NCERT Class 11 Biology Body Fluids and Circulartion Important Notes

Blood:

Blood is a connective tissue which is composed of a fluid matrix (plasma) and formed elements.

Plasma

Plasma is a straw-coloured and viscous fluid. Plasma constitutes about 55% of the blood. About 90% of plasma is water and about 6-8% is composed of proteins. The major plasma proteins are; fibrinogen, globulins and albumins. Fibrinogen play important role in blood coagulation. Globulins are mainly involved in defense mechanism and albumins help in osmotic balance. Small amounts of minerals; like Na⁺, Ca^{+ +}, Mg^{+ +}, HCO₃^– and Cl^–; are also present in plasma. Plasma also contains glucose, amino acids, lipids, etc. because these substances are always in transit in the body. Factors for clotting of blood are present in the plasma in an inactive form. Plasma without the clotting factors is called serum.

Formed Elements

The formed elements constitute about 45% of the blood. Erythrocytes, leucocytes and platelets are collectively called formed elements.

Erythrocytes or Red Blood Cells (RBCs): The RBCs are the most abundant cells in blood. In a healthy adult, about 5 million to 5.5 million RBCs are present per cubic mm of blood. RBCs are formed in the read bone marrow in the adults. In most of the mammals, nucleus is absent in the RBCs. RBCs are biconcave in shape. The red colour is because of an iron containing protein complex; called haemoglobin. In a healthy adult, each 100 ml of blood contains 12-16 gm blood. The average lifespan of RBCs is 120 days. RBCs are finally destroyed in the spleen and hence, spleen is also called the graveyard of RBCs. RBCs play a significant role in transport of respiratory gases.

Leucocytes or White Blood Cells (WBCs): The WBCs are nucleated and are relatively lesser in number than RBCs. In a healthy adult about 6000-8000 WBCs are present per cubic mm of blood. Leucocytes are generally short lived.

There are two main categories of WBCs:

• Granulocytes , e.g., neutrophils, eosinophils and basophils

• Agranulocytes. e.g., Lymphocytes and monocytes.

a. Neutrophils: Neutrophils are the most abundant cells among WBCs and comprise about 60-65%.

b. Monocytes: Monocytes comprise about 6-8% of WBCs. Neutrophils and monocytes are phagocytic cells.

c. Basophils: Basophils secrete histamine, serotonin, heparin, etc. They are involved in inflammatory reactions.

d. Eosinophils: Eosinophils comprise 2-3% of WBCs. These resist infections and are also associated with allergic reactions.

e. Lymphocytes: Lymphocytes comprise about 20-25% of WBCs. There are two major types of lymphocytes, viz. B and T types. Both the types are responsible for immune responses of the body. 

Platelets: Platelets are also known as thrombocytes. They are cell fragments produced from megakaryotcytes. Megakaryocytes are special cells in the bone marrow. Usually, one cubic mm of blood contains 150,000-350,000 platelets. Platelets can release a variety of substances. Most of these substances are involved in blood coagulation.

BLOOD GROUPS

Two such groupings – the ABO and Rh – are widely used all over the world.

ABO Grouping

ABO grouping is based on the presence of absence of two surface antigens on the RBCs, viz. A and B. Antigens are chemicals which can induce immune response. The plasma also contains two natural antibodies. Antibodies are proteins produced in response to antigens.

Importance of Blood Group: During blood transfusion, the donor blood needs to be carefully matched with the blood of a recipient. Transfusion of unmatched blood can lead to severe problems of clumping, i.e. destruction of RBC.

The blood group O can be donated to persons with any other blood group and hence, an individual with O group is called universal donor. A person with AB blood group can accept blood from all blood groups and hence, such an individual is called universal recipient.

Rh Grouping

The Rh antigen is similar to one present in Rhesus monkeys. It is also observed on the surface of RBCs of majority (nearly 80%) humans. Such individuals are called Rh positive (Rh +ve). A person without Rh antigen is called Rh negative (Rh –ve).

Significance of Rh Group: An Rh -ve person, if exposed to Rh +ve blood, will form specific antibodies against the Rh antigens. Hence, Rh group should also be matched before transfusions.

