Class 11 Biology Notes Chapter 24 (Chapter 24) – Examplar Problems (English) Book

Alright class, let's get focused. You've asked for notes on Chapter 24 from the NCERT Class 11 Biology Exemplar. However, we need to clarify something important first. The standard NCERT Class 11 Biology syllabus, and consequently the Exemplar book, concludes with Chapter 22: Chemical Coordination and Integration. There is no Chapter 24 in this specific curriculum.

It's possible you might be referring to a different numbering system or perhaps the final chapter. Chapter 22 is crucial for government exams as it covers the endocrine system and hormones. Assuming this might be the chapter you need, I will provide detailed notes and MCQs for Chapter 22: Chemical Coordination and Integration. If you intended a different chapter, please provide the correct name or number.

Chapter 22: Chemical Coordination and Integration - Detailed Notes for Government Exams

1. Introduction

• The neural system provides rapid point-to-point coordination.
• The endocrine system provides chemical coordination through hormones, which is generally slower but affects widespread targets.
• Both systems interact to coordinate physiological functions.

2. Endocrine Glands and Hormones

• Endocrine Glands: Ductless glands that secrete hormones directly into the bloodstream.
• Hormones: Non-nutrient chemical messengers produced in trace amounts that act as intercellular messengers. They are transported via blood to target organs/tissues.
• Target Tissues/Organs: Tissues/organs that have specific receptors for a particular hormone, enabling them to respond to it.

3. Human Endocrine System

• Consists of organized endocrine glands (Pituitary, Pineal, Thyroid, Adrenal, Pancreas, Parathyroid, Thymus, Gonads) and diffused tissues/cells secreting hormones (e.g., in GI tract, kidney, heart).

4. Key Endocrine Glands and Their Hormones:

**a) The Hypothalamus:**
*   Location: Basal part of the diencephalon (forebrain).
*   Function: Regulates a wide spectrum of body functions. Contains neurosecretory cells (nuclei) that produce hormones.
*   Hormones:
    *   **Releasing Hormones:** Stimulate secretion of pituitary hormones (e.g., GnRH - Gonadotropin Releasing Hormone).
    *   **Inhibiting Hormones:** Inhibit secretion of pituitary hormones (e.g., Somatostatin - inhibits GH release).
    *   **Oxytocin & Vasopressin (ADH):** Synthesized by the hypothalamus but stored and released by the *Posterior Pituitary*.
*   Control: Hypothalamus controls the anterior pituitary via hormones travelling through the hypophyseal portal system. It directly controls the posterior pituitary via neurons.

**b) The Pituitary Gland:**
*   Location: Bony cavity called *sella turcica*, attached to the hypothalamus by a stalk.
*   Divisions:
    *   **Adenohypophysis (Anterior Pituitary):**
        *   *Pars Distalis:* Secretes Growth Hormone (GH), Prolactin (PRL), Thyroid Stimulating Hormone (TSH), Adrenocorticotropic Hormone (ACTH), Luteinizing Hormone (LH), Follicle Stimulating Hormone (FSH).
        *   *Pars Intermedia:* (Almost merged with pars distalis in humans) Secretes Melanocyte Stimulating Hormone (MSH).
    *   **Neurohypophysis (Posterior Pituitary):**
        *   *Pars Nervosa:* Stores and releases Oxytocin and Vasopressin (ADH). *Does not synthesize these hormones.*
*   **Hormone Functions & Disorders:**
    *   **GH:** Body growth. *Disorders:* Dwarfism (low GH), Gigantism (high GH in childhood), Acromegaly (high GH in adults - disfigurement, especially of face).
    *   **PRL:** Mammary gland growth and milk production.
    *   **TSH:** Stimulates thyroid gland to secrete thyroid hormones.
    *   **ACTH:** Stimulates adrenal cortex to secrete glucocorticoids.
    *   **LH & FSH (Gonadotropins):** Stimulate gonadal activity. LH (males - androgen synthesis; females - ovulation, corpus luteum maintenance). FSH (males - spermatogenesis; females - ovarian follicle growth).
    *   **MSH:** Acts on melanocytes, regulates skin pigmentation.
    *   **Oxytocin:** Uterine contraction during childbirth, milk ejection (let-down reflex).
    *   **Vasopressin (ADH - Anti-Diuretic Hormone):** Water reabsorption by DCT and collecting ducts of kidney, prevents diuresis. *Disorder:* Diabetes Insipidus (low ADH - excessive urination, thirst).

**c) The Pineal Gland:**
*   Location: Dorsal side of forebrain.
*   Hormone: **Melatonin**.
*   Function: Regulates diurnal (24-hour) rhythms (sleep-wake cycle), body temperature, influences metabolism, pigmentation, menstrual cycle, defense capability.

