Class 11 Biology Notes Chapter 23 (Chapter 23) – Examplar Problems (English) Book

Detailed Notes with MCQs of Chapter 23: Chemical Coordination and Integration. This is a crucial chapter for understanding how our body regulates complex processes through chemical messengers. Pay close attention, as concepts from this chapter frequently appear in various government examinations.

Chapter 23: Chemical Coordination and Integration - Detailed Notes

1. Introduction to the Endocrine System

• Coordination: In multicellular organisms, neural and endocrine systems jointly coordinate and regulate physiological functions. Neural coordination is fast but short-lived. Endocrine coordination is slower but sustained.
• Endocrine Glands: These are ductless glands that secrete chemical messengers called hormones directly into the bloodstream or interstitial fluid.
• Hormones:
  • Non-nutrient chemicals.
  • Act as intercellular messengers.
  • Produced in trace amounts.
  • Transported via blood to target organs/tissues.
  • Bind to specific protein receptors on target cells (either on the cell membrane or inside the cell).
• Endocrine System: Consists of endocrine glands and scattered hormone-producing tissues/cells in different parts of the body.
• Exocrine Glands: Have ducts and secrete substances like mucus, saliva, earwax, oil, milk, digestive enzymes (e.g., salivary glands, sweat glands).

2. Human Endocrine System

The main organized endocrine glands in the human body are:

• Hypothalamus
• Pituitary Gland
• Pineal Gland
• Thyroid Gland
• Parathyroid Gland
• Thymus
• Adrenal Gland
• Pancreas (also an exocrine gland)
• Gonads (Testis in males, Ovary in females)

3. Detailed Study of Endocrine Glands

• Hypothalamus:

  • Location: Basal part of the diencephalon (forebrain).
  • Role: Connects the nervous system and endocrine system via the pituitary gland. Contains neurosecretory cells called nuclei that produce hormones.
  • Hormones:
    • Releasing Hormones: Stimulate secretion of pituitary hormones (e.g., Gonadotrophin releasing hormone - GnRH).
    • Inhibiting Hormones: Inhibit secretion of pituitary hormones (e.g., Somatostatin, which inhibits Growth Hormone release).
  • Control: These hormones reach the anterior pituitary through a portal circulatory system (hypophyseal portal system). The posterior pituitary is under direct neural regulation of the hypothalamus (axonal transport).

• Pituitary Gland:

  • Location: In a bony cavity called sella turcica, attached to the hypothalamus by a stalk.
  • Divisions:
    • Adenohypophysis:
      • Pars Distalis (Anterior Pituitary): Produces Growth Hormone (GH), Prolactin (PRL), Thyroid Stimulating Hormone (TSH), Adrenocorticotrophic Hormone (ACTH), Luteinizing Hormone (LH), Follicle Stimulating Hormone (FSH).
      • Pars Intermedia: Secretes Melanocyte Stimulating Hormone (MSH). (In humans, pars intermedia is almost merged with pars distalis).
    • Neurohypophysis (Posterior Pituitary):
      • Pars Nervosa: Stores and releases two hormones synthesized by the hypothalamus: Oxytocin and Vasopressin (Antidiuretic Hormone - ADH). These are transported axonally.
  • Functions & Disorders:
    • GH: Body growth. Disorders: Over-secretion leads to Gigantism (childhood) or Acromegaly (adulthood - severe disfigurement, especially of the face). Low secretion leads to Pituitary Dwarfism.
    • PRL: Regulates mammary gland growth and milk production.
    • TSH: Stimulates thyroid gland to synthesize and secrete thyroid hormones.
    • ACTH: Stimulates adrenal cortex to synthesize and secrete steroid hormones (glucocorticoids).
    • LH & FSH (Gonadotrophins): Stimulate gonadal activity.
      • LH (Males): Stimulates synthesis/secretion of androgens (testosterone) from testes.
      • FSH (Males): Regulates spermatogenesis (along with androgens).
      • LH (Females): Induces ovulation of mature follicles (Graafian follicles) and maintains the corpus luteum.
      • FSH (Females): Stimulates growth and development of ovarian follicles.
    • MSH: Acts on melanocytes, regulating skin pigmentation.
    • Oxytocin: Acts on smooth muscles. Stimulates uterine contraction during childbirth and milk ejection from mammary glands.
    • ADH (Vasopressin): Acts mainly at the kidney tubules. Stimulates water reabsorption from DCT and collecting ducts, reducing water loss (diuresis). Disorder: Deficiency causes impaired water reabsorption, leading to excessive water loss and dehydration - Diabetes Insipidus.

