Human Physiology – DNB CET Study Notes
(Prepared for the Doctor of National Board – Clinical Entrant Test, Biology stream)
Aim – Provide a self‑contained, exam‑oriented review of core physiological concepts with key formulae, derivations and “tricky” points that frequently appear in DNB CET.
Structure –
- Core concepts & terminology
- Systems (Cardiovascular, Respiratory, Renal, Endocrine, Digestive, Nervous, Muscular, Reproductive)
- Cross‑system principles (homeostasis, feedback loops, transport phenomena)
- Important equations & derivations
- Tricky points & common pitfalls
- Hard practice question
All the material is written in plain text with Markdown formatting for clarity and easy copy‑paste into your personal notes.
1. Core Concepts
| Term | Definition |
|---|---|
| Homeostasis | Maintenance of a stable internal environment. |
| Stability | The ability of a system to return to a set‑point after a perturbation. |
| Negative feedback | Decrease of the stimulus when the system variable deviates from the set‑point. |
| Positive feedback | Amplification of the stimulus; often used in short‑lived processes (e.g., labor, blood clotting). |
| Set‑point | The value of a variable that the body tries to maintain (e.g., 37 °C, 5.5 mm Hg PaO₂). |
| Physiological range | The interval of values that a variable can assume without compromising life. |
| Allosteric regulation | Regulation of enzyme activity by binding of a molecule at a site other than the active site. |
| Receptor‑cell coupling | Mechanism by which receptors transduce signals (second messenger cascades, ion‑channel opening, etc.). |
Key idea – Think of the body as a system of feedback loops with sensors, effectors, and controllers.
2. Cardiovascular System
| Sub‑topic | Core Points |
|---|---|
| Anatomy | Heart chambers, valves, systemic & pulmonary circuits, coronary circulation. |
| Hemodynamics | Blood pressure (P), flow (Q), resistance (R). |
| Cardiac Cycle | Isovolumetric contraction/relaxation, ejection, filling. |
| Cardiac Output (CO) | (CO = HR \times SV). |
| Stroke Volume (SV) | (SV = EDV - ESV). |
| Frank–Starling Law | Increase in preload → increase in SV. |
| Fick Principle | (VO₂ = CO \times (CaO₂ - CvO₂)). |
| Oxygen Transport | Hemoglobin‑oxygen dissociation curve, Bohr effect, P50. |
| Blood Viscosity & Reynolds Number | Laminar vs turbulent flow, impact of hematocrit. |
2.1 Derivation of Cardiac Output
- Heart Rate (HR) – beats per minute.
- Stroke Volume (SV) – volume ejected each beat.
- Cardiac Output: (CO = HR \times SV).
Tricky point – HR is not the sole determinant of CO; SV can change dramatically with preload, afterload, contractility.
2.2 Fick Principle Derivation
- Oxygen consumption (VO₂) is the amount of O₂ drawn from blood per unit time.
- (VO₂ = (CaO₂ - CvO₂) \times CO).
Where- (CaO₂) = arterial O₂ content ((1.34 \times Hb \times SaO₂ + 0.003 \times PaO₂)).
- (CvO₂) = venous O₂ content ((1.34 \times Hb \times SvO₂ + 0.003 \times PvO₂)).
Application – Used clinically to estimate CO when direct measurement is not possible.
2.3 Tricky Points (Cardio)
| Point | Why it’s tricky |
|---|---|
| Adrenaline vs Noradrenaline | Adrenaline ↑ HR & contractility but ↓ systemic vascular resistance; Noradrenaline ↑ resistance more. |
| Pulsus paradoxus | >10 mm Hg drop in systolic BP during inspiration; seen in tamponade. |
| Preload vs Afterload | Distinguish influences on SV: ↑ preload ↑ SV; ↑ afterload ↓ SV. |
| Left‑to‑right shunts | Affect oxygen saturation; differential cyanosis. |
3. Respiratory System
| Sub‑topic | Core Points |
|---|---|
| Anatomy | Nose, pharynx, larynx, trachea, bronchi, alveoli. |
| Ventilation | Tidal volume (VT), minute ventilation (V̇_E = VT \times RR). |
| Alveolar Gas Equation | (PAO₂ = FiO₂ (Pb - PH₂O) - PaCO₂ / R). |
| Diffusion | Fick’s law: (\dot{V} = \frac{A \times D \times (C_1 - C_2)}{T}). |
| Blood Gases | PaO₂, PaCO₂, SaO₂, pH; Henderson–Hasselbalch. |
| Ventilation‑Perfusion Matching | V/Q ratio; low V/Q → hypoxemia. |
3.1 Alveolar Gas Equation Derivation
- Total atmospheric pressure (Pb = 760) mm Hg.
- Water vapor pressure (PH₂O = 47\