Chemical Coordination and Integration Class 11 Biology NCERT Solutions

Step-by-step solution

1. 1(a) An exocrine gland is one whose secretion is delivered through a duct directly onto a body surface or into a cavity, so the product reaches its target by a tube rather than by the blood. Examples are salivary, sweat, sebaceous and gastric glands.
2. 2(b) An endocrine gland is ductless and releases its secretion straight into the surrounding tissue fluid, from which it enters the blood and is carried to the target. Examples are the pituitary, thyroid, adrenal, pancreas and gonads.
3. 3(b) The key contrast is therefore the duct: the endocrine gland has no duct, which is why these are also called ductless glands.
4. 4(c) A hormone is a non-nutrient organic chemical of very small quantity, released into the blood by an endocrine gland and carried to a distant target organ, where it acts at a specific receptor to bring about a change in the activity of that cell.
5. 5(c) Hormones act at very low concentrations and their effect is specific, because only the target cells carry the matching receptor, and they are quickly degraded so the effect is short-lived.

Step-by-step solution

1. 1The glands should be marked on a front-view outline of the body, because the positions are the whole content of this question.
2. 2In the head region, the hypothalamus and the pineal gland lie at the base and on the dorsal side of the brain, with the pituitary hanging just below the hypothalamus in the sella turcica of the skull; the thymus lies in the thoracic cavity just behind the sternum, above the heart.
3. 3In the neck, the thyroid and the parathyroid lie on either side of, and behind, the trachea, with the parathyroids on the posterior surface of the thyroid.
4. 4In the chest and abdomen, the two adrenal glands sit as caps on the upper poles of the two kidneys, and the pancreas lies transversely behind the stomach.
5. 5(a) The brain region: hypothalamus (with the pituitary immediately below it) and pineal, at the centre of the skull.
6. 6(b) The neck: thyroid, with the parathyroids on its posterior surface, on either side of the trachea.
7. 7(c) Thoracic cavity: thymus, behind the sternum and above the heart.
8. 8(d) Abdominal cavity: the two adrenals capping the kidneys, the kidneys themselves, and the pancreas behind the stomach.
9. 9(e) Pelvic cavity: the testes in the scrotum in males and the ovaries in the pelvic cavity in females.
10. 10(f) The atria of the heart also secrete a hormone, ANF, and the kidneys and the gastrointestinal tract secrete hormones as well, so those sites are also worth marking.

Step-by-step solution

1. 1(a) Hypothalamus: the releasing and inhibiting hormones GHRH, PRH, TRH, GnRH, MIH (dopamine) and somatostatin (GHIH), which control the anterior pituitary, and also oxytocin and vasopressin or ADH, which are released from the posterior pituitary but are made in the hypothalamus.
2. 2(b) Pituitary: the anterior lobe secretes growth hormone GH, thyroid-stimulating hormone TSH, adrenocorticotropic hormone ACTH, luteinising hormone LH, follicle-stimulating hormone FSH, prolactin and melanocyte-stimulating hormone MSH; the posterior lobe stores and releases oxytocin and vasopressin (ADH).
3. 3(c) Thyroid: the iodinated hormones triiodothyronine T3 and tetraiodothyronine T4 (thyroxine), plus thyrocalcitonin TCT, which is produced by the C cells and lowers blood calcium.
4. 4(d) Parathyroid: parathyroid hormone PTH, the only hormone secreted by this gland, which raises blood calcium.
5. 5(e) Adrenal: the cortex secretes the glucocorticoids (cortisol), the mineralocorticoids (aldosterone) and androgens; the medulla secretes adrenaline (epinephrine) and noradrenaline (norepinephrine).
6. 6(f) Pancreas: the alpha cells of the islets of Langerhans secrete glucagon and the beta cells secrete insulin.
7. 7(g) Testis: androgens, principally testosterone.
8. 8(h) Ovary: estrogens and progesterone.
9. 9(i) Thymus: thymosins, which are needed for the maturation of T lymphocytes.
10. 10(j) Atrium: atrial natriuretic factor or peptide (ANF), which is released when the atria are stretched by excess blood volume and lowers blood pressure by promoting sodium and water excretion.
11. 11(k) Kidney: erythropoietin, which stimulates red blood cell formation, and renin, which activates the renin–angiotensin–aldosterone mechanism.
12. 12(l) Gastrointestinal tract: gastrin from the stomach, and secretin and cholecystokinin (CCK) from the duodenum.

