Class 11 Biology Notes Chapter 22 (Chapter 22) – Examplar Problems (English) Book

Detailed Notes with MCQs of Chapter 22: Chemical Coordination and Integration. This is a crucial chapter for understanding how our body regulates complex processes through hormones. Pay close attention, as concepts from this chapter frequently appear in various government examinations.

Chapter 22: Chemical Coordination and Integration - Detailed Notes

1. Introduction: Endocrine System vs. Nervous System

• Both systems coordinate and regulate physiological functions.
• Nervous System: Provides rapid, point-to-point coordination via nerve impulses. Effects are short-lived.
• Endocrine System: Provides slower, widespread coordination via chemical messengers called hormones. Effects are generally longer-lasting.
• Hormones: Non-nutrient chemicals acting as intercellular messengers, produced in trace amounts by endocrine glands (ductless glands). They are released directly into the bloodstream or interstitial fluid and transported to target organs/tissues.

2. Human Endocrine System

Consists of organized endocrine glands and diffused hormone-producing cells/tissues. Key glands include:

• Hypothalamus
• Pituitary Gland
• Pineal Gland
• Thyroid Gland
• Parathyroid Gland
• Thymus
• Adrenal Gland
• Pancreas (Islets of Langerhans)
• Gonads (Testis and Ovary)

3. Hypothalamus

• Located at the basal part of the diencephalon (forebrain).
• Connects the nervous and endocrine systems.
• Contains neurosecretory cells called nuclei that produce hormones.
• Functions:
  • Regulates a wide spectrum of body functions.
  • Controls the synthesis and secretion of pituitary hormones.
• Hormones Produced:
  • Releasing Hormones: Stimulate secretion of pituitary hormones (e.g., Gonadotrophin releasing hormone - GnRH stimulates LH & FSH release).
  • 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.
  • The hypothalamus also directly synthesizes Oxytocin and Vasopressin (ADH), which are transported axonally to the posterior pituitary for storage and release.

4. Pituitary Gland ("Master Gland")

• Located in a bony cavity called sella turcica, attached to the hypothalamus by a stalk.

• Divided anatomically into:

  • Adenohypophysis (Anterior Pituitary):
    • Pars Distalis: Produces Growth Hormone (GH), Prolactin (PRL), Thyroid Stimulating Hormone (TSH), Adrenocorticotrophic 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), which are synthesized by the hypothalamus.

• Functions & Disorders of Pituitary Hormones:

  • GH: Body growth.
    • Hyposecretion: Pituitary Dwarfism.
    • Hypersecretion: Gigantism (childhood), Acromegaly (adulthood - severe disfigurement, especially of the face).
  • PRL: Regulates mammary gland growth and milk production (lactation).
  • TSH: Stimulates thyroid gland to synthesize and secrete thyroid hormones.
  • ACTH: Stimulates adrenal cortex to synthesize and secrete glucocorticoids (like cortisol).
  • LH & FSH (Gonadotrophins): Stimulate gonadal activity.
    • LH (Males): Stimulates synthesis and secretion of androgens (testosterone) from Leydig cells.
    • FSH (Males): Regulates spermatogenesis (along with androgens).
    • LH (Females): Induces ovulation of Graafian follicles, maintains corpus luteum.
    • FSH (Females): Stimulates growth and development of ovarian follicles.
  • MSH: Acts on melanocytes, regulating skin pigmentation.
  • Oxytocin: Stimulates uterine contraction during childbirth (parturition) and milk ejection (let-down reflex) from mammary glands.
  • Vasopressin (ADH - Anti-diuretic Hormone): Acts on kidney tubules (mainly DCT and collecting ducts) to promote water reabsorption, reducing water loss (diuresis).
    • Hyposecretion: Diabetes Insipidus (impaired water reabsorption leading to dehydration and excessive thirst/urination).

5. Pineal Gland

• Located on the dorsal side of the forebrain.
• Secretes Melatonin.
• Functions: Regulates diurnal (24-hour) rhythms (sleep-wake cycle, body temperature), influences metabolism, pigmentation, menstrual cycle, and defense capability.

