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Endocrine system 1st year mbbs
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I now have comprehensive content. Let me compile the full exam-focused notes and MCQs for 1st year MBBS Endocrine System.
Endocrine System - 1st Year MBBS
Exam-Focused Notes + MCQs
SECTION 1: OVERVIEW
The endocrine system maintains whole-body homeostasis through hormonal signaling. Unlike the nervous system (spatially precise, fast), endocrine effectors provide "broadcast" regulation - affecting multiple tissues simultaneously, with specificity determined by receptor expression on target organs.
Three classes of hormones:
| Class | Examples | Receptor location |
|---|---|---|
| Steroids | Cortisol, Aldosterone, Sex hormones | Intracellular |
| Peptides | GH, ACTH, TSH, ADH, Oxytocin, PTH, Insulin | Cell surface |
| Amines | Thyroid hormones (T3/T4), Epinephrine | Intracellular (T3/T4); Cell surface (Epi) |
Exam Trick: Thyroid hormone is an amine (derived from tyrosine) but behaves like a steroid - it uses an intracellular receptor. This is a classic MCQ trap!
SECTION 2: MASTER TABLE - All Glands & Hormones
(Source: Costanzo Physiology, 7th Ed.)
Hypothalamus (Releasing Hormones)
| Hormone | Type | Action |
|---|---|---|
| TRH (Thyrotropin-releasing hormone) | Peptide | Stimulates TSH + Prolactin |
| CRH (Corticotropin-releasing hormone) | Peptide | Stimulates ACTH |
| GnRH (Gonadotropin-releasing hormone) | Peptide | Stimulates LH + FSH |
| GHRH (Growth hormone-releasing hormone) | Peptide | Stimulates GH |
| Somatostatin (SRIF) | Peptide | Inhibits GH |
| Dopamine (PIF) | Amine | Inhibits Prolactin |
Anterior Pituitary (FLAT PiG mnemonic: FSH, LH, ACTH, TSH, Prolactin, GH, MSH)
| Hormone | Type | Action |
|---|---|---|
| TSH | Peptide | Stimulates synthesis & secretion of thyroid hormones |
| FSH | Peptide | Sperm maturation (Sertoli cells); Follicular development |
| LH | Peptide | Testosterone synthesis (Leydig cells); Ovulation |
| GH (Growth Hormone) | Peptide | Protein synthesis, overall growth |
| Prolactin | Peptide | Milk production & secretion |
| ACTH | Peptide | Stimulates adrenal cortex hormones |
| MSH | Peptide | Melanin synthesis |
Posterior Pituitary (stores, does NOT synthesize - made in hypothalamus)
| Hormone | Action |
|---|---|
| ADH (Vasopressin) | Water reabsorption in collecting ducts; arteriolar constriction |
| Oxytocin | Milk ejection; uterine contractions |
Thyroid Gland
| Hormone | Type | Action |
|---|---|---|
| T3 (Triiodothyronine) | Amine | ↑ BMR, growth, development, heart rate |
| T4 (Thyroxine) | Amine | Same as T3 (T4 converted to active T3 peripherally) |
| Calcitonin | Peptide | ↓ Serum Ca2+ (inhibits osteoclasts) |
Parathyroid Gland
| Hormone | Action |
|---|---|
| PTH (Parathyroid hormone) | ↑ Serum Ca2+, ↓ Phosphate; activates Vit D |
Adrenal Cortex (Zona mnemonic: GFR - Salt, Sugar, Sex)
| Zone | Hormone | Action |
|---|---|---|
| Zona Glomerulosa | Aldosterone (Mineralocorticoid) | ↑ Na+ reabsorption, ↑ K+ excretion (kidney) |
