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Small Group Discussion (SGD) - All 13 Topics Explained

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1. Erythropoiesis (24/11/25)

1. Proerythroblast - large cell, no hemoglobin yet
2. Basophilic erythroblast - ribosomes accumulate, hemoglobin synthesis begins
3. Polychromatophilic erythroblast - hemoglobin increases
4. Orthochromatophilic erythroblast - nucleus condenses
5. Reticulocyte - nucleus ejected, still has some RNA; enters bloodstream
6. Mature RBC (Erythrocyte) - biconcave disc, no nucleus, packed with hemoglobin

• Normal RBC lifespan: ~120 days
• Destroyed by macrophages in the spleen and liver
• EPO production is stimulated by hypoxia, anemia, high altitude
• Iron, Vitamin B12, and Folate are essential for normal erythropoiesis
• Ineffective erythropoiesis (RBCs destroyed before reaching circulation) occurs in thalassemia and megaloblastic anemia
• Henry's Clinical Diagnosis and Management by Laboratory Methods
• Histology: A Text and Atlas - Formation of Blood Cells

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2. Physiological Consequences of Sedentary Lifestyle (22/12/25)

• Reduced cardiac output and stroke volume
• Hypertension (due to poor vascular tone)
• Increased risk of coronary artery disease
• Higher resting heart rate

• Insulin resistance - leading to Type 2 Diabetes
• Dyslipidemia (high LDL, low HDL cholesterol)
• Obesity and increased visceral fat

• Muscle atrophy and sarcopenia (loss of muscle mass)
• Reduced bone mineral density - increased osteoporosis risk
• Joint stiffness

• Reduced lung capacity and efficiency
• Shallow breathing patterns

• Increased risk of depression and anxiety
• Cognitive decline with aging

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3. Physiological Consequences of Yoga and Meditation (15/12/25)

• Decreases heart rate and blood pressure (activates parasympathetic system)
• Reduces cortisol and adrenaline levels
• Improves heart rate variability (sign of good cardiac health)

• Pranayama (breathing exercises) increase tidal volume and lung capacity
• Slows respiratory rate, improves oxygen efficiency

• Reduces cortisol (stress hormone)
• Increases GABA, serotonin, and dopamine - improving mood
• Regulates thyroid function

• Shifts balance from sympathetic ("fight or flight") to parasympathetic ("rest and digest")
• Improves focus, reduces stress, and enhances neuroplasticity

• Improves flexibility, balance, and muscle tone
• Reduces chronic pain through endorphin release

• Reduces inflammatory markers (IL-6, CRP)
• Enhances natural killer cell activity

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4. Pulmonary and Coronary Circulation (12/11/26)

Pulmonary Circulation

• Right heart pumps deoxygenated blood to the lungs via the pulmonary arteries
• Blood is oxygenated in pulmonary capillaries (alveolar gas exchange)
• Oxygenated blood returns to the left heart via pulmonary veins
• It is a low-pressure circuit (normal pulmonary artery pressure ~25/10 mmHg)
• Pulmonary hypertension occurs when this pressure rises abnormally

Coronary Circulation

• The heart receives its own blood supply from the right and left coronary arteries, which arise from the aortic root just above the aortic valve
• Left coronary artery divides into:
  • Left anterior descending (LAD) - supplies anterior wall + septum
  • Left circumflex - supplies lateral wall
• Right coronary artery (RCA) - supplies right ventricle, inferior wall, and SA/AV nodes
• Coronary blood flow occurs mainly during diastole (when the heart muscle relaxes)
• Blockage leads to myocardial infarction (heart attack)
• Fuster and Hurst's The Heart, 15th Edition

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5. Gastric and Pancreatic Function Tests (13/11/26)

Gastric Function Tests

• Gastric acid secretion tests - measure basal acid output (BAO) and maximal acid output (MAO) after pentagastrin stimulation
• Used to diagnose Zollinger-Ellison syndrome (gastrinoma), peptic ulcer disease
• H. pylori testing - urea breath test, stool antigen, biopsy (CLO test)
• Serum gastrin levels - elevated in ZES and pernicious anemia

Pancreatic Function Tests

• Fecal elastase - low in chronic pancreatitis/exocrine insufficiency
• Secretin stimulation test - gold standard for exocrine function
• Fecal fat test - steatorrhea indicates malabsorption
• Amylase and Lipase - elevated in acute pancreatitis

• Fasting blood glucose and HbA1c - assess insulin secretion (diabetes)
• C-peptide - reflects endogenous insulin production
• Glucagon levels - assess alpha-cell function

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6. Liver Function Tests (LFTs) (31/1/26)

• Jaundice = bilirubin >2.5 mg/dL (visible yellowing)
• Cirrhosis is suggested by low albumin + prolonged PT + thrombocytopenia
• ALT is the most liver-specific enzyme
• Schwartz's Principles of Surgery, 11th Ed. - Liver Function Tests
• 22nd Edition Pye's Surgical Handicraft - Liver Function Tests

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7. Asphyxia, Drowning, and Cyanosis (7/2/26)

Asphyxia

• Suffocation - smothering, choking, overlaying
• Drowning - submersion in liquid
• Neck compression - hanging, strangulation
• Chest compression - traumatic asphyxia

1. Cyanosis (bluish discoloration)
2. Petechial hemorrhages (tiny burst blood vessels, especially in eyes/face)
3. Congestion and oedema of face
4. Unconsciousness and death

Drowning

• Dry drowning (~10-15%): laryngospasm prevents water entry; death from hypoxia
• Wet drowning (~85%): water floods the lungs, interfering with gas exchange
• Freshwater drowning - hypotonic water absorbed into blood → hemodilution and hemolysis
• Saltwater drowning - hypertonic water pulls fluid into alveoli → pulmonary edema

Cyanosis

• Blue-purple discoloration of skin/mucous membranes due to >5 g/dL of deoxygenated hemoglobin
• Central cyanosis - seen on tongue/lips; caused by respiratory or cardiac disease (lung disease, heart failure, shunts)
• Peripheral cyanosis - fingers/toes; caused by poor circulation (cold, shock)
• The Essentials of Forensic Medicine and Toxicology, 36th Ed.

