Chapter 19: Chemical Coordination and Integration Long Questions | biology Class 11 CBSE

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Chapter 19: Chemical Coordination and Integration Long Questions | biology Class 11 CBSE | ByteNotes.in

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Question 1

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Compare and contrast the structure and functions of the adenohypophysis and neurohypophysis, and explain the relationship of the pituitary gland with the hypothalamus.

The pituitary gland is located in the bony sella tursica and is attached to the hypothalamus by a stalk; it is divided into adenohypophysis (pars distalis and pars intermedia) and neurohypophysis (pars nervosa).
Pars distalis (anterior pituitary) produces six hormones: GH, PRL, TSH, ACTH, LH, and FSH; pars intermedia secretes only MSH but is nearly merged with pars distalis in humans.
Neurohypophysis stores and releases oxytocin and vasopressin, which are actually synthesised by the hypothalamus and transported axonally to the posterior pituitary.
Hypothalamic releasing and inhibiting hormones (e.g., GnRH stimulates, somatostatin inhibits) travel through the portal circulatory system to regulate anterior pituitary secretion.
The posterior pituitary is under direct neural regulation of the hypothalamus, making the hypothalamus the supreme regulator of the entire endocrine system.
Disorders of GH secretion illustrate adenohypophyseal dysfunction: gigantism from excess GH in childhood, pituitary dwarfism from deficiency, and acromegaly from excess GH in adults.

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Question 2

Long Form

Analyse the role of thyroid hormones in maintaining body physiology, and describe the consequences of both hypo- and hyperthyroidism.

The thyroid gland, composed of follicles and stromal tissues flanking the trachea, synthesises T3, T4 (requiring iodine), and thyrocalcitonin (TCT).
Thyroid hormones regulate basal metabolic rate, support RBC formation, control carbohydrate/protein/fat metabolism, and maintain water and electrolyte balance.
TCT is a protein hormone that lowers blood calcium levels, acting antagonistically to PTH in calcium homeostasis.
Hypothyroidism (from iodine deficiency) leads to goitre in adults; during pregnancy it causes cretinism—stunted growth, mental retardation, low IQ, abnormal skin, and deaf-mutism; in adult women it causes irregular menstrual cycles.
Hyperthyroidism results from cancer or nodular development in the thyroid, causing abnormally high hormone synthesis; Graves' disease (exophthalmic goitre) is one form, characterised by thyroid enlargement, protruding eyeballs, increased BMR, and weight loss.
Both hypo- and hyperthyroidism adversely affect multiple organ systems, underlining the thyroid's central role in metabolic homeostasis throughout life.

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Question 3

Long Form

Describe the structure of the adrenal gland and explain the physiological significance of hormones secreted by each of its regions.

Each adrenal gland (one above each kidney) has two regions: the outer adrenal cortex and the inner adrenal medulla.
The adrenal medulla secretes catecholamines—adrenaline and noradrenaline—in response to stress; these increase heart rate, respiration, alertness, blood glucose (via glycogenolysis), and stimulate lipolysis and proteolysis.
The adrenal cortex is divided into three layers: zona glomerulosa (mineralocorticoids—aldosterone), zona fasciculata (glucocorticoids—cortisol), and zona reticularis (androgenic steroids).
Aldosterone stimulates Na+ and water reabsorption and K+ excretion in renal tubules, maintaining electrolyte balance, osmotic pressure, and blood pressure.
Cortisol stimulates gluconeogenesis, lipolysis, and proteolysis; maintains cardiovascular and kidney function; suppresses immune responses; and stimulates RBC production.
Androgenic steroids from the adrenal cortex contribute to growth of axial, pubic, and facial hair during puberty; underproduction of adrenal cortex hormones causes Addison's disease.

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Question 4

Long Form

Explain how insulin and glucagon together maintain glucose homeostasis in the blood, and describe the condition that results when this balance is disturbed.