| Zona Fasciculata | Cortisol (Glucocorticoid) | ↑ Blood glucose, anti-inflammatory, stress response |
| Zona Reticularis | Androgens (DHEA) | Male secondary sex characteristics |
Adrenal Medulla
| Hormone | Type | Action |
|---|---|---|
| Epinephrine (80%) | Amine | Fight-or-flight: ↑HR, ↑BP, ↑glucose |
| Norepinephrine (20%) | Amine | Vasoconstriction |
Pancreas (Islets of Langerhans)
| Cell | Hormone | Action |
|---|---|---|
| Beta (β) | Insulin | ↓ Blood glucose (uptake, storage) |
| Alpha (α) | Glucagon | ↑ Blood glucose (glycogenolysis, gluconeogenesis) |
| Delta (δ) | Somatostatin | Inhibits both insulin & glucagon locally |
SECTION 3: KEY AXES (Important for MCQs)
Hypothalamic-Pituitary-Thyroid (HPT) Axis
Hypothalamus → TRH → Anterior Pituitary → TSH → Thyroid → T3/T4
T3/T4 provides NEGATIVE FEEDBACK to Hypothalamus & Pituitary
Hypothalamic-Pituitary-Adrenal (HPA) Axis
Hypothalamus → CRH → Anterior Pituitary → ACTH → Adrenal Cortex → Cortisol
Cortisol provides NEGATIVE FEEDBACK
Renin-Angiotensin-Aldosterone System (RAAS)
Low BP / Low Na+ → Kidney (Renin) → Angiotensin I → ACE (lungs) → Angiotensin II → Aldosterone (Zona Glomerulosa)
SECTION 4: COMMON DISORDERS (Clinical Correlation)
| Disorder | Gland | Too Much / Too Little | Key Features |
|---|---|---|---|
| Hypothyroidism | Thyroid | ↓ T3/T4 | Fatigue, cold intolerance, weight gain, bradycardia |
| Hyperthyroidism (Graves') | Thyroid | ↑ T3/T4 | Weight loss, heat intolerance, tachycardia, exophthalmos |
| Cushing's Syndrome | Adrenal cortex | ↑ Cortisol | Buffalo hump, moon face, striae, hyperglycemia |
| Addison's Disease | Adrenal cortex | ↓ Cortisol & Aldosterone | Hypotension, hyperpigmentation, hypoglycemia |
| Gigantism / Acromegaly | Anterior pituitary | ↑ GH | Gigantism (before epiphyseal closure); Acromegaly (adult) |
| Diabetes Insipidus | Posterior pituitary | ↓ ADH | Excessive dilute urine, extreme thirst |
| Hyperparathyroidism | Parathyroid | ↑ PTH | "Bones, Stones, Groans, Moans" (↑Ca2+) |
| Type 1 DM | Pancreas | ↓ Insulin | Autoimmune β-cell destruction |
| Type 2 DM | Pancreas | Insulin resistance | Obesity, hyperglycemia |
| Pheochromocytoma | Adrenal medulla | ↑ Epi/NE | Episodic hypertension, headache, sweating |
SECTION 5: MUST-KNOW MCQ MNEMONICS
Anterior Pituitary Hormones - "FLAT PiG"
- FSH, LH, ACTH, TSH, Prolactin, (intermediate - MSH), GH
Adrenal Cortex Zones - "GFR" (outside to inside)
- Glomerulosa → Mineralocorticoids (Aldosterone)
- Fasciculata → Glucocorticoids (Cortisol)
- Reticularis → Sex steroids (DHEA/Androgens)
Mnemonic: "Salt, Sugar, Sex" (outer to inner)
PTH vs Calcitonin - Antagonists
- PTH → ↑ Ca2+ (think: PTH = Push Ca into blood)
- Calcitonin → ↓ Ca2+ (think: Calcitonin = Calms down Ca)
SECTION 6: PRACTICE MCQs
Q1. Which hormone is the only one classified as an amine but acts via an intracellular receptor like a steroid?
- A) Epinephrine
- B) Norepinephrine
- C) Thyroid hormone (T3) ✓
- D) Dopamine
Q2. A patient presents with low serum Ca2+ after thyroid surgery. Which structure was most likely inadvertently removed?
