Lecture 12: The Endocrine System – Key Concepts & Exam Points

Lecture 12: The Endocrine System – Key Concepts & Exam Points Overview • Endocrine system = Ductless glands + Hormones • Works with nervous system to maintain homeostasis o Nervous system → fast, short-term response o Endocrine system → slow, long-term regulation Cell Signaling & Receptors • Cell signaling: Communication via chemical messengers • Receptors: Proteins that detect signals o Surface receptors → for protein hormones o Cytoplasmic receptors → for steroid hormones o Nuclear receptors → for thyroid hormones Types of Chemical Messengers • Endocrine: Hormones in bloodstream → distant targets • Paracrine: Nearby cells • Autocrine: Acts on same cell • Neurocrine: From neurons (includes neurotransmitters & neurohormones) • Cytokines: Immune signaling (e.g., interleukins, leptin) Glands • Exocrine glands: Use ducts (e.g., sweat, saliva) • Endocrine glands: Ductless (release hormones into blood) ➤ Major Endocrine Glands • Hypothalamus, Pituitary, Pineal, Thyroid, Parathyroid, Adrenal, Gonads, Pancreas, Kidney, Placenta Hormone Types 1. Protein hormones → Pituitary, pancreas (insulin), parathyroid 2. Steroid hormones → Adrenal cortex (cortisol), ovaries, testes 3. Tyrosine derivatives → Thyroid (T3, T4), adrenal medulla (epinephrine) Mechanism of Hormone Action 1. Bind receptor → hormone-receptor complex 2. Action mechanisms: o Alter cell membrane permeability o Activate enzymes via second messengers (e.g. cAMP) o Act on DNA → gene transcription (e.g., steroid, thyroid hormones) Regulation of Receptors • Downregulation: Excess hormone → ↓ receptor number • Upregulation: Deficiency → ↑ receptor number Lecture 13: Hypothalamus & Pituitary Gland Hypothalamus • Part of the brain that controls the pituitary gland. • Uses hormonal (anterior) and neural (posterior) control. • Connected via hypothalamic-hypophysial portal system. Pituitary Gland (Hypophysis) • Location: Sella turcica; connected to hypothalamus via stalk. • Two parts: o Anterior (Adenohypophysis) – hormonal control. o Posterior (Neurohypophysis) – neural control. Anterior Pituitary Hormones (6) 1. Growth Hormone (GH) – ↑ growth, protein synthesis, lipolysis; ↑ at night, stress. 2. ACTH – stimulates cortisol; follows circadian rhythm (↑ 8 a.m.). 3. TSH – stimulates thyroid; regulated by TRH, negative feedback by T3/T4. 4. Prolactin – milk production; ↑ by suckling, PRH; ↓ by dopamine (PIH). 5. FSH – gamete production; works with LH in menstrual cycle. 6. LH – ovulation (♀), testosterone (♂); surge triggers ovulation. Posterior Pituitary Hormones • ADH (Vasopressin) – ↑ water reabsorption (DCT/collecting duct); ↓ urine. • Oxytocin – uterine contractions, milk ejection; works via positive feedback. Disorders • Gigantism (child), Acromegaly (adult) – GH hypersecretion. • Pituitary Dwarfism – GH deficiency. • Diabetes Insipidus – ADH deficiency → polyuria, polydipsia. Lecture 15: Adrenal Gland – Key Concepts & Exam Points Anatomy • 2 small triangular glands above kidneys (suprarenal) • Enclosed in adipose capsule Divisions 1. Adrenal Cortex (outer, 80%) → 3 zones: o Zona glomerulosa → Mineralocorticoids (aldosterone) o Zona fasciculata → Glucocorticoids (cortisol) o Zona reticularis → Sex hormones (androgens) 2. Adrenal Medulla (central, 20%) o Produces catecholamines: Adrenaline & Noradrenaline o Controlled by sympathetic nervous system Adrenal Cortex Hormones Mineralocorticoids (Aldosterone) • • Acts on kidneys: o ↑ Na⁺ reabsorption o ↑ Water retention o ↑ Blood pressure o ↑ K⁺ excretion Stimulated by: o ↑ K⁺ in blood o Angiotensin II Glucocorticoids (Cortisol) • Regulated by ACTH (from anterior pituitary) • Has diurnal rhythm (↑ at 4–8 a.m., ↓ at midnight–3 a.m.) • Functions: o ↑ Gluconeogenesis, lipolysis, protein catabolism o ↑ Blood glucose (hyperglycemia) o Anti-inflammatory, immune suppression o Weak mineralocorticoid effect Sex Hormones • Mostly androgens • Minor role compared to gonads (ovaries/testes) Adrenal Medulla Hormones Adrenaline (Epinephrine) and Noradrenaline (Norepinephrine) • Released during stress ("fight or flight") • Stimulated by sympathetic nerves • Effects: o ↑ Heart rate & blood pressure o ↑ Metabolic rate o Blood directed to brain, heart, muscles o Pupil