MBBS Physiology Syllabus

Compare nicotinic and muscarinic acetylcholine receptors.

Nicotinic: ionotropic (ligand-gated cation channel), fast; found at neuromuscular junction, autonomic ganglia, adrenal medulla, CNS. Muscarinic: metabotropic (G-protein coupled), slower; found at parasympathetic effector organs and CNS. Acetylcholine is degraded by acetylcholinesterase.

What are the structural components of a typical neuron?

Cell body (soma) containing the nucleus and Nissl substance; dendrites (receive input); axon hillock (site of AP initiation); axon (conducts AP); myelin sheath with nodes of Ranvier; and axon terminals (synaptic boutons) for transmitter release.

Classify neurons by their structure (number of processes).

Multipolar (one axon, many dendrites; most CNS neurons), bipolar (one axon, one dendrite; retina, olfactory), unipolar/pseudounipolar (single process that splits; dorsal root ganglion sensory neurons), and anaxonic (no clear axon).

What are the functions of neuroglia: astrocytes, oligodendrocytes, microglia, and ependymal cells?

Astrocytes: support, blood-brain barrier, ion/neurotransmitter homeostasis. Oligodendrocytes: myelinate CNS axons (Schwann cells do so in the PNS). Microglia: immune/phagocytic cells of the CNS. Ependymal cells: line ventricles and produce/circulate CSF.

What are the main functional roles of the cerebellum?

Coordination of voluntary movement, regulation of posture and balance, motor learning, and fine-tuning of timing and accuracy of movements. Damage causes ataxia, intention tremor, dysmetria, and dysdiadochokinesia (not paralysis).

List the major functional areas of the cerebral cortex.

Frontal lobe: primary motor cortex, prefrontal (executive/personality), Broca's area (speech production). Parietal lobe: primary somatosensory cortex. Temporal lobe: auditory cortex, Wernicke's area (comprehension), memory. Occipital lobe: primary visual cortex.

Describe the gray and white matter organization of the spinal cord.

Centrally located H-shaped gray matter contains neuronal cell bodies: dorsal (posterior) horns receive sensory input, ventral (anterior) horns contain motor neurons, lateral horns (T1-L2) contain sympathetic neurons. Surrounding white matter contains ascending and descending myelinated tracts.

What is the difference between the ascending and descending spinal tracts, with examples?

Ascending (sensory) tracts carry information to the brain: dorsal columns (fine touch, proprioception), spinothalamic tract (pain, temperature). Descending (motor) tracts carry commands from the brain: corticospinal (pyramidal) tract for voluntary movement, and extrapyramidal tracts (rubrospinal, reticulospinal) for posture/tone.

How many pairs of cranial and spinal nerves are there, and how are spinal nerves distributed?

12 pairs of cranial nerves and 31 pairs of spinal nerves. Spinal nerves: 8 cervical, 12 thoracic, 5 lumbar, 5 sacral, and 1 coccygeal pair. Each spinal nerve has a dorsal (sensory) root and ventral (motor) root.

Classify the 12 cranial nerves as sensory, motor, or mixed.

Sensory only: I (olfactory), II (optic), VIII (vestibulocochlear). Motor only: III (oculomotor), IV (trochlear), VI (abducens), XI (accessory), XII (hypoglossal). Mixed: V (trigeminal), VII (facial), IX (glossopharyngeal), X (vagus).

Differentiate the somatic and autonomic nervous systems.

Somatic: voluntary control of skeletal muscle, single myelinated motor neuron from CNS to effector, neurotransmitter is acetylcholine (always excitatory). Autonomic: involuntary control of smooth/cardiac muscle and glands, two-neuron chain (pre- and postganglionic), can be excitatory or inhibitory.

Compare the anatomical origins of the sympathetic and parasympathetic divisions.

Sympathetic = thoracolumbar outflow (T1-L2/L3); short preganglionic, long postganglionic fibers; ganglia near the spinal cord (sympathetic chain). Parasympathetic = craniosacral outflow (CN III, VII, IX, X and S2-S4); long preganglionic, short postganglionic fibers; ganglia near/in the effector organ.

What neurotransmitters and receptors are used at autonomic synapses?

All preganglionic fibers (both divisions) release acetylcholine onto nicotinic receptors. Parasympathetic postganglionic fibers release acetylcholine onto muscarinic receptors. Sympathetic postganglionic fibers release norepinephrine onto adrenergic receptors (exceptions: sweat glands use ACh; adrenal medulla releases epinephrine into blood).

Contrast the dominant effects of sympathetic vs parasympathetic stimulation on the heart, pupils, and GI tract.

Sympathetic ('fight or flight'): increases heart rate/contractility, dilates pupils (mydriasis), inhibits GI motility. Parasympathetic ('rest and digest'): decreases heart rate, constricts pupils (miosis), stimulates GI motility and secretion.

Classify hormones by chemical structure with examples.

1) Peptide/protein hormones (insulin, glucagon, ADH, anterior pituitary hormones) — water-soluble, act via surface receptors. 2) Steroid hormones (cortisol, aldosterone, sex steroids) — lipid-soluble, intracellular receptors. 3) Amine hormones (thyroid hormones, catecholamines) derived from tyrosine.

How do steroid/thyroid hormones differ from peptide hormones in their mechanism of action?

Steroid and thyroid hormones are lipophilic, cross the cell membrane, bind intracellular (cytoplasmic/nuclear) receptors, and alter gene transcription — slow but long-lasting effects. Peptide hormones and catecholamines bind surface receptors and act via second messengers (cAMP, IP3/DAG, $\ce{Ca^2+}$) — fast, short-lived effects.

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.

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).

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.

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 $\ce{Ca^2+}$.

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).

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.

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.

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.

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.

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.

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 ($70\,\text{mL} \times 70\,\text{beats/min}$).

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.

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).

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.

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.

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.

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.

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.

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.

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.

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.

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).

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.

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).