MBBS Physiology Flashcards

24 sample cards from the Physiology deck

Sampled from the end of the deck, so these are different cards from the ones shown on the syllabus page.

1. What is the hypothalamic-pituitary axis and the difference between anterior and posterior pituitary control?

   The hypothalamus controls the pituitary. The anterior pituitary is regulated by hypothalamic releasing/inhibiting hormones carried via the hypophyseal portal system (vascular link). The posterior pituitary stores and releases ADH and oxytocin synthesized in hypothalamic neurons, delivered via direct axonal (neural) connection.

2. List the anterior pituitary hormones and their main target/effects.

   GH (growth, via IGF-1); TSH (stimulates thyroid); ACTH (stimulates adrenal cortex/cortisol); FSH and LH (gonads, gametogenesis and sex steroids); Prolactin (milk production). Posterior pituitary releases ADH (water reabsorption) and oxytocin (uterine contraction, milk ejection).

3. Describe the synthesis and actions of thyroid hormones $T_3$ and $T_4$.

   Made by iodination of tyrosine residues on thyroglobulin in follicular cells; $T_4$ (thyroxine) is the main secreted form, $T_3$ is the more active form (converted peripherally). They raise basal metabolic rate, heat production, $\ce{O2}$ consumption, and are essential for growth and CNS development. Controlled by TSH/TRH.

4. What are the functions of parathyroid hormone (PTH) in calcium regulation?

   PTH raises plasma $\ce{Ca^2+}$: it stimulates osteoclastic bone resorption, increases renal $\ce{Ca^2+}$ reabsorption and phosphate excretion, and activates renal $1\alpha$-hydroxylase to form active vitamin D (calcitriol), enhancing intestinal $\ce{Ca^2+}$ absorption. Calcitonin (from thyroid C cells) opposes it by lowering $\ce{Ca^2+}$.

5. Name the three zones of the adrenal cortex and their secretory products.

   Zona glomerulosa: mineralocorticoids (aldosterone). Zona fasciculata: glucocorticoids (cortisol). Zona reticularis: androgens (DHEA). Mnemonic: 'GFR' / 'Salt, Sugar, Sex.' The adrenal medulla secretes catecholamines (epinephrine, norepinephrine).

6. Compare the actions of insulin and glucagon from the pancreatic islets.

   Insulin (beta cells): lowers blood glucose — promotes glucose uptake (GLUT4), glycogenesis, lipogenesis, protein synthesis; anabolic. Glucagon (alpha cells): raises blood glucose — promotes glycogenolysis and gluconeogenesis; catabolic. Delta cells secrete somatostatin, which inhibits both.

7. What are the main physiological actions of estrogen, progesterone, and testosterone?

   Estrogen: female secondary sexual characteristics, endometrial proliferation, LH surge trigger. Progesterone: maintains secretory endometrium and pregnancy, raises basal body temperature. Testosterone: male secondary sexual characteristics, spermatogenesis, anabolic (muscle/bone) effects.

8. Explain negative feedback regulation of hormone secretion with the cortisol axis as an example.

   Hypothalamic CRH stimulates pituitary ACTH, which stimulates adrenal cortisol. Rising cortisol then inhibits both CRH (hypothalamus) and ACTH (pituitary) release, keeping levels within range. Most endocrine axes use such negative feedback; positive feedback (e.g. LH surge by estrogen, oxytocin in labor) is the exception.

9. Describe the normal conduction pathway of the cardiac impulse.

   SA node (pacemaker, ~70-80/min) → atrial muscle → AV node (delay, allows atrial filling) → bundle of His → right and left bundle branches → Purkinje fibers → ventricular myocardium. The SA node's intrinsic rate sets the heart rhythm.

10. What do the P wave, QRS complex, and T wave of the ECG represent?

    P wave: atrial depolarization. QRS complex: ventricular depolarization (atrial repolarization is masked within it). T wave: ventricular repolarization. The PR interval reflects AV conduction delay; the QT interval reflects ventricular depolarization plus repolarization.

11. Define cardiac output and give its formula.

    Cardiac output is the volume of blood pumped by each ventricle per minute. $$CO = SV \times HR$$ where $SV$ is stroke volume and $HR$ is heart rate. Typical resting value $\approx 5$ L/min ($70\,\text{mL} \times 70\,\text{beats/min}$).

12. State the Frank-Starling law of the heart.

    Within physiological limits, the force of ventricular contraction (stroke volume) increases with the end-diastolic volume (preload): the more the cardiac muscle is stretched during filling, the greater the force of contraction. This matches stroke volume to venous return.

