Chemical Coordination & Integration

Chemical Coordination and Integration

22.1 Endocrine Glands and Hormones

22.2 Human Endocrine System

22.3 Hormones of Heart, Kidney and Gastrointestinal Tract

22.4 Mechanism of Hormone Action

Q1 1. Define the following:

(a) Exocrine gland

(b) Endocrine gland

Ans.

(a) Endocrine glands

These are ductless glands (no tube to carry to various parts).

Their secretions are directly released into the blood which carries them to various parts of the body.

(a) Exocrine glands

The exocrine glands have ducts.

The secretions from these glands are carried through the ducts.

The ducts may open outside the body to release the secretions (e.g.sweat, milk) or may be released on to another surface within the body (e.g. Digestive juices)

These are chemical messengers that regulate physiological processes in living organisms.

They act upon specific cells/tissues/organs which are called target cells/tissues/organs.

There are many types of hormones that act on different aspects of bodily functions and processes like growth and development.

Q2 Diagrammatically indicate the location of the various endocrine glands in our body.

Ans. The endocrine system consists of glands widely separated from each other with no physical connections. Endocrine glands are groups of secretory cells surrounded by an extensive network of capillaries that facilitates diffusion of hormones from the secretory cells into the bloodstream.

The endocrine glands in the body are:

1) Pineal gland- located in the epithalamus, near the center of the brain.

2) Pituitary gland- located at the base of the brain, just below the hypothalamus.

3) Hypothalamus- located below the thalamus and above the pituitary gland and brain stem

4) Thyroid gland- located in the neck in front of the larynx and trachea

5) Parathyroid gland- located in the neck in the posterior surface of the thyroid gland

6) Adrenal gland- located on the upper pole of each kidney enclosed within the renal fascia

7) Pancreas- located deep inside the abdomen. The head of the pancreas is on the right side of the abdomen and is connected to the duodenum

8) Ovaries- located in the lower abdomen, laterally to the left and right of the uterus and inferior to the fallopian tubes

9) Testis- located between upper thighs suspended by the spermatic cord in a skin pouch called scrotum

10) Thymus gland- located in the upper anterior part of the chest directly behind the sternum and between the lungs

11) Heart- lies in the thoracic cavity in the mediastinum (space between the lungs)

12) Stomach- located in the superior aspect of the abdomen

13) Kidney- located against the back muscles in the upper abdominal area. The left kidney is located slightly more superior than the right kidney due to the larger size of the liver on the right side of the body.

Q3 List the hormones secreted by the following:

(a) Hypothalamus (b) Pituitary (c) Thyroid (d) Parathyroid

(e) Adrenal (f) Pancreas (g) Testis (h) Ovary

(i) Thymus (j) Atrium (k) Kidney (l) G-I Tract

Ans.

The hormones secreted by the following are:

(a) Hypothalamus- thyrotropin releasing hormone (TRH), Corticotropin releasing hormone (CRH), gonadotropin-releasing hormone (GnRH), growth hormonereleasing hormone (GHRH), somatostatin, dopamine, follistatin, Melanocyte-inhibiting factor (melanostatin), etc.

(b) Pituitary- Hormones secreted by the anterior pituitary are: Growth Hormone (GH), Thyroid Stimulating Hormone (TSH), Adenocorticotrophic hormone (ACTH), Prolactin (PRL), Follicle Stimulating Hormone (FSH) and Luteinising Hormone (LH). Hormones secreted by the posterior pituitary are: Oxytocin, Antidiuretic hormone (ADH)

(d) Parathyroid- Parathyroid hormone (PTH)

(e) Adrenal- Adrenal cortex secretes: glucocorticids, mineralocorticoids and sex hormones (androgens). Adrenal medulla secretes: Adrenaline (epinephrine) and Nor-Adrenaline (nor-epinephrine)

(f) Pancreas- Insulina and glucagon

(g) Testis- Inhibin

(h) Ovary- Inhibin

(i) Thymus- Thymosin

(j) Atrium- Atrial natriuretic peptide (ANP)

