class 11 notes

Class 11 Biology Notes Chapter 22 (Chemical coordination and integration) – Biology Book

Philoid

Philoid

— 7 min read

Biology
Alright class, let's delve into Chapter 22: Chemical Coordination and Integration. This chapter is crucial as it explains how our body coordinates various functions using chemical messengers called hormones, complementing the neural system. For your government exams, focus on the glands, the hormones they secrete, their specific functions, and the disorders associated with their imbalance.

Chapter 22: Chemical Coordination and Integration - Detailed Notes

1. Endocrine System and Hormones

  • Endocrine Glands: These are ductless glands that secrete chemical messengers directly into the bloodstream. Examples: Pituitary, Pineal, Thyroid, Adrenal, Pancreas, Parathyroid, Thymus, Gonads (Testis and Ovary).
  • Hormones:
    • Non-nutrient chemicals produced in trace amounts.
    • Act as intercellular messengers.
    • Transported via blood to target organs/tissues.
    • Bind to specific protein receptors on target cells (hormone receptors).
  • Difference from Nervous System: Hormonal coordination is generally slower but longer-lasting than neural coordination. Both systems often work together (neuro-endocrine system).

2. Human Endocrine System

  • Hypothalamus:

    • Location: Basal part of the diencephalon (forebrain).
    • Function: Regulates a wide spectrum of body functions. Contains neurosecretory cells (nuclei) that produce hormones. Connects nervous and endocrine systems. Controls the pituitary gland.
    • Hormones:
      • Releasing Hormones: Stimulate secretion of pituitary hormones (e.g., Gonadotrophin Releasing Hormone - GnRH, Thyrotropin Releasing Hormone - TRH, Corticotropin Releasing Hormone - CRH, Growth Hormone Releasing Hormone - GHRH).
      • Inhibiting Hormones: Inhibit secretion of pituitary hormones (e.g., Somatostatin - inhibits GH release, Dopamine/Prolactin Inhibiting Hormone - PIH).
      • Synthesizes Oxytocin & Vasopressin (ADH): These are transported axonally to the posterior pituitary for storage and release.

  • Pituitary Gland:

    • Location: Bony cavity called Sella turcica, attached to the hypothalamus by a stalk.
    • Divisions:
      • Adenohypophysis (Anterior Pituitary): Consists of Pars distalis and Pars intermedia (almost merged with pars distalis in humans).
      • Neurohypophysis (Posterior Pituitary): Pars nervosa. Stores and releases hormones from the hypothalamus.
    • Hormones of Adenohypophysis (Pars Distalis):
      • Growth Hormone (GH): Body growth. Disorders: Dwarfism (low GH in childhood), Gigantism (excess GH in childhood), Acromegaly (excess GH in adulthood - severe disfigurement, especially of the face).
      • Prolactin (PRL): Growth of mammary glands and milk production.
      • Thyroid Stimulating Hormone (TSH): Stimulates synthesis and secretion of thyroid hormones from the thyroid gland.
      • Adrenocorticotrophic Hormone (ACTH): Stimulates synthesis and secretion of steroid hormones (glucocorticoids) from the adrenal cortex.
      • Luteinizing Hormone (LH): In males: stimulates synthesis and secretion of androgens (testosterone) from testes. In females: induces ovulation of Graafian follicles, maintains corpus luteum.
      • Follicle Stimulating Hormone (FSH): In males: regulates spermatogenesis along with androgens. In females: stimulates growth and development of ovarian follicles. (LH & FSH are collectively called Gonadotrophins).
    • Hormones of Pars Intermedia (if distinct):
      • Melanocyte Stimulating Hormone (MSH): Acts on melanocytes, regulating skin pigmentation (role less significant in humans).
    • Hormones released by Neurohypophysis (Synthesized by Hypothalamus):
      • Oxytocin: Acts on smooth muscles. Stimulates uterine contraction during childbirth and milk ejection (let-down reflex) from mammary glands.
      • Vasopressin (Antidiuretic Hormone - ADH): Acts mainly at the kidney (DCT, collecting ducts). Stimulates water reabsorption, reducing water loss (diuresis). Also causes vasoconstriction (increases blood pressure). Disorder: Diabetes Insipidus (impaired synthesis/release of ADH leads to diminished water reabsorption, dehydration, excessive thirst and urination).

  • 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.