Step-by-step solution

1. 1(a) Hypothalamic hormones act on the anterior pituitary, the master gland, which is why the pituitary is called the master gland of the body. This is a trophic chain: hypothalamus to pituitary to a peripheral endocrine gland.
2. 2(b) Thyrotrophin or TSH is secreted by the anterior pituitary and acts on the thyroid gland, stimulating it to release T3 and T4.
3. 3(c) Corticotrophin or ACTH is secreted by the anterior pituitary and acts on the adrenal cortex, stimulating secretion of glucocorticoids.
4. 4(d) Gonadotrophins, LH and FSH, are secreted by the anterior pituitary and act on the gonads, that is the testis and the ovary.
5. 5(e) Melanotrophin or MSH is secreted by the anterior pituitary and acts on the melanocytes of the skin, stimulating the production of the pigment melanin, so a rise in MSH deepens skin colour.
6. 6The pattern to notice is that (b) to (e) are all tropic hormones of the anterior pituitary, each naming a different peripheral target.

Step-by-step solution

1. 1(a) PTH is secreted by the parathyroid gland and acts on the bone, kidney and intestine to raise the blood calcium level. It stimulates the osteoclasts indirectly so that bone resorption releases calcium, increases the reabsorption of calcium by the renal tubules, and increases the absorption of calcium from the gut by activating vitamin D. Its overall effect is hypercalcemic, and it is opposed by thyrocalcitonin.
2. 2(b) The thyroid hormones T3 and T4 are the main hormones of the thyroid, and they regulate the basal metabolic rate. They support the normal rate of growth of the body, promote mental development and the maturation of the nervous system, keep body temperature and heart rate normal, and increase the heart's output. They also promote the uptake and utilisation of glucose and so raise blood glucose on overdose. Their deficiency in adult life causes myxoedema and in early life causes cretinism, while goitre results from iodine deficiency.
3. 3(c) Thymosins are secreted by the thymus gland and play an important role in the development of the immune system. They promote the production of T lymphocytes, that is the differentiation of the lymphocytes that carry out cell-mediated immunity, and so they are essential for a competent immune response.
4. 4(d) Androgens, principally testosterone, are the male sex hormones secreted by the testis. They stimulate the production of sperm, bring about the development of the male secondary sexual characters such as a deep voice, facial and axillary hair and masculine behaviour, and promote the growth of muscles and bones.
5. 5(e) Estrogens are the female sex hormones secreted by the ovary. They stimulate the growth and activity of the female secondary sex organs, bring about the female secondary sexual characters such as a developed breast and high-pitched voice, and are essential for the menstrual cycle and for the implantation and maintenance of pregnancy.
6. 6(f) Insulin, secreted by the beta cells of the islets of Langerhans, lowers blood glucose by promoting its uptake and oxidation in the cells and converting it to glycogen in the liver and muscle, so it is hypoglycemic. Glucagon, secreted by the alpha cells of the same islets, acts in the opposite way by stimulating glycogenolysis and gluconeogenesis in the liver, raising blood glucose, so it is hyperglycemic.