(k) Kidney- Erythropoietin

(i) G-I Tract- Gastrin, Secretin, Cholecystokinin (CCK)

Q4 Fill in the blanks:

Hormones Target gland

(a) Hypothalamic hormones __________________

(b) Thyrotrophin (TSH) __________________

(d) Gonadotrophins (LH, FSH) __________________

(e) Melanotrophin (MSH) __________________

Ans.

a) Hypothalamic hormone- Pituitary gland

∙ Hypothalamic hormones include all the hormones like

1) thyrotropin-releasing

2) gonadotropin-releasing

3) growth hormone-releasing

4) corticotropin-releasing

5) somatostatin

6) dopamine hormones.

∙ Directly these hormones are released into the blood through the capillaries which travel to the pituitary gland and further processes occur.

b) Thyrotrophin(TSH)- Thyroid gland

∙ Thyrotropin(TSH) is produced by the master gland which works on the thyroid gland in stimulating the secretion of thyroxine hormone.

c) Corticotropin(ACTH)- Adrenal gland

∙ ACTH hormone is released by the master gland and stimulates the working of adrenal gland.

d) Gonadotrophins( LH, FSH)- Ovary and testis

∙ In males LH stimulates leydig cells which later release testosterone whereas FSH stimulates sertoli cells which stimulates spermatogenesis.

∙ In females ovaries are stimulated by both these hormones.

e) Melanotropin (MSH)- Melanocyte cells

∙ MSH directly stimulates the melanocyte cells present in the skin which release melanin which ultimately determines the skin color.

Q5 Write short notes on the functions of the following hormones:

(a) Parathyroid hormone (PTH) (b) Thyroid hormones

(e) Estrogens (f) Insulin and Glucagon

Ans. (a) Parathyroid hormone

The principal/chief cells of the parathyroid produce the parathyroid hormone, also called the parathormone. The function of this hormone is

To maintain calcium and phosphate balance in the blood and other tissues.

To increase calcium reabsorption from the intestine as well as from the nephrons of the kidney

To initiate bone resorption (e.g. reabsorption of calcium from bones), in case the blood calcium levels drop.

(b) Thyroid hormone

Both the thyroid hormones T4 (Thyroxine) and T3 (active form) are secreted by the thyroid gland. The thyroid hormones control the metabolism of carbohydrates, protein and fats. They play an important role in regulating the Basal Metabolic Rate (BMR) They are also important for maintenance of water and electrolyte balance. Thyroid hormones also regulate the RBC production. The thyrocalcitonin maintains the blood calcium levels and promotes the bone formation.

The thymus actively secretes the hormones called thymosins (only till pre-pubescence)

The stimulation, development and differntiation of T-lymphocytes.

The development of cell-mediated immunity (T-lymphocytes mediated immunity)

The production of antibodies (Humoral immunity).

(d) Androgens

Androgens are the hormones which are responsible for the development of secondary sexual characters. The Leydig cells of testis produce androgens such as testosterone.

Androgens are also produced by the adrenal cortex of the adrenal gland and the ovaries

(e) Estrogens

In Non-pregnant females, they are predominantly secreted by the ovaries. However, during pregnancy, the placenta secretes a lot of estrogens.

The three types of estrogens are; β-estradiol, estrone and estriol.

The most active and the principal estrogen produced by the ovaries is the β-estradiol.

They play an important role in the growth and development of ovarian follicles and breast

They are responsible for the development of secondary sexual characteristics (e.g. high pitch voice)

They inhibit osteoclastic activity and stimulate bone growth. Osteoporosis in menopausal women is because of reduced estrogen levels.

They also influence the texture of the skin and female sexual behaviour

(f) Insulin and Glucagon

Glucagon

It increases the blood glucose levels by initiating glycogenolysis (glycogen degradation) and stimulating gluconeogenesis (synthesis of glucose from non-carbohydrate molecules) in the liver cells.

