Handwritten medical exam answer on ruled notebook paper with blue ink pen, neat student handwriting style, for MD Physiology 10-mark question. Page 1 of 4. Title at top center: "HOMEOSTASIS" (underlined, larger heading) Below: "Q. Discuss homeostasis under: Concept, Regulatory Mechanisms and Disorders." Subheading: "I. CONCEPT OF HOMEOSTASIS" (underlined) Definition section: "Homeostasis = the ability of the body to maintain a relatively constant internal environment despite changes in external conditions." "(From Greek: homos = same, stasis = standing still)" Historical background: "• Claude Bernard (1857): coined concept of 'milieu intérieur' (internal environment)" " → 'La fixité du milieu intérieur est la condition de la vie libre et indépendante'" " → The constancy of the internal environment is the condition of free, independent life" "• W.B. Cannon (1929): coined term HOMEOSTASIS" " → Described physiologic arrangements that restore normal state once disturbed" What is regulated (bullet list): "Parameters maintained by homeostasis:" " ✦ Arterial blood pressure (MAP ~93 mmHg)" " ✦ Body core temperature (37°C)" " ✦ Blood glucose (70–100 mg/dL fasting)" " ✦ Plasma osmolality (~285–295 mOsm/kg)" " ✦ Blood pH (7.35–7.45)" " ✦ PaO₂ (80–100 mmHg), PaCO₂ (35–45 mmHg)" " ✦ Serum K⁺ (3.5–5.0 mEq/L), Ca²⁺ (8.5–10.5 mg/dL)" " ✦ Blood volume (~5 L)" Key concept box (hand-drawn box): "Homeostasis ≠ Equilibrium" "It is a STEADY STATE maintained by continuous energy expenditure" "Equilibrium requires no energy; homeostasis does (e.g., Na⁺/K⁺ ATPase)" At bottom right: "Page 1/4" and date line for student to fill in

Handwritten medical exam answer on ruled notebook paper, blue ink pen, neat student handwriting, MD Physiology exam. Page 2 of 4. Title: "II. REGULATORY MECHANISMS" (underlined, bold heading) Subheading: "A. NEGATIVE FEEDBACK (Most Common & Important)" (underlined) Text: "The principal mechanism for homeostasis. Works to oppose a change and restore set-point." "Four Essential Components of Negative Feedback:" " 1. SENSOR/RECEPTOR — Detects change in the controlled variable" " e.g., baroreceptors in carotid sinus detecting ↑BP" " 2. COMPARATOR/CONTROL CENTRE — Compares signal to set-point, generates error signal" " e.g., medullary cardiovascular centre" " 3. EFFECTOR — Produces response to correct the error" " e.g., heart, blood vessels" " 4. FEEDBACK PATHWAY — Returns corrected signal to sensor" Below this: A hand-drawn circular diagram showing the feedback loop: [CONTROLLED VARIABLE] → (arrow up = DISTURBANCE) → [SENSOR] → [COMPARATOR (set-point)] → error signal → [EFFECTOR] → corrective response → back to [CONTROLLED VARIABLE] With a curved arrow labeled "NEGATIVE FEEDBACK" looping back "Key feature: Output OPPOSES the input (hence 'negative')" "Result: Controlled variable returns to set-point" Examples table (hand-drawn two-column table): "Variable | Sensor | Effector" "Blood pressure ↑ | Baroreceptors | ↓HR, vasodilation" "Blood glucose ↑ | Pancreatic β-cells | ↑Insulin secretion" "Body temp ↑ | Hypothalamus | Sweating, vasodilation" "PaO₂ ↓ | Peripheral chemoreceptors | ↑Ventilation" "Blood volume ↓ | JGA (kidney) | RAAS activation" "Ca²⁺ ↓ | Parathyroid chief cells | ↑PTH secretion" At bottom right: "Page 2/4"