Rh Incompatibility of Foetus and Mother: A special case of Rh incompatibility is observed between the Rh –ve blood of a pregnant mother with Rh +ve blood of the foetus. Rh antigens of the foetus do not get exposed to the Rh –ve blood of the mother in the first pregnancy because the two bloods are well separated by the placenta. But during the delivery of the first child, there is a possibility of exposure of the maternal blood to small amounts of Rh +ve blood from the foetus. In such an eventuality, the mother starts preparing antibodies against Rh in her blood. In case of her becoming pregnant again, the Rh antibodies from the mother (Rh –ve) can leak into the blood of the foetus (Rh +ve) and destroy the foetal RBCs. This can prove fatal to the foetus or can cause severe anemia and jaundice to the baby. This condition is called erythroblastosis foetalis. This can be avoided by administering anti-Rh antibodies to the mother immediately after the delivery of the first child.

Coagulation of Blood

Blood coagulates in response to an injury or trauma. Coagulation is a mechanism to prevent excessive loss of blood in case of injury. Clot is a dark reddish brown scum which is formed at the site of an injury over a period of time. This is formed by a network of threads called fibrins in which dead and damaged formed elements of blood are trapped.

Process of Blood Clotting: Inactive fibrinogen is present in the plasma. It is converted by the enzyme thrombin into active fibrin. Thrombin is formed from the inactive prothrombin. An enzyme complex, thrombokinase, is responsible for this conversion. This complex is formed by a series of linked enzymatic reactions (cascade process). The process involves a number of factors present in the plasma in an inactive state. An injury stimulates the platelets to release certain factors which activate the mechanism of coagulation. Calcium ions play a very important role in clotting.

Haemophilia: Haemophilia is a clotting disorder which prevents blood clotting. A person suffering from haemophilia is always at a risk of excessive blood loss in case of injury.

LYMPH (TISSUE FLUID)

When the blood passes through the capillaries in tissues, some water; along with many small water-soluble substances move out into the spaces between the cells. Larger proteins and most of the formed elements are left in the blood vessels. This fluid is called the interstitial fluid or tissue fluid. Exchange of nutrients, gases, etc. between the blood and the cells always occur through this fluid.

There is an elaborate network of vessels called the lymphatic system. The lymphatic system collects this fluid and drains it back to the major veins. The fluid present in the lymphatic system is called lymph.

Lymph is a colourless fluid. It contains specialized lymphocytes. Lymph also carries nutrients, hormones, etc. Fats are absorbed through lymph in the lacteals present in the intestinal villi.

CIRCULATORY PATHWAYS

There are two types of circulatory pathways in the animals, viz. open or closed.

Open Circulatory System:

In open circulatory system, blood pumped by the heart passes through large vessels and drained into open spaces or body cavities; called sinuses. This type of circulatory system is present in arthropods and molluscs.

Closed Circulatory System:

In closed circulatory system blood pumped by the heart is circulated through a closed network of blood vessels. This type of system is present in annelids and chordates. The closed circulatory system is more advantageous because the flow of fluid can be more precisely regulated.

Chambered Heart: A muscular chambered heart is present in all vertebrates. The fishes have a 2-chambered heart; with an atrium and a ventricle. Amphibians and reptiles have a 3-chambered heart; with two atria and one ventricle. But crocodiles have 4-chambered heart. Birds and mammals have 4-chambered heart; with two atria and two ventricles.

Single Circulation: In fishes, the heart pumps out deoxygenated blood to the gills. The oxygenated blood from the gills is supplied to the body parts. Deoxygenated blood is then returned from different body parts to the heart. In single circulation, the blood passes through the heart only once.

Incomplete Double Circulation: In amphibians and reptiles, incomplete double circulation is present. Oxygenated blood is received by the left atrium and deoxygenated blood is received by the right atrium. But, both the bloods get mixed up in the single ventricle which pumps out the mixed blood. In incomplete double circulation, the blood comes to the heart through two different routes, but goes out through a single route.

Complete Double Circulation: Complete double circulation is present in birds and mammals. In this case, the oxygenated blood is received by the left atrium and the deoxygenated blood is received by the right atrium. The oxygenated blood is pumped out through the left ventricle, while the deoxygenated blood is pumped out through the right ventricle. In complete double circulation, there are two separate pathways for oxygenated and deoxygenated bloods.