6. Thyroid Gland

• Located on either side of the trachea, composed of two lobes connected by an isthmus.
• Composed of follicles (follicular cells enclosing a cavity) and stromal tissues.
• Hormones:
  • Thyroxine (T4) and Triiodothyronine (T3): Synthesized by follicular cells. Iodine is essential for their normal synthesis rate.
    • Functions: Regulate Basal Metabolic Rate (BMR), support RBC formation, control metabolism of carbohydrates, proteins, and fats, maintain water and electrolyte balance, essential for normal growth and mental development.
    • Hypothyroidism (Iodine deficiency/gland defect):
      • Goitre: Enlargement of the thyroid gland.
      • Cretinism: Hypothyroidism during pregnancy causes stunted growth, mental retardation, low IQ, abnormal skin, deaf-mutism in the baby.
      • Myxoedema: Hypothyroidism in adult women (often associated with menstrual irregularities).
    • Hyperthyroidism (due to cancer/nodules): Increased BMR, weight loss, protrusion of eyeballs.
      • Exophthalmic Goitre (Graves' Disease): Autoimmune disorder causing hyperthyroidism, characterized by enlarged thyroid, protruding eyeballs (exophthalmos), increased BMR, weight loss.
  • Thyrocalcitonin (TCT): A protein hormone secreted by C-cells. Regulates blood calcium levels (lowers blood calcium - hypocalcemic).

7. Parathyroid Gland

• Four small glands located on the back side of the thyroid gland (one pair in each lobe).
• Secretes Parathyroid Hormone (PTH) - a peptide hormone.
• Functions: Regulates circulating calcium levels.
  • Increases blood Ca²⁺ levels (Hypercalcemic hormone).
  • Acts on bones (stimulates resorption/demineralization), kidneys (increases Ca²⁺ reabsorption), and indirectly on intestines (increases Ca²⁺ absorption from digested food).
  • Works antagonistically with TCT to maintain calcium homeostasis.
  • Hypoparathyroidism: Low blood Ca²⁺, leading to muscle tetany (rapid spasms).
  • Hyperparathyroidism: High blood Ca²⁺, bone demineralization, potential kidney stones.

8. Thymus

• Located between the lungs behind the sternum (on the ventral side of the aorta).
• Plays a major role in the development of the immune system.
• Secretes peptide hormones called Thymosins.
• Functions:
  • Differentiation of T-lymphocytes (provide cell-mediated immunity - CMI).
  • Promote antibody production (for humoral immunity).
• Degenerates in old age, leading to decreased thymosin production and weaker immune response.

9. Adrenal Gland ("Suprarenal Gland")

• Located on the anterior part (top) of each kidney (one pair).
• Composed of two tissues:
  • Adrenal Cortex (Outer): Divided into 3 layers: Zona reticularis (inner), Zona fasciculata (middle), Zona glomerulosa (outer).
    • Secretes Corticoids.
    • Glucocorticoids (mainly Cortisol): Secreted by Zona fasciculata.
      • Functions: Regulate carbohydrate metabolism (gluconeogenesis, lipolysis, proteolysis), anti-inflammatory effects, suppress immune response, maintain cardiovascular system and kidney functions, stimulate RBC production. Involved in stress response.
    • Mineralocorticoids (mainly Aldosterone): Secreted by Zona glomerulosa.
      • Functions: Act on renal tubules (DCT) to stimulate Na⁺ and water reabsorption, and K⁺ and phosphate ion excretion. Maintain electrolyte balance, body fluid volume, osmotic pressure, blood pressure.
    • Androgenic Steroids: Secreted in small amounts by Zona reticularis. Play a role in the growth of axial, pubic, and facial hair during puberty.
    • Disorders:
      • Addison's Disease: Hyposecretion of corticoids. Causes weakness, fatigue, weight loss, low blood sugar, low Na⁺, high K⁺, bronzing of skin.
      • Cushing's Syndrome: Hypersecretion of cortisol. Causes high blood sugar, obesity (especially trunk), muscle wasting, high blood pressure, poor wound healing.
  • Adrenal Medulla (Inner):
    • Secretes Catecholamines: Adrenaline (Epinephrine) and Noradrenaline (Norepinephrine).
    • Called "emergency hormones" or "hormones of Fight or Flight".
    • Released during stress/emergency situations.
    • Functions: Increase alertness, pupillary dilation, piloerection (goosebumps), sweating, increase heart rate, strength of heart contraction, respiration rate. Stimulate glycogenolysis (breakdown of glycogen -> glucose), lipolysis.