Handwritten medical exam answer on ruled notebook paper, blue ink pen, neat student handwriting, MD Physiology exam. Page 3 of 4. Heading: "B. POSITIVE FEEDBACK" (underlined) "• Output AMPLIFIES rather than opposes the input" "• Takes system AWAY from set-point — leads to a self-perpetuating cycle" "• Physiological examples (limited):" " 1. LH surge at ovulation: rising estrogen → LH surge → more estrogen → ovulation" " 2. Parturition: fetal head on cervix → oxytocin release → stronger contractions → more pressure" " 3. Action potential: Na⁺ influx → depolarization → more Na⁺ channels open → more Na⁺ influx" " 4. Blood clotting (coagulation cascade)" "• Pathological positive feedback: ↑BP → vascular damage → more ↑BP; shock → ↓perfusion → more shock" Heading: "C. FEEDFORWARD (ANTICIPATORY) CONTROL" (underlined) "• Responds BEFORE a disturbance occurs, based on prediction" "• Faster than feedback; prevents error before it develops" "• Example: Sight/smell of food → anticipatory insulin release (cephalic phase)" "• Example: Exercise anticipation → ↑HR before exercise begins" Heading: "D. REDUNDANCY" (underlined) "• Multiple parallel systems control the same vital parameter" "• Ensures survival if one mechanism fails" "• Example: Blood pressure controlled by:" " - Baroreceptor reflex (seconds)" " - Renin-Angiotensin-Aldosterone System (minutes-hours)" " - ADH / vasopressin secretion" " - Atrial Natriuretic Peptide" Heading: "E. HIERARCHY OF CONTROL" (underlined) "• Controls are arranged in levels of priority" "• Higher priority system overrides lower priority when conflicting" "• Example: Blood volume > body temperature" " During severe exercise + heat: body reduces sweating to preserve blood volume" " even at the cost of hyperthermia" "• Hypothalamus → Anterior pituitary → Adrenal cortex → Cortisol → Blood glucose" " (hierarchical endocrine axis)" Small note at bottom: "All mechanisms require ENERGY → homeostasis is metabolically active process" "Page 3/4"

Handwritten medical exam answer on ruled notebook paper, blue ink pen, neat student handwriting, MD Physiology exam. Page 4 of 4. Heading: "III. DISORDERS OF HOMEOSTASIS" (underlined, bold) Introductory line: "Disease = failure of homeostatic mechanisms to maintain vital parameters within normal range." Subheading: "A. Classification of Homeostatic Disorders" (underlined) Hand-drawn table with 3 columns: "Category | Mechanism | Examples" "Hypofunction | Reduced effector activity | Hypothyroidism (↓BMR), Adrenal insufficiency (Addison's)" "Hyperfunction | Excessive effector activity | Hyperthyroidism, Cushing's syndrome (↑cortisol)" "Sensor failure | Abnormal set-point detection | Diabetes insipidus (ADH receptor defect)" "Set-point shift | Altered reference level | Essential hypertension, Fever (pyrogen resets thermostat)" "Effector failure | Unable to respond | Type 2 DM (insulin resistance), Heart failure" "Feedback failure | Loop is broken | SIADH (no feedback inhibition of ADH)" Subheading: "B. System-wise Examples" (underlined) "1. CARDIOVASCULAR:" " • Hypertension — baroreceptor reflex reset to higher set-point" " • Heart failure — ↓CO → RAAS activation → fluid overload → worsening failure (pathological +ve feedback)" "2. GLUCOSE HOMEOSTASIS:" " • Diabetes Mellitus Type 1 — β-cell destruction → no insulin → hyperglycemia" " • Diabetes Mellitus Type 2 — insulin resistance → effector failure" "3. ACID-BASE:" " • Metabolic acidosis/alkalosis — failure of renal/respiratory compensation" " • Example: Renal tubular acidosis — H⁺ excretion mechanism fails" "4. TEMPERATURE:" " • Fever — IL-1, IL-6, PGE₂ reset hypothalamic thermostat upward" " • Heat stroke — thermoregulation overwhelmed, +ve feedback cycle begins" "5. CALCIUM:" " • Hypoparathyroidism → ↓PTH → hypocalcemia → tetany" " • Hyperparathyroidism → ↑PTH → hypercalcemia → bones, stones, groans, psychic moans" "6. FLUID BALANCE:" " • SIADH — ADH secreted despite low osmolality (sensor/feedback failure) → hyponatremia" " • Diabetes insipidus — no ADH or no response → hypernatremia" Conclusion box (hand-drawn rectangle): "CONCLUSION:" "Homeostasis is a dynamic, energy-dependent process maintained through" "redundant, hierarchical, and feedback-driven mechanisms. Disruption at any" "level — sensor, comparator, effector, or feedback loop — results in disease." Bottom right: "Page 4/4" with small star doodle