HUMAN CIRCULATORY SYSTEM

The human circulatory system is composed of a muscular heart, a network of closed branching blood vessels and blood.

Heart:

Location and Size: Heart is a mesodermally derived organ. It is situated in the thoracic cavity; in between the two lungs and slightly tilted to the left. It is the size of a clenched fist.

Structure: The heart is protected by a double-walled membrane; called pericardium. The pericardial fluid is filled in this membranous bag.

There are four chambers in the human heart:

a. The two upper chambers are called atria and are relatively smaller.

b. The two lower chambers are called ventricles and are relatively larger.

A thin, muscular wall separates the right and the left atria and is called the inter-atrial septum. A thick muscular wall separates the left and the right ventricles and is called the inter-ventricular septum. The atrium and ventricle on the same side are separate by a thick fibrous tissue; called the atrio-ventricular septum. Each of these septa has an opening through which the atrium and the ventricle of the same side are connected.

The opening between the right atrium and the right ventricle is guarded by a valve. This valve has three flaps or cusps and hence is called the tricuspid valve. Similarly, a bicuspid or mitral valve guards the opening between the left atrium and the left ventricle.

The openings of the right and the left ventricles into the pulmonary artery and the aorta; respectively; are provided with the semi-lunar valves. These valves allow the flow of blood in only one direction and prevent any backward flow.

Conduction of Heart Beat:

The heart is made of cardiac muscles. The walls of the ventricles are much thicker than the walls of the atria. A specialized cardiac musculature; called the nodal tissue is also distributed in the heart. The detail of these nodal tissues is as follows:

SA Node: The Sino-Atrial Node (SA Node) is present in the right upper corner of the right atrium.

AV Node: The atrio-ventricular node is present in the lower left corner of the right atrium; close to the atrio-ventricular septum.

Bundle of His: A bundle of nodal fibres; called atrio-ventricular bundle (AV Bundle); continues from the AVN and passes through the atrio-ventricular septa to emerge on the top of the inter-ventricular septum. Then, this bundle divides into a right and left bundle. These branches give rise to minute fibres throughout the ventricular musculature of the respective sides and are called Purkinje fibres. These fibres; along with right and left bundles; are known as Bundle of His.

Generation of Heart Beat: The nodal musculature is autoexcitable, which means it has the ability to generate action potentials without any external stimuli. The number of action potentials which could be generated per minute varies at different parts of the nodal system. The SA Node can generate the maximum number of action potentials, i.e. 70-75 per minute. The SA Node is responsible for initiating and maintaining the rhythmic contractile activity or beating of the heart. Due to this, the SA Node is called the pacemaker. The human heart normally beats 70-75 times per minute.

Cardiac Cycle

The sequential contraction and dilatation of different chambers of heart in a cyclical manner is called cardiac cycle. A cardiac cycle happens in following steps:

• All the four chambers of heart are in a relaxed state; to begin with. When the tricuspid and bicuspid valves are open, blood from the pulmonary veins and the vena cava flows into the left and the right ventricles respectively through the left and right atria. At this stage, the semilunar valves are closed.

• Now, the SA Node generates and action potential which stimulates both the atria to undergo a simultaneous contraction; the atrial systole. This increases the blood flow into the ventricles by about 30%. 

• The action potential is conducted to ventricular side by the AV Node and AV bundle from where the Bundle of His transmits it through the entire ventricular musculature. This results in ventricular systole coinciding with the atrial diastole.

• Ventricular systole increases the ventricular pressure causing the closure of tricuspid and bicuspid valves due to the attempted backflow of blood into the auricles. With further increase in the ventricular pressure, the semilunar valves are forced open. Opening of the semilunar valves allows the blood from ventricles into the pulmonary artery (right side) and into the aorta (left side).

• Now the ventricles relax and the resultant fall in ventricular pressure causes the closure of semi-lunar valves. Closure of semi-lunar valves prevents the backflow of blood into the ventricles. With further reduction in ventricular pressure, the tricuspid and bicuspid valves are pushed open by the pressure in the atria exerted by the blood coming to atria.