**d) Thyroid Gland:**
*   Location: Two lobes on either side of the trachea, connected by an isthmus. Composed of follicles and stromal tissues.
*   Hormones:
    *   **Thyroxine (T4) & Triiodothyronine (T3):** Synthesized from iodine and tyrosine within follicular cells. Regulate Basal Metabolic Rate (BMR), support RBC formation, control metabolism of carbohydrates, proteins, fats, maintain water/electrolyte balance, essential for normal growth and mental development.
    *   **Thyrocalcitonin (TCT):** Protein hormone. Regulates (lowers) blood calcium levels.
*   **Disorders:**
    *   **Hypothyroidism:** Low thyroid hormone levels. Causes: Iodine deficiency (Simple Goitre - enlargement of thyroid), developmental issues (Cretinism - stunted growth, mental retardation in infants), Myxedema (in adults).
    *   **Hyperthyroidism:** High thyroid hormone levels. Cause: Cancer or nodules in thyroid. Leads to increased BMR, weight loss. Exophthalmic Goitre (Graves' Disease) - enlargement of thyroid, protrusion of eyeballs, increased BMR, weight loss.

**e) Parathyroid Gland:**
*   Location: Four glands on the back side of the thyroid gland (one pair in each lobe).
*   Hormone: **Parathyroid Hormone (PTH)** - Peptide hormone.
*   Function: Increases blood Ca2+ levels (hypercalcemic hormone). Acts on bones (promotes resorption/demineralization), kidneys (increases Ca2+ reabsorption), and indirectly on intestines (increases Ca2+ absorption). Works antagonistically to TCT.
*   **Disorder:** Hypoparathyroidism leads to low blood Ca2+, causing Tetany (rapid muscle spasms).

**f) Thymus:**
*   Location: Lobular structure between lungs, behind sternum on the ventral side of the aorta.
*   Hormone: **Thymosins** - Peptide hormones.
*   Function: Major role in differentiation of T-lymphocytes (provide cell-mediated immunity). Also promote antibody production (humoral immunity).
*   Note: Degenerates in old individuals, leading to decreased immune response.

**g) Adrenal Gland:**
*   Location: Pair of glands at the anterior part (top) of each kidney.
*   Structure: Outer Adrenal Cortex and Inner Adrenal Medulla.
*   **Adrenal Cortex:** (Steroid hormones - corticoids)
    *   *Zona Glomerulosa (outer):* Mineralocorticoids (mainly **Aldosterone**). Function: Regulates water and electrolyte balance (acts on renal tubules - Na+ reabsorption, K+ excretion). Stimulated by RAAS.
    *   *Zona Fasciculata (middle):* Glucocorticoids (mainly **Cortisol**). Function: Carbohydrate metabolism (gluconeogenesis, lipolysis, proteolysis), anti-inflammatory reactions, suppresses immune response, maintains cardiovascular system & kidney functions, stimulates RBC production.
    *   *Zona Reticularis (inner):* Androgenic steroids (small amounts). Role in growth of axial, pubic, facial hair during puberty.
    *   *Disorders:* Addison's Disease (hyposecretion - weakness, fatigue, bronzing of skin), Cushing's Syndrome (hypersecretion - high blood sugar, obesity, wasting of limb muscles).
*   **Adrenal Medulla:** (Catecholamines)
    *   Hormones: **Adrenaline (Epinephrine)** and **Noradrenaline (Norepinephrine)**.
    *   Function: Secreted rapidly in response to stress ('emergency hormones' or 'hormones of Fight or Flight'). Increase alertness, pupillary dilation, piloerection, sweating, heart rate, respiration rate, breakdown of glycogen (hyperglycemia), lipids, proteins.

**h) Pancreas:**
*   Nature: Composite gland (both exocrine and endocrine).
*   Endocrine Part: **Islets of Langerhans** (1-2 million islets, 1-2% of pancreatic tissue).
*   Cells & Hormones:
    *   **α-cells:** Secrete **Glucagon** (peptide hormone). Function: Hyperglycemic - increases blood glucose by stimulating glycogenolysis and gluconeogenesis.
    *   **β-cells:** Secrete **Insulin** (peptide hormone). Function: Hypoglycemic - decreases blood glucose by enhancing cellular glucose uptake and utilization, stimulates glycogenesis.
*   **Disorder:** **Diabetes Mellitus:** Prolonged hyperglycemia due to insulin deficiency or resistance. Leads to glucose loss through urine, formation of ketone bodies. Type 1 (insulin-dependent) and Type 2 (non-insulin-dependent).

**i) Gonads:**
*   **Testis (Male):** Primary sex organ and endocrine gland.
    *   Location: Scrotal sac.
    *   Endocrine Cells: Leydig cells (interstitial cells).
    *   Hormone: **Androgens** (mainly **Testosterone** - steroid).
    *   Function: Development, maturation, function of male accessory sex organs; stimulate muscular growth, growth of facial/axillary hair, aggressiveness, low voice pitch; stimulate spermatogenesis; anabolic effects on protein/carbohydrate metabolism. Regulated mainly by LH (from pituitary).
*   **Ovary (Female):** Primary sex organ and endocrine gland.
    *   Location: Abdomen.
    *   Structure: Ovarian follicles and stromal tissues.
    *   Hormones:
        *   **Estrogen** (steroid): Synthesized and secreted mainly by growing ovarian follicles. Function: Stimulate growth/activities of female secondary sex organs, development of growing follicles, female secondary sex characters (high voice pitch, mammary gland development), female sexual behaviour. Regulated by FSH & LH.
        *   **Progesterone** (steroid): Secreted mainly by Corpus Luteum (formed after ovulation). Function: Supports pregnancy, acts on mammary glands (alveoli formation, milk secretion).

