Chemical Coordination and Integration Class 11 Notes

Chemical coordination is achieved by hormones. A hormone is a non-nutrient chemical messenger released in minute quantities into the blood by an endocrine gland, and it is carried to a distant target tissue that carries the matching receptor.

• Endocrine glands are ductless, so they pour their secretions directly into the blood rather than through a duct.
• Hypothalamus, pineal gland, pituitary, thyroid, parathyroid, thymus, adrenal, pancreas, testes and ovaries are the glands of the endocrine system.
• The pancreas is both endocrine and exocrine, since its islets of Langerhans release hormones into the blood while the rest of the gland releases digestive juice through a duct.
• The testes and ovaries are endocrine glands as well as gonads, because they also secrete testosterone, oestrogen and progesterone.
• Some glands such as the pancreas, gonads and thymus also serve as non-endocrine organs, so their hormones alone do not define them.

• A nervous signal is an electrical impulse, is rapid, is short lived, and acts on a nearby target.
• An endocrine signal is a chemical hormone, is slower, is long lasting, and travels through the blood to a distant target.

The pituitary gland, or hypophysis, is the master gland of the body. It is attached to the hypothalamus by a stalk and sits in a depression at the base of the brain, and it secretes a large number of hormones.

• Growth hormone, GH — stimulates the growth of the body and of all its organs; a deficiency in childhood causes pituitary dwarfism.
• Thyroid stimulating hormone, TSH — stimulates the thyroid gland to secrete its hormones.
• Adrenocorticotrophic hormone, ACTH — stimulates the adrenal cortex to secrete glucocorticoids.
• Follicle stimulating hormone, FSH — stimulates spermatogenesis in the testes and, with LH, helps ovulation and milk production in the ovary.
• Luteinising hormone, LH — stimulates ovulation, formation of the corpus luteum, secretion of testosterone in the testis and milk secretion.
• Prolactin, PRL — regulates growth of the mammary glands and milk production.
• Melanocyte stimulating hormone, MSH — stimulates the pigmentation of the skin.
• Oxytocin — causes contraction of the uterus during pregnancy and milk ejection from the mammary glands.
• Anti-diuretic hormone, ADH, or vasopressin — increases water reabsorption in the kidney tubules to prevent excessive water loss, and constricts blood vessels to raise blood pressure.

The thyroid gland is a two-lobed gland at the front of the neck wrapped around the larynx, and it is the only gland that stores its hormone in extracellular space before releasing it.

• Thyroid hormones, thyroxine T4 and triiodothyronine T3 — require iodine for their synthesis; they regulate the basal metabolic rate, and T3 is the more active of the two.
• Calcitonin, from the parafollicular or C cells — lowers the blood calcium level by stimulating bone resorption inhibition, and it works against parathyroid hormone.
• Parathyroid hormone, PTH, from the parathyroid glands — raises the blood calcium level by mobilising calcium from bone, so it is a hypercalcemic hormone.
• Glucocorticoids, such as cortisol, from the adrenal cortex — mainly regulate the metabolism of carbohydrates, fats and proteins.
• Mineralocorticoids, such as aldosterone, from the adrenal cortex — regulate the metabolism of sodium and potassium and the water balance.
• Adrenaline, or epinephrine, and noradrenaline, or norepinephrine, from the adrenal medulla — the emergency hormones, which are secreted during stress and prepare the body to act.
• Insulin, from the beta cells of the islets of Langerhans — lowers blood glucose by promoting its uptake and storage.
• Glucagon, from the alpha cells of the islets of Langerhans — raises blood glucose by stimulating glycogenolysis in the liver.

• Pineal gland — secretes melatonin, which regulates the diurnal rhythm, that is the 24-hour cycle of the body, maintaining a normal sleep and wake pattern. It is active in darkness.
• Thymus — active in the young, secretes thymosins, which play a role in the maturation of T-lymphocytes and therefore in cell-mediated immunity. The gland shrinks with age.
• Testis — secretes androgens, the principal one being testosterone, which is responsible for the secondary sexual characters of the male.
• Ovary — secretes oestrogen, which is responsible for the secondary sexual characters of the female, and progesterone which supports pregnancy.

Hormones are of two chemical types, lipid soluble and water soluble, and each type has to act on a target cell in a different way because the cell membrane blocks anything that is not lipid soluble.

