Class 11 Biology Notes Chapter 25 (Chapter 25) – Examplar Problems (English) Book

Detailed Notes with MCQs of Chemical Coordination and Integration. This chapter is fundamental for understanding how different physiological processes in our body are regulated over longer durations compared to the rapid responses of the nervous system. For your government exam preparation, pay close attention to the glands, the hormones they secrete, their specific functions, and the disorders associated with their imbalance.

Chapter 22: Chemical Coordination and Integration - Detailed Notes

(Note: Standard NCERT Class 11 Biology has this topic as Chapter 22. We will cover the content under this standard numbering.)

1. Introduction

• The neural system provides point-to-point rapid coordination.
• The endocrine system provides chemical integration through hormones.
• Hormones are non-nutrient chemicals acting as intercellular messengers, produced in trace amounts.
• Endocrine glands are ductless glands that secrete hormones directly into the bloodstream, which then transports them to target organs/tissues.
• Neuroendocrine System: The hypothalamus acts as the crucial link between the nervous and endocrine systems.

2. Human Endocrine System

• Consists of organized endocrine glands and diffused hormone-secreting cells/tissues.
• Main Endocrine Glands: Hypothalamus, Pituitary, Pineal, Thyroid, Parathyroid, Thymus, Adrenal, Pancreas (Islets of Langerhans), Gonads (Testis and Ovary).

3. The Hypothalamus

• Location: Basal part of the diencephalon (forebrain).
• Function: Regulates a wide spectrum of body functions. Contains neurosecretory cells called nuclei which produce hormones.
• Hormones Regulating Pituitary:
  • Releasing Hormones: Stimulate secretion of pituitary hormones (e.g., Gonadotrophin releasing hormone - GnRH).
  • Inhibiting Hormones: Inhibit secretion of pituitary hormones (e.g., Somatostatin inhibits Growth Hormone release).
  • These hormones reach the anterior pituitary via the hypophyseal portal system.
• Hormones Synthesized (Released by Posterior Pituitary):
  • Oxytocin: Synthesized by hypothalamus, transported axonally to the posterior pituitary for storage and release. Acts on smooth muscles (uterine contraction during childbirth, milk ejection).
  • Antidiuretic Hormone (ADH) / Vasopressin: Synthesized by hypothalamus, transported axonally to the posterior pituitary. Acts on kidney tubules (DCT, collecting duct) to promote water reabsorption, reducing water loss (diuresis). Constricts blood vessels (vasopressor effect).
  • Disorder: Deficiency of ADH leads to Diabetes Insipidus (excessive urination, dehydration, thirst).

4. The Pituitary Gland

• Location: Bony cavity called sella turcica, attached to the hypothalamus by a stalk.
• Divided anatomically into Adenohypophysis and Neurohypophysis.
  • Adenohypophysis:
    • Pars Distalis (Anterior Pituitary):
      • Growth Hormone (GH): Body growth. Oversecretion -> Gigantism; Low secretion -> Pituitary Dwarfism. Oversecretion in adults -> Acromegaly (severe disfigurement, especially of the face).
      • Prolactin (PRL): Growth of mammary glands and milk production.
      • Thyroid Stimulating Hormone (TSH): Stimulates thyroid gland to secrete thyroid hormones.
      • Adrenocorticotropic Hormone (ACTH): Stimulates adrenal cortex to secrete glucocorticoids (like cortisol).
      • Luteinizing Hormone (LH): In males (also called ICSH - Interstitial Cell Stimulating Hormone), stimulates Leydig cells for androgen synthesis/secretion. In females, induces ovulation, maintains corpus luteum.
      • Follicle Stimulating Hormone (FSH): In males, regulates spermatogenesis (with androgens). In females, stimulates growth and development of ovarian follicles.
      • (LH and FSH are collectively called Gonadotrophins).
    • Pars Intermedia: (Almost merged with pars distalis in humans) Secretes Melanocyte Stimulating Hormone (MSH) - regulates skin pigmentation.
  • Neurohypophysis (Posterior Pituitary / Pars Nervosa):
    • Stores and releases Oxytocin and ADH (synthesized by the hypothalamus).