10. Pancreas (Composite Gland)

• Acts as both an exocrine (secretes digestive enzymes) and endocrine gland.
• Endocrine part consists of Islets of Langerhans (1-2 million islets, 1-2% of pancreatic tissue).
• Main cell types in Islets:
  • α-cells: Secrete Glucagon (peptide hormone).
  • β-cells: Secrete Insulin (peptide hormone).
• Functions (Glucose Homeostasis):
  • Glucagon: Hyperglycemic hormone. Acts mainly on liver cells (hepatocytes). Stimulates glycogenolysis (glycogen -> glucose) and gluconeogenesis (synthesis of glucose from non-carbohydrate sources). Reduces cellular glucose uptake.
  • Insulin: Hypoglycemic hormone. Acts mainly on hepatocytes and adipocytes. Enhances cellular glucose uptake and utilization. Stimulates glycogenesis (glucose -> glycogen) in target cells. Reduces gluconeogenesis.
• Disorder:
  • Diabetes Mellitus: Prolonged hyperglycemia due to insulin deficiency or insulin resistance.
    • Symptoms: Loss of glucose through urine (glycosuria), formation of ketone bodies (ketonuria), excessive thirst (polydipsia), excessive urination (polyuria).
    • Type 1: Autoimmune destruction of β-cells (insulin-dependent).
    • Type 2: Insulin resistance (non-insulin-dependent, often related to lifestyle).

11. Gonads

• Primary sex organs.
• Testis (Male):
  • Located in the scrotal sac. Performs dual functions: primary sex organ and endocrine gland.
  • Composed of seminiferous tubules and interstitial (stromal) tissue.
  • Leydig cells (Interstitial cells): Located in intertubular spaces. Produce Androgens (mainly Testosterone).
  • Functions of Testosterone: Regulates development, maturation, and function of male accessory sex organs (epididymis, vas deferens, seminal vesicles, prostate, urethra). Stimulates muscular growth, growth of facial/axillary hair, aggressiveness, low pitch voice. Stimulates spermatogenesis. Influence male sexual behaviour (libido). Anabolic (protein, carbohydrate metabolism) effects.
• Ovary (Female):
  • Located in the abdomen. Primary female sex organ. Produces ova and steroid hormones.
  • Composed of ovarian follicles and stromal tissues.
  • Estrogen: Synthesized and secreted mainly by growing ovarian follicles.
    • Functions: Stimulate growth and activities of female secondary sex organs. Development of growing ovarian follicles. Appearance of female secondary sex characters (high pitch voice, etc.), mammary gland development. Regulate female sexual behaviour.
  • Progesterone: Secreted mainly by the Corpus Luteum (formed after ovulation).
    • Functions: Supports pregnancy. Acts on mammary glands (stimulates alveoli formation and milk secretion). Maintains endometrium for implantation. Inhibits uterine contractions during pregnancy.

12. Hormones of Heart, Kidney, and Gastrointestinal Tract

• Hormones are also secreted by tissues outside organized endocrine glands.
• Heart (Atrial Wall): Secretes Atrial Natriuretic Factor (ANF) - a peptide hormone.
  • Function: Decreases blood pressure. When BP increases, ANF causes dilation of blood vessels and promotes Na⁺/water excretion by kidneys, thus reducing blood volume and pressure. (Antagonistic to RAAS mechanism).
• Kidney (Juxtaglomerular cells): Produce Erythropoietin - a peptide hormone.
  • Function: Stimulates erythropoiesis (RBC formation).
• Gastrointestinal Tract: Endocrine cells in different parts secrete peptide hormones:
  • Gastrin: Acts on gastric glands; stimulates HCl and pepsinogen secretion.
  • Secretin: Acts on exocrine pancreas; stimulates secretion of water and bicarbonate ions. (First discovered hormone).
  • Cholecystokinin (CCK): Acts on pancreas and gall bladder; stimulates secretion of pancreatic enzymes and bile juice release, respectively.
  • Gastric Inhibitory Peptide (GIP): Inhibits gastric secretion and motility.

