Chemical Coordination and IntegrationClass 11 Biology NCERT Solutions
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Q1Exercises
Define the following:
(a)
Exocrine gland
(b)
Endocrine gland
(c)
Hormone
Solution
(a) Exocrine gland: These are glands that have ducts through which they release their secretions to a specific location. For example, the exocrine part of the pancreas releases digestive enzymes into the gastrointestinal tract.
(b) Endocrine gland: As stated in the text, "Endocrine glands lack ducts and are hence, called ductless glands." Their secretions, called hormones, are released directly into the blood, which then transports them to target organs.
(c) Hormone: The text provides two definitions:
- Classical definition: A chemical produced by endocrine glands, released into the blood, and transported to a distantly located target organ.
- Current scientific definition: "Hormones are non-nutrient chemicals which act as intercellular messengers and are produced in trace amounts."
Q2Exercises
Diagrammatically indicate the location of the various endocrine glands in our body.
Solution
To see the diagrammatic representation of the locations of endocrine glands, please refer to Figure 19.1 in the provided textbook chapter. The locations are as follows:
- In the brain: Hypothalamus, Pituitary gland, and Pineal gland.
- In the neck region: Thyroid gland and Parathyroid glands (on the back side of the thyroid).
- In the upper chest: Thymus gland, located between the lungs behind the sternum.
- In the abdomen: Pancreas and Adrenal glands (located above the kidneys).
- In the pelvic region/scrotum: Gonads, which are the ovaries in females (in the abdomen) and testes in males (in the scrotal sac).
Q3Exercises
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
Solution
The hormones secreted by the following are:
(a) Hypothalamus:
* Releasing hormones (e.g., Gonadotrophin releasing hormone - GnRH)
* Inhibiting hormones (e.g., Somatostatin)
* It also synthesizes Oxytocin and Vasopressin, which are released by the pituitary.
(b) Pituitary:
* Anterior Pituitary (Pars distalis): Growth Hormone (GH), Prolactin (PRL), Thyroid Stimulating Hormone (TSH), Adrenocorticotrophic Hormone (ACTH), Luteinizing Hormone (LH), Follicle Stimulating Hormone (FSH).
* Pars intermedia: Melanocyte Stimulating Hormone (MSH).
* Posterior Pituitary (Neurohypophysis): Releases Oxytocin and Vasopressin (or Antidiuretic Hormone - ADH).
(c) Thyroid:
* Tetraiodothyronine or Thyroxine ()
* Triiodothyronine ()
* Thyrocalcitonin (TCT)
(d) Parathyroid:
* Parathyroid Hormone (PTH)
(e) Adrenal:
* Adrenal Medulla: Adrenaline (Epinephrine) and Noradrenaline (Norepinephrine).
* Adrenal Cortex: Glucocorticoids (mainly Cortisol), Mineralocorticoids (mainly Aldosterone), and Androgenic steroids.
(f) Pancreas:
* Glucagon (from -cells)
* Insulin (from -cells)
(g) Testis:
* Androgens (mainly Testosterone)
(h) Ovary:
* Estrogen
* Progesterone
(i) Thymus:
* Thymosins
(j) Atrium (of Heart):
* Atrial Natriuretic Factor (ANF)
(k) Kidney:
* Erythropoietin
(l) G-I Tract:
* Gastrin, Secretin, Cholecystokinin (CCK), and Gastric Inhibitory Peptide (GIP).
Q4Exercises
Fill in the blanks: Hormones
(a)
Hypothalamic hormones
(b)
Thyrotrophin (TSH)
(c)
Corticotrophin (ACTH)
(d)
Gonadotrophins (LH, FSH)
(e) Melanotrophin (MSH)
Target gland
Solution
Hormones Target gland
(a) Hypothalamic hormones Pituitary gland
(b) Thyrotrophin (TSH) Thyroid gland
(c) Corticotrophin (ACTH) Adrenal cortex
(d) Gonadotrophins (LH, FSH) Gonads (Testis and Ovary)
(e) Melanotrophin (MSH) Melanocytes (in skin)
Q5Exercises
Write short notes on the functions of the following hormones:
(a)
Parathyroid hormone (PTH)
(b)
Thyroid hormones
(c)
Thymosins
(d)
Androgens
(e) Estrogens
(f) Insulin and Glucagon
Solution
(a) Parathyroid hormone (PTH): PTH is a hypercalcemic hormone, meaning it increases the blood calcium () levels. It acts on bones to stimulate bone resorption (demineralisation), on renal tubules to stimulate reabsorption of , and increases absorption from digested food. It plays a significant role in calcium balance in the body along with TCT.
