100 USMLE-Level MCQs on Medical Physiology with Answers
Based on the most recent guidelines from the American College of Cardiology, I will create 100 high-quality USMLE-level multiple-choice questions covering key concepts in medical physiology. 1
Cardiovascular Physiology
Question 1
A 45-year-old patient presents with a regular rhythm at 70 bpm. The ECG shows a QRS complex that occurs after each P wave with a constant PR interval of 0.16 seconds. Which of the following best describes this cardiac conduction? A) First-degree AV block B) Normal sinus rhythm C) Second-degree AV block, Mobitz type I D) Junctional rhythm E) Sinus bradycardia
Answer: B) Normal sinus rhythm The PR interval is within normal range (0.12-0.20 seconds) with 1:1 conduction between atria and ventricles at a normal rate. 1
Question 2
The specialized cardiac pacemaker cells in the sinoatrial node have which unique property that allows them to generate spontaneous action potentials? A) Increased sodium channel density B) Spontaneous phase 4 depolarization C) Prolonged phase 2 plateau D) Absence of calcium channels E) Hyperpolarized resting membrane potential
Answer: B) Spontaneous phase 4 depolarization SA node cells exhibit spontaneous diastolic depolarization during phase 4, allowing them to reach threshold potential and generate action potentials without external stimulation. 1
Question 3
Which ion channel is primarily responsible for the rapid depolarization (phase 0) of the ventricular myocyte action potential? A) Slow calcium channels B) Fast sodium channels C) Potassium channels D) Chloride channels E) HCN channels
Answer: B) Fast sodium channels Fast sodium channels are responsible for the rapid upstroke (phase 0) of the action potential in ventricular myocytes. 1
Question 4
A 60-year-old patient has an ECG showing a QRS complex of 0.14 seconds with an rSR' pattern in V1 and wide, slurred S waves in leads I and V6. Which conduction abnormality is present? A) Left bundle branch block B) Right bundle branch block C) Left anterior fascicular block D) Left posterior fascicular block E) Nonspecific intraventricular conduction delay
Answer: B) Right bundle branch block The ECG findings of QRS duration >0.12 seconds with rSR' pattern in V1 and wide, slurred S waves in leads I and V6 are classic for complete right bundle branch block. 1
Question 5
During cardiac cycle, which phase corresponds to ventricular filling? A) Isovolumic contraction B) Rapid ejection C) Isovolumic relaxation D) Diastasis E) Reduced ejection
Answer: D) Diastasis Diastasis is the middle phase of ventricular diastole when ventricular filling occurs passively due to pressure gradient between atria and ventricles. 1
Question 6
Which of the following best describes the Frank-Starling mechanism? A) Increased heart rate in response to sympathetic stimulation B) Increased stroke volume in response to increased end-diastolic volume C) Decreased cardiac output in response to increased afterload D) Increased contractility in response to parasympathetic stimulation E) Decreased stroke volume in response to increased preload
Answer: B) Increased stroke volume in response to increased end-diastolic volume The Frank-Starling mechanism describes how increased ventricular filling (preload) leads to increased force of contraction and stroke volume. 2
Question 7
A patient with atrial fibrillation has an irregular ventricular rhythm. Which of the following best explains this finding? A) Multiple ectopic foci in the ventricles B) Irregular conduction of atrial impulses through the AV node C) Complete heart block D) Accelerated junctional rhythm E) Ventricular escape rhythm
Answer: B) Irregular conduction of atrial impulses through the AV node In atrial fibrillation, numerous atrial impulses bombard the AV node, which conducts them irregularly to the ventricles, resulting in an irregular ventricular rhythm. 1
Question 8
Which of the following is the primary determinant of myocardial oxygen consumption? A) Heart rate B) Contractility C) Preload D) Afterload E) Wall tension
Answer: E) Wall tension Wall tension is the primary determinant of myocardial oxygen consumption, as described by Laplace's law. 1
Question 9
A 50-year-old patient has an ECG showing a QRS complex of 0.13 seconds with a QS or rS pattern in V1 and broad, notched R waves in leads I and V6. Which conduction abnormality is present? A) Left bundle branch block B) Right bundle branch block C) Left anterior fascicular block D) Left posterior fascicular block E) Nonspecific intraventricular conduction delay
Answer: A) Left bundle branch block The ECG findings of QRS duration >0.12 seconds with QS or rS pattern in V1 and broad, notched R waves in leads I and V6 are characteristic of complete left bundle branch block. 1
Question 10
Which of the following best describes the effect of increased parasympathetic tone on the heart? A) Increased heart rate B) Increased contractility C) Decreased AV nodal conduction D) Increased automaticity of Purkinje fibers E) Increased conduction velocity in the ventricles
Answer: C) Decreased AV nodal conduction Increased parasympathetic tone decreases AV nodal conduction velocity, which can lead to prolonged PR intervals or even AV block. 1