5. The Pineal Gland

• Location: Dorsal side of the forebrain.
• Hormone: Melatonin.
• Functions: Regulates diurnal (24-hour) rhythms (sleep-wake cycle, body temperature). Influences metabolism, pigmentation, menstrual cycle, and defense capability.

6. The Thyroid Gland

• Location: Two lobes on either side of the trachea, connected by an isthmus. Composed of follicles and stromal tissues. Follicular cells synthesize thyroid hormones.
• Requires Iodine for normal hormone synthesis.
• Hormones:
  • Thyroxine (T4 - tetraiodothyronine) and Triiodothyronine (T3): Regulate Basal Metabolic Rate (BMR), support RBC formation, control metabolism of carbohydrates, proteins, fats, maintain water & electrolyte balance.
  • Thyrocalcitonin (TCT): Protein hormone. Regulates blood calcium levels (lowers calcium - hypocalcemic effect).
• Disorders:
  • Hypothyroidism: Iodine deficiency leads to Goitre (enlargement of thyroid). In pregnancy, can cause defective development in the baby (Cretinism - stunted growth, mental retardation, low IQ, abnormal skin, deaf-mutism). In adult women, can cause irregular menstrual cycles.
  • Hyperthyroidism: Due to cancer or nodules. Increased metabolic rate, weight loss. Exophthalmic Goitre (Graves' disease) - enlargement of thyroid, protrusion of eyeballs, increased BMR, weight loss.

7. The Parathyroid Gland

• Location: Four glands on the back side of the thyroid gland (one pair in each lobe).
• Hormone: Parathyroid Hormone (PTH) - Peptide hormone.
• Functions: Increases blood calcium levels (hypercalcemic hormone). Acts on bones (stimulates resorption/demineralization), kidneys (calcium reabsorption), and promotes calcium absorption from digested food. PTH and TCT work antagonistically to maintain calcium balance.
• Disorder: Hypoparathyroidism can lead to Tetany (rapid muscle spasms due to low blood calcium).

8. The Thymus Gland

• Location: Lobular structure between lungs behind the sternum on the ventral side of the aorta.
• Hormone: Thymosins - Peptide hormones.
• Functions: Major role in the development of the immune system. Differentiation of T-lymphocytes (provide cell-mediated immunity). Also promote antibody production (humoral immunity).
• Note: Thymus degenerates in old individuals, leading to decreased production of thymosins and a weaker immune response.

9. The Adrenal Gland

• Location: One pair, located at the anterior part (top) of each kidney.
• Composed of two tissues: Adrenal Medulla (central) and Adrenal Cortex (outer).
  • Adrenal Medulla:
    • Hormones: Adrenaline (Epinephrine) and Noradrenaline (Norepinephrine). Collectively called Catecholamines.
    • Functions: Secreted rapidly in response to stress (emergency situations) - called Emergency Hormones or Hormones of Fight or Flight. Increase alertness, pupillary dilation, piloerection, sweating, heart rate, heart contraction strength, respiratory rate. Stimulate glycogenolysis (-> increased blood glucose), lipolysis, proteolysis.
  • Adrenal Cortex: (Divided into 3 layers: zona reticularis (inner), zona fasciculata (middle), zona glomerulosa (outer))
    • Hormones: Many hormones, collectively called Corticoids.
      • Glucocorticoids: (Mainly Cortisol) Secreted by zona fasciculata. Involved in carbohydrate metabolism (gluconeogenesis, lipolysis, proteolysis). Anti-inflammatory effects, suppress immune response. Stimulates RBC production. Regulated by ACTH.
      • Mineralocorticoids: (Mainly Aldosterone) Secreted by zona glomerulosa. Act on renal tubules (DCT) to stimulate Na+ and water reabsorption, and K+ and phosphate excretion. Maintain electrolytes, body fluid volume, osmotic pressure, blood pressure.
      • Androgenic Steroids: Small amounts secreted by zona reticularis. Play a role in the growth of axial, pubic, and facial hair during puberty.
    • Disorders:
      • Addison's Disease: Underproduction of corticoids. Alters carbohydrate metabolism, causing acute weakness, fatigue.
      • Cushing's Syndrome: Overproduction of cortisol. High blood sugar, obesity (especially central), muscle wasting, high blood pressure, poor wound healing.

