Class 11 Biology Chapter 22 Question Answer | Chemical Coordination and Integration | English Medium

Class 11 Biology Chapter 22 Question Answer | Chemical Coordination and Integration | English Medium | ASSEB

Class 11 Biology Chapter 22 — Chemical Coordination and Integration

Welcome to HSLC Guru. On this page you will find the complete English-medium summary, textbook question answers and additional practice for Chapter 22 — Chemical Coordination and Integration of the ASSEB Class 11 Biology syllabus. Notes are organised in an exam-friendly format covering the endocrine system, all major endocrine glands, their hormones, mechanism of hormone action and common endocrine disorders, useful for HS 1st Year Final Examination preparation.

Summary

The endocrine system is the body’s second great coordinating system, complementing the nervous system. Endocrine glands are ductless and release their secretions, called hormones, directly into the bloodstream where they travel to target organs. Compared with nerve signalling, hormonal communication is slower in onset, longer in duration and operates over wider distances. The major endocrine glands in humans are the hypothalamus, pituitary, pineal, thyroid, parathyroid, thymus, adrenal, pancreas and gonads (testes/ovaries); some organs like the heart, kidney and gastrointestinal tract also secrete hormones. The hypothalamus controls the anterior pituitary through releasing and inhibiting hormones, while the posterior pituitary stores oxytocin and vasopressin (ADH).

The pituitary gland (master gland) has anterior, intermediate and posterior lobes. Anterior secretes growth hormone (GH), prolactin, thyroid-stimulating hormone (TSH), adrenocorticotropic hormone (ACTH), follicle-stimulating hormone (FSH) and luteinising hormone (LH). The intermediate lobe releases melanocyte-stimulating hormone (MSH) while the posterior lobe stores and releases oxytocin and vasopressin/ADH. The pineal gland secretes melatonin which regulates the sleep-wake cycle. The thyroid produces thyroxine (T4) and triiodothyronine (T3) which regulate metabolic rate, growth and BMR; it also secretes calcitonin which lowers blood calcium. The parathyroid glands secrete parathyroid hormone (PTH) which raises blood calcium. The thymus produces thymosin which promotes T-lymphocyte differentiation and antibody-mediated immunity.

The adrenal gland has two regions: the cortex secretes glucocorticoids (cortisol — gluconeogenesis, anti-inflammatory) and mineralocorticoids (aldosterone — Na+/water reabsorption); the medulla secretes adrenaline and noradrenaline (catecholamines / “fight-or-flight” hormones). The pancreas Islets of Langerhans contain α-cells (glucagon — raises blood glucose), β-cells (insulin — lowers blood glucose by promoting glycogenesis and glucose uptake) and δ-cells (somatostatin). The gonads — testes secrete testosterone (male secondary sexual characters, spermatogenesis) and ovaries secrete oestrogen (female secondary sexual characters) and progesterone (maintains pregnancy). The heart’s atrium secretes ANF (Atrial Natriuretic Factor — lowers blood pressure), the kidney secretes erythropoietin (RBC production) and renin, and the GI tract secretes gastrin, secretin, CCK and GIP.

Hormones act through two main mechanisms. Steroid (lipophilic) hormones diffuse through the plasma membrane and bind intracellular receptors; the hormone-receptor complex enters the nucleus and regulates gene expression. Peptide and amine (hydrophilic) hormones bind to membrane-bound receptors and operate via second messengers like cyclic AMP, IP3 / DAG or Ca²⁺ to activate kinase cascades. Common endocrine disorders include dwarfism (deficiency of GH in children), gigantism (excess GH in children), acromegaly (excess GH in adults), goitre (iodine deficiency / thyroid dysfunction), cretinism, myxoedema, exophthalmic goitre / Graves’ disease, diabetes insipidus (ADH deficiency), diabetes mellitus type I & II (insulin deficiency / resistance), Addison’s disease and Cushing’s syndrome (adrenal cortex dysfunction).