- A) Thyroid follicular cells
- B) Parathyroid glands ✓
- C) Adrenal cortex
- D) Parafollicular (C) cells
Q3. Which pituitary hormone is INHIBITED (not stimulated) by its hypothalamic regulator?
- A) TSH
- B) ACTH
- C) Prolactin ✓ (inhibited by Dopamine/PIF)
- D) GH
Q4. The zona glomerulosa of the adrenal cortex primarily produces:
- A) Aldosterone ✓
- B) Cortisol
- C) DHEA
- D) Epinephrine
Q5. A patient with Cushing's syndrome shows central obesity, striae, and hyperglycemia. The primary hormone responsible is:
- A) Aldosterone
- B) Cortisol ✓
- C) ACTH
- D) GH
Q6. Somatostatin is secreted by which of the following?
- A) Anterior pituitary only
- B) Hypothalamus AND pancreatic delta cells ✓
- C) Posterior pituitary
- D) Adrenal medulla
Q7. Calcitonin is secreted by which cell type of the thyroid?
- A) Follicular cells
- B) Parafollicular (C) cells ✓
- C) Chief cells
- D) Oxyphil cells
Q8. Which of the following is the "second messenger" used by peptide hormones?
- A) Lipid-soluble receptor
- B) cAMP or IP3/DAG (cell surface receptor pathways) ✓
- C) DNA binding
- D) mRNA transcription directly
Q9. Posterior pituitary hormones are actually synthesized in the:
- A) Anterior pituitary
- B) Hypothalamic nuclei (supraoptic & paraventricular) ✓
- C) Adrenal medulla
- D) Pineal gland
Q10. In the RAAS pathway, ACE (Angiotensin Converting Enzyme) is found primarily in:
- A) Kidneys
- B) Lungs ✓
- C) Liver
- D) Adrenal gland
SECTION 7: HIGH-YIELD FACTS FOR VIVA/SHORT NOTES
- Master gland of the body = Pituitary (but the "master of the master" = Hypothalamus)
- Posterior pituitary does NOT synthesize hormones - it only stores and releases ADH & Oxytocin (made in hypothalamus)
- Insulin is the ONLY hormone that lowers blood glucose
- Cortisol is the primary stress hormone; peaks in early morning
- T3 is the biologically active thyroid hormone (T4 is a prohormone, converted peripherally)
- Aldosterone acts on principal cells of renal collecting duct - Na+ in, K+ out, H+ out
- Growth Hormone acts partly through IGF-1 (Insulin-like Growth Factor-1) produced in the liver
- Glucagon acts on liver (glycogenolysis + gluconeogenesis) = ↑ blood glucose
- POMC (Pro-opiomelanocortin) is the precursor for both ACTH and MSH in the anterior pituitary
- Diabetes Insipidus (central) = ↓ ADH → treated with desmopressin (ADH analog)
Sources: Costanzo Physiology 7th Ed.; Ganong's Review of Medical Physiology 26th Ed.
Want me to go deeper on any specific gland, hormone axis, or add more MCQs on a particular topic? I can also make notes on thyroid, adrenal, or pituitary disorders in more detail.
Create a summary PDF with diagrams of hormone axes
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Endocrine System MBBS
PDF Document · PDF
What's inside the PDF (8 pages):
| Page | Content |
|---|---|
| 1 | Cover page with topic index |
| 2 | Hormone classification table + key abbreviations (ACTH, ADH, TRH, etc.) |
| 3 | Visual axis diagrams - HPT, HPA, HPG axes side-by-side with negative feedback arrows; RAAS and GH/IGF-1 axes |
| 4 | Master hormone table - all glands color-coded (hypothalamus through pancreas) |
| 5 | Adrenal cortex cross-section diagram + Islets of Langerhans diagram + GFR mnemonic table |
| 6 | Clinical disorders table (15 conditions with key features) |
| 7 | 10 exam-style MCQs with answers + explanations |
| 8 | FLAT PiG mnemonic diagram + 15 high-yield viva facts + Ca2+ regulation comparison table (PTH vs Calcitonin vs Vit D) |
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