• Pineal Gland:

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

• Thyroid Gland:

  • Location: Neck region, ventral to the larynx, on either side of the trachea. Two lobes connected by an isthmus (connective tissue).
  • Structure: Composed of follicles and stromal tissues. Follicular cells synthesize thyroid hormones.
  • Hormones:
    • Thyroxine (T4 - tetraiodothyronine)
    • Triiodothyronine (T3)
    • Thyrocalcitonin (TCT) (Protein hormone, secreted by parafollicular cells)
  • Requirement: Normal rate of hormone synthesis requires Iodine.
  • Functions of T3/T4:
    • Regulation of Basal Metabolic Rate (BMR).
    • Support RBC formation.
    • Metabolism of carbohydrates, proteins, and fats.
    • Maintenance of water and electrolyte balance.
  • Function of TCT: Regulates blood calcium levels (lowers blood calcium - hypocalcemic).
  • Disorders:
    • Hypothyroidism: Iodine deficiency leads to enlargement of the thyroid gland (Goitre). Hypothyroidism during pregnancy can cause defective development of the baby, leading to Cretinism (stunted growth, mental retardation, low IQ, abnormal skin, deaf-mutism). In adult women, it may cause irregular menstrual cycles.
    • Hyperthyroidism: Due to cancer or nodules in the thyroid. Abnormal high levels of thyroid hormones adversely affect physiology. Exophthalmic goitre (Graves' disease) is a form characterized by thyroid enlargement, protrusion of eyeballs, increased BMR, and weight loss.

• Parathyroid Gland:

  • Location: Four small glands on the back side of the thyroid gland (one pair in each lobe).
  • Hormone: Parathyroid Hormone (PTH) - a peptide hormone.
  • Function: Regulates circulating calcium levels. PTH is a hypercalcemic hormone (increases blood Ca2+ levels). It acts on bones (stimulates resorption/demineralization), kidneys (stimulates Ca2+ reabsorption), and indirectly on the intestine (increases Ca2+ absorption from digested food). Works antagonistically with TCT to maintain calcium homeostasis.

• Thymus Gland:

  • Location: Lobular structure located between the lungs behind the sternum on the ventral side of the aorta.
  • Hormone: Thymosins (peptide hormones).
  • Function: Major role in the development of the immune system. Promotes differentiation of T-lymphocytes (provide cell-mediated immunity - CMI). Also promotes the production of antibodies (humoral immunity).
  • Note: Thymus degenerates in old individuals, leading to decreased production of thymosins and a weaker immune response.

• Adrenal Gland:

  • Location: Paired glands located on the anterior part (top) of each kidney ('ad-renal').
  • Structure: Composed of two types of tissues:
    • Adrenal Medulla (Central): Secretes catecholamines.
    • Adrenal Cortex (Outer): Secretes corticoids.
  • Adrenal Medulla Hormones:
    • Adrenaline (Epinephrine) and Noradrenaline (Norepinephrine).
    • Called Catecholamines or Emergency Hormones or Hormones of Fight or Flight.
    • Functions: Secreted rapidly in response to stress. Increase alertness, pupillary dilation, piloerection (raising of hairs), sweating, increase heart rate, strength of heart contraction, respiration rate. Stimulate glycogenolysis (breakdown of glycogen -> glucose) and lipolysis (breakdown of lipids).
  • Adrenal Cortex Hormones (Corticoids): Divided into 3 layers: Zona reticularis (inner), Zona fasciculata (middle), Zona glomerulosa (outer).
    • Glucocorticoids (mainly Cortisol): Secreted by Zona fasciculata. Involved in carbohydrate metabolism (gluconeogenesis, lipolysis, proteolysis). Cortisol produces anti-inflammatory reactions, suppresses the immune response, stimulates RBC production, maintains cardiovascular system and kidney functions. Regulated by ACTH.
    • Mineralocorticoids (mainly Aldosterone): Secreted by Zona glomerulosa. Regulate water and electrolyte balance. Aldosterone acts on renal tubules, stimulating Na+ and water reabsorption, and K+ and phosphate ion excretion. Helps maintain electrolytes, body fluid volume, osmotic pressure, and 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 hormones by the adrenal cortex. Alters carbohydrate metabolism, causing acute weakness, fatigue.
    • Cushing's Syndrome: Overproduction of cortisol. Symptoms include high blood sugar, obesity (especially central), muscle wasting, high blood pressure, etc.