  • Thyroid Gland:

    • Location: Two lobes on either side of the trachea, interconnected by an isthmus (connective tissue). 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, and fats, maintain water and electrolyte balance.
      • Thyrocalcitonin (TCT): A protein hormone. 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 (Cretinism - stunted growth, mental retardation, low IQ, abnormal skin, deaf-mutism). In adult women, it may cause irregular menstrual cycles. General symptoms include weight gain, lethargy. Myxedema is hypothyroidism in adults.
      • Hyperthyroidism: Due to thyroid cancer or nodules. Abnormal high secretion leads to increased BMR, weight loss, protrusion of eyeballs (Exophthalmos). Known as Graves' disease or Exophthalmic goitre.

  • Parathyroid Gland:

    • Location: Four glands located 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/demineralisation), kidneys (stimulates calcium reabsorption), and indirectly on intestines (increases calcium absorption from digested food). Works antagonistically with TCT to maintain calcium homeostasis.

  • Thymus Gland:

    • Location: Lobular structure located 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. Promotes differentiation of T-lymphocytes (provide cell-mediated immunity - CMI). Also promotes antibody production (for humoral immunity).
    • Note: Degenerates in old individuals, leading to decreased production of thymosins and a weaker immune response.

  • Adrenal Gland:

    • Location: One pair located at the anterior part (top) of each kidney.
    • Structure: Outer Adrenal Cortex and Inner Adrenal Medulla.
    • Adrenal Medulla Hormones (Catecholamines):
      • Adrenaline (Epinephrine) & Noradrenaline (Norepinephrine).
      • Functions: Secreted rapidly in response to stress (emergency hormones or hormones of Fight or Flight). Increase alertness, pupillary dilation, piloerection (raising of hairs), sweating, heart rate, heart contraction strength, respiration rate. Stimulate glycogen breakdown (hyperglycemia) and lipid/protein breakdown.
    • 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 (stimulate gluconeogenesis, lipolysis, proteolysis; inhibit cellular uptake of amino acids). Maintain cardiovascular system and kidney functions. Produce anti-inflammatory reactions, suppress immune response. Stimulate RBC production.
      • Mineralocorticoids (mainly Aldosterone): Secreted by Zona glomerulosa. Regulate water and electrolyte balance. Act on renal tubules (DCT) stimulating 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 hair, pubic hair, and facial hair during puberty.
    • Disorders: Underproduction of adrenal cortex hormones alters carbohydrate metabolism causing acute weakness and fatigue - Addison's disease.

  • Pancreas:

    • Type: 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).
      • β-cells: Secrete Insulin (peptide hormone).
    • Functions (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). 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.
    • Disorder: Diabetes Mellitus. Prolonged hyperglycemia. Due to insulin deficiency/resistance. Loss of glucose through urine (Glycosuria), formation of ketone bodies (Ketonuria). Can lead to diabetic coma. Treated with insulin therapy.

  • Testis:

    • Location: Scrotal sac (outside abdomen).
    • Function: Primary male sex organ and endocrine gland. Composed of seminiferous tubules and stromal/interstitial tissue.
    • Cells & Hormones: Leydig cells (Interstitial cells) in the inter-tubular spaces produce androgens, mainly Testosterone.
    • Functions of Testosterone: Regulates development, maturation, and functions of male accessory sex organs (epididymis, vas deferens, seminal vesicles, prostate, urethra). Stimulates muscular growth, growth of facial/axillary hair, aggressiveness, low pitch voice (secondary sexual characters). Stimulates spermatogenesis. Anabolic (synthetic) effects on protein and carbohydrate metabolism.

  • Ovary:

    • Location: Abdomen. Primary female sex organ.
    • Function: Produces one ovum per menstrual cycle. Also an endocrine gland. Composed of ovarian follicles and stromal tissues.
    • Hormones:
      • 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 (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 stimulating alveoli formation (store milk) and milk secretion.