Respiratory Physiology
Question 11
Which of the following best describes the primary stimulus for breathing in a healthy individual at rest? A) Decreased arterial PO₂ B) Increased arterial PCO₂ C) Decreased arterial pH D) Increased arterial bicarbonate E) Decreased cerebrospinal fluid pH
Answer: B) Increased arterial PCO₂ In healthy individuals, central chemoreceptors respond primarily to increases in arterial PCO₂, which is the main stimulus for breathing at rest. 2
Question 12
A 25-year-old healthy individual has the following pulmonary function test results: FEV₁ = 4.0 L, FVC = 5.0 L. What is the FEV₁/FVC ratio? A) 60% B) 70% C) 80% D) 90% E) 100%
Answer: C) 80% FEV₁/FVC ratio = 4.0/5.0 = 0.8 or 80%, which is within normal range (>70% in adults). 2
Question 13
Which of the following best describes the relationship between alveolar ventilation and arterial PCO₂? A) Direct linear relationship B) Inverse linear relationship C) Exponential relationship D) Logarithmic relationship E) No consistent relationship
Answer: B) Inverse linear relationship Arterial PCO₂ is inversely proportional to alveolar ventilation; when ventilation doubles, PCO₂ is halved. 2
Question 14
A patient with severe emphysema is most likely to have which of the following changes in pulmonary function tests? A) Increased FEV₁/FVC ratio B) Decreased total lung capacity C) Decreased residual volume D) Decreased FEV₁ E) Increased diffusing capacity
Answer: D) Decreased FEV₁ Emphysema is characterized by decreased elastic recoil leading to decreased expiratory flow rates, most notably a decreased FEV₁. 2
Question 15
Which of the following best describes the ventilation-perfusion ratio in the apex of the lung compared to the base in an upright individual? A) Higher at the apex B) Lower at the apex C) Equal throughout the lung D) Randomly distributed E) Higher at the apex during inspiration, higher at the base during expiration
Answer: A) Higher at the apex The apex of the lung has higher ventilation-perfusion ratios due to relatively greater ventilation than perfusion compared to the base. 2
Question 16
Which of the following best describes the primary mechanism of hypoxic pulmonary vasoconstriction? A) Increased pulmonary blood flow B) Decreased alveolar oxygen tension C) Increased alveolar carbon dioxide tension D) Decreased pulmonary vascular resistance E) Increased left atrial pressure
Answer: B) Decreased alveolar oxygen tension Hypoxic pulmonary vasoconstriction is triggered by decreased alveolar oxygen tension, which causes constriction of pulmonary arterioles to redirect blood flow to better-ventilated areas. 2
Question 17
A 30-year-old patient has the following arterial blood gas values: pH = 7.30, PCO₂ = 60 mmHg, HCO₃⁻ = 28 mEq/L. Which acid-base disorder is present? A) Metabolic acidosis B) Respiratory acidosis C) Metabolic alkalosis D) Respiratory alkalosis E) Mixed metabolic and respiratory acidosis
Answer: B) Respiratory acidosis The elevated PCO₂ with pH below normal indicates respiratory acidosis. The slightly elevated bicarbonate suggests early renal compensation. 2
Question 18
Which of the following best describes the oxygen-hemoglobin dissociation curve shift that occurs with increased temperature? A) Shift to the right B) Shift to the left C) No shift, only increased oxygen carrying capacity D) No shift, only decreased oxygen carrying capacity E) Biphasic shift depending on PO₂
Answer: A) Shift to the right Increased temperature shifts the oxygen-hemoglobin dissociation curve to the right, decreasing hemoglobin's affinity for oxygen and facilitating oxygen unloading to tissues. 2
Question 19
What is the primary buffer system in extracellular fluid? A) Hemoglobin B) Phosphate C) Bicarbonate D) Protein E) Ammonia
Answer: C) Bicarbonate The bicarbonate/carbonic acid system is the primary buffer system in extracellular fluid. 2
Question 20
A patient with a vital capacity of 4.5 L and a residual volume of 1.5 L has which of the following total lung capacities? A) 3.0 L B) 4.5 L C) 6.0 L D) 7.5 L E) 9.0 L
Answer: C) 6.0 L Total lung capacity = Vital capacity + Residual volume = 4.5 L + 1.5 L = 6.0 L. 2
Renal Physiology
Question 21
Which nephron segment reabsorbs the highest percentage of filtered sodium? A) Proximal tubule B) Loop of Henle C) Distal convoluted tubule D) Collecting duct E) Bowman's capsule
Answer: A) Proximal tubule The proximal tubule reabsorbs approximately 65-70% of filtered sodium. 2
Question 22
Which of the following best describes the countercurrent multiplier mechanism? A) Active transport of sodium in the ascending limb of loop of Henle B) Passive diffusion of water in the collecting duct C) Active transport of urea in the proximal tubule D) Passive diffusion of chloride in the distal tubule E) Active transport of potassium in Bowman's capsule
Answer: A) Active transport of sodium in the ascending limb of loop of Henle The countercurrent multiplier mechanism relies on active transport of sodium (via Na-K-2Cl cotransporter) in the thick ascending limb of the loop of Henle. 2
Question 23