Textbook Question Answers — Very Short Answer (1 Mark)

Q1. What is a hormone?

Answer: A non-nutrient chemical messenger secreted by an endocrine gland in trace amounts that acts on a specific target organ.

Q2. Which gland is called the “master gland”?

Answer: The pituitary gland (anterior lobe).

Q3. Name the hormone secreted by the pineal gland.

Answer: Melatonin.

Q4. Which hormone regulates blood calcium levels — raising it?

Answer: Parathyroid hormone (PTH).

Q5. Name the hormones secreted by the α-cells and β-cells of the Islets of Langerhans.

Answer: α-cells secrete glucagon and β-cells secrete insulin.

Q6. What is the function of ADH?

Answer: Antidiuretic hormone (vasopressin) promotes water reabsorption from the distal tubules and collecting ducts of the kidney.

Q7. Which hormone is called the “fight-or-flight” hormone?

Answer: Adrenaline (epinephrine), secreted by the adrenal medulla.

Q8. Name the hormones secreted by the testes and ovaries.

Answer: Testes — testosterone; Ovaries — oestrogen and progesterone.

Q9. Which hormone is responsible for milk ejection during lactation?

Answer: Oxytocin.

Q10. What disease is caused by an iodine-deficient diet?

Answer: Simple goitre (enlargement of the thyroid gland).

Textbook Question Answers — Short Answer (2-3 Marks)

Q11. Differentiate between hormonal and neural coordination.

Answer: Neural coordination is fast, point-to-point, short-lived, transmitted by neurons through electrical/chemical impulses. Hormonal coordination is slower, transported by blood, longer-lasting, and acts on distant target organs through specific receptors.

Q12. Explain the role of insulin and glucagon in blood-glucose regulation.

Answer: Insulin (β-cells) is hypoglycaemic — it lowers blood glucose by promoting glucose uptake in muscle/adipose tissue, glycogenesis in liver/muscle and inhibiting gluconeogenesis. Glucagon (α-cells) is hyperglycaemic — it raises blood glucose by stimulating glycogenolysis and gluconeogenesis in the liver. Together they keep plasma glucose ~70-110 mg/dL.

Q13. List the hormones secreted by the anterior pituitary and their main functions.

Answer: GH (growth/protein synthesis), prolactin (milk production), TSH (stimulates thyroid), ACTH (stimulates adrenal cortex), FSH (gametogenesis — follicle/sperm), LH (ovulation, testosterone secretion).

Q14. Differentiate between adrenal cortex and adrenal medulla hormones.

Answer: Adrenal cortex secretes corticoids — glucocorticoids (cortisol — gluconeogenesis, anti-inflammatory) and mineralocorticoids (aldosterone — Na+/water reabsorption); secretion is regulated by ACTH. Adrenal medulla secretes catecholamines — adrenaline and noradrenaline — for emergency response (raise heart rate, BP, alertness, glycogenolysis).

Q15. What are the functions of thymus and thymosins?

Answer: The thymus is a lobed lymphoid organ that secretes thymosins, which promote differentiation of T-lymphocytes (cell-mediated immunity) and production of antibodies (humoral immunity). Thymus shrinks (involutes) with age, weakening immunity.

Q16. Briefly describe the role of hypothalamus.

Answer: The hypothalamus links nervous and endocrine systems. It secretes releasing hormones (GHRH, TRH, CRH, GnRH, etc.) and inhibiting hormones (somatostatin, prolactin-inhibiting hormone) that regulate anterior pituitary; it also synthesises oxytocin and ADH which are stored and released by the posterior pituitary. It controls body temperature, thirst, hunger, sleep and emotions.

Textbook Question Answers — Long Answer (5-7 Marks)

Q17. Describe the structure and functions of the human pituitary gland.