The pancreas is a composite gland; its endocrine portion consists of Islets of Langerhans (1-2 million), which make up only 1-2% of pancreatic tissue but are critical for glucose regulation.
Alpha cells of the Islets secrete glucagon—a hyperglycaemic peptide hormone that acts on hepatocytes to stimulate glycogenolysis and gluconeogenesis, raising blood glucose, and also reduces cellular glucose uptake.
Beta cells secrete insulin—a hypoglycaemic peptide hormone that acts on hepatocytes and adipocytes to enhance cellular glucose uptake and utilisation, and stimulates glycogenesis (glucose to glycogen), lowering blood glucose.
Together, insulin and glucagon form a feedback-regulated system: when blood glucose rises, insulin is released; when it falls, glucagon is released, ensuring homeostasis.
Prolonged hyperglycaemia due to insulin deficiency or resistance causes diabetes mellitus, associated with glucose loss in urine (glycosuria) and formation of harmful ketone bodies.
Diabetic patients are successfully treated with insulin therapy, highlighting the critical role of this hormone in cellular glucose metabolism.

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Question 5

Long Form

Describe the two mechanisms by which hormones act on target cells, clearly distinguishing between protein hormones and steroid hormones in terms of receptor location and downstream events.

Hormones exert effects by binding to specific proteins called receptors present only in target tissues; each receptor is specific to one hormone, ensuring selectivity of hormonal action.
Membrane-bound receptors are present on the cell membrane of target cells and bind protein/peptide hormones (e.g., insulin, FSH) which do not enter the cell.
Binding of protein hormones to membrane-bound receptors generates second messengers such as cyclic AMP, IP3, or Ca2+, which regulate intracellular metabolic processes.
Intracellular (nuclear) receptors are present inside the target cell and bind lipid-soluble hormones such as steroid hormones (cortisol, testosterone) and iodothyronines (T3, T4), which can cross the cell membrane.
The hormone-receptor complex formed with intracellular receptors interacts directly with the genome, regulating gene expression or chromosome function, leading to synthesis of specific proteins.
Cumulative biochemical actions from both pathways result in physiological and developmental effects in the target tissues; steroid effects are typically slower but more prolonged than second-messenger-mediated effects.

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Question 6

Long Form

Compare the roles of estrogen and progesterone in female physiology, and explain how the ovary functions both as a primary sex organ and an endocrine gland.

The ovaries (a pair, located in the abdomen) are primary female sex organs producing one ovum per menstrual cycle and functioning endocrinologically by secreting estrogen and progesterone.
Estrogen is synthesised and secreted by the growing ovarian follicles; progesterone is secreted mainly by the corpus luteum formed after ovulation from the remnants of the ruptured graafian follicle.
Estrogens stimulate growth and activities of female secondary sex organs, development of ovarian follicles, appearance of female secondary sex characters (e.g., high-pitched voice), mammary gland development, and regulate female sexual behaviour.
Progesterone supports pregnancy by maintaining the uterine environment; it also acts on mammary glands to stimulate formation of alveoli (milk-storing sac-like structures) and promote milk secretion (lactation).
Both hormones are steroid in nature and act via intracellular receptors to regulate gene expression, producing long-term developmental effects.
The cyclic interplay between estrogen (follicular phase) and progesterone (luteal phase) governs the menstrual cycle, pregnancy, and lactation, demonstrating the integrative endocrine function of the ovary.

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Question 7

Long Form

Explain the structure and multiple functions of the thymus gland, and analyse why immune responses weaken with advancing age.

The thymus is a lobular structure located between the lungs behind the sternum on the ventral side of the aorta.
The thymus secretes peptide hormones called thymosins, which are critical for the development of the immune system.
Thymosins play a major role in the differentiation of T-lymphocytes, which are responsible for cell-mediated immunity (e.g., destruction of infected or abnormal cells).
Thymosins also promote production of antibodies by B-lymphocytes, thereby providing humoral immunity.
The thymus is a functional and active gland during childhood and early adulthood; however, it undergoes degeneration in old individuals.
As the thymus degenerates in old age, production of thymosins decreases significantly, resulting in reduced differentiation of T-lymphocytes and antibody production, making elderly individuals more susceptible to infections and diseases.

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Question 8

Long Form

Describe the endocrine functions of the testis, and analyse how androgens regulate both reproductive and non-reproductive physiological processes.