• Pancreas:

  • Type: Composite gland (both exocrine and endocrine).
  • Endocrine Part: Islets of Langerhans (1-2 million islets, 1-2% of pancreatic tissue). Contain two main cell types:
    • α-cells: Secrete Glucagon.
    • β-cells: Secrete Insulin.
  • Hormones & Functions (Glucose Homeostasis):
    • Glucagon (Peptide hormone): 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 and utilization.
    • Insulin (Peptide hormone): Hypoglycemic hormone. Acts mainly on hepatocytes and adipocytes. Enhances cellular glucose uptake and utilization. Stimulates glycogenesis (glucose -> glycogen) in target cells.
  • Disorder:
    • Diabetes Mellitus: Prolonged hyperglycemia. Caused by insulin deficiency or insulin resistance. Leads to loss of glucose through urine (glycosuria) and formation of ketone bodies (ketonuria). Can lead to complications like diabetic ketoacidosis.
      • Type 1: Insulin-dependent (autoimmune destruction of β-cells).
      • Type 2: Non-insulin-dependent (insulin resistance). Treated with insulin therapy or lifestyle changes/medication.

• Gonads:

  • Testis (Male): Primary sex organ and endocrine gland.
    • Structure: Seminiferous tubules and stromal/interstitial tissue. Leydig cells (interstitial cells) produce androgens.
    • Hormone: Androgens (mainly Testosterone) - Steroid hormones.
    • Functions: Regulate development, maturation, and function of male accessory sex organs (epididymis, vas deferens, seminal vesicles, prostate, urethra). Stimulate muscular growth, growth of facial/axillary hair, aggressiveness, low pitch voice (secondary sexual characters). Stimulate spermatogenesis. Anabolic effect on protein and carbohydrate metabolism. Regulated mainly by LH (from pituitary).
  • Ovary (Female): Primary sex organ and endocrine gland.
    • Structure: Produces one ovum per menstrual cycle. Contains ovarian follicles and stromal tissues. Growing follicles synthesize estrogen. After ovulation, the ruptured follicle forms the Corpus Luteum, which secretes progesterone.
    • Hormones:
      • Estrogen (mainly Estradiol): Steroid hormone, synthesized mainly by growing ovarian follicles.
      • Progesterone: Steroid hormone, secreted mainly by the corpus luteum.
    • Functions:
      • Estrogen: Stimulates growth/activities of female secondary sex organs, development of growing follicles, female secondary sex characters (e.g., high pitch voice), mammary gland development. Regulates female sexual behavior.
      • Progesterone: Supports pregnancy. Acts on mammary glands (stimulates alveoli formation - sacs storing milk) and milk secretion. Maintains the endometrium for implantation.

4. Hormones of Heart, Kidney, and Gastrointestinal Tract

• Endocrine cells are also present in other organs.
• Heart: Atrial wall secretes Atrial Natriuretic Factor (ANF) - a peptide hormone. Decreases blood pressure by causing vasodilation and promoting Na+ excretion.
• Kidney: Juxtaglomerular cells (JGA) produce Erythropoietin - a peptide hormone. Stimulates erythropoiesis (RBC formation).
• Gastrointestinal Tract: Endocrine cells 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.
  • Cholecystokinin (CCK): Acts on pancreas and gallbladder. Stimulates secretion of pancreatic enzymes and bile juice release.
  • Gastric Inhibitory Peptide (GIP): Inhibits gastric secretion and motility.
• Growth Factors: Several non-endocrine tissues secrete hormone-like growth factors essential for normal growth, tissue repair/regeneration.

