. 174)

Question 1. When does urine appear deeply coloured?
Answer: Urine can appear deeply coloured due to various reasons:
- Severe dehydration resulting in production of concentrated urine.
- Consumption of foodstuff like beet root, which contain coloured pigments.
- Some medications can also cause the urine to appear deeply coloured.
In simple words: Urine appears deeply colored primarily due to dehydration (making it concentrated), consumption of certain foods like beet root, or the influence of some medications.

🎯 Exam Tip: Simple observations about body fluids, like urine color, can be linked to physiological states or external factors, making them good short-answer questions.

 

Think about it. (Textbook Page No. 174)

Question 1. Do organisms differ in type of metabolic wastes they produce?
Answer: Yes, organisms differ in the type of metabolic wastes they produce. Some organisms excrete ammonia while some excrete urea or uric acid as metabolic wastes.
In simple words: Yes, organisms produce different types of metabolic wastes, like ammonia, urea, or uric acid, depending on their species, environment, and metabolic pathways.

🎯 Exam Tip: Recognizing the diversity in metabolic waste products among different organisms is fundamental to understanding adaptations in excretion.

 

Question 2. Do environment or evolution have any effect on type of waste produced by an organism?
Answer:
- The theory of evolution proposes that life started in an aquatic environment.
- Aquatic organisms are generally ammonotelic. It is believed that the urea cycle evolved to adapt to a changing environment when terrestrial life forms evolved.
- Arid conditions probably led to the evolution of the uric acid pathway as a means of conserving water.
- However, the correlation between evolution and type of waste production is uncertain.
In simple words: Yes, the environment significantly influences the type of waste produced, as seen in the evolution of urea excretion for terrestrial life and uric acid excretion for arid conditions, both optimizing water conservation.

🎯 Exam Tip: Connect evolutionary adaptations and environmental pressures to the type of nitrogenous waste excreted, as this highlights the survival advantages of different excretory strategies.

 

Question 3. How do thermoregulation and food habits affect saste production?
Answer:
1. To generate heat. endotherms convert the food that they eat into energy through a process called metabolism. Hence, they consume more tì.od in order to meet their energy requirements.
2. Also, carnivorous diet contains more proteins than herbivores.
3. Consumption of high protein or more food containing proteins can result in production of large amount of nitrogenous waste
4. These animals would also require more energy to eliminate the high levels oF nitrogenous wastes which build up when animal protein is digested.
In simple words: Thermoregulation in endotherms requires more energy and thus more food consumption, which, along with a high-protein diet (common in carnivores), leads to increased production of nitrogenous wastes that require energy to eliminate.

🎯 Exam Tip: Understand how metabolic rate and dietary composition directly impact the quantity of waste products, particularly nitrogenous wastes, in different organisms.

Find Out. (Textbook Page No 176)

 

Question 1. How do freshwater fishes and marine fishes carry out osmoregulation?
Answer:Osmoregulation is the process of maintaining an internal concentration of salt and water in the body of fishes.
i. Freshwater fishes:
The salt concentration inside the body of freshwater fishes is higher than their surrounding water. Due to this, water enters the body due to osmosis. If the flow of water into the body is not regulated, fishes would swell and get bigger. To compensate this, the kidneys produce a large amount of urine. Excretion of large amounts of urine regulates the level of water in the body but results in the loss of salts. Thus, in order to maintain a sufficient salt level, special cells in the gills (chloride cells) take up ions from the water, which are then directly transported into the blood.
ii. Marine fishes:
Since the salt content in blood of marine fishes is much lower than that of seawater, they constantly tend to lose water and build up salt. To replace the water loss, they continually need to drink seawater. Since their small kidney can only excrete a relatively small amount of urine, salt is additionally excreted through gills, where chloride cells work in reverse as in freshwater fishes.
In simple words: Freshwater fish excrete large amounts of dilute urine to remove excess water, while marine fish drink seawater and excrete excess salt through gills and concentrated urine to conserve water.

🎯 Exam Tip: Understanding the specific adaptations of different aquatic organisms for osmoregulation is crucial for high scores.

Make A Table. (Textbook Page No. 178)

 

Question 1. The details of modes of excretion of nitrogenous wastes.
Answer:The three main modes of excretion in animals are as follows:
i. Ammonotelism:
1. Elimination of nitrogenous wastes in the form of ammonia is called as ammonotelism.
2. Ammonia is basic in nature and hence it can disturb the pH of the body, if not eliminated immediately.
3. Any change in pH would disturb all enzyme catalyzed reactions in the body and would also make the plasma membrane unstable.
4. Ammonia is readily soluble in water and needs large quantity of water to dilute and reduce its toxicity.
5. This is however an energy saving mechanism of excretion and hence all animals that have plenty of water available for dilution of ammonia, excrete nitrogenous wastes in the form of ammonia.
6. Animals that follow this mode of excretion are known as ammonotelic animals.
7. 1 gm ammonia needs about 300 - 500 ml of water for elimination.
8. Ammonotelic animals excrete ammonia through general body surface (skin), gills and kidneys.
e.g. Ammonotelism is found in aquatic invertebrates, bony fishes, and aquatic / larval amphibians. Animals without excretory system (Protozoa) are also ammonotelic.
ii. Ureotelism:
1. Elimination of nitrogenous wastes in the form of urea is called as ureotelism.
2. Urea is comparatively less toxic and less water-soluble than ammonia. Hence, it can be concentrated to some extent in body.
3. The body requires less water for elimination.
4. Since it is less toxic and less water soluble, ureotelism is suitable for animals that need to conserve water to some extent. Hence, ureotelism is common in terrestrial animals, as they have to conserve water.
5. It takes about 50 ml H2O for removal of 1 gm NH2 in form of urea.
6. Ureotelic animals generally convert ammonia to urea in the liver by operating ornithine / urea cycle in which 3 ATP molecules are used to produce one molecule of urea.
e.g. Mammals, cartilaginous fishes (sharks and rays), many aquatic reptiles, most of the adult amphibians, etc. are ureotelic.
iii. Uricotelism:
1. Elimination of nitrogenous wastes in the form of uric acid is called as uricotelism.
2. Uric acid is least toxic and hence, it can be retained in the body for some time in concentrated form.
3. It is least soluble in water. Hence there is minimum (about 5 - 10 ml for 1 gm) or no need of water for its elimination.
4. Those animals which need to conserve more water follow uricotelism. However, these animals need to spend more energy.
5. Ammonia is converted into uric acid by 'inosinic acid pathway' in the liver of birds, e.g. Birds, some insects, many reptiles, land snails, are uricotelic.

