DNB CET Physiology Syllabus

Define tidal volume, residual volume, and functional residual capacity.

Tidal volume (~500 mL): air moved in/out per normal breath. Residual volume (~1200 mL): air remaining after maximal expiration. Functional residual capacity = expiratory reserve volume + residual volume (~2400 mL): air remaining after normal expiration.

Why can't residual volume and functional residual capacity be measured by simple spirometry?

Spirometry only measures air that is moved in and out of the lungs. Residual volume (and any capacity that includes it) represents air that cannot be exhaled, so it must be measured by helium dilution, nitrogen washout, or body plethysmography.

What is the role of pulmonary surfactant and which cells produce it?

Surfactant (produced by type II alveolar pneumocytes) lowers alveolar surface tension, preventing alveolar collapse, increasing compliance, and reducing the work of breathing. Per Laplace's law it stabilizes small alveoli.

State the alveolar gas equation for PAO2.

PAO2 = PiO2 - (PaCO2 / R), where PiO2 = FiO2 × (Patm - PH2O), and R is the respiratory quotient (~0.8). Simplified at sea level on room air: PAO2 ≈ 150 - (PaCO2/0.8).

What is the normal V/Q ratio and how does it differ at the apex versus base of the upright lung?

Overall normal ventilation/perfusion ratio is about 0.8. At the apex V/Q is high (~3, more ventilation than perfusion); at the base V/Q is low (~0.6, more perfusion than ventilation).

Describe the two main forms in which CO2 is transported in blood and the major one.

CO2 is transported as: bicarbonate (HCO3-, ~70%, the major form via carbonic anhydrase), bound to hemoglobin as carbaminohemoglobin (~23%), and dissolved (~7%).

What is the Bohr effect and the Haldane effect?

Bohr effect: increased CO2/H+ (lower pH) shifts the oxygen-hemoglobin dissociation curve right, decreasing O2 affinity and aiding O2 unloading in tissues. Haldane effect: deoxygenated hemoglobin carries more CO2; oxygenation in lungs promotes CO2 release.

State Poiseuille's law and how vessel radius affects resistance to blood flow.

Resistance R = 8ηL / (πr^4). Resistance is inversely proportional to the fourth power of the radius, so small changes in vessel radius cause large changes in resistance/flow.

Write the relationship between blood flow, pressure gradient, and resistance.

Flow = Pressure gradient / Resistance (Q = ΔP/R). For the systemic circulation, Cardiac output = (Mean arterial pressure - Right atrial pressure) / Total peripheral resistance.

Where is resistance to blood flow highest in the systemic circulation and why is it important?

Arterioles are the major site of resistance ('resistance vessels'). Their variable smooth muscle tone regulates total peripheral resistance and distributes blood flow to organs.

State the Starling forces governing fluid movement across capillaries.

Net filtration depends on hydrostatic pressures (capillary Pc favors filtration, interstitial Pi opposes) and oncotic pressures (capillary πc opposes filtration, interstitial πi favors). Net = (Pc - Pi) - (πc - πi). Filtration at the arteriolar end, reabsorption at the venular end; excess returns via lymph.

Calculate mean arterial pressure (MAP) from systolic and diastolic pressures.

MAP = Diastolic pressure + 1/3 (Systolic - Diastolic) = DBP + 1/3 pulse pressure. Normal ≈ 93 mmHg for 120/80.

Define glomerular filtration rate (GFR) and give its normal value.

GFR is the volume of plasma filtered by the glomeruli per unit time; normal is about 125 mL/min (~180 L/day).

Why is inulin the ideal marker for measuring GFR?

Inulin is freely filtered, and neither reabsorbed, secreted, nor metabolized by the tubules, so its clearance equals GFR. Creatinine clearance is a clinical approximation (slightly overestimates GFR due to small tubular secretion).

State the renal clearance formula.

Clearance (C) = (Urine concentration × Urine flow rate) / Plasma concentration = (U × V) / P, expressed in mL/min.

How is renal plasma flow estimated, and which substance is used?

Effective renal plasma flow is estimated by the clearance of para-aminohippuric acid (PAH), which is filtered and almost completely secreted, so it is nearly cleared in one pass at low concentrations.

Where in the nephron is most of the filtered Na+ and water reabsorbed?

The proximal convoluted tubule reabsorbs about 65-67% of filtered Na+ and water (isosmotic reabsorption), along with most glucose, amino acids, and bicarbonate.

What is the action of aldosterone on the nephron?

Aldosterone acts on the principal cells of the late distal tubule/collecting duct to increase Na+ reabsorption (via ENaC and Na+/K+-ATPase) and K+ and H+ secretion, raising blood volume/pressure.

