PART - B: Full Answers

Q.1 Long Answer Question (15 Marks)

a) Probable Diagnosis (3 Marks)

• Random Blood Sugar (RBS) of 210 mg/dL (normal < 140 mg/dL; diabetic if ≥ 200 mg/dL with symptoms)
• Glycosuria on dipstick

• Diagnosis of DM is confirmed when RBS ≥ 200 mg/dL WITH classic symptoms of hyperglycemia. This patient fulfills both criteria.
• Fasting plasma glucose ≥ 126 mg/dL OR HbA1c ≥ 6.5% can also confirm the diagnosis.

b) Hormone Responsible (3 Marks)

• In Type 2 DM: there is relative insulin deficiency combined with peripheral insulin resistance.
• In Type 1 DM: there is absolute insulin deficiency due to autoimmune destruction of beta cells.
• Insulin is the primary anabolic hormone responsible for glucose uptake into cells (especially muscle and adipose tissue), suppression of hepatic glucose output, and promotion of glycogen, fat, and protein synthesis.
• In this patient, insufficient insulin action leads to hyperglycemia and its downstream effects.

c) Physiological Basis of Clinical Signs & Symptoms (4 Marks)

• Weight loss (in Type 1) - increased fat and protein catabolism due to insulin lack
• Fatigue - cells unable to use glucose as fuel

d) Physiological Actions of Insulin (5 Marks)

• Increases GLUT-4 translocation to cell membranes in muscle and adipose tissue → increased glucose uptake
• Promotes glycolysis - activates phosphofructokinase and pyruvate kinase
• Promotes glycogenesis - activates glycogen synthase; inhibits glycogen phosphorylase
• Inhibits gluconeogenesis in the liver - reduces hepatic glucose output
• Net effect: lowers blood glucose

• Promotes lipogenesis - promotes conversion of excess glucose to fatty acids
• Inhibits lipolysis - inhibits hormone-sensitive lipase in adipose tissue, reducing FFA release
• Inhibits ketogenesis - by reducing FFA availability for oxidation to ketone bodies

• Promotes amino acid uptake and protein synthesis (anabolic)
• Inhibits protein degradation (anti-catabolic)
• Promotes growth - synergistic with growth hormone

• Drives K⁺ into cells by stimulating Na⁺/K⁺-ATPase → lowers serum potassium
• Clinically used with glucose to treat hyperkalemia
• Also promotes phosphate and magnesium uptake by cells

Q.2 Short Notes (15 Marks, 3 × 5)

a) Errors of Refraction

• Eyeball is too long (axial myopia) OR cornea/lens is too curved (refractive myopia)
• Parallel rays focus in front of the retina
• Distant vision blurred; near vision clear
• Corrected with concave (diverging) lenses

• Eyeball is too short OR refractive power is too weak
• Parallel rays focus behind the retina
• Near vision blurred (and distant in severe cases)
• Corrected with convex (converging) lenses

• Unequal curvature of the cornea in different meridians
• Rays in different planes focus at different points - produces distorted/blurred vision at all distances
• Corrected with cylindrical lenses

• Age-related loss of accommodation due to hardening of the lens and weakening of ciliary muscles
• Near vision is impaired
• Corrected with convex lenses (reading glasses)

b) Synthesis and Functions of Thyroid Hormones

1. Iodide trapping: Iodide (I⁻) is actively transported from blood into follicular cells via the Sodium-Iodide Symporter (NIS) - a Na⁺-dependent active transport ("iodide pump").
2. Oxidation of iodide: Trapped I⁻ is oxidized to active iodine (I₂) by thyroid peroxidase (TPO) using H₂O₂ as oxidant.
3. Organification (Iodination of thyroglobulin): Active iodine is attached to tyrosine residues of thyroglobulin (TG) - forming monoiodotyrosine (MIT) and diiodotyrosine (DIT) - also by TPO.
4. Coupling reaction: Two DIT molecules couple to form T4 (thyroxine), or one MIT + one DIT couple to form T3 (triiodothyronine) - catalyzed by TPO.
5. Storage: The iodinated thyroglobulin is stored as colloid in the follicular lumen (provides 2-3 months' supply).
6. Release: TSH stimulates endocytosis of colloid → lysosomal proteolysis of TG → release of free T3 and T4 into the blood. T4 is the main secretory product (90%); T3 is more potent (3-5×).
7. Peripheral conversion: Most circulating T3 is generated by de-iodination of T4 in peripheral tissues (liver, kidney, muscle).

c) Combined Oral Contraceptive Pills (COCPs)

1. Inhibition of ovulation (primary mechanism):
   • Estrogen suppresses FSH → prevents follicular development
   • Progestogen suppresses LH surge → prevents ovulation
   • Together they suppress the hypothalamic GnRH pulse as well
2. Changes in cervical mucus:
   • Progestogen makes cervical mucus thick, viscous, and hostile to sperm penetration
3. Endometrial changes:
   • Progestogen causes an atrophic, hostile endometrium unfavorable for implantation

• Regulation of menstrual cycle; treatment of dysmenorrhea
• Reduced risk of ovarian and endometrial cancer
• Treatment of endometriosis, PCOS, acne (some formulations)