No.	Ureotelism	Uricotelism
i.	It is the elimination of nitrogenous waste in the form of urea.	It is the elimination of nitrogenous waste in the form of uric acid.
ii.	Excretion of urea requires less (moderate) amount of water.	Excretion of uric acid requires negligible amount of water.
iii.	Removal of 1 gm of urea requires 50 ml of water.	Removal of 1 gm of uric acid requires 5 - 10 ml of
iv.	rea is less toxic.	Uric acid is least toxic.
e.g.	It is generally seen in terrestrial animals. Mammals, cartilaginous fishes (sharks and rays), many aquatic reptiles, most adult amphibians, etc.	It is seen in birds, some insects, many reptiles, land snails, etc.

No.	Ammonotelism	Uricotelism
i.	It is the elimination of nitrogenous waste in the form of ammonia.	It is the elimination of nitrogenous waste in the form of uric acid.
ii.	Excretion of ammonia requires plenty of water.	Excretion of uric acid requires negligible amount of water.
iii.	Removal of 1 gm of ammonia requires 300 - 500 ml of water.	Removal of 1 gm of uric acid requires 10ml of water.
iv.	Ammonia is very toxic.	Uric acid is less toxic.
e.g.	It is found in aquatic invertebrates, bony fishes and aquatic/ larval amphibians, etc.	It is seen in birds, some insects, many reptiles, land snails, etc.

[Students can Refer these and make a chart on their own.]
In simple words: Animals excrete nitrogenous wastes as ammonia, urea, or uric acid depending on water availability and toxicity, with ammonia being most toxic and requiring most water, and uric acid being least toxic and requiring minimal water.

🎯 Exam Tip: Be able to compare and contrast ammonotelism, ureotelism, and uricotelism, including examples and water conservation implications.

 

Use Your Brain Power. (Textbook Page No. 178)

 

Question 1. Creatinine is considered as index of kidney function. Give reason.
Answer:1. Plasma creatinine is produced from catabolism of creatinine phosphate during skeletal muscle contraction.
2. It provides a ready source of high energy phosphate.
3. Normally blood creatinine levels remain steady because the rate of production matches its excretion in urine.
4. Hence, plasma creatinine is used as an index of kidney function and its level above normal is an indication of poor renal function.
[Note: Plasma creatinine is a waste product produced by muscles from the breakdown of a compound called 'creatine phosphate '.
In simple words: Creatinine levels indicate kidney function because it's a constant byproduct of muscle metabolism that healthy kidneys efficiently remove from the blood. High levels suggest impaired kidney filtration.

🎯 Exam Tip: Remember that consistent creatinine production and its primary excretion via kidneys make it a reliable marker for kidney health.

 

Make A Table. (Textbook Page No. 178)

 

Question 1. The excretory organs found in various animal phyla.
Answer:

Sr. No.	Animal Phyla	Excretory organs
i.	Porifera	Lack excretory organ instead rely on water transport system/ Canal system
ii.	Coelenterata	Lack specialised excretory organs. Excretion takes place through simple diffusion or through the mouth.
iii.	Ctenophora	Lack specialised excretory organs
iv.	Platyhelminthes	Protonephridia or Flame cells
v.	Aschelminthes	Excretory tube and pore
vi.	Annelida	Nephridia
vii.	Arthropoda	Malpighian tubules
viii.	Mollusca	Organ of Bojanus
ix.	Echinodermata	Lack specialized excretory organs, waste materials directly diffuse into water or are excreted through tube feet
x.	Hemichordata	Proboscis gland
xi.	Chordata	Kidney

In simple words: Excretory organs vary greatly across animal phyla, ranging from simple diffusion in Porifera to complex kidneys in Chordata, reflecting diverse evolutionary adaptations.

🎯 Exam Tip: Memorize the key excretory structures for at least 5-7 major phyla to demonstrate comprehensive knowledge.

 

Observe And Complete. (Textbook Page No. 178)

 

Question 1. Label the diagram and complete following paragraphs.

ℹ️ चित्र व्याख्या (Diagram Explanation): यह चित्र मानव उत्सर्जन तंत्र को दर्शाता है जिसमें मुख्य अंग जैसे गुर्दे, मूत्रवाहिनी, मूत्राशय और मूत्रमार्ग शामिल हैं। यह गुर्दे की स्थिति, रक्त वाहिकाओं जैसे गुर्दे की धमनी और शिरा, और गुर्दे से मूत्राशय तक मूत्र के मार्ग को दिखाता है।
Answer:

ℹ️ चित्र व्याख्या (Diagram Explanation): यह चित्र मानव उत्सर्जन तंत्र को दर्शाता है जिसमें सभी अंगों को उनके सही नामों से नामांकित किया गया है। यह गुर्दे, अधिवृक्क ग्रंथि, वृक्क धमनी, वृक्क शिरा, गुर्दे का श्रोणि, वृक्क मज्जा, वृक्क प्रांतस्था, मूत्रवाहिनी, मूत्राशय और मूत्रमार्ग जैसे घटकों को स्पष्ट रूप से दिखाता है।
i. Kidney: A pair of bean shaped kidneys are present on either side of the backbone from 12th thoracic to 3rd lumbar vertebra. Kidneys are present behind peritoneum. Hence are called retroperitoneal. Dimensions of each kidney are 10 × 5 × 4 cms. Average weight is 150 g in males and 135 g in females. Outer surface is convex and inner is concave. Notch on the inner concave surface is called hilum. Renal artery enters and renal vein as well as ureter leave the kidney through hilus. Each kidney has almost 1 million functional units called nephron.
ii. Ureters: A pair of ureters arise from hilum of each kidney. Each ureter is a long muscular tube 25 - 30 cm in length. Ureters open into urinary bladder by separate openings, which are not guarded by valves. They pass obliquely through the wall of urinary bladder. This helps in prevention of backward flow of urine due to compression of ureters while bladder is filled.
iii. Urinary bladder: It is a median pear-shaped sac. A hollow muscular organ, the bladder is situated in pelvic cavity posterior to pubic symphysis. At the base of the urinary bladder there is a small inverted triangular area called trigone. At the apex of this triangle is opening of urethra. At the two points of the base of the triangle are openings of ureters. Urinary bladder is covered externally by peritoneum. Inner to peritoneum is muscular layer. It is formed by detrusor muscles which consist of three layers of smooth muscles. Longitudinal - circular - longitudinal respectively. Innermost layer is made up of transitional epithelial tissue. It helps bladder to stretch.
iv. Urethra: It is a fibromuscular tube-like structure arising from urinary bladder and opening to the exterior of the body. There are two urethral sphincters between urinary bladder and urethra.
a. Internal sphincter: Made up of detrusor muscles, involuntary in nature.
b. External sphincter: Made up of striated muscles, voluntary in nature.
If this valve is not functioning properly during inflammation of bladder, it can lead to kidney infection.
In simple words: The human excretory system includes two bean-shaped retroperitoneal kidneys, paired ureters connecting kidneys to the pear-shaped urinary bladder, and a single urethra for urine expulsion, with muscles and sphincters regulating flow.

🎯 Exam Tip: Ensure you can accurately label all parts of the human excretory system and describe the function of each component for structural and physiological questions.

 

Internet Is My Friend. (Textbook Page No. 179)

 

Question 1. Find out what is floating kidney.
Answer:1. Floating kidney or nephroptosis, is an inferior displacement or dropping of the kidney.
2. This condition occurs when the kidney slips from its normal position because it is not held securely in place by the adjacent organs or its fat covering.
3. It generally develops in extremely thin people whose adipose capsule or renal fascia is deficient.
4. It may result in twisting of the ureter and cause blockage of urine flow. The resulting backup of urine would put pressure on the kidney and damage the tissues.
5. Twisting of the ureter may also cause pain and discomfort.
6. This condition is more common in females than males and happens commonly among one in four people.
7. Weakening of the fibrous bands that hold the kidney in place can predispose to floating kidney.
In simple words: A floating kidney, or nephroptosis, occurs when a kidney drops from its normal position due to weak supporting tissues, potentially causing ureter twisting, urine blockage, and pain.

🎯 Exam Tip: Focus on understanding the cause (weak support) and main consequences (ureter twisting, blockage) of floating kidney.

 

Can You Recall? (Textbook Page No. 179)

 

Question 1. Observe the figure carefully and label various regions of L.S. of kidney.

ℹ️ चित्र व्याख्या (Diagram Explanation): यह चित्र गुर्दे के अनुदैर्ध्य खंड (L.S. of Kidney) को दर्शाता है। इसमें गुर्दे के मुख्य आंतरिक संरचनात्मक भाग जैसे वृक्क प्रांतस्था, छोटे और बड़े गुर्दे के गुहा (calyx), वृक्क पैपिला, वृक्क मज्जा, वृक्क स्तंभ और वृक्क पिरामिड दिखाए गए हैं।
Answer:
In simple words: A kidney's longitudinal section reveals an outer renal cortex, an inner renal medulla with pyramids, and a central renal pelvis leading to the ureter, all crucial for filtration and urine collection.

🎯 Exam Tip: Precisely labelling each internal part of the kidney in a diagram is essential for anatomy questions.

 

Can You Tell? (Textbook Page No.182)

 

Question 1. Why are kidneys called 'retroperitoneal'?
Answer:Kidneys are located in abdomen. Kidneys are not surrounded by peritoneum instead they are located posterior to it. Thus, kidneys are called retroperitoneal.
In simple words: Kidneys are called 'retroperitoneal' because they lie behind the peritoneum, the membrane lining the abdominal cavity, rather than being enclosed within it.

🎯 Exam Tip: This term describes the anatomical position of the kidneys; understanding it helps visualize their location within the body.

 

Question 2. Why urinary tract infections are more common in females than males?
Answer:• The urethra in women (4 cm) is much shorter than that of males (20 cm).
• This allows easy passage of bacteria into the urinary bladder.
Hence, urinary tract infections are more common in females than males.
In simple words: Urinary tract infections are more common in females because their urethra is significantly shorter than in males, providing bacteria an easier path to the bladder.

🎯 Exam Tip: Relate the anatomical difference (urethral length) directly to the increased risk of bacterial ascent in females.

 

Question 3. What is nephron? Which are its main parts? Why are they important?
Answer:Nephron is the structural and functional unit of kidney.
Structure of nephron:
A nephron (uriniferous tubule) is a thin walled, coiled duct, lined by a single layer of epithelial cells. Each nephron is divided into two main parts:
i. Malpighian body
ii. Renal tubule