The testis, present in the scrotal sac of males, performs dual functions: as a primary sex organ (producing spermatozoa) and as an endocrine gland (producing androgens).
The testis is composed of seminiferous tubules and stromal/interstitial tissue; Leydig cells (interstitial cells) in the intertubular spaces secrete androgens, mainly testosterone.
Androgens regulate the development, maturation, and functions of male accessory sex organs such as the epididymis, vas deferens, seminal vesicles, prostate gland, and urethra.
Androgens stimulate male secondary sex characteristics including muscular growth, facial and axillary hair growth, low-pitched voice, and aggressiveness.
Androgens play a major stimulatory role in spermatogenesis (formation of spermatozoa); they also act on the central neural system to influence male sexual behaviour (libido).
Androgens produce anabolic effects on protein and carbohydrate metabolism, promoting tissue synthesis, and LH from the pituitary controls testosterone production in the testis, illustrating hypothalamo-pituitary-gonadal axis regulation.

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Question 9

Long Form

Describe the role of the hypothalamus as the master regulator of the endocrine system, using specific examples of its hormones and their targets.

The hypothalamus is the basal part of the diencephalon, forebrain, and regulates a wide spectrum of body functions through its neurosecretory cells (nuclei).
It produces two types of hormones: releasing hormones (stimulate pituitary hormone secretion) and inhibiting hormones (inhibit pituitary hormone secretion).
For example, Gonadotrophin Releasing Hormone (GnRH) stimulates the anterior pituitary to synthesise and release gonadotrophins (LH and FSH), which then regulate gonadal activity.
Somatostatin from the hypothalamus inhibits the release of growth hormone from the pituitary, demonstrating fine-tuned negative regulation.
Hypothalamic hormones originate in neurosecretory neurons, pass through axons, and are released from nerve endings to reach the anterior pituitary via a portal circulatory system.
The posterior pituitary is under direct neural regulation of the hypothalamus; oxytocin and vasopressin are synthesised by hypothalamic neurons and transported axonally to the neurohypophysis for storage and release.

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Question 10

Long Form

Examine the roles of hormones secreted by non-classical endocrine tissues (heart, kidney, and gastrointestinal tract) and discuss their significance in maintaining homeostasis.

Not all hormones are produced by organised endocrine glands; several non-glandular tissues secrete hormones, consistent with the modern definition of hormones as intercellular messengers.
The atrial wall of the heart secretes atrial natriuretic factor (ANF), a peptide hormone that decreases blood pressure by dilating blood vessels when blood pressure is abnormally high.
The juxtaglomerular cells of the kidney produce erythropoietin, a peptide hormone that stimulates erythropoiesis (RBC formation), linking renal function to blood cell production.
Endocrine cells in the gastrointestinal tract secrete four major peptide hormones: gastrin (stimulates HCl and pepsinogen secretion), secretin (stimulates pancreatic water and bicarbonate secretion), CCK (stimulates pancreatic enzymes and bile), and GIP (inhibits gastric secretion and motility).
These GI hormones coordinate digestion by regulating secretion of digestive juices at the right time and place, demonstrating local hormonal control.
Non-endocrine tissues also secrete growth factors essential for normal tissue growth, repair, and regeneration, broadening the understanding of chemical coordination beyond classical endocrinology.

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Chapter 19: Chemical Coordination and Integration | Long Questions

Compare and contrast the structure and functions of the adenohypophysis and neurohypophysis, and explain the relationship of the pituitary gland with the hypothalamus.

Analyse the role of thyroid hormones in maintaining body physiology, and describe the consequences of both hypo- and hyperthyroidism.

Describe the structure of the adrenal gland and explain the physiological significance of hormones secreted by each of its regions.

Explain how insulin and glucagon together maintain glucose homeostasis in the blood, and describe the condition that results when this balance is disturbed.

Describe the two mechanisms by which hormones act on target cells, clearly distinguishing between protein hormones and steroid hormones in terms of receptor location and downstream events.

Compare the roles of estrogen and progesterone in female physiology, and explain how the ovary functions both as a primary sex organ and an endocrine gland.

Explain the structure and multiple functions of the thymus gland, and analyse why immune responses weaken with advancing age.

Describe the endocrine functions of the testis, and analyse how androgens regulate both reproductive and non-reproductive physiological processes.

Describe the role of the hypothalamus as the master regulator of the endocrine system, using specific examples of its hormones and their targets.

Examine the roles of hormones secreted by non-classical endocrine tissues (heart, kidney, and gastrointestinal tract) and discuss their significance in maintaining homeostasis.

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