Hormone output is not left to run freely. The hypothalamus and the pituitary release their hormones in response to a fall in the blood level of the target hormone, and the target gland in turn inhibits the pituitary once its hormone is restored.

Hormones can be detected in the blood and in the urine, and their estimation is done by radioimmunoassay and by immunoassay techniques. Because the concentration of a hormone is very small, these methods depend on the hormone and its antibody binding, which is why they are the standard clinical test for an endocrine disorder.

Almost every disorder NCERT lists is a fault of over-secretion or under-secretion, so the first step in answering is to decide which of the two the symptom describes.

• Hyperglycaemia — blood glucose rises because insulin secretion falls short, producing glycosuria and diabetes mellitus.
• Hypoglycaemia — blood glucose falls because too much insulin is secreted, and the low glucose can lead to coma and even death.
• Gigantism — excess growth hormone in childhood, so the body grows abnormally tall.
• Acromegaly — excess growth hormone in adulthood, so the hands, feet, jaw and facial bones enlarge.
• Pituitary dwarfism — a deficiency of growth hormone in childhood, so the body remains very small but proportions are normal and the intelligence is normal.
• Pituitary diabetes insipidus — a deficiency of ADH, so the kidney tubules fail to reabsorb water and large volumes of dilute urine are passed.
• Simmonds' disease — a deficiency of the gonadotropins, which leads to premature atrophy of the gonads.
• Goitre — any enlarged thyroid gland, and in the commonest case it follows a deficiency of iodine, so less thyroxine is made and the gland enlarges in an attempt to compensate.
• Cretinism — hypo-secretion of the thyroid hormone in a child, causing stunted growth, mental retardation, deaf-mutism, a defective skin and abnormal teeth.
• Myxoedema — hypo-secretion of the thyroid hormone in an adult, causing the skin to become puffy and rough, the hair to fall out, and the body weight and pulse rate to rise, with the person feeling lethargic.
• Cushing's syndrome — excess glucocorticoids from the adrenal cortex.
• Addison's disease — hypo-secretion of the adrenal cortex hormones, so the body cannot cope with stress, and there is increased pigmentation, weakness, fatigue, low blood pressure and low blood sugar.
• Obesity — excess fat deposition, which can lead to abnormal insulin secretion and diabetes.

Exercises (NCERT Q1–Q9)

• 1) Define the following: (a) Exocrine gland (b) Endocrine gland (c) Hormone
• 2) Diagrammatically indicate the location of the various endocrine glands in our body.
• 3) 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
• 4) Fill in the blanks: Hormones Target gland (a) Hypothalamic hormones __________________ (b) Thyrotrophin (TSH) __________________ (c) Corticotrophin (ACTH) __________________ (d) Gonadotrophins (LH, FSH) __________________ (e) Melanotrophin (MSH) __________________
• 5) 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
• 6) 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
• 7) Which hormonal deficiency is responsible for the following: (a) Diabetes mellitus (b) Goitre (c) Cretinism
• 8) Briefly mention the mechanism of action of FSH.
• 9) Match the following: Column I Column II (a) T4 (i) Hypothalamus (b) PTH (ii) Thyroid (c) GnRH (iii) Pituitary (d) LH (iv) Parathyroid