A patient with a plasma creatinine of 2.0 mg/dL has a creatinine clearance of 60 mL/min. What is the approximate glomerular filtration rate (GFR)? A) 30 mL/min B) 60 mL/min C) 90 mL/min D) 120 mL/min E) 150 mL/min
Answer: B) 60 mL/min Creatinine clearance approximates GFR, so the GFR would be approximately 60 mL/min. 2
Question 24
Which hormone is primarily responsible for sodium reabsorption in the collecting duct? A) Antidiuretic hormone (ADH) B) Aldosterone C) Parathyroid hormone D) Atrial natriuretic peptide E) Calcitonin
Answer: B) Aldosterone Aldosterone acts on principal cells in the collecting duct to increase sodium reabsorption and potassium secretion. 2
Question 25
A patient with diabetes insipidus would most likely present with which of the following? A) Oliguria and edema B) Polyuria and hypernatremia C) Oliguria and hyponatremia D) Polyuria and hyponatremia E) Normal urine output and hypernatremia
Answer: B) Polyuria and hypernatremia Diabetes insipidus is characterized by inability to concentrate urine due to ADH deficiency or resistance, leading to polyuria and subsequent hypernatremia. 2
Question 26
Which of the following best describes the function of the macula densa? A) Regulation of renin release in response to changes in distal tubular sodium concentration B) Secretion of erythropoietin in response to hypoxia C) Reabsorption of glucose via SGLT2 transporters D) Production of ammonia to buffer excess hydrogen ions E) Secretion of potassium in exchange for sodium
Answer: A) Regulation of renin release in response to changes in distal tubular sodium concentration The macula densa cells sense sodium chloride concentration in the distal tubule and signal the juxtaglomerular cells to release renin when sodium concentration decreases. 2
Question 27
Which of the following is the primary mechanism for potassium secretion in the distal nephron? A) Na⁺-K⁺ ATPase at the basolateral membrane B) ROMK channels at the apical membrane C) Na⁺-K⁺-2Cl⁻ cotransporter D) Na⁺-H⁺ exchanger E) Cl⁻-HCO₃⁻ exchanger
Answer: B) ROMK channels at the apical membrane Potassium secretion in the distal nephron occurs primarily through ROMK (renal outer medullary potassium) channels at the apical membrane of principal cells. 2
Question 28
A patient with metabolic acidosis would be expected to have which of the following changes in urine composition? A) Increased urine pH B) Decreased ammonium excretion C) Increased bicarbonate excretion D) Increased titratable acid excretion E) Decreased phosphate excretion
Answer: D) Increased titratable acid excretion In metabolic acidosis, the kidneys increase acid excretion through increased titratable acid (primarily phosphate) and ammonium excretion. 2
Question 29
Which of the following substances has the highest filtration fraction (ratio of filtered to plasma concentration) at the glomerulus? A) Albumin B) Glucose C) Sodium D) Inulin E) Creatinine
Answer: D) Inulin Inulin has a filtration fraction of 1.0 (freely filtered) and is neither reabsorbed nor secreted, making it an ideal marker for GFR measurement. 2
Question 30
Which of the following is the primary driving force for water reabsorption in the proximal tubule? A) Active transport of water B) Osmotic gradient created by sodium reabsorption C) Hydrostatic pressure gradient D) Oncotic pressure gradient E) Active transport of chloride
Answer: B) Osmotic gradient created by sodium reabsorption Water reabsorption in the proximal tubule occurs passively along the osmotic gradient created by active sodium reabsorption. 2
Gastrointestinal Physiology
Question 31
Which of the following best describes the primary stimulus for gastric acid secretion during the cephalic phase? A) Distension of the stomach B) Protein in the stomach C) Vagal stimulation D) Secretin release E) Cholecystokinin release
Answer: C) Vagal stimulation The cephalic phase of gastric secretion is mediated by vagal stimulation in response to the sight, smell, taste, or thought of food. 2
Question 32
Which of the following hormones stimulates pancreatic bicarbonate secretion? A) Gastrin B) Cholecystokinin C) Secretin D) Ghrelin E) Motilin
Answer: C) Secretin Secretin stimulates pancreatic ductal cells to secrete bicarbonate-rich fluid in response to acidic chyme entering the duodenum. 2
Question 33
Which of the following best describes the migrating motor complex (MMC)? A) Coordinated contractions that occur during digestion B) Peristaltic waves that propel food from the mouth to the stomach C) Cyclical pattern of contractions that occur during fasting D) Segmentation contractions that mix intestinal contents E) Contractions that prevent reflux of duodenal contents into the stomach
Answer: C) Cyclical pattern of contractions that occur during fasting The migrating motor complex is a cyclical pattern of contractions that occurs during fasting to clear undigested material from the GI tract. 2
Question 34
Which of the following substances is primarily absorbed in the duodenum? A) Vitamin B12 B) Bile salts C) Iron D) Water E) Short-chain fatty acids
Answer: C) Iron Iron is primarily absorbed in the duodenum, with absorption decreasing progressively in more distal segments of the small intestine. 2
Question 35
