ICSE Class 10 Biology Chapter 10 Endocrine Glands

Endocrine Glands - "The Producers of Chemical Messengers"

Syllabus: Endocrine System: General study of the following glands: Adrenal, Pancreas, Thyroid and Pituitary. Difference in Endocrine and Exocrine glands.

Scope of syllabus: Correct location and shape of the gland in the human body should be discussed along with the hormones they secrete (Pancreas: insulin and glucagon to be taught; Thyroid: only thyroxin to be taught). Effects of hypo-secretion and hyper-secretion of hormones must be discussed. The term tropic hormones should be explained in the study of pituitary. Brief idea of feedback mechanism must be given.

Endocrine glands are such glands which secrete hormones. Hormones are extremely important secretions for the regulation of body activities. The full set of endocrine glands in the body includes numerous glands, but the syllabus specifies only a few of them as mentioned above.

10.1 Need For The Regulation Of Body Activities

The activities in our body are highly complex and they need to be so regulated that every activity takes place at a proper time and in a correct sequence. For example, the gastric juice, bile and pancreatic juice should be poured into the food canal only when there is food in it. Though this kind of regulation is done to some extent by the nervous system (Chapter 9), it is also brought about by chemical regulators called hormones (horma: to stir up / to excite / to put into action).

Seven major differences in the action of the nervous system and of hormones in the regulatory mechanism in our body are listed in Table 10.1 below:

Hormones are secretions from specific cells or glands in the body, and are carried to all parts by the blood, but their effect is produced in one or more specific parts (target organ or cells) only.

Most hormones are secreted by special glands, the endocrine glands (endo: inside, crine: separate) meaning "Secrete internally", also called ductless glands because their secretions are poured directly into the blood and not through any special duct.

Certain hormones are also produced from some such glands or body parts which otherwise have a different primary function; for example, the stomach and duodenum.

Differences Between Hormonal Control And Nervous Control

Teacher's Note

When you feel fear or excitement, your heart races - that is your nervous system at work. But when you feel hungry or thirsty, hormones are preparing your body for eating and digestion - a slower but longer-lasting adjustment.

Endocrine system. Endocrine system consists of several glands/glandular cells which bring about the overall common function of chemical coordination in the body. Almost all endocrine glands act in a coordinated manner. They activate each other and work as a system of organs called endocrine system. A system is defined as a group of organs performing an overall common function.

10.2 General Properties Of Hormones

1. Hormones are secreted from their source directly into the blood (and not into lymph).

2. They regulate the physiological processes by chemical means. They affect the enzyme systems of the body.

3. They act on target organs or cells usually away from their source.

4. Hormones produced in one species usually show similar influence in other species.

5. They are produced in very small quantities and are biologically very active. For example, adrenaline is active even in a concentration of 1 part in 300,000,000 parts.

6. Chemically, some hormones are peptides (proteins such as insulin) which are water soluble, some are amines (derived from amino acids such as adrenaline) again water-soluble and some are steroids derived from cholesterol such as testosterone which are lipid-soluble.

7. Their excess (hypersecretion/oversecretion) or deficiency (hyposecretion/undersecretion), both may lead to serious consequences.

8. Hormones are not stored in the body and are excreted from the system.

Hormone is a secretion from some glandular part of the body, which is poured into blood and which acts on the target organs or cells of the same individual, bringing about coordination between distant parts of the body.

Progress Check

1. Fill in the blanks by selecting the appropriate alternative from those given in brackets.

(i) Regulation of activities inside the body are brought about by and systems.

(nervous/digestive/endocrine)

(ii) Hormones are secreted directly into the

(organs/lymph/blood).

(iii) Chemically, some hormones are some steroids, some (proteins/amines/carbohydrates).

2. Give the characteristics of hormones pertaining to

(i) Site of action

(ii) Chemical nature

(iii) Manner of transportation

10.3 Endocrine Glands

The principal endocrine (hormone-producing) glands in the human body have been shown in Fig. 10.1.

These are enumerated below (only the ones in bold face are included in the syllabus):

1. Adrenal 2. Pancreas

3. Thyroid 4. Pituitary

5. Parathyroid 6. Thymus

7. Gonads

We shall try to explain the major functions of each endocrine gland.

1. Adrenal Glands

The adrenal glands are like caps above the kidneys (ad: near, renal: kidney). Each adrenal gland consists of two parts - (i) a central medulla and (ii) a peripheral cortex.

(i) Adrenal medulla secretes adrenaline (also called epinephrine and noradrenaline). Adrenaline is a hormone, which prepares the body to meet any emergency situation, for "fight" i.e. to face danger or for "flight", to run away from it. Extra energy and strength is provided to the body in that situation. Extra hormone is released into the blood at the time of emotional stress. When excited or angry our adrenals produce a lot of adrenaline. The gland itself is stimulated by the nerve endings of the autonomic nervous system

Table 10.2 below lists the effects of adrenaline on the different body parts.