5. Mechanism of Hormone Action

• Hormones produce effects by binding to specific hormone receptors located on target cells only.
• Receptors can be:
  • Membrane-bound Receptors: On the cell membrane (for peptide, protein, catecholamine hormones).
  • Intracellular Receptors: Inside the target cell, mostly nuclear receptors (for steroid hormones, iodothyronines).
• Mechanism based on Receptor Type:
  • Membrane-Bound Receptors (e.g., FSH, Insulin, Glucagon, Adrenaline):
    1. Hormone (1st messenger) binds to the receptor on the cell surface.
    2. Causes conformational change in the receptor.
    3. Leads to the generation of Second Messengers inside the cell (e.g., cyclic AMP (cAMP), IP3, Ca++).
    4. Second messengers activate existing enzymes or intracellular pathways.
    5. Leads to a cascade effect, amplifying the signal.
    6. Results in specific physiological responses (e.g., ovarian growth by FSH).
  • Intracellular Receptors (e.g., Cortisol, Testosterone, Estrogen, Progesterone, Thyroxine):
    1. Lipid-soluble hormones easily pass through the cell membrane.
    2. Bind to specific intracellular receptors (mostly in the nucleus).
    3. The hormone-receptor complex binds to specific regions of the DNA (genome).
    4. This interaction regulates gene expression (stimulates or inhibits transcription of specific genes -> mRNA formation -> protein synthesis).
    5. Leads to physiological and developmental effects (long-term effects).

Key Points for Exams:

• Know the location of each gland.
• Memorize the hormones secreted by each gland.
• Understand the primary function(s) of each hormone.
• Learn the diseases/disorders associated with hypersecretion or hyposecretion.
• Differentiate between the mechanisms of action for peptide vs. steroid hormones.
• Understand the concept of feedback regulation (though not explicitly detailed here, it's implied in hypothalamic-pituitary axes).
• Pay attention to hormones acting antagonistically (e.g., Insulin/Glucagon, PTH/TCT).
• Remember hormones produced by non-traditional endocrine organs (Heart, Kidney, GIT).

Multiple Choice Questions (MCQs)

Here are 10 MCQs based on Chapter 23 for your practice:

1. Which of the following hormones is stored and released by the neurohypophysis but synthesized in the hypothalamus?
   a) Growth Hormone (GH)
   b) Prolactin (PRL)
   c) Antidiuretic Hormone (ADH)
   d) Adrenocorticotrophic Hormone (ACTH)

2. Graves' disease is characterized by the hypersecretion of which gland?
   a) Adrenal Cortex
   b) Thyroid Gland
   c) Pituitary Gland
   d) Parathyroid Gland

3. Which hormone plays a crucial role in regulating the 24-hour diurnal rhythm of our body?
   a) Thyroxine
   b) Melatonin
   c) Cortisol
   d) Adrenaline

4. Identify the pair of hormones that act antagonistically to regulate blood calcium levels.
   a) Insulin and Glucagon
   b) Aldosterone and ANF
   c) PTH and TCT
   d) Estrogen and Progesterone

5. Which of the following is a steroid hormone that binds to intracellular receptors?
   a) Insulin
   b) Epinephrine
   c) FSH
   d) Cortisol

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

7. The Leydig cells of the testes are stimulated to produce testosterone by which hormone?
   a) Follicle Stimulating Hormone (FSH)
   b) Luteinizing Hormone (LH)
   c) Adrenocorticotrophic Hormone (ACTH)
   d) Prolactin (PRL)

8. Which hormone is primarily responsible for stimulating gluconeogenesis, lipolysis, and proteolysis, and also has anti-inflammatory effects?
   a) Aldosterone
   b) Insulin
   c) Cortisol
   d) Thyroxine

9. The hormone Erythropoietin, which stimulates RBC formation, is secreted by:
   a) The heart's atrial wall
   b) The juxtaglomerular cells of the kidney
   c) The alpha cells of the pancreas
   d) The adrenal medulla

10. Hormones like FSH and LH act by:
    a) Binding to intracellular receptors and regulating gene expression.
    b) Passing through the cell membrane and activating enzymes directly.
    c) Binding to membrane-bound receptors and generating second messengers.
    d) Entering the nucleus and binding directly to DNA without a receptor.

Answer Key for MCQs:

1. c) Antidiuretic Hormone (ADH)
2. b) Thyroid Gland
3. b) Melatonin
4. c) PTH and TCT
5. d) Cortisol
6. c) Vasopressin (ADH)
7. b) Luteinizing Hormone (LH)
8. c) Cortisol
9. b) The juxtaglomerular cells of the kidney
10. c) Binding to membrane-bound receptors and generating second messengers.

Study these notes thoroughly. Focus on understanding the functions and regulation of hormones. Practice these MCQs and look for similar questions from previous exam papers. Let me know if any specific part needs further clarification. Good luck with your preparation!