Give the Henderson-Hasselbalch equation as applied to the bicarbonate buffer system.

pH = 6.1 + log([HCO3-] / (0.03 × PaCO2)). Normal: pH 7.4 = 6.1 + log(24 / 1.2).

How do the lungs and kidneys compensate for a metabolic acidosis?

Lungs compensate rapidly by hyperventilation to blow off CO2 (lowering PaCO2). Kidneys compensate over days by increasing H+ secretion, generating new HCO3-, and increasing ammonium (NH4+) excretion.

Classify the four primary acid-base disorders by pH, PaCO2, and HCO3-.

Metabolic acidosis: low pH, low HCO3-. Metabolic alkalosis: high pH, high HCO3-. Respiratory acidosis: low pH, high PaCO2. Respiratory alkalosis: high pH, low PaCO2.

How is the anion gap calculated and what does an elevated value suggest?

Anion gap = Na+ - (Cl- + HCO3-); normal ~8-12 mEq/L. An elevated anion gap suggests metabolic acidosis from added acids (e.g., ketoacidosis, lactic acidosis, renal failure, toxins).

List the major GI secretions and their key components.

Saliva (amylase, lipase, mucus). Gastric juice (HCl, pepsinogen, intrinsic factor, mucus). Pancreatic juice (bicarbonate, amylase, lipase, trypsinogen/proteases). Bile (bile salts, bilirubin). Intestinal secretions (mucus, enzymes).

What cells secrete gastric acid and what stimulates them?

Parietal (oxyntic) cells secrete HCl via the H+/K+-ATPase. They are stimulated by acetylcholine (vagal), gastrin (from G cells), and histamine (from ECL cells acting on H2 receptors).

Describe the migrating motor complex (MMC).

The MMC is a cyclic pattern of GI motility during fasting (every ~90-120 min) that sweeps residual contents and bacteria from the stomach through the small intestine. It is regulated by motilin.

What is the function of bile salts in fat absorption?

Bile salts emulsify dietary fats and form micelles that solubilize fatty acids, monoglycerides, and fat-soluble vitamins, transporting them to enterocyte brush borders for absorption. Most bile salts are reabsorbed in the terminal ileum (enterohepatic circulation).

Describe the hypothalamic-pituitary-thyroid axis with its feedback.

Hypothalamus releases TRH -> anterior pituitary releases TSH -> thyroid releases T3/T4. T3/T4 exert negative feedback on both the hypothalamus (TRH) and pituitary (TSH).

Which hormones are released from the posterior pituitary and where are they synthesized?

ADH (vasopressin) and oxytocin are released from the posterior pituitary but synthesized in the hypothalamus (supraoptic and paraventricular nuclei) and transported down axons for storage and release.

Compare the actions of T3/T4 (thyroid hormones) on metabolism.

Thyroid hormones increase basal metabolic rate, O2 consumption, heat production, carbohydrate/lipid metabolism, and potentiate catecholamine effects (increasing heart rate and contractility). They are essential for normal growth and CNS development.

List the hormone layers of the adrenal cortex and their main products (with mnemonic).

Zona Glomerulosa -> mineralocorticoids (aldosterone); Zona Fasciculata -> glucocorticoids (cortisol); Zona Reticularis -> androgens (DHEA). Mnemonic: GFR / Salt, Sugar, Sex (deeper = sweeter/saltier outside).

Contrast the actions of insulin and glucagon on blood glucose.

Insulin (beta cells) lowers blood glucose by promoting glucose uptake (GLUT4), glycogenesis, lipogenesis, and protein synthesis. Glucagon (alpha cells) raises blood glucose via glycogenolysis and gluconeogenesis in the liver.

Define temporal and spatial summation at synapses.

Temporal summation: rapid successive impulses from one presynaptic neuron add up to reach threshold. Spatial summation: simultaneous inputs from multiple presynaptic neurons add up to reach threshold.

Differentiate EPSPs from IPSPs.

EPSP (excitatory postsynaptic potential) is a depolarization that moves the membrane toward threshold (e.g., Na+ influx). IPSP (inhibitory postsynaptic potential) is a hyperpolarization that moves it away from threshold (e.g., Cl- influx or K+ efflux).

Describe the components of a monosynaptic stretch (myotatic) reflex arc.

Muscle spindle (receptor) -> Ia afferent neuron -> single synapse in spinal cord -> alpha motor neuron (efferent) -> extrafusal muscle fibers (effector), causing contraction of the stretched muscle. Example: knee-jerk reflex.

What is reciprocal innervation in reflexes?

When a stretch reflex activates a muscle, an inhibitory interneuron simultaneously inhibits the antagonist muscle's motor neuron, allowing coordinated movement (the agonist contracts while the antagonist relaxes).

Trace the visual pathway from retina to visual cortex.