ℹ️ चित्र व्याख्या (Diagram Explanation): यह चित्र एक नेफ्रॉन और पेरिट्यूबुलर केशिकाओं के नेटवर्क को दर्शाता है, जो गुर्दे की कार्यात्मक इकाई है। इसमें अभिवाही धमनी, अपवाही धमनी, केशिकागुच्छ, बोमन कैप्सूल, समीपस्थ और दूरस्थ संवलित नलिका, हेनले लूप और संग्रह वाहिनी जैसे विभिन्न भाग शामिल हैं।
i. Malpighian body: Each Malpighian body is about 200pm in diameter and consists of a Bowman's capsule and glomerulus.
a. Glomerulus:
Glomerulus is a bunch of fine blood capillaries located in the cavity of Bowman's capsule. A small terminal branch of the renal artery, called as afferent arteriole enters the cup cavity (Bowman capsule) and undergoes extensive fine branching to form network of several capillaries. This bunch is called as glomerulus. The capillary wall is fenestrated (perforated). All capillaries reunite and form an efferent arteriole that leaves the cup cavity. The diameter of the afferent arteriole is greater than the efferent arteriole. This creates a high hydrostatic pressure essential for ultrafiltration, in the glomerulus.
b. Bowman's capsule:
It is a cup-like structure having double walls composed of squamous epithelium. The outer wall is called as parietal wall and the inner wall is called as visceral wall. The parietal wall is thin consisting of simple squamous epithelium. There is a space called as capsular space / urinary space in between two walls. Visceral wall consists of special type of squamous cells called podocytes having a foot-like pedicel. These podocytes are in close contact with the walls of capillaries of glomerulus. There are small slits called as filtration slits in between adjacent podocytes.
ii. Renal tubule:
a. Neck:
The Bowman's capsule continues into the neck. The wall of neck is made up of ciliated epithelium. The lumen of the neck is called the urinary pole. The neck leads to proximal convoluted tubule.
b. Proximal Convoluted Tubule :
This is highly coiled part of nephron which is lined by cuboidal cells with brush border (microvilli) and surrounded by peritubular capillaries. Selective reabsorption occurs in PCT. Due to convolutions (coiling), filtrate flows slowly and remains in the PCT for longer duration, ensuring that maximum amount of useful molecules are reabsorbed.
c. Loop of Henle :
This is 'U' shaped tube consisting of descending and ascending limb. The descending limb is thin walled and permeable to water and lined with simple squamous epithelium. The ascending limb is thick walled and impermeable to water and is lined with simple cuboidal epithelium. The LoH is surrounded by capillaries called vasa recta. Its function is to operate counter current system - a mechanism for osmoregulation.
The ascending limb of Henle's loop leads to DCT.
d. Distal convoluted tubule:
This is another coiled part of the nephron. Its wall consists of simple cuboidal epithelium. DCT performs tubular secretion / augmentation / active secretion in which, wastes are taken up from surrounding capillaries and secreted into passing urine. DCT helps in water reabsorption and regulation of pH of body fluids.
e. Collecting tubule:
This is a short, straight part of the DCT which reabsorbs water and secretes protons. The collecting tubule opens into the collecting duct.
In simple words: The nephron, the kidney's functional unit, consists of the Malpighian body (Bowman's capsule and glomerulus for filtration) and the renal tubule (PCT, Loop of Henle, DCT, collecting tubule) for selective reabsorption and secretion, collectively forming urine and maintaining body fluid balance.

🎯 Exam Tip: Accurately describing the structure and function of each nephron part, especially filtration, reabsorption, and secretion mechanisms, is essential for comprehensive answers.

 

Think About It. (Textbook Page No. 182)

 

Question 1. How much blood is supplied to kidney?
Answer:Around 600 ml of blood passes through each kidney per minute.
In simple words: Approximately 600 ml of blood is supplied to each kidney per minute for filtration.

🎯 Exam Tip: Remember this value as it highlights the high blood flow and critical role of kidneys in circulating blood.

 

Do This. (Textbook Page No. 183)

 

Question 1. Check blood reports of patients and comment about possibility of glucosuria.
Answer:Glucosuria is the presence of glucose sugar in urine. High glucose in urine is usually indicative of diabetes mellitus.

Condition	Glucose range in urine
Normal	0 to 15 mg/dL (0 to 0.8 mmol/L)
Prediabetes	100 to 125 mg/dL (5.6 to 6.9 mmol/L)
Diabetes	126 mg/dL (7 mmol/L)

[Students can get access to sample reports on the internet and refer the above table to comment on blood reports of patients on their own.]
In simple words: Glucosuria, or glucose in urine, often signals diabetes mellitus because high blood sugar overwhelms the kidneys' reabsorption capacity, causing glucose to spill into the urine.

🎯 Exam Tip: Understand the physiological link between blood glucose levels, kidney reabsorption limits, and the appearance of glucose in urine.

 

Use Your Brain Power. (Textbook Page No. 185)

 

Question 1. In which regions of nephron the filtrate will he isotonic to blood?
Answer:Filtrate leasing the proximal convoluted tubule (PCT) is isotonic to the blood plasma.
In simple words: The filtrate in the proximal convoluted tubule (PCT) remains isotonic to blood plasma because water and solutes are reabsorbed proportionally.

🎯 Exam Tip: Recall that the PCT is where the bulk of reabsorption occurs, maintaining the isotonic nature of the filtrate with plasma.

 

Can You Tell? (Textbook Page No. 185)

 