5. Hormones of Heart, Kidney, and Gastrointestinal Tract

• Heart (Atrial Wall): Atrial Natriuretic Factor (ANF) - peptide hormone. Secreted when blood pressure increases. Causes vasodilation, reduces blood pressure. Decreases Na+ reabsorption (checks RAAS).
• Kidney (Juxtaglomerular cells): Erythropoietin (EPO) - peptide hormone. Stimulates erythropoiesis (RBC formation).
• Gastrointestinal Tract:
  • Gastrin: Stimulates HCl and pepsinogen secretion.
  • Secretin: Acts on exocrine pancreas, stimulates secretion of water and bicarbonate ions.
  • Cholecystokinin (CCK): Acts on pancreas (enzyme secretion) and gallbladder (bile release).
  • Gastric Inhibitory Peptide (GIP): Inhibits gastric secretion and motility.

6. 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, protein, catecholamine hormones (water-soluble, cannot cross cell membrane). Binding leads to:
    1. Generation of second messengers (e.g., cyclic AMP, IP3, Ca++).
    2. Activation of intracellular cascades.
    3. Physiological response (e.g., enzyme activation).
  • Intracellular Receptors (mostly nuclear): For steroid hormones, iodothyronines (lipid-soluble, can cross cell membrane). Binding leads to:
    1. Interaction of hormone-receptor complex with the genome.
    2. Altered gene expression (mRNA synthesis).
    3. Synthesis of specific proteins.
    4. Physiological and developmental effects.

7. Classification of Hormones based on Chemical Nature:

• Peptide, Polypeptide, Protein Hormones: Insulin, Glucagon, Pituitary hormones, Hypothalamic hormones, etc. (Water-soluble)
• Steroids: Cortisol, Testosterone, Estradiol, Progesterone. (Lipid-soluble)
• Iodothyronines: Thyroid hormones (T3, T4). (Lipid-soluble)
• Amino-acid derivatives: Epinephrine, Norepinephrine. Melatonin. (Variable solubility)

Multiple Choice Questions (MCQs) for Practice

1. Which of the following hormones is stored and released from the neurohypophysis but synthesized in the hypothalamus?
   a) Prolactin
   b) Vasopressin (ADH)
   c) Growth Hormone (GH)
   d) Thyroid Stimulating Hormone (TSH)

2. Graves' disease is characterized by all the following EXCEPT:
   a) Enlargement of the thyroid gland
   b) Protrusion of the eyeballs (exophthalmos)
   c) Weight gain
   d) Increased Basal Metabolic Rate (BMR)

3. Which hormone acts antagonistically to Parathyroid Hormone (PTH) in calcium homeostasis?
   a) Insulin
   b) Thyrocalcitonin (TCT)
   c) Aldosterone
   d) Glucagon

4. Select the incorrect match regarding the hormone and its primary function:
   a) Cortisol - Increases blood glucose (gluconeogenesis)
   b) Aldosterone - Sodium and water reabsorption
   c) Melatonin - Regulation of diurnal rhythm
   d) Oxytocin - Stimulation of spermatogenesis

5. Identify the hormone which is a modified amino acid:
   a) Progesterone
   b) Epinephrine
   c) Insulin
   d) Glucagon

6. Diabetes Insipidus is caused by the hyposecretion of:
   a) Insulin
   b) Aldosterone
   c) ADH (Vasopressin)
   d) Glucagon

7. Which of the following hormones binds to intracellular receptors?
   a) Insulin
   b) FSH
   c) Adrenaline
   d) Testosterone

8. The Leydig cells found in the human body are the secretory source of:
   a) Progesterone
   b) Intestinal mucus
   c) Glucagon
   d) Androgens

9. Atrial Natriuretic Factor (ANF) is secreted in response to:
   a) Low blood pressure
   b) High blood pressure
   c) Low blood glucose
   d) High blood calcium

10. The hormone responsible for the differentiation of T-lymphocytes is secreted by:
    a) Thyroid gland
    b) Adrenal gland
    c) Thymus gland
    d) Pineal gland

Answer Key for MCQs:

1. b) Vasopressin (ADH)
2. c) Weight gain (Hyperthyroidism causes weight loss)
3. b) Thyrocalcitonin (TCT)
4. d) Oxytocin - Stimulation of spermatogenesis (Oxytocin causes uterine contraction and milk ejection; Spermatogenesis is influenced by FSH and Androgens)
5. b) Epinephrine (derived from tyrosine)
6. c) ADH (Vasopressin)
7. d) Testosterone (Steroid hormones bind to intracellular receptors)
8. d) Androgens
9. b) High blood pressure
10. c) Thymus gland (secretes Thymosins)

Remember to correlate these notes with your NCERT textbook and Exemplar problems for comprehensive preparation. Focus on the functions, sources, and disorders related to each hormone, as these are frequently tested areas in government exams. Good luck!