dilation o Adrenaline → stronger on heart & metabolism o Noradrenaline → stronger on blood vessels Stress Response • Stressors: Exercise, fasting, fear, infection, temperature, emotions • Short-term → via sympathetic nervous system • Long-term → via adrenal hormones Lecture 14: Thyroid & Parathyroid Glands Thyroid Gland • • Butterfly-shaped, anterior neck, secretes: o T3, T4 (↑ BMR, protein synthesis, growth). o Calcitonin (↓ blood calcium). Stimulated by TSH from anterior pituitary. Thyroid Hormone Synthesis 1. Iodide trapping 2. Oxidation of Iodide 3. Organification (MIT, DIT) 4. Coupling → T3 (MIT+DIT), T4 (DIT+DIT) 5. Stored in colloid (thyroglobulin). Functions of T3 & T4 • ↑ BMR, heat, growth, protein, fat & carb metabolism. • ↑ cardiac output, CNS excitability, GIT motility. Calcitonin (by C-cells) • ↓ blood Ca²⁺ by inhibiting osteoclasts. Parathyroid Gland • 4 glands behind thyroid. • Secretes PTH (Parathormone): o ↑ blood Ca²⁺ by ↑ bone resorption, renal reabsorption, and intestinal absorption (via Vit D activation). Disorders • Hyperthyroidism: Graves’ disease (↑ T3/T4). • Hypothyroidism: Myxoedema (adult), Cretinism (child). • Goiter: Thyroid enlargement. • Hyperparathyroidism: ↑ Ca²⁺ → bone demineralization. • Hypoparathyroidism: ↓ Ca²⁺ → tetany, carpopedal spasm. Lecture 16: Pancreas Structure • Mixed gland (exocrine + endocrine). • Endocrine part = Islets of Langerhans: o α-cells → Glucagon. o β-cells → Insulin. o δ-cells → Somatostatin. Insulin • Lowers blood glucose (anabolic). • Promotes: • o Glucose uptake, glycogenesis. o Protein & fat synthesis. Stimulated by ↑ glucose, amino acids, parasympathetic activity. Glucagon • Raises blood glucose (catabolic). • Promotes: • o Glycogenolysis. o Gluconeogenesis. Stimulated by ↓ glucose, exercise. Somatostatin (GHRIH) • Inhibits insulin, glucagon, GH. Diabetes Mellitus • Type 1: Insulin deficiency (juvenile, autoimmune). • Type 2: Insulin resistance (adult-onset, obesity-related). Lecture 17: Gonads & Hormones Male Gonads (Testes) • Produce sperm and androgens (mainly testosterone). • Testosterone by Leydig cells: • o Develops male genitalia & secondary sex characteristics. o ↑ muscle, bone, RBCs, BMR. Regulated by: o GnRH → stimulates LH (→ testosterone) and FSH (→ spermatogenesis). Female Gonads (Ovaries) • Produce ova and hormones: Estrogen, Progesterone, Inhibin. • Estrogen: • o Puberty changes (uterus, vagina, breast). o ↑ bone growth, soft skin, fat deposition. Progesterone: o Prepares uterus for pregnancy. o Inhibits uterine contraction. o Promotes breast lobule development. Regulation • Estrogen + Progesterone = Negative feedback on LH & FSH. • Inhibin from corpus luteum → inhibits FSH. MCQS Hypothalamus & Pituitary Gland 1. Which gland is known as the master gland? o A) Hypothalamus o B) Pituitary gland o C) Thyroid gland o D) Adrenal gland 2. The hypothalamic-hypophyseal portal system connects: o A) Hypothalamus to thyroid o B) Hypothalamus to anterior pituitary o C) Hypothalamus to adrenal gland o D) Pituitary to pineal gland 3. Growth hormone (GH) secretion is highest: o A) During exercise only o B) In the early morning o C) During sleep o D) After meals 4. ACTH stimulates the production of: o A) Insulin o B) Cortisol o C) Thyroxine o D) Testosterone 5. Which hormone stimulates milk production? o A) Oxytocin o B) Prolactin o C) Estrogen o D) FSH 6. Gigantism is due to: o A) ADH deficiency o B) Excess GH before epiphyseal closure o C) Excess cortisol o D) Excess TSH 7. Diabetes insipidus is caused by a deficiency of: o A) Insulin o B) Aldosterone o C) ADH o D) GH 8. LH surge in females causes: o A) Menstruation o B) Ovulation o C) Implantation o D) Lactation 9. GHRIH is another name for: o A) Prolactin o B) Somatostatin o C) Oxytocin o D) Vasopressin 10. Oxytocin secretion is regulated by: o A) Negative feedback o B) Positive feedback o C) Blood pressure o D) Thyroxine levels Thyroid & Parathyroid Glands 11. The thyroid gland is located: o A) Behind the ear o B) In front of the trachea below the larynx o C) Below the diaphragm o D) Posterior to the heart 12. Thyroid hormones are stored in: o A) Adrenal cortex o B) Colloid o C) Blood plasma o D) Posterior pituitary 13. Main function of T3 and T4 is to: o A) Increase calcium level o B) Inhibit