Question 1. Explain the process of urine formation in details.
Answer:Process of urine formation is completed in three steps, namely;
i. Ultrafiltration/ Glomerular filtration,
ii. Selective reabsorption,
iii. Tubular secretion / Augmentation
i. Ultrafiltration / Glomerular filtration:
Diameter of afferent arteriole is greater than the efferent arteriole. The diameter of capillaries is still smaller than both arterioles. Due to the difference in diameter, blood flows with greater pressure through the glomerulus. This is called as glomerular hydrostatic pressure (GHP) and normally, it is about 55 mmHg. GHP is opposed by osmotic pressure of blood (normally, about 30 mm Hg) and capsular pressure (normally, about 15 mm Hg).
Hence net / effective filtration pressure (EFP) is 10 mm Hg.
\(EFP = Hydrostatic pressure in glomerulus - (Osmotic pressure of blood + Filtrate Hydrostatic pressure)\)
\( = 55 - (30 + 15)\)
\( = 10 mm Hg\)
Under the effect of high pressure, the thin walls of the capillary become permeable to major components of blood (except blood cells and macromolecules like protein).
Thus, plasma except proteins oozes out through wall of capillaries.
About 600 ml blood passes through each kidney per minute.
The blood (plasma) flowing through kidney (glomeruli) is filtered as glomerular filtrate, at a rate of 125 ml / min. (180 L/d).
Glomerular filtrate / deproteinized plasma / primary urine is alkaline, contains urea, amino acids, glucose, pigments, and inorganic ions.
Glomerular filtrate passes through filtration slits into capsular space and then reaches the proximal convoluted tubule.
ii. Selective reabsorption :
Selective reabsorption occurs in proximal convoluted tubule (PCT). It is highly coiled so that glomerular filtrate passes through it very slowly. Columnar cells of PCT are provided with microvilli due to which absorptive area increases enormously.
This makes the process of reabsorption very effective.
These cells perform active (ATP mediated) and passive (simple diffusion) reabsorption.
Substances with considerable importance (high threshold) like - glucose, amino acids, vitamin C, Ca++, K+, Na+, Cl¯ are absorbed actively, against the concentration
In simple words: Urine formation involves three steps: ultrafiltration in the glomerulus, where blood plasma is filtered; selective reabsorption in the tubules, recovering essential substances back into the blood; and tubular secretion, where waste products are actively moved from blood to filtrate, resulting in concentrated urine.

🎯 Exam Tip: Be sure to detail the pressures involved in ultrafiltration and specify the key substances reabsorbed or secreted in different parts of the nephron.

iii. Tubular secretion / Augmentation :

Finally filtrate reaches the distal convoluted tubule via loop of Henle. Peritubular capillaries surround DCT. Cells of distal convoluted tubule and collecting tubule actively absorb the wastes like creatinine and ions like K+, H+ from peritubular capillaries and secrete them into the lumen of DCT and CT, thereby augmenting the concentration of urine and changing its pH from alkaline to acidic.
Secretion of H+ ions in DCT and CT is an important homeostatic mechanism for pH regulation of blood. Tubular secretion is the only process of excretion in marine bony fishes and desert amphibians.

ℹ️ चित्र व्याख्या (Diagram Explanation): यह एक प्रवाह चार्ट है जो मूत्र निर्माण की प्रक्रिया को दर्शाता है, जिसमें ग्लोमेरुलर निस्पंदन, ट्यूबलर पुनरावशोषण और ट्यूबलर स्राव शामिल हैं। यह विभिन्न भागों जैसे एफरेंट और एफरेंट आर्टेरियोल, ग्लोमेरुलस, नेफ्रॉन लूप, पीसीटी, डीसीटी, कलेक्टिंग ट्यूबल, ग्लोमेरुलर कैप्सूल और वासा रेक्टा को उनके कार्यात्मक संबंधों के साथ दिखाता है।

Question 2. How does counter current mechanism help concentration of urine?
Answer: Under the conditions like low water intake or high water loss due to sweating, humans can produce concentrated urine. This urine can be concentrated around four times i.e. 1200 mOsm/L than the blood (300 mOsm/L). Hence, a mechanism called countercurrent mechanism is operated in the human kidneys. The countercurrent mechanism operating in the Limbs of Henle's loop of juxtamedullary nephrons and vasa recta is as follows:
1. It involves the passage of fluid from descending to ascending limb of Henle's loop.
2. This mechanism is called countercurrent mechanism, since the flow of tubular fluid is in opposite direction through both limbs.
3. In case of the vasa recta, blood flows from ascending to descending parts of itself.
4. Wall of descending limb is thin and permeable to water, hence, water diffuses from tubular fluid into tissue fluid due to which, tubular fluid becomes concentrated.
5. The ascending limb is thick and impermeable to water. Its cells can reabsorb Na+ and Cl- from tubular fluid and release into tissue fluid.
6. Due to this, tissue fluid around descending limb becomes concentrated. This makes more water to move out from descending limb into tissue fluid by osmosis.
7. Thus, as tubular fluid passes down through descending limb, its osmolarity (concentration) increases gradually due to water loss and on the other hand progressively decreases due to Na+ and Cl- secretion as it flows up through ascending limb.
8. Whenever retention of water is necessary, the pituitary secretes ADH. ADH makes the cells in the wall of collecting ducts permeable to water.
9. Due to this, water moves from tubular fluid into tissue fluid, making the urine concentrated.
10. Cells in the wall of deep medullar part of collecting ducts are permeable to urea. As concentrated urine flows through it, urea diffuses from urine into tissue fluid and from tissue fluid into the tubular fluid flowing through thin ascending limb of Henle's loop.
11. This urea cannot pass out from tubular fluid while flowing through thick segment of ascending limb, DCT and cortical portion of collecting duct due to impermeability for it in these regions.
12. However, while flowing through collecting duct, water reabsorption is operated under the influence of ADII. Due to this, urea concentration increases in the tubular fluid and same urea again diffuses into tissue fluid in deep medullar region.
13. Thus, same urea is transferred between segments of renal tubule and tissue fluid of inner medulla. This is called urea recycling; operated for more and more water reabsorption from tubular fluid and thereby excreting small volumes of concentrated urine.
14. Osmotic gradient is essential in the renal medulla for water reabsorption by counter current multiplier system.
15. This osmotic gradient is maintained by vasa recta by operating counter current exchange system.
16. Vasa recta also have descending and ascending limbs. Blood that enters the descending limb of the vasa recta has normal osmolarity of about 300 mOsm/L.
17. As it flows down in the region of renal medulla where tissue fluid becomes increasingly concentrated, Na+, Cl- and urea molecules diffuse from tissue fluid into blood and water diffuse from blood into tissue fluid.
18. Due to this, blood becomes more concentrated which now flows through ascending part of vasa recta. This part runs through such region of medulla where tissue fluid is less concentrated.
19. Due to this, Na+, Cl- and urea molecules diffuse from blood to tissue fluid and water from tissue fluid to blood. This mechanism helps to maintain the osmotic gradient.
In simple words: The countercurrent mechanism in the kidney's loop of Henle and vasa recta creates a concentration gradient in the renal medulla. This gradient allows for efficient reabsorption of water, helping the body produce concentrated urine and conserve water.