Which of the following best describes the function of cholecystokinin (CCK)? A) Stimulation of gastric acid secretion B) Inhibition of gastric emptying C) Stimulation of pancreatic enzyme secretion D) Stimulation of gastric motility E) Inhibition of pancreatic bicarbonate secretion
Answer: C) Stimulation of pancreatic enzyme secretion CCK stimulates pancreatic acinar cells to secrete digestive enzymes in response to fat and protein in the duodenum. 2
Question 36
Which of the following is the primary site of vitamin B12 absorption? A) Duodenum B) Jejunum C) Ileum D) Cecum E) Colon
Answer: C) Ileum Vitamin B12 bound to intrinsic factor is absorbed in the terminal ileum. 2
Question 37
Which of the following best describes the function of the hepatocyte canalicular membrane? A) Uptake of bile acids from portal blood B) Secretion of bile into bile canaliculi C) Uptake of bilirubin from systemic circulation D) Secretion of plasma proteins into sinusoids E) Uptake of glucose for glycogen synthesis
Answer: B) Secretion of bile into bile canaliculi The canalicular membrane of hepatocytes is responsible for secreting bile components into the bile canaliculi. 2
Question 38
Which of the following is the primary mechanism for glucose absorption in the small intestine? A) Simple diffusion B) Facilitated diffusion C) Na⁺-glucose cotransport (SGLT1) D) GLUT-2 transporter E) Pinocytosis
Answer: C) Na⁺-glucose cotransport (SGLT1) Glucose is primarily absorbed in the small intestine via Na⁺-glucose cotransporters (SGLT1) at the apical membrane of enterocytes. 2
Question 39
Which of the following best describes the function of intrinsic factor? A) Stimulation of gastric acid secretion B) Facilitation of iron absorption C) Binding of vitamin B12 for absorption D) Inhibition of gastrin release E) Stimulation of pepsinogen secretion
Answer: C) Binding of vitamin B12 for absorption Intrinsic factor, secreted by gastric parietal cells, binds vitamin B12 and facilitates its absorption in the terminal ileum. 2
Question 40
Which of the following is the primary stimulus for secretin release? A) Fatty acids in the duodenum B) Amino acids in the duodenum C) Acid in the duodenum D) Distension of the stomach E) Hypoglycemia
Answer: C) Acid in the duodenum Secretin is released from S cells in the duodenum in response to acidic chyme entering from the stomach. 2
Endocrine Physiology
Question 41
Which of the following best describes the mechanism of action of steroid hormones? A) Binding to membrane receptors and activating G proteins B) Binding to intracellular receptors and altering gene transcription C) Opening ion channels in the cell membrane D) Activating membrane-bound adenylyl cyclase E) Binding to extracellular receptors and triggering endocytosis
Answer: B) Binding to intracellular receptors and altering gene transcription Steroid hormones are lipophilic and pass through the cell membrane to bind to intracellular receptors, forming complexes that alter gene transcription. 2
Question 42
Which of the following hormones has the primary role in stimulating gluconeogenesis during fasting? A) Insulin B) Glucagon C) Epinephrine D) Growth hormone E) Thyroxine
Answer: B) Glucagon Glucagon is the primary hormone stimulating hepatic gluconeogenesis during fasting to maintain blood glucose levels. 2
Question 43
Which of the following best describes the action of parathyroid hormone (PTH) on the kidney? A) Decreased calcium reabsorption B) Increased phosphate reabsorption C) Decreased 1,25-dihydroxyvitamin D production D) Increased calcium reabsorption E) Decreased magnesium reabsorption
Answer: D) Increased calcium reabsorption PTH increases calcium reabsorption in the distal tubule and thick ascending limb of the loop of Henle. 2
Question 44
Which of the following best describes the effect of thyroid hormone on metabolic rate? A) No effect B) Decrease C) Increase D) Initial increase followed by decrease E) Initial decrease followed by increase
Answer: C) Increase Thyroid hormone increases basal metabolic rate by stimulating Na⁺-K⁺ ATPase activity and mitochondrial oxidative phosphorylation. 2
Question 45
Which of the following is the primary stimulus for aldosterone secretion? A) Hyponatremia B) Hyperkalemia C) Angiotensin II D) Atrial natriuretic peptide E) Dopamine
Answer: C) Angiotensin II Angiotensin II is the primary physiological stimulus for aldosterone secretion from the zona glomerulosa of the adrenal cortex. 2
Question 46
Which of the following best describes the action of insulin on skeletal muscle? A) Decreased glucose uptake B) Increased protein breakdown C) Increased glycogen synthesis D) Decreased amino acid uptake E) Increased gluconeogenesis
Answer: C) Increased glycogen synthesis Insulin stimulates glycogen synthesis in skeletal muscle by activating glycogen synthase. 2
Question 47
Which of the following hormones is primarily responsible for initiating lactation after childbirth? A) Estrogen B) Progesterone C) Prolactin D) Oxytocin E) Human placental lactogen
Answer: C) Prolactin Prolactin stimulates milk production in the mammary glands after childbirth. 2
Question 48