Step-by-step solution

1. 1(a) The hyperglycemic hormones raise blood glucose, and glucagon is the principal example, with adrenaline, the glucocorticoids and growth hormone also acting in this way; the hypoglycemic hormone is insulin, which is the only one that lowers blood glucose.
2. 2(b) The hypercalcemic hormone is parathyroid hormone PTH, which raises blood calcium; the opposite hormone is thyrocalcitonin TCT.
3. 3(c) The gonadotrophic hormones are LH and FSH, both secreted by the anterior pituitary, and they act on the gonads, LH mainly on the corpus luteum and Leydig cells and FSH on the follicles and Sertoli cells.
4. 4(d) The progestational hormone is progesterone, secreted by the corpus luteum of the ovary and by the placenta, and it prepares the endometrium for implantation and maintains pregnancy.
5. 5(e) The blood pressure lowering hormone is atrial natriuretic factor ANF, released from the atria when they are stretched; it promotes sodium and water excretion and hence reduces blood volume and pressure. ANP is the other name for it.
6. 6(f) The androgens are the male sex hormones, testosterone being the principal one, secreted mainly by the testes; the estrogens are the female sex hormones, secreted mainly by the ovaries.

Step-by-step solution

1. 1(a) Diabetes mellitus is caused by a deficiency of insulin, the hypoglycemic hormone secreted by the beta cells of the islets of Langerhans, so glucose cannot be taken up and used and blood glucose rises above normal.
2. 2(a) This is a disorder of carbohydrate metabolism; the loss of insulin also causes the cells to oxidise fats and proteins for energy and leads to the accumulation of ketone bodies.
3. 3(b) Goitre is caused by a deficiency of the thyroid hormones T3 and T4, and the usual underlying cause is a dietary deficiency of iodine, the raw material from which thyroxine is made.
4. 4(b) The low level of thyroid hormones removes the negative feedback on the pituitary, so TSH is secreted in excess and the thyroid enlarges to form the goitre; so goitre is an enlarged thyroid, not a diseased hormone.
5. 5(c) Cretinism is caused by a deficiency of the thyroid hormones during the early developmental period of life, so mental development and body growth are both retarded, producing a stunted, mentally retarded individual.
6. 6(c) The cause of that deficiency is most often iodine deficiency in the mother's diet during pregnancy; the same hormone deficiency in an adult gives myxoedema instead, since growth has already been completed.

Step-by-step solution

1. 1FSH is a glycoprotein gonadotrophin secreted by the anterior pituitary, so it reaches its target in the blood and acts on the target tissue by binding to a specific membrane receptor, because FSH is a peptide hormone and cannot cross the membrane.
2. 2The hormone–receptor complex activates adenylyl cyclase in the membrane, which raises cyclic AMP, and cAMP acts as the second messenger that carries the signal inside the cell.
3. 3In the male, FSH acts on the Sertoli cells of the seminiferous tubules, where it stimulates spermatogenesis, that is the formation of sperm, and promotes the secretion of androgen binding protein, which concentrates testosterone in the tubule.
4. 4In the female, FSH acts on the granulosa cells of the ovarian follicles, where it promotes the growth of the follicles and stimulates them to secrete estrogen.
5. 5The overall effect is therefore that FSH governs the production of the gametes, by preparing the Sertoli cells to respond to FSH and testosterone in the male and the follicles to grow and produce estrogen in the female.

Step-by-step solution

1. 1(a) T4 is tetraiodothyronine, or thyroxine, and it is secreted by the thyroid gland, so T4 matches (ii) Thyroid.
2. 2(b) PTH is parathyroid hormone, and it is the only hormone of the parathyroid glands, so it matches (iv) Parathyroid.
3. 3(c) GnRH is gonadotrophin releasing hormone, and it is one of the releasing hormones made in the hypothalamus, so it matches (i) Hypothalamus.
4. 4(d) LH is luteinising hormone, one of the gonadotrophins secreted by the anterior pituitary, so it matches (iii) Pituitary.
5. 5Each item in Column I and each item in Column II is used exactly once, and note the two-step chain the question is testing: GnRH from the hypothalamus acts on the pituitary, which secretes LH.