🎯 Exam Tip: Focus on understanding the roles of the loop of Henle, vasa recta, and collecting ducts in establishing and maintaining the osmotic gradient for urine concentration.

ℹ️ चित्र व्याख्या (Diagram Explanation): यह एक विस्तृत आरेख है जो नेफ्रॉन और वासा रेक्टा के माध्यम से मूत्र के संकेंद्रण को दर्शाता है। यह ग्लोमेरुलस, बोमन कैप्सूल, पीसीटी, हेनले लूप के उतरते और चढ़ते अंग, डीसीटी और कलेक्टिंग डक्ट में सोडियम, क्लोराइड, यूरिया और पानी की गति को 300 से 1200 mOsm/L तक की बढ़ती सांद्रता के साथ दिखाता है।

Try This. (Textbook Page No. 185)

Question 1. Read the given urine report and prepare a note on composition of normal urine.
Answer: The composition of normal urine is as follows:
1. A volume of 1 - 2 litres of urine in 24 hours is normal. This volume can however vary considerably as it depends on fluid intake, physical activity, temperature, etc.
2. The colour of normal urine is generally pale yellow due to urochrome (pigment produced by breakdown of bile). The colour of urine may vary slightly due to urochrome concentration and diet.
3. The appearance of urine is generally clear and transparent.
4. Any form of deposits (sediments/ crystals) is generally absent in normal urine.
5. The pH of normal urine is acidic and is generally around 6.0 (Range: 4.6 to 8.0). The pH varies considerably with the diet of a person.
6. The specific gravity of urine is an average of 1.02 (Range : 1.001 to 1.035).
7. Albumin, sugar, bile salts bile pigments, ketone bodies and casts are absent in normal urine.
8. Occult blood is generally not seen in normal urine.
In simple words: Normal urine is typically pale yellow, clear, and ranges from 1-2 liters per day with a slightly acidic pH and specific gravity around 1.02. It should be free from abnormal substances like protein, sugar, bile, or blood.

🎯 Exam Tip: Remember the key characteristics of normal urine, including its volume, color, pH, specific gravity, and the absence of abnormal components, as these are critical indicators of kidney health.

Think (Textbook Page No. 185)

Question 1. What would happen if ADH secretion decreases due to any reason?
Answer: In absence of ADH, diuresis (dilution of urine) takes place and person tends to excrete large amount of dilute urine. This condition called as diabetes insipidus. Frequent excretion of large amount of dilute urine may cause a person to feel thirsty.
In simple words: If ADH secretion decreases, the kidneys reabsorb less water, leading to the excretion of a large volume of dilute urine and increased thirst, a condition known as diabetes insipidus.

🎯 Exam Tip: Understand that Antidiuretic Hormone (ADH) is crucial for water reabsorption. A decrease in ADH directly impairs the body's ability to concentrate urine, leading to excessive water loss.

Think And Appreciate. (Textbook Page No. 185)

Question 1. How do kidneys bring about homeostasis? Is there any role of neuro endocrine system in it?
Answer: The composition of urine depends upon food and fluid consumed by an individual There are two ways in which it the composition is regulated. They are as follows:
i. Regulating water reabsorption through ADH
ii. Electrolyte reabsorption though RAAS
iii. Atrial Natriuretic Peptide
i. Regulating water reabsorption through ADH:
Hypothalamus in the midbrain has special receptors called osmoreceptors which can detect change in osmolarity (measure of total number of dissolved particles per liter of solution) of blood.
If osmolarity of blood increases due to water loss from the body (after eating namkeen or due to sweating), osmoreceptors trigger release of Antidiuretic hormone (ADH) from neurohypophysis (posterior pituitary). ADH stimulates reabsorption of water from last part of DCT and entire collecting duct by increasing the permeability of cells.
This leads to reduction in urine volume and decrease in osmolarity of blood.
Once the osmolarity of blood comes to normal, activity of osmoreceptor cells decreases leading to decrease in ADH secretion. This is called negative feedback. In case of hemorrhage or severe dehydration too, osmoreceptors stimulate ADH secretion. ADH is important in regulating water balance through kidneys.
In absence of ADH, diuresis (dilution of urine) takes place and person tends to excrete large amount of dilute urine. This condition called as diabetes insipidus.
[Note: Hypothalamus is a part of forebrain]
ii. Electrolyte reabsorption through RAAS:
Another regulatory mechanism is RAAS (Renin Angiotensin Aldosterone System) by Juxta Glomerular Apparatus (JGA).
Whenever blood supply (due to change in blood pressure or blood volume) to afferent arteriole decreases (e.g. low BP/dehydration), JGA cells release Renin.
Renin converts angiotensinogen secreted by hepatocytes in liver to Angiotensin I. 'Angiotensin converting enzyme' further modifies Angiotensin I to Angiotensin II, the active form of hormone. It stimulates adrenal cortex to release another hormone called aldosterone that stimulates DCT and collecting ducts to reabsorb more Na and water, thereby increasing blood volume and pressure.
iii. Atrial natriuretic peptide (ANP): A large increase in blood volume and pressure stimulates atrial wall to produce atrial natriuretic peptide (ANP). ANP inhibits Na+ and Cl- reabsorption from collecting ducts inhibits release of renin, reduces aldosterone and ADH release too. This leads to a condition called Natriuresis (increased excretion of Na+ in urine) and diuresis.
No. Both ADH and RAAS are essential for homeostasis.
1. Only ADH can lower blood Na+ concentration by way of water reabsorption in DCI and collecting duct. whereas RAAS stimulates Na+ reabsorption and maintains osmolarity of body fluid.
2. Action of ADH and RAAS leads to increase in blood volume and osmolarity.
3. For mechanism of Atrial natriuretic peptide:
Atrial natriuretic peptide (ANP): A large increase in blood volume and pressure stimulates atrial wall to produce atrial natriuretic peptide (ANP). ANP inhibits Na+ and Cl- reabsorption from collecting ducts inhibits release of renin, reduces aldosterone and ADH release too. This leads to a condition called Natriuresis (increased excretion of Na+ in urine) and diuresis.
ADH is produced by the hypothalamus and is stored and released by the posterior pituitary or the neurohypophysis in response to appropriate trigger. Hence, there is a role of the neuroendocrine system in homeostasis.
In simple words: Kidneys maintain homeostasis by regulating water and electrolyte balance through hormonal mechanisms like ADH, RAAS, and ANP, all part of the neuroendocrine system, which adjust urine volume and composition based on body fluid needs.