10. The Pancreas

• Composite gland: Acts as both exocrine (secretes digestive enzymes) and endocrine gland.
• Endocrine part: Islets of Langerhans (1-2 million islets, 1-2% of pancreatic tissue).
  • α-cells (Alpha cells): Secrete Glucagon (peptide hormone).
  • β-cells (Beta cells): Secrete Insulin (peptide hormone).
• Functions: Maintain glucose homeostasis.
  • Glucagon: Hyperglycemic hormone. Acts mainly on liver cells (hepatocytes). Stimulates glycogenolysis (breakdown of glycogen to glucose) and gluconeogenesis (synthesis of glucose from non-carbohydrate sources). Increases blood glucose. Reduces cellular glucose uptake and utilization.
  • Insulin: Hypoglycemic hormone. Acts mainly on hepatocytes and adipocytes. Enhances cellular glucose uptake and utilization. Stimulates glycogenesis (conversion of glucose to glycogen) in target cells. Decreases blood glucose.
• Disorder:
  • Diabetes Mellitus: Prolonged hyperglycemia. Due to insulin deficiency or insulin resistance. Loss of glucose through urine (glycosuria), formation of ketone bodies (ketonuria). Can lead to diabetic coma. Treated with insulin therapy.

11. Gonads

• Primary sex organs acting as endocrine glands.
  • Testis (Male):
    • Location: Scrotal sac.
    • Endocrine tissue: Interstitial cells or Leydig cells (in intertubular spaces).
    • Hormone: Androgens (mainly Testosterone).
    • Functions: Regulate development, maturation, and function of male accessory sex organs. Stimulate muscular growth, growth of facial/axillary hair, aggressiveness, low pitch voice. Stimulate spermatogenesis. Anabolic (synthetic) effects on protein and carbohydrate metabolism. Regulated mainly by GnRH -> LH (ICSH).
  • Ovary (Female):
    • Location: Abdomen.
    • Produces ova and steroid hormones.
    • Endocrine tissue: Ovarian follicles and Corpus luteum.
    • Hormones:
      • Estrogen: Synthesized and secreted mainly by growing ovarian follicles. Functions: Stimulate growth and activities of female secondary sex organs, development of growing follicles, appearance of female secondary sex characters (e.g., high pitch voice), mammary gland development. Regulates female sexual behaviour.
      • Progesterone: Secreted mainly by Corpus Luteum (formed after ovulation). Functions: Supports pregnancy. Acts on mammary glands (stimulates alveoli formation, milk secretion). Maintains endometrium for implantation.
    • Regulation: Controlled by GnRH -> LH and FSH.

12. Hormones of Heart, Kidney, and Gastrointestinal Tract

• These organs also secrete hormones.
  • Heart: Atrial wall secretes Atrial Natriuretic Factor (ANF) (peptide hormone). Decreases blood pressure by causing vasodilation and promoting Na+ excretion (hence water loss).
  • Kidney: Juxtaglomerular cells produce Erythropoietin (peptide hormone). Stimulates erythropoiesis (RBC formation). Also involved in Renin-Angiotensin mechanism (though Renin is an enzyme).
  • Gastrointestinal Tract: Endocrine cells secrete hormones:
    • Gastrin: Acts on gastric glands, stimulates HCl and pepsinogen secretion.
    • Secretin: Acts on exocrine pancreas, stimulates secretion of water and bicarbonate ions.
    • Cholecystokinin (CCK): Acts on pancreas (stimulates enzyme secretion) and gallbladder (stimulates bile release).
    • Gastric Inhibitory Peptide (GIP): Inhibits gastric secretion and motility.