Which of the following best describes the action of antidiuretic hormone (ADH) on the kidney? A) Increased sodium reabsorption in the proximal tubule B) Decreased water permeability in the collecting duct C) Increased water permeability in the collecting duct D) Increased potassium secretion in the distal tubule E) Decreased urea reabsorption in the medullary collecting duct
Answer: C) Increased water permeability in the collecting duct ADH increases water permeability in the collecting duct by stimulating insertion of aquaporin-2 water channels into the apical membrane. 2
Question 49
Which of the following best describes the primary action of growth hormone? A) Direct stimulation of bone growth B) Stimulation of insulin-like growth factor-1 (IGF-1) production C) Inhibition of protein synthesis D) Direct stimulation of glucose uptake by tissues E) Inhibition of lipolysis
Answer: B) Stimulation of insulin-like growth factor-1 (IGF-1) production Growth hormone stimulates production of IGF-1, primarily in the liver, which mediates many of growth hormone's growth-promoting effects. 2
Question 50
Which of the following best describes the effect of cortisol on blood glucose? A) No effect B) Decrease C) Increase D) Initial increase followed by decrease E) Initial decrease followed by increase
Answer: C) Increase Cortisol increases blood glucose by stimulating gluconeogenesis and inhibiting glucose uptake and utilization in peripheral tissues. 2
Neurophysiology
Question 51
Which of the following neurotransmitters is the primary inhibitory neurotransmitter in the central nervous system? A) Glutamate B) Acetylcholine C) Dopamine D) GABA E) Norepinephrine
Answer: D) GABA Gamma-aminobutyric acid (GABA) is the primary inhibitory neurotransmitter in the central nervous system. 2
Question 52
Which of the following best describes the function of the cerebellum? A) Initiation of voluntary movement B) Processing of visual information C) Coordination of movement and motor learning D) Regulation of autonomic functions E) Processing of auditory information
Answer: C) Coordination of movement and motor learning The cerebellum is primarily responsible for coordination of movement, posture, and motor learning. 2
Question 53
Which of the following best describes the Goldman-Hodgkin-Katz equation? A) Describes the relationship between membrane potential and ion concentrations B) Calculates the velocity of nerve conduction C) Determines the threshold potential for action potential generation D) Measures the refractory period of neurons E) Quantifies synaptic strength
Answer: A) Describes the relationship between membrane potential and ion concentrations The Goldman-Hodgkin-Katz equation describes how membrane potential depends on ion concentrations and membrane permeabilities. 2
Question 54
Which of the following is the primary neurotransmitter at the neuromuscular junction? A) Norepinephrine B) Serotonin C) Acetylcholine D) Dopamine E) Glutamate
Answer: C) Acetylcholine Acetylcholine is the neurotransmitter released by motor neurons at the neuromuscular junction. 2
Question 55
Which of the following best describes the function of the basal ganglia? A) Initiation and planning of movement B) Primary processing of sensory information C) Regulation of body temperature D) Processing of language E) Storage of declarative memory
Answer: A) Initiation and planning of movement The basal ganglia are primarily involved in the initiation and planning of movement and motor learning. 2
Question 56
Which of the following best describes saltatory conduction? A) Continuous propagation of action potentials along unmyelinated axons B) Discontinuous jumping of action potentials between nodes of Ranvier C) Retrograde transmission of signals from dendrites to axons D) Transmission of graded potentials across synapses E) Simultaneous activation of all ion channels along an axon
Answer: B) Discontinuous jumping of action potentials between nodes of Ranvier Saltatory conduction refers to the jumping of action potentials from one node of Ranvier to the next in myelinated axons. 2
Question 57
Which of the following is the primary mechanism for long-term potentiation in the hippocampus? A) Decreased presynaptic glutamate release B) Increased NMDA receptor activation and calcium influx C) Decreased postsynaptic receptor density D) Increased GABA release E) Decreased calcium influx
Answer: B) Increased NMDA receptor activation and calcium influx Long-term potentiation in the hippocampus primarily involves NMDA receptor activation, calcium influx, and subsequent strengthening of synaptic connections. 2
Question 58
Which of the following best describes the function of the dorsal column-medial lemniscus pathway? A) Transmission of pain and temperature sensation B) Transmission of fine touch and proprioception C) Control of voluntary movement D) Regulation of autonomic functions E) Processing of visual information
Answer: B) Transmission of fine touch and proprioception The dorsal column-medial lemniscus pathway transmits fine touch, vibration, and proprioceptive information from the periphery to the cerebral cortex. 2
Question 59