13. Mechanism of Hormone Action

• Hormones produce effects on target tissues by binding to specific hormone receptors (proteins) located either on the cell membrane or inside the target cells.
• Types 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 (Water-soluble).
• Mechanism based on Receptor Location:
  • Membrane-Bound Receptors (for water-soluble hormones like peptides, catecholamines):
    • Hormone (1st messenger) binds to receptor on the cell surface.
    • Generates second messengers inside the cell (e.g., cyclic AMP (cAMP), IP₃, Ca²⁺).
    • Second messengers activate existing enzymes, leading to a cascade effect and physiological response (e.g., ovarian growth, glycogenolysis).
  • Intracellular Receptors (for lipid-soluble hormones like steroids, iodothyronines):
    • Hormones easily pass through the cell membrane.
    • Bind to receptors located inside the target cell (mostly nuclear receptors).
    • Hormone-receptor complex binds to specific regions of DNA (genome).
    • Regulates gene expression (transcription of mRNA -> translation -> protein synthesis).
    • Leads to physiological and developmental effects (e.g., tissue growth and differentiation).

14. Feedback Control

• Hormone secretion is regulated, often by feedback mechanisms.
• Negative Feedback: Most common. Increased level of a hormone (or its effect) inhibits further secretion of that hormone or the hormones controlling it (e.g., High T3/T4 inhibits TSH and TRH release).
• Positive Feedback: Less common. Increased level of a hormone stimulates further secretion (e.g., LH surge triggered by estrogen before ovulation).

Now, let's test your understanding with some Multiple Choice Questions.

MCQs:

1. Which of the following hormones is synthesized in the hypothalamus but stored and released from the posterior pituitary?
   a) Growth Hormone (GH)
   b) Luteinizing Hormone (LH)
   c) Antidiuretic Hormone (ADH)
   d) Thyroid Stimulating Hormone (TSH)

2. Graves' disease is characterized by hypersecretion of thyroid hormones. Which symptom is typically associated with this condition?
   a) Lethargy and weight gain
   b) Protrusion of the eyeballs (exophthalmos)
   c) Low body temperature
   d) Decreased heart rate

3. Which hormone acts as a hyperglycemic agent by stimulating glycogenolysis and gluconeogenesis?
   a) Insulin
   b) Aldosterone
   c) Glucagon
   d) Thyrocalcitonin (TCT)

4. Steroid hormones exert their influence by:
   a) Binding to membrane-bound receptors and activating cAMP.
   b) Entering the cell and binding to intracellular receptors, altering gene expression.
   c) Activating G-proteins on the cell surface.
   d) Stimulating the release of second messengers like IP₃.

5. Addison's disease results from the hyposecretion of hormones from which gland?
   a) Thyroid gland
   b) Adrenal cortex
   c) Anterior pituitary
   d) Pancreas

6. Which hormone is primarily responsible for the differentiation of T-lymphocytes and promoting cell-mediated immunity?
   a) Erythropoietin
   b) Thymosin
   c) Melatonin
   d) Cortisol

7. The hormone responsible for regulating the 24-hour diurnal rhythm of our body is:
   a) Estrogen
   b) Prolactin
   c) Melatonin
   d) Adrenaline

8. Which of the following pairs of hormones have antagonistic effects on blood calcium levels?
   a) Insulin and Glucagon
   b) Aldosterone and ANF
   c) PTH and TCT
   d) FSH and LH

9. Diabetes Insipidus is caused by the deficiency of which hormone?
   a) Insulin
   b) Vasopressin (ADH)
   c) Aldosterone
   d) Glucagon

10. Leydig cells, found in the interstitial spaces of testes, are responsible for synthesizing:
    a) Progesterone
    b) Estrogen
    c) Testosterone
    d) FSH

Answer Key:

1. c) Antidiuretic Hormone (ADH)
2. b) Protrusion of the eyeballs (exophthalmos)
3. c) Glucagon
4. b) Entering the cell and binding to intracellular receptors, altering gene expression.
5. b) Adrenal cortex
6. b) Thymosin
7. c) Melatonin
8. c) PTH and TCT
9. b) Vasopressin (ADH)
10. c) Testosterone

Revise these notes thoroughly. Understanding the specific functions, sources, and regulation of each hormone, along with the associated disorders, is key for your exam preparation. Good luck!