🎯 Exam Tip: When explaining kidney's role in homeostasis, emphasize the interconnectedness of ADH, RAAS, and ANP, and how their regulation ensures fluid balance, blood pressure control, and proper electrolyte levels, highlighting the neuroendocrine system's critical involvement.

Use Your Brain Power. (Textbook Page No. 186)

Question 1. Can we use this knowledge in treatment of high blood pressure? Why high BP medicines are many a times diuretics?
Answer: 1. Yes, the knowledge of homoeostasis is used in the treatment of high blood pressure.
2. Some commonly used theories for treatment of high blood pressure are as follows:
• Angiotensin II receptor blockers (ARBs) are used as medications to treat high blood pressure. These medications block the action of angiotensin II by preventing angiotensin II from binding to angiotensin II receptors on the muscles surrounding blood vessels. As a result, blood vessels enlarge (dilate), and blood pressure is reduced.
• Another method is the use of 'Angiotensin converting enzyme' ACE blockers. These inhibitors inhibit activity of ACE and therefore decrease the production of angiotensin II. As a result, these medications cause the blood vessels to enlarge or dilate, and this reduces blood pressure.
3. Vasodilation reduces arterial pressure. Reduced angiotensin II leads to natriuresis (increased excretion of Na+ in urine) and diuresis, thereby reducing blood pressure.
4. Too much salt can cause extra fluid to build up in the blood vessels, raising blood pressure. Diuretics are substances that slow renal absorption of water and thereby cause diuresis (elevated urine flow rate) which in turn reduces blood volume and blood pressure by flushing out salt and extra fluid. Hence, high BP medicines are many a times diuretics.
In simple words: Yes, understanding kidney regulation helps treat high blood pressure, often by using diuretics that increase urine output to reduce fluid volume and blood pressure, or by targeting the RAAS system to relax blood vessels.

🎯 Exam Tip: Highlight the direct link between fluid volume and blood pressure. Diuretics reduce blood volume by increasing water and salt excretion, which is a primary mechanism for lowering high blood pressure.

Can You Tell? (Textbook Page No. 186)

Question 1. How do skin and lungs help in excretion?
OR
Can You Tell? (Textbook Page No. 187)
Explain role of lungs and skin in excretion.
Answer: Yes, various organs other than the kidney participate in excretion. They are as follows:
i. Skin:
Skin acts as an accessory excretory organ. The skin of many organisms is thin and permeable. It helps in diffusion of waste products like ammonia.
Human skin however is thick and impermeable. It shows presence of two types of glands namely, sweat glands and sebaceous glands.
• Sweat glands are distributed all over the skin. They are abundant in the palm and facial regions.
These simple, unbranched, coiled, tubular glands open on the surface of the skin through an opening called sweat pore. Sweat is primarily produced for thermoregulation but it also excretes substances like water, NaCl, lactic acid and urea.
• Sebaceous glands are present at the neck of hair follicles. They secrete oily substance called sebum.
It forms a lubricating layer on skin making it softer. It protects skin from infection and injury.
ii. Lungs:
Lungs are the accessory excretory organs. They help in excretion of volatile substances like CO2 and water vapour produced during cellular respiration. Along with CO2, lungs also remove excess of H2O in the form of vapours during expiration. They also excrete volatile substances present in spices and other food stuff.
In simple words: The skin helps excrete water, salts, urea, and lactic acid through sweat glands, while lungs eliminate carbon dioxide and water vapor during respiration, along with some volatile food substances.

🎯 Exam Tip: Remember that while kidneys are primary, accessory excretory organs like skin and lungs play crucial roles in maintaining overall waste balance, especially for volatile compounds and heat regulation.

Can You Tell? (Textbook Page No. 187)

Question 1. When does kidney produce renin? Where is it produced in kidney?
Answer: Kidney produces renin whenever blood supply (due to change in blood pressure or blood volume) to afferent arteriole decreases (e.g. low BP/dehydration).
The juxtaglomerular Apparatus (JGA) cells secrete renin.
In simple words: The kidney produces renin when blood supply or pressure decreases, and it is secreted by the juxtaglomerular apparatus (JGA) cells within the kidney.

🎯 Exam Tip: Know that renin's release is a critical initial step in the Renin-Angiotensin-Aldosterone System (RAAS), which is vital for regulating blood pressure and fluid balance.