• Side effects: nausea, breakthrough bleeding, mood changes, breast tenderness, mild hypertension
• Absolute contraindications: current or history of VTE/thromboembolism, stroke, breast cancer, active liver disease, smokers > 35 years (due to ↑ thrombotic risk with estrogen)

Q.3 Short Answer Questions (10 Marks, 5 × 2)

a) Obligatory Urine Volume

• The minimum volume of urine that must be excreted per day to eliminate the metabolic waste products (mainly urea, uric acid, creatinine, sulfates) is called the Obligatory Urine Volume.
• It is approximately 500 mL/day in a healthy adult.
• This is determined by the maximum concentrating ability of the kidney (maximum urine osmolality ~1200-1400 mOsm/kg) and the total solute load that must be excreted daily (~600 mOsm).
• Obligatory Urine Volume = Total daily solute load / Maximum urine osmolality = 600 mOsm ÷ 1200 mOsm/kg ≈ 0.5 L/day
• If water intake falls below this, dehydration and uremic waste accumulation occur.

b) Labelled Diagram of a Nephron

Glomerulus (Bowman's capsule)
        ↓
Proximal Convoluted Tubule (PCT) — reabsorbs 65% Na+, glucose, AA, water
        ↓
Loop of Henle
   - Descending limb (permeable to water)
   - Thin ascending limb
   - Thick ascending limb (impermeable to water; Na+/K+/2Cl- reabsorption)
        ↓
Distal Convoluted Tubule (DCT) — aldosterone acts here
        ↓
Collecting Duct — ADH acts here (water reabsorption)
        ↓
Renal Pelvis → Ureter → Bladder

c) Functions of Sertoli Cells

1. Mechanical support and nutrition of developing germ cells (spermatogonia → spermatozoa)
2. Blood-testis barrier: Tight junctions between adjacent Sertoli cells form a physical barrier that protects developing sperm from immune attack and maintains a specialized microenvironment for spermatogenesis
3. Phagocytosis of excess cytoplasm shed during spermiogenesis (residual bodies)
4. Secretion of Androgen-Binding Protein (ABP): ABP binds testosterone and concentrates it in the seminiferous tubule lumen, facilitating spermatogenesis
5. Secretion of Inhibin: Inhibin (B) provides negative feedback on FSH secretion from the pituitary
6. Secretion of testicular fluid and other factors (transferrin, ceruloplasmin, activin, Müllerian Inhibiting Factor (MIS/AMH) - the latter in fetal life)
7. Regulation of spermatogenesis: Respond to FSH; translate hormonal signals to germ cells (germ cells have no FSH receptors)

d) Physiological Actions of Parathyroid Hormone (PTH)

e) Neuro-Immuno-Endocrine Axis

1. Nervous → Immune: The hypothalamus and autonomic nervous system (via catecholamines, neuropeptides) regulate immune cell function. Stress activates the HPA axis → cortisol → immunosuppression (↓ lymphocyte proliferation, ↓ cytokines).
2. Endocrine → Immune:
   • Cortisol (stress hormone): major immunosuppressant
   • Growth hormone, prolactin, thyroid hormones: generally immunostimulatory
   • Sex hormones: estrogen is immunostimulatory (partly explains female predominance in autoimmune diseases); testosterone is immunosuppressive
3. Immune → Nervous/Endocrine:
   • Cytokines (IL-1, IL-6, TNF-α) produced by immune cells act on the hypothalamus → fever, HPA activation, sickness behavior
   • Immune cells express receptors for hormones and neurotransmitters
4. Clinical significance:
   • Explains why chronic stress impairs immunity
   • Basis for psychoneuroimmunology
   • Role in autoimmune diseases, cancer susceptibility, and wound healing

Q.4 Multiple Choice Questions (10 Marks)

MCQ 1: Hormone secreted by Posterior Pituitary is:

• The posterior pituitary (neurohypophysis) does NOT synthesize hormones - it stores and releases hormones synthesized in the hypothalamus.
• It releases two hormones:
  1. ADH (Vasopressin/AVP) - made in supraoptic nucleus
  2. Oxytocin - made in paraventricular nucleus
• Prolactin is secreted by anterior pituitary (lactotroph cells)
• TSH (Thyroid Stimulating Hormone) is secreted by anterior pituitary (thyrotroph cells)
• MSH (Melanocyte Stimulating Hormone) is secreted by the intermediate lobe of the pituitary (or anterior pituitary in humans)

MCQ 2: ACTH level is highest during:

• ACTH (and cortisol) follow a circadian (diurnal) rhythm driven by the suprachiasmatic nucleus of the hypothalamus via CRH release.
• Peak levels occur in the early morning (around 6-8 AM), shortly before waking.
• Levels are lowest around midnight.
• This circadian pattern means cortisol is highest in early morning to prepare the body for the metabolic demands of the day.
• Clinical relevance: Steroid replacement therapy should be given in the morning to mimic this natural pattern; cortisol stimulation tests are typically done in the morning.

Sources: Ganong's Review of Medical Physiology (26th Ed), Guyton & Hall Textbook of Medical Physiology (14th Ed), Harrison's Principles of Internal Medicine (22nd Ed), Goldman-Cecil Medicine, Kanski's Clinical Ophthalmology (10th Ed), Kaplan & Sadock's Comprehensive Textbook of Psychiatry.