Answer: The pituitary (hypophysis) is a pea-sized gland in the sella turcica below the hypothalamus. It has three parts:

Anterior pituitary (adenohypophysis): secretes GH (excess → gigantism/acromegaly; deficiency → dwarfism), prolactin (milk production), TSH (stimulates thyroid), ACTH (stimulates adrenal cortex), FSH and LH (gametogenesis & ovulation/testosterone).
Intermediate lobe (pars intermedia): secretes MSH (melanin synthesis, skin pigmentation).
Posterior pituitary (neurohypophysis): stores and releases oxytocin (uterine contraction, milk ejection) and vasopressin/ADH (water reabsorption in kidneys; deficiency → diabetes insipidus).

Q18. Describe the structure and hormones of the human thyroid gland.

Answer: The thyroid is a bilobed gland on either side of the trachea connected by an isthmus. It is composed of follicles filled with colloid and follicular cells secreting thyroxine (T4) and triiodothyronine (T3), with parafollicular C-cells secreting calcitonin. Iodine is essential — deficiency causes goitre. T3/T4 raise BMR, regulate carbohydrate/protein/fat metabolism, RBC formation, growth and brain development. Hyperthyroidism → exophthalmic goitre / Graves’ disease; Hypothyroidism in adults → myxoedema; in children → cretinism. Calcitonin lowers blood Ca²⁺ by depositing it into bones.

Q19. Explain the mechanism of hormone action.

Answer: Hormones bind to specific receptors on/in target cells. Two main mechanisms:

Steroid / thyroid hormones (lipid-soluble): diffuse through plasma membrane → bind intracellular (cytoplasmic/nuclear) receptors → hormone-receptor complex enters nucleus → binds DNA → regulates gene transcription → mRNA → new proteins → physiological response. Examples: cortisol, oestrogen, testosterone, T3/T4.
Peptide / amine hormones (water-soluble): bind plasma-membrane receptors → activate G-proteins → activate adenylate cyclase → ATP → cyclic AMP (second messenger) → activates protein kinase A → phosphorylates target enzymes → physiological response. Examples: insulin, glucagon, adrenaline, FSH, LH, ACTH.

Q20. Discuss diabetes mellitus — types, causes, symptoms and management.

Answer: Diabetes mellitus is a metabolic disorder characterised by hyperglycaemia.

Type I (Insulin-Dependent / IDDM / Juvenile): auto-immune destruction of β-cells → no insulin; treated with insulin injections.
Type II (Non-Insulin-Dependent / NIDDM / Adult-onset): insulin resistance + relative insulin deficiency; common in obesity; managed with diet, exercise and oral hypoglycaemic drugs (sulphonylureas, biguanides like metformin).
Symptoms: polyuria (excess urination), polydipsia (excess thirst), polyphagia (excess hunger), weight loss, glycosuria, fatigue, blurred vision, slow wound healing.
Complications: ketoacidosis, retinopathy, nephropathy, neuropathy, cardiovascular disease.
Management: balanced diet, regular exercise, blood-glucose monitoring, insulin injections / oral drugs, lifestyle modification.

Q21. Compare the male and female reproductive hormones.

Answer: Male — testes (Leydig cells) secrete testosterone (under LH control) which promotes spermatogenesis, secondary sexual characters (beard, voice, muscle, libido) and accessory gland development; FSH stimulates Sertoli cells. Female — ovaries secrete oestrogen (under FSH) which promotes secondary sexual characters (breast, hip, voice), regulates menstrual cycle, and progesterone (under LH from corpus luteum) which prepares endometrium and maintains pregnancy. The hypothalamic-pituitary-gonadal axis (GnRH → FSH/LH → gonads) coordinates reproduction.

Additional Questions — Multiple Choice (MCQ)

Q22. The master endocrine gland is: (a) thyroid (b) adrenal (c) pituitary (d) pancreas.

Q23. The hormone that regulates the sleep-wake cycle is: (a) thyroxine (b) melatonin (c) adrenaline (d) insulin.