Which of the following best describes the function of the hypothalamus? A) Processing of auditory information B) Coordination of movement C) Regulation of homeostasis and endocrine function D) Storage of procedural memory E) Processing of visual information
Answer: C) Regulation of homeostasis and endocrine function The hypothalamus plays a central role in regulating homeostasis and controlling the endocrine system through its connections with the pituitary gland. 2
Question 60
Which of the following best describes the all-or-none principle of action potentials? A) Either all neurons in a circuit fire or none do B) Either a stimulus triggers a full action potential or none at all C) Either all neurotransmitter is released or none is released D) Either all ion channels open or all remain closed E) Either all receptors are activated or none are activated
Answer: B) Either a stimulus triggers a full action potential or none at all The all-or-none principle states that if a stimulus reaches threshold, a full action potential occurs; if not, no action potential occurs. 2
Muscle Physiology
Question 61
Which of the following best describes the sliding filament theory of muscle contraction? A) Shortening of actin filaments B) Shortening of myosin filaments C) Sliding of actin and myosin filaments past each other D) Compression of Z discs E) Elongation of the sarcomere
Answer: C) Sliding of actin and myosin filaments past each other The sliding filament theory states that muscle contraction occurs when actin and myosin filaments slide past each other without changing their lengths. 2
Question 62
Which of the following is the immediate source of energy for muscle contraction? A) Glucose B) Glycogen C) ATP D) Creatine E) Fatty acids
Answer: C) ATP ATP hydrolysis by myosin ATPase provides the immediate energy for muscle contraction. 2
Question 63
Which of the following best describes the role of calcium in skeletal muscle contraction? A) Binding to myosin to expose actin binding sites B) Binding to troponin C to expose myosin binding sites on actin C) Direct activation of myosin ATPase D) Facilitation of ATP synthesis E) Inhibition of tropomyosin
Answer: B) Binding to troponin C to expose myosin binding sites on actin Calcium binds to troponin C, causing a conformational change that moves tropomyosin and exposes myosin binding sites on actin. 2
Question 64
Which of the following best describes the length-tension relationship in skeletal muscle? A) Maximum tension occurs at minimum sarcomere length B) Maximum tension occurs at maximum sarcomere length C) Maximum tension occurs at optimal overlap of thick and thin filaments D) Tension is constant regardless of sarcomere length E) Tension increases linearly with sarcomere length
Answer: C) Maximum tension occurs at optimal overlap of thick and thin filaments Maximum tension is generated when there is optimal overlap between actin and myosin filaments, allowing maximum cross-bridge formation. 2
Question 65
Which of the following best describes the function of the sarcoplasmic reticulum in skeletal muscle? A) ATP synthesis B) Calcium storage and release C) Myosin synthesis D) Glycogen storage E) Acetylcholine synthesis
Answer: B) Calcium storage and release The sarcoplasmic reticulum stores calcium and releases it upon stimulation, triggering muscle contraction. 2
Question 66
Which of the following best describes the difference between fast-twitch and slow-twitch muscle fibers? A) Fast-twitch fibers have more mitochondria than slow-twitch fibers B) Slow-twitch fibers have higher myosin ATPase activity than fast-twitch fibers C) Fast-twitch fibers fatigue more rapidly than slow-twitch fibers D) Slow-twitch fibers have less myoglobin than fast-twitch fibers E) Fast-twitch fibers rely primarily on oxidative phosphorylation
Answer: C) Fast-twitch fibers fatigue more rapidly than slow-twitch fibers Fast-twitch fibers have higher contraction velocity but fatigue more rapidly than slow-twitch fibers due to lower oxidative capacity. 2
Question 67
Which of the following best describes the function of creatine phosphate in skeletal muscle? A) Direct energy source for contraction B) Storage form of glucose C) Rapid regeneration of ATP D) Transport of calcium into sarcoplasmic reticulum E) Activation of myosin ATPase
Answer: C) Rapid regeneration of ATP Creatine phosphate serves as a rapid energy reserve to regenerate ATP during intense muscle activity. 2
Question 68
Which of the following best describes the mechanism of smooth muscle contraction? A) Calcium binding to troponin C B) Calcium-calmodulin activation of myosin light chain kinase C) Direct binding of calcium to myosin D) Calcium-induced calcium release from T-tubules E) ATP binding directly to actin
Answer: B) Calcium-calmodulin activation of myosin light chain kinase In smooth muscle, calcium binds to calmodulin, activating myosin light chain kinase, which phosphorylates myosin to enable contraction. 2
Question 69
Which of the following best describes the role of T-tubules in skeletal muscle? A) Storage of calcium B) Synthesis of ATP C) Propagation of action potentials into the muscle fiber interior D) Storage of glycogen E) Synthesis of acetylcholine