Question 2. Explain how electrolyte balance of blood plasma maintained.
Answer: The composition of urine depends upon food and fluid consumed by an individual. There are two ways in which it the composition is regulated. They are as follows:
i. Regulating water reabsorption through ADH
ii. Electrolyte reabsorption though RAAS
iii. Atrial Natriuretic Peptide
i. Regulating water reabsorption through ADH:
Hypothalamus in the midbrain has special receptors called osmoreceptors which can detect change in osmolarity (measure of total number of dissolved particles per liter of solution) of blood.
If osmolarity of blood increases due to water loss from the body (after eating namkeen or due to sweating), osmoreceptors trigger release of Antidiuretic hormone (ADH) from neurohypophysis (posterior pituitary). ADH stimulates reabsorption of water from last part of DCT and entire collecting duct by increasing the permeability of cells.
This leads to reduction in urine volume and decrease in osmolarity of blood.
Once the osmolarity of blood comes to normal, activity of osmoreceptor cells decreases leading to decrease in ADH secretion. This is called negative feedback. In case of hemorrhage or severe dehydration too, osmoreceptors stimulate ADH secretion. ADH is important in regulating water balance through kidneys.
In absence of ADH, diuresis (dilution of urine) takes place and person tends to excrete large amount of dilute urine. This condition called as diabetes insipidus.
[Note: Hypothalamus is a part of forebrain]
ii. Electrolyte reabsorption through RAAS:
Another regulatory mechanism is RAAS (Renin Angiotensin Aldosterone System) by Juxta Glomerular Apparatus (JGA).
Whenever blood supply (due to change in blood pressure or blood volume) to afferent arteriole decreases (e.g. low BP/dehydration), JGA cells release Renin.
Renin converts angiotensinogen secreted by hepatocytes in liver to Angiotensin I. 'Angiotensin converting enzyme' further modifies Angiotensin I to Angiotensin II, the active form of hormone. It stimulates adrenal cortex to release another hormone called aldosterone that stimulates DCT and collecting ducts to reabsorb more Na and water, thereby increasing blood volume and pressure.
iii. Atrial natriuretic peptide (ANP): A large increase in blood volume and pressure stimulates atrial wall to produce atrial natriuretic peptide (ANP). ANP inhibits Na+ and Cl- reabsorption from collecting ducts inhibits release of renin, reduces aldosterone and ADH release too. This leads to a condition called Natriuresis (increased excretion of Na+ in urine) and diuresis.
No. Both ADH and RAAS are essential for homeostasis.
1. Only ADH can lower blood Na+ concentration by way of water reabsorption in DCI and collecting duct. whereas RAAS stimulates Na+ reabsorption and maintains osmolarity of body fluid.
2. Action of ADH and RAAS leads to increase in blood volume and osmolarity.
3. For mechanism of Atrial natriuretic peptide:
Atrial natriuretic peptide (ANP): A large increase in blood volume and pressure stimulates atrial wall to produce atrial natriuretic peptide (ANP). ANP inhibits Na+ and Cl- reabsorption from collecting ducts inhibits release of renin, reduces aldosterone and ADH release too. This leads to a condition called Natriuresis (increased excretion of Na+ in urine) and diuresis.
ADH is produced by the hypothalamus and is stored and released by the posterior pituitary or the neurohypophysis in response to appropriate trigger. Hence, there is a role of the neuroendocrine system in homeostasis.
In simple words: Electrolyte balance in blood plasma is maintained by hormones like ADH, RAAS, and ANP. ADH regulates water reabsorption, RAAS increases sodium and water reabsorption to raise blood pressure, and ANP lowers blood pressure by increasing sodium and water excretion, ensuring overall fluid and electrolyte homeostasis.

🎯 Exam Tip: Mastering the regulatory loops of ADH, RAAS, and ANP is essential. Understand how these hormones interact to fine-tune water and electrolyte levels, impacting blood volume and pressure.

Can You Tell? (Textbook Page No. 187)

Question 1. What is the composition of sweat?
Answer: Sweat is composed of water, NaCl, lactic acid and urea.
In simple words: Sweat is primarily water, along with small amounts of sodium chloride (table salt), lactic acid, and urea.

🎯 Exam Tip: Remember that sweat's composition reflects its dual role in thermoregulation and excretion, with water being the primary component for cooling and salts/urea for minor waste removal.

Internet My Friend. (Textbook Page No. 189)

Question 1. Treatments other than surgical removal of kidney stone like Lithotripsy. (Breaking down of kidney stones using shock waves).
Answer: a. Cystoscopy and ureteroscopy:
During cystoscopy, the doctor uses a cystoscope to look inside the urethra and bladder to find a stone in the urethra or bladder.
During ureteroscopy, the doctor uses a ureteroscope, which is longer and thinner than a cystoscope, to see detailed images of the lining of the ureters and kidneys.
The doctor inserts the cystoscope or ureteroscope through the urethra to see the rest of the urinary tract. Once the stone is found, the doctor can remove it or break it into smaller pieces.
The doctor performs these procedures in the hospital with anesthesia.
b. Percutaneous nephrolithotomy:
The doctor uses a thin viewing tool, called a nephroscope, to locate and remove the kidney stone.
The doctor inserts the tool directly into your kidney through a small cut made in your back.
For larger kidney stones, the doctor also may use a laser to break the kidney stones into small pieces. The doctor performs percutaneous nephrolithotomy in a hospital with anesthesia.
c. Generally for smaller stones doctors recommend drinking lots of water, consuming pain relievers and consuming medicines like alpha blocker to relax the ureter muscles, and help pass the kidney stones more quickly and with less pain
In simple words: Beyond surgery and lithotripsy, kidney stone treatments include cystoscopy/ureteroscopy to remove or break stones via endoscopic tools, percutaneous nephrolithotomy for larger stones, and conservative management with increased water intake and medication for smaller stones.

🎯 Exam Tip: Be aware of non-surgical options for kidney stones, focusing on how each method (e.g., lithotripsy, ureteroscopy) aims to break or remove stones with minimal invasiveness compared to traditional surgery.

Question 2. Dietary restrictions suggested for kidney patients.
Answer: Dietary restrictions for kidney patients include the following:
1. Drinking large amounts of water.
2. Reduce consumption of oxalate rich food like rhubarb, beets, okra, spinach, Swiss chard, sweet potatoes, nuts, tea, chocolate and soy products.
3. Follow a diet low in salt and animal protein.
4. Reduce consumption of calcium supplements (if any) but consume appropriate amount of calcium in food.
In simple words: Kidney patients should drink plenty of water, reduce high-oxalate foods, limit salt and animal protein, and manage calcium intake to prevent stone formation and reduce kidney burden.

🎯 Exam Tip: Emphasize that dietary management for kidney patients primarily involves balancing fluid intake, restricting specific minerals (like oxalate), and controlling protein and salt to reduce metabolic stress on the kidneys.

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