Q24. Which hormone is called the “emergency hormone”? (a) insulin (b) thyroxine (c) adrenaline (d) cortisol.

Q25. Diabetes insipidus is due to deficiency of: (a) insulin (b) glucagon (c) ADH (d) cortisol.

Q26. The hormone secreted by atrial wall of heart is: (a) erythropoietin (b) gastrin (c) ANF (d) renin.

Q27. Insulin is secreted by: (a) α-cells (b) β-cells (c) δ-cells (d) acinar cells.

Q28. Calcitonin is secreted by: (a) parathyroid (b) thyroid (C-cells) (c) thymus (d) adrenal medulla.

Q29. The hormone responsible for the milk-ejection reflex is: (a) prolactin (b) progesterone (c) oxytocin (d) FSH.

Q30. Cretinism in children is caused by: (a) excess GH (b) deficiency of GH (c) deficiency of T3/T4 (d) excess insulin.

Q31. Aldosterone is a: (a) glucocorticoid (b) mineralocorticoid (c) androgen (d) catecholamine.

Additional Questions — Fill in the Blanks

The pituitary gland is also known as the ___ gland. (master)
Iodine is necessary for the synthesis of ___. (thyroxine / T4)
The hormone that lowers blood glucose is ___. (insulin)
Oxytocin and vasopressin are released from the ___ pituitary. (posterior)
The endocrine gland located on top of each kidney is the ___. (adrenal gland)

Additional Questions — True / False

The pancreas is both an exocrine and an endocrine gland. — True
Glucagon is secreted by β-cells of the pancreas. — False (α-cells)
The thymus shrinks with age. — True
ANF raises blood pressure. — False (lowers BP)
Steroid hormones bind intracellular receptors. — True

Glossary / Key Terms

Term	Meaning
Hormone	Chemical messenger secreted by an endocrine gland in trace amount.
Endocrine gland	Ductless gland releasing hormones directly into blood.
Hypothalamus	Brain region linking nervous and endocrine systems via releasing/inhibiting hormones.
Pituitary	Master gland with anterior, intermediate and posterior lobes.
GH	Growth hormone — promotes growth and protein synthesis.
TSH	Thyroid-stimulating hormone — stimulates thyroid.
ACTH	Adrenocorticotropic hormone — stimulates adrenal cortex.
FSH / LH	Gonadotropins regulating gametogenesis and ovulation.
Oxytocin	Causes uterine contraction and milk ejection.
ADH (vasopressin)	Antidiuretic — promotes water reabsorption in kidney.
Melatonin	Pineal hormone regulating sleep-wake cycle.
Thyroxine (T4) / T3	Iodinated thyroid hormones regulating BMR.
Calcitonin	Lowers blood Ca²⁺ by depositing it in bone.
PTH	Parathyroid hormone — raises blood Ca²⁺.
Thymosin	Thymus hormone — promotes T-cell differentiation.
Cortisol	Glucocorticoid — gluconeogenesis, anti-inflammatory.
Aldosterone	Mineralocorticoid — Na+/water reabsorption.
Adrenaline	Catecholamine — fight-or-flight response.
Insulin	Pancreatic β-cell hormone — lowers blood glucose.
Glucagon	Pancreatic α-cell hormone — raises blood glucose.
Testosterone	Male sex hormone secreted by Leydig cells.
Oestrogen	Female sex hormone — secondary sexual characters.
Progesterone	Maintains pregnancy; secreted by corpus luteum.
ANF	Atrial natriuretic factor — lowers blood pressure.
Erythropoietin	Kidney hormone stimulating RBC production.
Diabetes mellitus	Hyperglycaemia from insulin deficiency or resistance.
Diabetes insipidus	Polyuria due to ADH deficiency.
Goitre	Enlargement of thyroid (often iodine deficiency).
Acromegaly	Excess GH in adults — enlarged extremities.
cAMP	Cyclic AMP — second messenger of peptide hormones.