• The whole cycle is repeated.

Stroke Volume: The volume of blood pumped by the heart in one cardiac cycle is called stroke volume. This is about 70 ml.

Cardiac Output: The volume of blood pumped by the heart in one minute is called the cardiac output. The average cardiac output is 5000 ml or 5 litre per minute.

Lub and Dub Sounds: Two prominent sounds are produced during each cardiac cycle. These sounds can be easily heard through a stethoscope. The first sound is called lub and is associated with the closure of the tricuspid and bicuspid valves. The second sound is called dub and is associated with the closure of the semi-lunar valves. These sounds are important for clinical diagnosis.

Electrocardiograph (ECG)

The graphical representation of the electrical activity of the heart during a cardiac cycle is called ECG. For obtaining an ECG, a patient is usually connected to the machine with three electrical leads; one to each wrist and to the left ankle. These leads continuously monitor the activity of heart.

Each peak in the ECG is identified with a letter from P to T (PQSRT) which corresponds to a specific electrical activity of the heart.

• The P-wave represents the electrical excitation or depolarization of the atria. Depolarisation of atria leads to atricular systole.

• The QRS complex represents the depolarization of the ventricles which initiates ventricular systole.

• The T-wave represents the return of the ventricles from excited to normal state (repolarisation). The end of T-wave marks the end of systole. 

Any deviation in the normal POQRST pattern of ECG indicates towards possible heart ailment.

DOUBLE CIRCULATION

Pulmonary Circulation: The blood flow to and from the lungs is called pulmonary circulation. Deoxygenated blood goes to the lungs for oxygenation and then oxygenated blood comes back to the heart. Pulmonary circulation takes place through pulmonary artery and pulmonary vein.

Systemic Circulation: The oxygenated blood is pumped to different parts of the body through the aorta and various arteries. Deoxygenated blood is collected by veins and finally reaches the right auricle through vena cava. Thus, the arterial and venous blood supply comprises the systemic circulation.

Hepatic Portal Circulation: The hepatic portal system is a unique vascular connection which exists between the digestive tract and liver. Blood from the intestine is first sent to the liver through hepatic portal system and then to the systemic circulation.

Coronary Circulation: There is a special system of blood vessels which provide blood circulation exclusively to the cardiac muscles. This is called coronary circulation.

REGULATION OF CARDIAC ACTIVITY

Normal activities of the heart are intrinsically regulated, i.e. auto regulated by the nodal tissues. Due to this, the heart is called myogenic.

There is a special neural centre in the medulla which can moderate the cardiac function through autonomic nervous system (ANS). The sympathetic nervous system can increase the heart rate, can increase the strength of ventricular contraction and thus the cardiac output. On the other hand, the parasympathetic nervous system decreases the heart rate, and thus the cardiac output. Adrenal medullary hormone can also increase the cardiac output.

DISORDERS OF CIRCULATORY SYSTEM

High Blood Pressure (Hypertension): The normal blood pressure in human beings is 120/80 mm Hg. If the blood pressure is more than this range, this condition is called hypertension. If the blood pressure comes in the range of 140/90 mm Hg on repeated checks, then the person is diagnosed with hypertension. The higher value, i.e. 120 mm Hg shows the systolic blood pressure, while the lower value shows the diastolic blood pressure. Hypertension finally progresses into heart diseases and also affects vital organs; like brain and kidney.

Blood Pressure: The resistance offered by the lumen of the artery to the flow of blood is called blood pressure.

Coronary Artery Disease (CAD): Deposition of fat, cholesterol, calcium and fibrous tissues makes the lumen of the coronary artery narrower. This leads to coronary artery disease. This is also known as atherosclerosis. There is reduced blood supply to the cardiac muscles in this condition.

Angina: This is usually called angina pectoris; which means a pain in the chest region. Angina pectoris is a symptom of underlying heart disease. This happens because of mismatch in demand and supply of oxygen to the cardiac muscles.

Myocardial Infarction: This is commonly known as heart failure. When oxygen supply is obstructed to a part of the cardiac muscle for a prolonged period of a few minutes, it leads to cell death in that part. This is called myocardial ischemia and is accompanied by sudden stoppage of the beating of heart. The stoppage of the beating of heart is called heart attack or myocardial infarction.