Answer: C) Propagation of action potentials into the muscle fiber interior T-tubules conduct action potentials from the surface membrane into the interior of the muscle fiber to ensure synchronized contraction. 2
Question 70
Which of the following best describes the primary energy source during prolonged moderate exercise? A) Creatine phosphate B) Anaerobic glycolysis C) Fatty acid oxidation D) Protein catabolism E) Stored ATP
Answer: C) Fatty acid oxidation During prolonged moderate exercise, fatty acid oxidation becomes the predominant energy source. 2
Blood and Immunology
Question 71
Which of the following best describes the function of erythropoietin? A) Stimulation of platelet production B) Stimulation of leukocyte production C) Stimulation of erythrocyte production D) Inhibition of iron absorption E) Stimulation of hemoglobin breakdown
Answer: C) Stimulation of erythrocyte production Erythropoietin stimulates erythrocyte (red blood cell) production in the bone marrow in response to hypoxia. 2
Question 72
Which of the following best describes the function of platelets? A) Oxygen transport B) Carbon dioxide transport C) Phagocytosis D) Hemostasis E) Antibody production
Answer: D) Hemostasis Platelets play a crucial role in hemostasis by adhering to damaged endothelium and forming platelet plugs. 2
Question 73
Which of the following cells is primarily responsible for antibody production? A) T lymphocytes B) Plasma cells C) Macrophages D) Neutrophils E) Natural killer cells
Answer: B) Plasma cells Plasma cells, which differentiate from activated B lymphocytes, are primarily responsible for antibody production. 2
Question 74
Which of the following best describes the function of the complement system? A) Antibody production B) Antigen presentation C) Enhancement of phagocytosis and cell lysis D) Suppression of inflammation E) Production of memory cells
Answer: C) Enhancement of phagocytosis and cell lysis The complement system enhances phagocytosis through opsonization and can directly lyse cells through the membrane attack complex. 2
Question 75
Which of the following best describes the primary function of major histocompatibility complex (MHC) class I molecules? A) Presentation of extracellular antigens to CD4+ T cells B) Presentation of intracellular antigens to CD8+ T cells C) Direct killing of virus-infected cells D) Production of antibodies E) Activation of complement
Answer: B) Presentation of intracellular antigens to CD8+ T cells MHC class I molecules present peptides derived from intracellular antigens to CD8+ T cells. 2
Question 76
Which of the following best describes the primary function of CD4+ T cells? A) Direct killing of virus-infected cells B) Antibody production C) Phagocytosis D) Helper function for B cells and other immune cells E) Suppression of immune responses
Answer: D) Helper function for B cells and other immune cells CD4+ T cells (helper T cells) provide essential signals for activation and differentiation of B cells and other immune cells. 2
Question 77
Which of the following best describes the mechanism of action of heparin? A) Inhibition of vitamin K-dependent clotting factors B) Activation of antithrombin III C) Direct inhibition of thrombin D) Inhibition of platelet aggregation E) Activation of tissue plasminogen activator
Answer: B) Activation of antithrombin III Heparin binds to and activates antithrombin III, which then inhibits several coagulation factors, particularly thrombin and factor Xa. 2
Question 78
Which of the following best describes the function of natural killer (NK) cells? A) Antibody production B) Antigen presentation C) Direct killing of virus-infected and tumor cells D) Phagocytosis of bacteria E) Production of inflammatory mediators
Answer: C) Direct killing of virus-infected and tumor cells Natural killer cells directly recognize and kill virus-infected cells and tumor cells without prior sensitization. 2
Question 79
Which of the following is the primary stimulus for thrombopoietin production? A) Low platelet count B) High platelet count C) Low red blood cell count D) High red blood cell count E) Low white blood cell count
Answer: A) Low platelet count Thrombopoietin production is inversely related to platelet mass; low platelet counts stimulate increased thrombopoietin production. 2
Question 80
Which of the following best describes the function of dendritic cells? A) Antibody production B) Direct killing of pathogens C) Antigen presentation to T cells D) Production of erythrocytes E) Blood clotting
Answer: C) Antigen presentation to T cells Dendritic cells are professional antigen-presenting cells that capture antigens in peripheral tissues and present them to T cells in lymphoid organs. 2
Reproductive Physiology
Question 81
Which of the following hormones is primarily responsible for maintaining the corpus luteum during early pregnancy? A) Estrogen B) Progesterone C) Human chorionic gonadotropin (hCG) D) Follicle-stimulating hormone (FSH) E) Luteinizing hormone (LH)
Answer: C) Human chorionic gonadotropin (hCG) hCG produced by the developing placenta maintains the corpus luteum during early pregnancy until the placenta can produce sufficient progesterone. 2
Question 82