Answers at a glance

1. 1
   Q1 → (a) An exocrine gland delivers its secretion through a duct onto a surface or into a cavity. (b) An endocrine or ductless gland releases its secretion directly into the tissue fluid and hence the blood, which carries it to a distant target. (c) A hormone is a non-nutrient organic chemical of very small amount, secreted by an endocrine gland and carried in the blood to a specific target cell, where it acts on a receptor to alter that cell's activity.
2. 2
   Q2 → Mark, on a front view of the body: hypothalamus and pituitary in the head with the pineal above them; thyroid with the parathyroids on its posterior surface in the neck beside the trachea; thymus in the thoracic cavity behind the sternum; the two adrenal glands capping the kidneys in the abdomen, with the pancreas behind the stomach; and testes in the scrotum or ovaries in the pelvic cavity. The atria of the heart, the kidneys and the gastrointestinal tract also secrete hormones and may be marked.
3. 3
   Q3 → (a) GHRH, PRH, TRH, GnRH, MIH, somatostatin, plus oxytocin and ADH. (b) GH, TSH, ACTH, LH, FSH, prolactin, MSH, plus oxytocin and ADH. (c) T3, T4 and thyrocalcitonin. (d) PTH. (e) Cortisol, aldosterone and androgens from the cortex; adrenaline and noradrenaline from the medulla. (f) Glucagon and insulin. (g) Androgens. (h) Estrogens and progesterone. (i) Thymosins. (j) ANF. (k) Erythropoietin and renin. (l) Gastrin, secretin and cholecystokinin.
4. 4
   Q4 → (a) Anterior pituitary; (b) Thyroid gland; (c) Adrenal cortex; (d) Gonads, that is the testis and the ovary; (e) Melanocytes of the skin.
5. 5
   Q5 → (a) PTH raises blood calcium by increasing bone resorption, renal reabsorption of calcium and intestinal absorption through vitamin D. (b) T3 and T4 regulate basal metabolic rate and support normal growth, mental development, body temperature and heart rate; deficiency causes cretinism in children, myxoedema in adults and goitre with iodine deficiency. (c) Thymosins promote the maturation of T lymphocytes and are essential for the immune system. (d) Androgens promote spermatogenesis and the male secondary sexual characters. (e) Estrogens promote the female secondary sexual characters, the menstrual cycle and pregnancy. (f) Insulin is hypoglycemic, promoting glucose uptake and its conversion to glycogen, while glucagon is hyperglycemic, promoting glycogenolysis and gluconeogenesis in the liver.
6. 6
   Q6 → (a) Hyperglycemic: glucagon, adrenaline, glucocorticoids and growth hormone; hypoglycemic: insulin. (b) Hypercalcemic: PTH. (c) Gonadotrophic: LH and FSH. (d) Progestational: progesterone. (e) Blood pressure lowering: ANF, or ANP. (f) Androgens: testosterone; estrogens: the ovarian estrogens such as estradiol.
7. 7
   Q7 → (a) Diabetes mellitus is caused by deficiency of insulin, which reduces glucose uptake and raises blood glucose. (b) Goitre is caused by deficiency of the thyroid hormones, usually from iodine deficiency, which removes the negative feedback and so enlarges the thyroid through excess TSH. (c) Cretinism is caused by deficiency of the thyroid hormones during early life, which retards both physical growth and mental development.
8. 8
   Q8 → FSH is a peptide hormone from the anterior pituitary, so it binds a membrane receptor and activates adenylyl cyclase, with cAMP acting as the second messenger inside the target cell. In the male it acts on the Sertoli cells to stimulate spermatogenesis and androgen binding protein secretion; in the female it acts on the granulosa cells to promote follicular growth and estrogen secretion.
9. 9
   Q9 → (a) T4 — (ii) Thyroid; (b) PTH — (iv) Parathyroid; (c) GnRH — (i) Hypothalamus; (d) LH — (iii) Pituitary.

MCQ Questions

1 Mark Questions

1. 1
   Where are the islets of Langerhans located? (Ans: the pancreas)
2. 2
   Name the hormone that promotes metamorphosis of a tadpole to a frog. (Ans: thyroxine)
3. 3
   Which hormone is called the 'sleep hormone'? (Ans: melatonin from the pineal gland)
4. 4
   What is a hormone? (Ans: a chemical messenger secreted by endocrine glands into the blood acting on target organs)

2 Mark Questions

1. 1
   Differentiate between endocrine and exocrine glands with one example each.
2. 2
   Give two functions of the thyroid hormones (T3/T4). (Ans: basal metabolic rate, growth, development, body temperature)
3. 3
   What are the effects of hypothyroidism and hyperthyroidism? (Ans: goitre, cretinism/myxoedema vs exophthalmic goitre)

3 Mark Questions

1. 1
   Explain how peptide hormones act through second messengers, using glucagon or adrenaline as an example.
2. 2
   Describe the disorders caused by hypo- and hypersecretion of the pituitary growth hormone (dwarfism, gigantism, acromegaly).
3. 3
   Describe the feedback regulation of hormone secretion with the example of the thyroid (TRH–TSH–T3/T4 axis).

5 Mark Questions

1. 1
   Describe the hormones secreted by the anterior and posterior pituitary, their target organs and their functions, mentioning the disorders of hyposecretion.
2. 2
   Describe the structure and hormonal function of the pancreas and adrenal gland, and explain how blood glucose level is regulated by insulin and glucagon, including the effect of their deficiency. (Ans: diabetes mellitus for insulin deficiency)