NCERT Solution for Class 11 Biology Body Fluids and Circulartion  

Question 1. Name the components of the formed elements in the blood and mention one major function of each of them.

Answer:  

Question 2. What is the importance of plasma proteins?

Answer: The major plasma proteins are; fibrinogen, globulins and albumins. Fibrinogen play important role in blood coagulation. Globulins are mainly involved in defense mechanism and albumins help in osmotic balance.

Question 3. Match Column I with Column II:

Question 4. Why do we consider blood as a connective tissue?

Answer: Blood is mesodermally derived; as other connective tissues. Blood serves the purpose of connecting the body systems; by transporting substances. Moreover, blood too has a matric; like other connective tissues. Hence, blood is considered as a connective tissue.

Question 5. What is the difference between lymph and blood?

Answer:      

Question 6. What is meant by double circulation? What is its significance?

Answer: Complete double circulation is present in birds and mammals. In this case, the oxygenated blood is received by the left atrium and the deoxygenated blood is received by the right atrium. The oxygenated blood is pumped out through the left ventricle, while the deoxygenated blood is pumped out through the right ventricle. In complete double circulation, there are two separate pathways for oxygenated and deoxygenated bloods. There is complete separation of oxygenated and deoxygenated blood in case of complete double circulation. This provides better efficiency to the organism in terms of energy generation.

Question 7. Write the differences between:

(a) Open and Closed system of circulation

Answer: The organs are directly bathed in blood in case of open circulatory system. In case of closed circulatory system, the blood is channelized through closed vessels.

(c) Systole and Diastole

Answer: Contraction of heart muscles is called systole, while dilatation is called diastole.

(d) P-wave and T-wave

Answer: P-wave marks the depolarization of atria, while T-wave marks the return of ventricles to repolarised state.

Question 8. Describe the evolutionary change in the pattern of heart among the vertebrates.

Answer: A muscular chambered heart is present in all vertebrates. The fishes have a 2-chambered heart; with an atrium and a ventricle. Amphibians and reptiles have a 3-chambered heart; with two atria and one ventricle. But crocodiles have 4-chambered heart. Birds and mammals have 4-chambered heart; with two atria and two ventricles.

Question 9. Why do we call our heart myogenic?

Answer: Normal activities of the heart are intrinsically regulated, i.e. auto regulated by the nodal tissues. Due to this, the heart is called myogenic.

Question 10. Sino-atrial node is called the pacemaker of our heart. Why?

Answer: The SA Node is responsible for initiating and maintaining the rhythmic contractile activity or beating of the heart. Due to this, the SA Node is called the pacemaker.

Question 11. What is the significance of atrio-ventricular node and atrio-ventricular bundle in the functioning of heart?

Answer: AV Node and AV Bundles are responsible for conduction of heart beat to different parts of the heart after initiation in the SA node.

Question 12. Define a cardiac cycle and the cardiac output.

Answer: Cardiac Cycle: The sequential contraction and dilatation of different chambers of heart in a cyclical manner is called cardiac cycle.

Cardiac Output: The volume of blood pumped by the heart in one minute is called the cardiac output. The average cardiac output is 5000 ml or 5 litre per minute.

Question 13. Explain heart sounds.

Answer: Lub and Dub Sounds: Two prominent sounds are produced during each cardiac cycle. These sounds can be easily heard through a stethoscope. The first sound is called lub and is associated with the closure of the tricuspid and bicuspid valves. The second sound is called dub and is associated with the closure of the semi-lunar valves. These sounds are important for clinical diagnosis.

Question 14. Draw a standard ECG and explain the different segments in it.

Answer: Each peak in the ECG is identified with a letter from P to T (PQSRT) which corresponds to a specific electrical activity of the heart.

The P-wave represents the electrical excitation or depolarization of the atria. Depolarisation of atria leads to atricular systole.

The QRS complex represents the depolarization of the ventricles which initiates ventricular systole. 

The T-wave represents the return of the ventricles from excited to normal state (repolarisation). The end of T-wave marks the end of systole.