(b) Thyroid hormones ( and ): These hormones are crucial for regulating the basal metabolic rate. They support the formation of red blood cells, control the metabolism of carbohydrates, proteins, and fats, and help maintain water and electrolyte balance. They are also essential for the proper development and maturation of the central nervous system.
(c) Thymosins: These peptide hormones play a major role in the development of the immune system. They are involved in the differentiation of T-lymphocytes, which are responsible for cell-mediated immunity. Thymosins also promote the production of antibodies, which provide humoral immunity.
(d) Androgens (e.g., Testosterone): Androgens regulate the development, maturation, and functions of male accessory sex organs. They stimulate muscular growth, growth of facial and axillary hair, aggressiveness, and low pitch of voice. They play a major stimulatory role in spermatogenesis and influence male sexual behavior (libido).
(e) Estrogens: Estrogens are responsible for the stimulation of growth and activities of female secondary sex organs. They also stimulate the development of growing ovarian follicles, the appearance of female secondary sex characters (like high pitch of voice), and mammary gland development. Estrogens also regulate female sexual behavior.
(f) Insulin and Glucagon: These two hormones jointly maintain glucose homeostasis in the blood.
- Glucagon is a hyperglycemic hormone; it increases blood glucose levels by stimulating glycogenolysis (breakdown of glycogen) and gluconeogenesis (synthesis of glucose) in the liver.
- Insulin is a hypoglycemic hormone; it decreases blood glucose levels by enhancing the uptake and utilization of glucose by cells (hepatocytes and adipocytes) and stimulating the conversion of glucose to glycogen (glycogenesis).
Q6Exercises
Give example(s) of:
(a)
Hyperglycemic hormone and hypoglycemic hormone
(b)
Hypercalcemic hormone
(c)
Gonadotrophic hormones
(d)
Progestational hormone
(e) Blood pressure lowering hormone
(f) Androgens and estrogens
Solution
(a) Hyperglycemic hormone: Glucagon. Hypoglycemic hormone: Insulin.
(b) Hypercalcemic hormone: Parathyroid hormone (PTH).
(c) Gonadotrophic hormones: Luteinizing hormone (LH) and Follicle-stimulating hormone (FSH).
(d) Progestational hormone: Progesterone.
(e) Blood pressure lowering hormone: Atrial natriuretic factor (ANF).
(f) Androgens: Testosterone. Estrogens: Estradiol.
Q7Exercises
Which hormonal deficiency is responsible for the following:
(a)
Diabetes mellitus
(b)
Goitre
(c)
Cretinism
Solution
(a) Diabetes mellitus: This disorder is caused by prolonged hyperglycemia, which results from a deficiency of insulin or from insulin resistance.
(b) Goitre: This is caused by a deficiency of iodine in the diet, which leads to hypothyroidism (deficient synthesis of thyroid hormones) and enlargement of the thyroid gland.
(c) Cretinism: This condition is caused by hypothyroidism (deficiency of thyroid hormones) during pregnancy, leading to defective development and maturation of the growing baby.
Q8Exercises
Briefly mention the mechanism of action of FSH.
Solution
Follicle-stimulating hormone (FSH) is a protein hormone. Its mechanism of action involves binding to a specific receptor on the cell membrane of its target cells (e.g., cells of ovarian follicles). This mechanism can be described in the following steps:
- Binding to Receptor: FSH, being a protein hormone, cannot enter the target cell. It binds to a specific membrane-bound receptor on the surface of the target cell.
- Formation of Hormone-Receptor Complex: The binding of FSH to its receptor forms a hormone-receptor complex.
- Generation of Second Messenger: This complex formation triggers a response inside the cell, leading to the generation of a second messenger, such as cyclic AMP () or .
- Biochemical Cascade: The second messenger then activates a series of existing enzymes in the cell, leading to a cascade of biochemical reactions.
- Physiological Response: This cascade ultimately results in the physiological and developmental effects associated with FSH, such as the growth and development of ovarian follicles in females.
Q9Exercises
Match the following: Column I (a) (b) PTH (c) GnRH (d) LH Column II
(i)
Hypothalamus
(ii)
Thyroid
(iii)
Pituitary
(iv)
Parathyroid
Solution
The correct matches are as follows:
- (a) is tetraiodothyronine (thyroxine), a hormone secreted by the (ii) Thyroid gland.
- (b) PTH is Parathyroid Hormone, secreted by the (iv) Parathyroid gland.
- (c) GnRH is Gonadotrophin releasing hormone, secreted by the (i) Hypothalamus.
- (d) LH is Luteinizing Hormone, secreted by the (iii) Pituitary gland.
Therefore, the correct matching is:
(a) - (ii)
(b) - (iv)
(c) - (i)
(d) - (iii)