13. Mechanism of Hormone Action

• Hormones produce effects by binding to specific hormone receptors located on target cells only.
• Receptors can be:
  • Membrane-bound Receptors: For peptide, polypeptide, protein hormones, catecholamines. Binding leads to:
    1. Generation of second messengers (e.g., cyclic AMP (cAMP), IP3, Ca++).
    2. Activation of existing enzymes -> biochemical changes -> physiological response.
  • Intracellular Receptors: (Mostly nuclear receptors). For steroid hormones, iodothyronines (T3, T4). Binding leads to:
    1. Interaction of hormone-receptor complex with the genome.
    2. Alters gene expression (regulates transcription of specific genes -> mRNA -> protein synthesis).
    3. Cumulative biochemical actions -> physiological and developmental effects.

14. Classification of Hormones (Based on Chemical Nature)

• Peptide, Polypeptide, Protein Hormones: Insulin, Glucagon, Pituitary hormones, Hypothalamic hormones, TCT, PTH, Thymosins, Relaxin, ANF, Erythropoietin, GIT hormones.
• Steroids: Cortisol, Aldosterone, Testosterone, Estrogen, Progesterone.
• Iodothyronines: Thyroid hormones (T3, T4).
• Amino-acid Derivatives: Epinephrine, Norepinephrine, Melatonin.

Multiple Choice Questions (MCQs)

1. Which hormone is responsible for the reabsorption of water in the distal convoluted tubule (DCT) and collecting duct of the nephron?
   A) Aldosterone
   B) Oxytocin
   C) Antidiuretic Hormone (ADH)
   D) Atrial Natriuretic Factor (ANF)

2. Graves' disease is characterized by all the following EXCEPT:
   A) Enlargement of the thyroid gland
   B) Protrusion of the eyeballs (exophthalmos)
   C) Decreased Basal Metabolic Rate (BMR)
   D) Weight loss

3. Which of the following hormones acts via intracellular receptors and modulates gene expression?
   A) Insulin
   B) Epinephrine
   C) Cortisol
   D) Glucagon

4. The Leydig cells or interstitial cells of the testis are stimulated to produce testosterone by:
   A) Follicle Stimulating Hormone (FSH)
   B) Luteinizing Hormone (LH) / ICSH
   C) Adrenocorticotropic Hormone (ACTH)
   D) Prolactin (PRL)

5. Which pair of hormones has antagonistic effects on blood calcium levels?
   A) Insulin and Glucagon
   B) Aldosterone and ANF
   C) Parathyroid Hormone (PTH) and Thyrocalcitonin (TCT)
   D) Estrogen and Progesterone

6. Diabetes Mellitus is primarily caused by a deficiency or malfunctioning of which hormone?
   A) Glucagon
   B) Insulin
   C) Thyroxine
   D) Growth Hormone

7. The 'Fight or Flight' response is mediated by hormones secreted from the:
   A) Adrenal Cortex
   B) Thyroid Gland
   C) Adrenal Medulla
   D) Pancreas (Islets of Langerhans)

8. Which hormone plays a significant role in the differentiation of T-lymphocytes and promoting immunity?
   A) Melatonin
   B) Thymosin
   C) Erythropoietin
   D) Cortisol

9. Which of the following is NOT a function of Growth Hormone (GH)?
   A) Stimulating body growth
   B) Promoting protein anabolism
   C) Stimulating milk production
   D) Increasing blood glucose levels (diabetogenic effect in excess)

10. Atrial Natriuretic Factor (ANF) is secreted in response to increased blood pressure and volume. Its primary action is to:
    A) Increase Na+ reabsorption in the kidney
    B) Cause vasoconstriction
    C) Decrease blood pressure by promoting Na+ excretion
    D) Stimulate aldosterone secretion

Answer Key:

1. C
2. C
3. C
4. B
5. C
6. B
7. C
8. B
9. C
10. C

Study these notes thoroughly. Remember the specific functions, the glands involved, and especially the disorders related to hormonal imbalances, as these are frequent targets for exam questions. Good luck with your preparation!