13. Define preload and afterload.

    Preload: the degree of ventricular stretch at the end of diastole (end-diastolic volume/wall tension), determined by venous return. Afterload: the resistance/pressure the ventricle must overcome to eject blood (largely aortic/arterial pressure and systemic vascular resistance).

14. What is the equation relating mean arterial pressure (MAP), cardiac output, and systemic vascular resistance?

    $$MAP = CO \times SVR$$ where $CO$ is cardiac output and $SVR$ is systemic vascular resistance. MAP can be estimated as $MAP \approx DBP + \frac{1}{3}(SBP - DBP)$, where the difference $SBP - DBP$ is the pulse pressure.

15. How does the baroreceptor reflex respond to a fall in arterial blood pressure?

    Reduced stretch of carotid sinus/aortic arch baroreceptors decreases afferent firing to the medulla, causing increased sympathetic and decreased parasympathetic output. This raises heart rate, contractility, and vasoconstriction (increasing SVR), restoring blood pressure toward normal.

16. State Poiseuille's law and explain its key implication for blood flow.

    $$Q = \frac{\pi \Delta P\, r^{4}}{8 \eta L}$$ Flow $Q$ is proportional to the pressure gradient $\Delta P$ and the fourth power of the radius $r$, and inversely proportional to viscosity $\eta$ and vessel length $L$. Because of $r^{4}$, small changes in vessel radius cause large changes in flow and resistance — arterioles are the chief resistance vessels.

17. Compare the structural and functional features of arteries, capillaries, and veins.

    Arteries: thick muscular/elastic walls, carry blood under high pressure away from heart. Arterioles: main resistance vessels, regulate flow. Capillaries: single endothelial layer, site of exchange. Veins: thin walls, high capacitance (blood reservoir, ~65% of blood volume), valves prevent backflow, return blood to heart at low pressure.

18. What are the Starling forces governing fluid exchange across capillaries?

    Net filtration depends on hydrostatic and oncotic (colloid osmotic) pressures: $$J_v = K_f[(P_c - P_i) - \sigma(\pi_c - \pi_i)]$$ Capillary hydrostatic pressure ($P_c$) pushes fluid out; plasma oncotic pressure ($\pi_c$, from proteins) pulls fluid in. Net filtration occurs at the arterial end, net reabsorption at the venous end; excess is drained by lymphatics.

19. Trace the path of air and the structures of the conducting versus respiratory zones.

    Conducting zone (no gas exchange, anatomical dead space): nose → pharynx → larynx → trachea → bronchi → bronchioles → terminal bronchioles. Respiratory zone (gas exchange): respiratory bronchioles → alveolar ducts → alveolar sacs → alveoli.

20. What is pulmonary surfactant, where is it produced, and what is its function?

    A phospholipid (mainly dipalmitoylphosphatidylcholine) secreted by type II alveolar pneumocytes. It reduces alveolar surface tension, increases lung compliance, prevents alveolar collapse (atelectasis) at end-expiration, and stabilizes alveoli of different sizes. Its deficiency causes neonatal respiratory distress syndrome.

21. Describe the mechanics of quiet inspiration and expiration.

    Inspiration is active: the diaphragm and external intercostals contract, expanding the thorax, lowering intrapleural pressure, so alveolar pressure falls below atmospheric and air flows in. Quiet expiration is passive: muscles relax and elastic recoil of lungs/chest wall raises alveolar pressure above atmospheric, expelling air.

22. Define the four lung volumes: tidal volume, inspiratory reserve, expiratory reserve, and residual volume.

    Tidal volume ($V_T \approx 500$ mL): air moved in a normal breath. Inspiratory reserve volume (IRV $\approx 3000$ mL): extra air inhaled beyond tidal. Expiratory reserve volume (ERV $\approx 1100$ mL): extra air exhaled beyond tidal. Residual volume (RV $\approx 1200$ mL): air remaining after maximal expiration (cannot be exhaled).

23. Define the lung capacities and their component volumes.

    Inspiratory capacity $IC = V_T + IRV$. Functional residual capacity $FRC = ERV + RV$ (air left after normal expiration). Vital capacity $VC = V_T + IRV + ERV$ (max exhalable after max inhalation). Total lung capacity $TLC = VC + RV \approx 5800$ mL.

24. What is the difference between pulmonary (minute) ventilation and alveolar ventilation?

    Minute ventilation $\dot{V}_E = V_T \times f$ (respiratory rate) — total air moved per minute (~6 L/min). Alveolar ventilation $\dot{V}_A = (V_T - V_D) \times f$, where $V_D$ is dead space (~150 mL); it is the volume of fresh air reaching alveoli per minute and is the physiologically effective ventilation (~4.2 L/min).

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