3. Hormones of Heart, Kidney, and Gastrointestinal Tract

  • These organs also secrete hormones, not traditionally considered endocrine glands.
  • Heart: Atrial wall secretes Atrial Natriuretic Factor (ANF) (peptide hormone) when blood pressure increases. Causes vasodilation (decreases blood pressure) and promotes Na+ excretion, reducing blood volume.
  • Kidney: Juxtaglomerular cells produce Erythropoietin (peptide hormone). Stimulates erythropoiesis (RBC formation).
  • Gastrointestinal Tract: Endocrine cells in different parts secrete:
    • 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 gall bladder; stimulates secretion of pancreatic enzymes and bile juice respectively.
    • Gastric Inhibitory Peptide (GIP): Inhibits gastric secretion and motility.
    • Several other non-endocrine tissues secrete growth factors essential for normal growth and repair/regeneration.

4. Mechanism of Hormone Action

  • Hormones produce effects by binding to specific hormone receptors located on target cells only. Receptors can be:

    • Membrane-bound receptors: Located on the cell membrane. Usually for peptide, polypeptide, protein hormones, and catecholamines (e.g., Insulin, Glucagon, FSH, LH, Adrenaline).
      • Mechanism: Hormone binding -> Receptor activation -> Response 1 (e.g., changes in membrane permeability) -> Generation of Second Messengers (e.g., cyclic AMP, IP3, Ca++) -> Activation of existing enzymes -> Physiological response (e.g., ovarian growth).
    • Intracellular receptors: Located inside the target cell (mostly nuclear receptors). Usually for steroid hormones (Cortisol, Testosterone, Estrogen, Progesterone) and iodothyronines (Thyroid hormones).
      • Mechanism: Hormone enters cell -> Binds to intracellular receptor -> Hormone-receptor complex forms -> Complex binds to specific region of DNA (genome) -> Regulates gene expression (transcription of mRNA) -> Synthesis of specific proteins -> Physiological and developmental effects.

  • Classification of Hormones based on Chemical Nature:

    • Peptide, polypeptide, protein hormones: Insulin, Glucagon, Pituitary hormones, Hypothalamic hormones, etc.
    • Steroids: Cortisol, Testosterone, Estradiol, Progesterone.
    • Iodothyronines: Thyroid hormones (T3, T4).
    • Amino-acid derivatives: Epinephrine, Norepinephrine.

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) Oxytocin
    (b) Aldosterone
    (c) Vasopressin (ADH)
    (d) Glucagon

  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 of the following hormones acts via intracellular receptors?
    (a) Insulin
    (b) Adrenaline
    (c) FSH
    (d) Cortisol

  4. Identify the hormone pair that works antagonistically to regulate blood calcium levels.
    (a) Insulin and Glucagon
    (b) Aldosterone and ANF
    (c) Thyrocalcitonin (TCT) and Parathyroid Hormone (PTH)
    (d) Estrogen and Progesterone

  5. The Leydig cells found in the human body are the secretory source of:
    (a) Progesterone
    (b) Intestinal juice
    (c) Glucagon
    (d) Androgens (Testosterone)

  6. Which hormone plays a significant role in the differentiation of T-lymphocytes?
    (a) Thyroxine
    (b) Thymosin
    (c) Aldosterone
    (d) Gonadotropins

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

  8. Which of the following is NOT a function of catecholamines (Adrenaline/Noradrenaline)?
    (a) Increased heart rate
    (b) Stimulation of glycogen synthesis (Glycogenesis)
    (c) Piloerection
    (d) Pupil dilation

  9. The hormone responsible for stimulating ovulation and maintaining the corpus luteum is:
    (a) FSH
    (b) LH
    (c) Prolactin
    (d) Oxytocin

  10. Which hormone, secreted by the gastrointestinal tract, stimulates the secretion of pancreatic enzymes and bile juice?
    (a) Gastrin
    (b) Secretin
    (c) Cholecystokinin (CCK)
    (d) Gastric Inhibitory Peptide (GIP)

Answer Key for MCQs:

  1. (c) Vasopressin (ADH)
  2. (b) Thyroid Gland
  3. (d) Cortisol
  4. (c) Thyrocalcitonin (TCT) and Parathyroid Hormone (PTH)
  5. (d) Androgens (Testosterone)
  6. (b) Thymosin
  7. (b) Vasopressin (ADH)
  8. (b) Stimulation of glycogen synthesis (Glycogenesis) - Catecholamines stimulate glycogenolysis (breakdown)
  9. (b) LH
  10. (c) Cholecystokinin (CCK)

Study these notes thoroughly, focusing on the specific functions and associated disorders. Remember to link the hypothalamic-pituitary axis where applicable. Good luck with your preparation!

Read more