GH o C) Increase BMR o D) Decrease protein synthesis 14. The enzyme required for iodination is: o A) Tyrosinase o B) Hydrolase o C) Thyroid peroxidase o D) Amylase 15. Calcitonin is secreted by: o A) Follicular cells o B) Parafollicular cells (C cells) o C) Pituitary gland o D) Pancreas 16. Parathyroid hormone increases blood calcium by: o A) Decreasing bone resorption o B) Stimulating osteoclasts o C) Inhibiting kidneys o D) Increasing insulin 17. Goitre is caused by: o A) GH excess o B) Thyroid gland enlargement o C) ADH deficiency o D) Excess calcitonin 18. Myxoedema is: o A) Hyperthyroidism in adults o B) Hypothyroidism in adults o C) Iodine toxicity o D) Calcium deficiency 19. Which hormone inhibits TSH secretion? o A) TRH o B) Prolactin o C) T3/T4 (negative feedback) o D) ACTH 20. Graves' disease is associated with: o A) Hypothyroidism o B) Hyperthyroidism o C) PTH deficiency o D) Diabetes Pancreas 21. The endocrine part of the pancreas is: o A) Acini o B) Islets of Langerhans o C) Duct cells o D) Beta ducts 22. Insulin is secreted by: o A) Alpha cells o B) Beta cells o C) Delta cells o D) C cells 23. Glucagon increases: o A) Protein synthesis o B) Blood glucose o C) Lipogenesis o D) Calcium levels 24. Function of somatostatin: o A) Stimulates insulin o B) Increases GH o C) Inhibits insulin, glucagon, and GH o D) Promotes glycogen storage 25. Type 1 diabetes is due to: o A) Beta cell destruction o B) Insulin resistance o C) Excess insulin o D) Obesity 26. Type 2 diabetes is most commonly caused by: o A) GH excess o B) Insulin resistance o C) Iodine deficiency o D) Adrenal tumors 27. Normal fasting blood glucose is: o A) 40–70 mg/dl o B) 80–120 mg/dl o C) 150–180 mg/dl o D) 200–300 mg/dl 28. Which hormone opposes insulin? o A) Somatostatin o B) Estrogen o C) Glucagon o D) Prolactin 29. Insulin promotes: o A) Glycogenolysis o B) Gluconeogenesis o C) Glycogenesis o D) Ketone production 30. Glucagon is secreted when: o A) Glucose is high o B) Glucose is low o C) Insulin is high o D) Somatostatin is high Gonads & Hormones 31. Male gonads are: o A) Ovaries o B) Testes o C) Adrenal glands o D) Thyroid 32. Testosterone is secreted by: o A) Sertoli cells o B) Leydig cells o C) Follicular cells o D) Beta cells 33. LH in males stimulates: o A) Spermatogenesis o B) Testosterone secretion o C) Estrogen production o D) GH release 34. FSH in males stimulates: o A) Testosterone production o B) Spermatogenesis o C) Seminal fluid production o D) Leydig cells 35. Main female sex hormones: o A) FSH and LH o B) Testosterone and Estrogen o C) Estrogen and Progesterone o D) Insulin and Estrogen 36. Function of estrogen: o A) Inhibits lactation o B) Develops secondary sex characteristics in females o C) Stimulates ADH o D) Increases hair loss 37. Progesterone prepares: o A) Mammary gland for milk o B) Uterus for implantation o C) Ovaries for ovulation o D) Pituitary for FSH secretion 38. Testosterone increases: o A) Voice pitch o B) Muscle mass o C) Menstrual cycle o D) Estrogen production 39. Which hormone causes breast development? o A) LH o B) FSH o C) Estrogen o D) Prolactin 40. Inhibin is secreted by: o A) Pituitary o B) Follicle o C) Sertoli cells (♂) and Corpus luteum (♀) o D) Beta cells Mixed Concepts 41. Which hormone follows a positive feedback loop? o A) Prolactin o B) Oxytocin o C) TSH o D) ADH 42. The hormone that causes uterine contractions: o A) Prolactin o B) Oxytocin o C) Estrogen o D) FSH 43. Hyperparathyroidism results in: o A) Hypocalcemia o B) Hypercalcemia o C) Hypernatremia o D) Hypoglycemia 44. ADH acts on which kidney part? o A) DCT and collecting ducts o B) Loop of Henle o C) Glomerulus o D) PCT 45. T3 is produced by: o A) DIT + DIT o B) MIT + DIT o C) MIT + MIT o D) DIT + TSH 46. Which hormone increases heart rate and cardiac output? o A) GH o B) T3/T4 o C) Prolactin o D) Glucagon 47. Deficiency of iodine leads to: o A) Goiter o B) Acromegaly o C) Diabetes o D) Tetany 48. Which hormone decreases plasma calcium? o A) PTH o B) Calcitonin o C) GH o D) Aldosterone 49. Which hormone increases sodium reabsorption in kidneys (slightly)? o A) ADH o B) Calcitonin o C) Testosterone o D) Oxytocin 50. Which cell type secretes glucagon? o A) Beta cells o B) Alpha cells o C) Delta cells o D) Chief cells