Responses To Adrenaline

In addition, adrenaline also increases clotting capacity of the blood, dilates pupil of the eye, stimulates uterine contraction during labour (delivery of baby), stimulates muscle of the hair follicles. (These functions are in general the same as those of the sympathetic autonomic nervous system).

Teacher's Note

When you see a snake or hear a loud noise suddenly, your adrenaline spikes and you feel a rush - your hands shake, your heart races, and you feel ready to act. This is adrenaline preparing you for "fight or flight".

Women with beard and Men with breasts!

If there is an overgrowth of adrenal cortex in a mature woman, she develops certain male characteristics, such as, a beard, moustaches and deep male voice. The condition is known as adrenal virilism (Latin Virilism: maleness).

If the overgrowth occurs in mature men, they may develop some feminine characteristics, such as, enlargement of breasts.

Hyposecretion from adrenal cortex causes Addison's disease. Symptoms are loss of energy, skin pigmentation, loss of weight, nausea, hypoglycemia (low blood sugar), sensitivity to cold and pain, increased susceptibility to infections, etc.

Hypersecretion of adrenal cortex causes Cushing's syndrome. Symptoms are obesity, hyperglycemia (higher blood sugar), osteoporosis, weakness, salt and water retention.

2. Pancreas

Pancreas is both a duct gland as well as a ductless gland. As a duct gland, its secretion (pancreatic juice) is poured into the duodenum for digestion. As a ductless gland, it has special groups of hormone-secreting cells called Islets of Langerhans, which are scattered in the entire gland (islets: little islands) (Fig. 10.3). The islet cells produce three hormones - insulin, glucagon and somatostatin from three different kinds of cells called beta, alpha and delta cells respectively. (Note: Somatostatin from Delta cells is excluded from syllabus).

1. Insulin secreted by beta cells checks rise of sugar level in blood. This it does in two principal ways:

(i) It promotes glucose utilisation by the body cells.

(ii) It stimulates deposition of extra glucose of the blood as glycogen in liver and muscles.

Abnormalities in insulin - shortage and excess.

Insufficient secretion of insulin causes diabetes (more correctly diabetes mellitus or hyperglycemia). The word "mellitus" means honey, referring to the passage of sugar (glucose) in urine.

A diabetic person:

- has high concentration of sugar in blood (hyperglycemia, hyper: excess, glyce: sugar glucose), emia: blood.

- excretes a great deal of urine loaded with sugar.

- feels thirsty because of the loss of water through too much urination.

- loses weight and becomes weaker and weaker. In certain cases, the person loses eye sight or vision.

The usual treatment by administering insulin is not a cure, but only a method of supplying the hormone which is not being produced by the pancreas.

Over-secretion of insulin

- Sugar level in the blood is lowered (hypoglycemia, hypo: below) and

- Brain may enter a state of coma if the level becomes too low even for a few minutes.

A similar thing may happen to a diabetic patient if an overdose of insulin is given - the patient may become unconscious. This is called insulin shock or hypoglycemia and a prompt bite of sweet biscuits or sugar candy is helpful.

Caution in answering a question.

It is wrong to say "insulin converts glucose to glycogen."

Instead, "insulin enables the cells to absorb glucose and use it or convert it into glycogen."

2. Glucagon is secreted from alpha cells. It stimulates the breakdown of glycogen in the liver to glucose, thus it raises sugar level in the blood.

Progress Check

1. Mention against the three types of cells of the islets of Langerhans, the name of the hormone they secrete.

(i) Alpha cells

(ii) Beta cells

(iii) Delta cells

2. Mention the two principal ways in which insulin acts:

(i)

(ii)

3. Name the following conditions:

(i) Passage of much glucose in urine

(ii) Overdose of insulin makes the diabetic patient unconscious

4. List any three symptoms of diabetes mellitus.

(i)

(ii)

(iii)

5. List any two effects of adrenaline

(i)

(ii)

6. Name the two categories of hormones secreted by adrenal cortex.

(i)

(ii)

3. Thyroid

The thyroid is a bilobed (butterfly-shaped) structure (Fig. 10.5) situated in front of the neck just below the larynx. The two lobes are joined by a narrow isthmus (interconnection). It secretes two hormones thyroxine and calcitonin. (Note: Calcitonin is not included in the syllabus).

Thyroxine regulates the basal metabolism, i.e., the rate of cellular oxidation resulting in heat production at rest. An increase in the secretion increases metabolism and a decrease in secretion lowers it. It also influences the general growth of the body, ossification of bones, body temperature, mental development, etc.

A. Undersecretion (Hypothyroidism):

Insufficient secretion of thyroxine may lead to three conditions - simple goitre, cretinism and myxoedema.

(i) Simple goitre is the enlargement of the thyroid and is visible as a swelling in the neck (Fig. 10.6). This is due to insufficient quantity of iodine in food. This condition is common in the people living in hilly regions where iodine is deficient in soil and hence in the food grown there.

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