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8. Physiology of Growth (24/3/26)

• Growth Hormone (GH) - secreted by anterior pituitary; stimulates IGF-1 from the liver
• IGF-1 (Insulin-like Growth Factor 1) - directly promotes bone and tissue growth
• Thyroid hormones - essential for normal bone maturation and brain development
• Sex hormones (estrogen/testosterone) - cause pubertal growth spurt and eventual growth plate closure
• Insulin - anabolic hormone supporting tissue growth

1. Infancy - rapid growth driven by nutrition and GH
2. Childhood - steady, GH-dependent growth
3. Puberty - rapid growth spurt (sex hormones + GH)
4. Adulthood - growth plates fuse (epiphyseal closure), growth stops

• GH excess before puberty → Gigantism
• GH excess after puberty → Acromegaly
• GH deficiency → Dwarfism
• Hypothyroidism in children → Stunted growth and intellectual disability

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9. Brain Death (28/4/26)

1. Deep coma - no response to stimuli
2. No spontaneous breathing - apnea test confirms no respiratory drive
3. Absent brainstem reflexes:
   • No pupillary light reflex
   • No corneal reflex
   • No oculocephalic (doll's eye) reflex
   • No gag/cough reflex
   • No vestibulo-ocular reflex
4. Confirmatory tests (if needed): EEG (isoelectric = flat), cerebral angiography (no blood flow), nuclear scan

• Legal and ethical basis for organ donation
• Distinguished from: persistent vegetative state (cortex non-functional, brainstem intact), coma, locked-in syndrome
• Reversible causes must be excluded (drugs, hypothermia, metabolic disorders)
• Plum and Posner's Diagnosis and Treatment of Stupor and Coma

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10. Chemical Transmission in the Nervous System (29/4/26)

1. Action potential arrives at the presynaptic terminal
2. Voltage-gated Ca²+ channels open → Ca²+ flows in
3. Synaptic vesicles fuse with the membrane (exocytosis)
4. Neurotransmitter is released into the synaptic cleft
5. Neurotransmitter binds to postsynaptic receptors
6. Generates EPSP (excitatory) or IPSP (inhibitory) in postsynaptic cell
7. Neurotransmitter is removed by: reuptake (most), enzymatic degradation (ACh), or diffusion

• Eric Kandel - Principles of Neural Science, 6th Ed.
• Neuroscience: Exploring the Brain, 5th Ed.
• Lippincott Illustrated Reviews: Pharmacology

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11. Physiology of Cough (2/5/26)

1. Irritant receptors in the larynx, trachea, and bronchi are stimulated (by mucus, dust, infection, smoke, acid from reflux)
2. Afferent signal travels via the vagus nerve (CN X) to the cough center in the medulla
3. Efferent signals cause:
   • Deep inspiration
   • Glottis closure + expiratory muscle contraction → builds up intrathoracic pressure (up to 300 mmHg)
   • Sudden glottis opening → explosive expulsion of air at ~500 mph

• Productive cough - mucus cleared; common in bronchitis, pneumonia
• Dry/non-productive cough - no mucus; seen in viral infections, ACE inhibitor use, GERD

1. Post-nasal drip
2. Asthma
3. GERD
4. ACE inhibitors (bradykinin accumulation)

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12. Physiology of Headache (19/5/26)

• Cortical Spreading Depression (CSD) - wave of neuronal depolarization followed by suppression
• Activation of the trigemino-vascular system → release of CGRP (calcitonin gene-related peptide)
• CGRP causes vasodilation and neurogenic inflammation
• Modern migraine drugs (triptans, anti-CGRP antibodies like erenumab) target this pathway

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13. Physiology of Puberty (2/6/26)

1. GnRH pulses → pituitary releases LH and FSH
2. Gonads (testes/ovaries) respond → produce testosterone / estrogen
3. These hormones drive all secondary sex changes

• Girls: Starts ~8-13 years. Thelarche (breast development) first, then pubarche (pubic hair), then menarche (first period). Growth spurt earlier than boys.
• Boys: Starts ~9-14 years. Testicular enlargement first, then pubic/axillary hair, voice change, growth spurt.

• Rapid growth spurt (GH + sex hormones)
• Increase in muscle mass (especially in boys, due to testosterone)
• Fat redistribution
• Bone mineralization and eventual epiphyseal fusion
• Development of secondary sexual characteristics
• Sebaceous gland activation (acne)
• Psychological and behavioral changes (limbic system activation)

• Testosterone - anabolic, masculinizing, promotes spermatogenesis
• Estradiol - feminizing, bone protection, triggers LH surge for ovulation
• GH + IGF-1 - growth
• Adrenal androgens (DHEA) - pubic/axillary hair (adrenarche, begins before gonadarche)
• Harrison's Principles of Internal Medicine, 22nd Ed.

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Summary Table