Retinal ganglion cells -> optic nerve -> optic chiasm (nasal fibers cross) -> optic tract -> lateral geniculate nucleus of thalamus -> optic radiations -> primary visual cortex (occipital lobe, area V1).

Explain phototransduction in rods.

In darkness, cGMP keeps Na+ channels open (depolarized, glutamate released). Light isomerizes rhodopsin (11-cis to all-trans retinal) -> activates transducin -> activates phosphodiesterase -> cGMP breaks down -> Na+ channels close -> hyperpolarization -> decreased glutamate release.

Compare rods and cones.

Rods: high sensitivity, function in dim light (scotopic), no color vision, more numerous, concentrated peripherally, contain rhodopsin. Cones: lower sensitivity, function in bright light (photopic), provide color vision and high acuity, concentrated in the fovea, three opsin types (red/green/blue).

How does the cochlea perform frequency (pitch) discrimination?

By tonotopic organization of the basilar membrane (place theory): the base (stiff, narrow) responds to high frequencies and the apex (floppy, wide) responds to low frequencies. Hair cells at different positions are maximally stimulated by specific frequencies.

Describe auditory transduction by cochlear hair cells.

Sound vibrates the basilar membrane, bending stereocilia against the tectorial membrane. Tip-link tension opens mechanoelectrical K+ channels -> K+ influx (from endolymph) depolarizes the hair cell -> Ca2+ entry -> neurotransmitter release onto auditory (cochlear) nerve fibers.

What do the semicircular canals and the otolith organs (utricle/saccule) detect?

Semicircular canals detect rotational/angular acceleration (via endolymph movement bending the cupula). The utricle and saccule (otolith organs) detect linear acceleration and head position relative to gravity (via otoliths on the macula).

Contrast the sympathetic and parasympathetic divisions of the ANS by outflow and ganglia location.

Sympathetic: thoracolumbar outflow (T1-L2/3), short preganglionic and long postganglionic fibers, ganglia near the spinal cord (paravertebral chain). Parasympathetic: craniosacral outflow (CN III, VII, IX, X and S2-S4), long preganglionic and short postganglionic fibers, ganglia near/in target organs.

What neurotransmitters and receptors are used at autonomic synapses?

All preganglionic neurons release ACh acting on nicotinic receptors. Parasympathetic postganglionic neurons release ACh on muscarinic receptors. Most sympathetic postganglionic neurons release norepinephrine on adrenergic receptors (exception: sweat glands use ACh on muscarinic receptors).

List the major effects of sympathetic activation (fight-or-flight).

Increased heart rate and contractility, bronchodilation, pupil dilation (mydriasis), decreased GI motility, glycogenolysis/lipolysis, sweating, and vasoconstriction in skin/gut with vasodilation in skeletal muscle.

Describe the EEG waveforms and their associated states.

Beta (>13 Hz): alert, awake, active mental activity. Alpha (8-13 Hz): awake, relaxed, eyes closed. Theta (4-7 Hz): drowsiness, light sleep, children. Delta (<4 Hz): deep sleep (slow-wave sleep).

Contrast REM and non-REM (NREM) sleep.

NREM (slow-wave) sleep has delta waves, decreased muscle tone, and is restorative. REM sleep shows EEG resembling wakefulness (desynchronized, beta-like), vivid dreaming, rapid eye movements, and skeletal muscle atonia (paralysis). REM episodes lengthen toward morning.

What is the role of the muscle spindle versus the Golgi tendon organ?

Muscle spindle detects muscle length and rate of stretch (afferent Ia/II), mediating the stretch reflex. Golgi tendon organ detects muscle tension/force (afferent Ib), mediating the inverse stretch reflex that inhibits the muscle to protect against excessive force.

State Laplace's law as applied to alveoli and its physiological significance.

P = 2T/r (for a sphere/alveolus, T = surface tension, r = radius). Smaller alveoli have higher collapsing pressure; surfactant reduces T more in small alveoli, equalizing pressures and preventing collapse of smaller alveoli into larger ones.

Define the oxygen-hemoglobin dissociation curve and factors that shift it to the right.

It is a sigmoid curve relating PO2 to hemoglobin O2 saturation. A right shift (decreased O2 affinity, easier unloading) is caused by increased CO2, increased H+ (low pH), increased temperature, and increased 2,3-DPG.

What is the countercurrent multiplier mechanism in the kidney?

The loop of Henle establishes a medullary osmotic gradient: the thick ascending limb actively pumps out NaCl (impermeable to water), while the descending limb is permeable to water. This multiplied gradient enables ADH-dependent water reabsorption and concentrated urine production.

How does antidiuretic hormone (ADH) regulate water balance?

ADH (vasopressin), released from the posterior pituitary in response to high plasma osmolality or low blood volume, increases water permeability of the collecting duct by inserting aquaporin-2 channels, increasing water reabsorption and producing concentrated urine.