Since it increases the blood glucose levels it is a hyperglycemic (hyper-more, glycemic-sugar levels) hormone

It also initiates lipolysis (degradation of lipid) in the adipose tissue.

Insulin

It is released when the glucose level in the blood raises.

It lowers blood sugar levels in different ways; increasing the uptake of glucose by all the cells in the body, initiating glycogenesis (glycogen synthesis) in the liver and muscle.

It initiates lipogenesis (synthesis of lipids/fat) and storage of fat in adipose tissue and inhibits gluconeogenesis

It is a hypoglycemic (hypo=less) hormone as it reduces the sugar levels in the blood

Q6 Give example(s) of:

(a) Hyperglycemic hormone and hypoglycemic hormone

(b) Hypercalcemic hormone

(d) Progestational hormone

(e) Blood pressure lowering hormone

(f) Androgens and estrogens

Ans.

a. Hyperglycemic hormone is glucagon, while hypoglycemic hormone is insulin.

b. Hypercalcemic hormone example is parathyroid hormone (PTH).

c. Gonadotrophic hormone examples are: LH (Luteinizing hormone) and FSH (Follicle stimulating hormone).

d. Progestational hormone example is progesterone.

e. Blood pressure lowering hormone example is Nor-adrenalin.

f. Androgen example is testosterone where as an example of estrogen is estradiol.

Q7 Which hormonal deficiency is responsible for the following:

(a) Diabetes mellitus (b) Goitre (c) Cretinism

Ans. (a) Diabetes mellitus is characterized by abnormally high glucose levels in the blood due to the deficiency of hormone, called insulin. Insulin helps the body use food for energy. When a person has diabetes, the pancreas either cannot produce enough insulin, or the body becomes resistant to insulin or both. Insulin stimulates the cells to uptake glucose. Lack of insulin or the inability of the cells to respond to insulin can lead to problems with the glucose uptake. Since the glucose is not taken up by the cells, the body will not get enough energy and several other problems associated with the increased blood glucose levels are also manifested.

(b) Goitre is characterized by an abnormal enlargement of the thyroid gland due to the deficiency of thyroxine hormone in the body. Symptoms of a goiter include enlargement of the throat, ranging from a small lump to a huge mass, swallowing problems and breathing problems.

(c) Cretinism is characterized by stunted growth in the baby due to the deficiency of thyroid hormone in the body. It usually results from a congenital defect (e.g., an absence of the thyroid, the presence of only a rudimentary gland, the inability of the gland to produce thyroxine). However, it can develop later if there is a lack of iodine in the diet, or if the thyroid is diseased or surgically removed.

Q8 . Briefly mention the mechanism of action of FSH.

Ans. (Follicle stimulating hormone) being glycoprotein is insoluble in lipids, therefore, cannot enter the target cells. It binds to the specific receptor molecules located on the surface of the cell membrane to form the hormone-receptor complex. This complex causes the release of an enzyme adenylate cyclase from the receptor site. This enzyme forms the cell cyclic adenosine monophosphate (cAMP) from ATP. The cAMP activates the existing enzyme system of the cell this accelerates the metabolic reactions in the cell. The hormone is called the first messenger and the cAMP is termed the second messenger. The hormone-receptor complex changes the permeability of the cell membrane to facilitate the passage of materials through it. this increases the activities of the cell as it receives the desired materials.

Column I

Column II

(a)T4................(i) Hypothalamus

(b) PTH............(ii) Thyroid

(d) LH...............(iv) Parathyroid.

Q9 9. Match the following:

Column I Column II

(a) T4 (i) Hypothalamus

(b) PTH (ii) Thyroid

(d) LH (iv) Parathyroid

Ans. T4 is a hormone produced by the thyroid gland. PTH is parathyroid hormone or parathormone produced by the parathyroid gland. GnRH is the gonadotropin-releasing hormone secreted by the hypothalamus and LH is luteinizing hormone secreted by the pituitary gland.