Which of the following best describes the function of inhibin in males? A) Stimulation of spermatogenesis B) Inhibition of FSH secretion C) Stimulation of testosterone production D) Inhibition of LH secretion E) Stimulation of secondary sexual characteristics
Answer: B) Inhibition of FSH secretion Inhibin produced by Sertoli cells provides negative feedback to the pituitary to inhibit FSH secretion. 2
Question 83
Which of the following best describes the primary function of the Sertoli cells? A) Production of testosterone B) Production of inhibin C) Support and nourishment of developing sperm D) Production of seminal fluid E) Contraction during ejaculation
Answer: C) Support and nourishment of developing sperm Sertoli cells provide structural and nutritional support for developing spermatocytes and spermatids. 2
Question 84
Which of the following hormones is primarily responsible for the LH surge that triggers ovulation? A) Progesterone B) Inhibin C) Estrogen D) FSH E) Prolactin
Answer: C) Estrogen High levels of estrogen exert positive feedback on the hypothalamus and pituitary, triggering the LH surge that induces ovulation. 2
Question 85
Which of the following best describes the function of the placenta in hormone production during pregnancy? A) Production of hCG only B) Production of estrogen and progesterone only C) Production of hCG, estrogen, progesterone, and other hormones D) No hormone production E) Production of oxytocin only
Answer: C) Production of hCG, estrogen, progesterone, and other hormones The placenta produces multiple hormones including hCG, estrogen, progesterone, human placental lactogen, and others. 2
Question 86
Which of the following best describes the primary function of testosterone in males? A) Stimulation of spermatogenesis only B) Development of secondary sexual characteristics only C) Both stimulation of spermatogenesis and development of secondary sexual characteristics D) Inhibition of FSH secretion E) Stimulation of LH secretion
Answer: C) Both stimulation of spermatogenesis and development of secondary sexual characteristics Testosterone stimulates spermatogenesis and is responsible for the development and maintenance of male secondary sexual characteristics. 2
Question 87
Which of the following best describes the function of the zona pellucida? A) Protection of the developing embryo after implantation B) Barrier to polyspermy C) Source of nutrition for the developing embryo D) Stimulation of uterine contractions E) Facilitation of implantation
Answer: B) Barrier to polyspermy The zona pellucida undergoes changes after fertilization that prevent additional sperm from entering the oocyte (block to polyspermy). 2
Question 88
Which of the following best describes the primary function of oxytocin during labor? A) Stimulation of uterine contractions B) Dilation of the cervix C) Stimulation of prostaglandin production D) Inhibition of premature labor E) Stimulation of fetal lung maturation
Answer: A) Stimulation of uterine contractions Oxytocin stimulates powerful uterine contractions during labor and delivery. 2
Question 89
Which of the following best describes the function of antimüllerian hormone (AMH) in males? A) Stimulation of testosterone production B) Development of male external genitalia C) Regression of müllerian ducts D) Stimulation of spermatogenesis E) Development of male secondary sexual characteristics
Answer: C) Regression of müllerian ducts AMH produced by Sertoli cells causes regression of the müllerian ducts, which would otherwise develop into female reproductive structures. 2
Question 90
Which of the following best describes the primary function of the corpus luteum? A) Production of estrogen only B) Production of progesterone only C) Production of both estrogen and progesterone D) Production of inhibin only E) Production of hCG
Answer: C) Production of both estrogen and progesterone The corpus luteum produces both estrogen and progesterone during the luteal phase of the menstrual cycle and early pregnancy. 2
Integrative Physiology
Question 91
Which of the following best describes the primary response to acute hemorrhage? A) Decreased heart rate B) Decreased peripheral vascular resistance C) Increased renin-angiotensin-aldosterone system activation D) Decreased antidiuretic hormone release E) Increased venous capacitance
Answer: C) Increased renin-angiotensin-aldosterone system activation Acute hemorrhage triggers increased renin-angiotensin-aldosterone system activation to restore blood volume and pressure. 2
Question 92
Which of the following best describes the primary ventilatory response to metabolic acidosis? A) Decreased respiratory rate B) Increased respiratory rate and depth C) No change in ventilation D) Periodic breathing E) Decreased respiratory depth
Answer: B) Increased respiratory rate and depth Metabolic acidosis stimulates central and peripheral chemoreceptors, leading to increased respiratory rate and depth to eliminate CO₂ and raise pH. 2
Question 93
Which of the following best describes the primary renal response to metabolic alkalosis? A) Increased bicarbonate excretion B) Decreased hydrogen ion excretion C) Increased potassium reabsorption D) Decreased sodium reabsorption E) Increased phosphate excretion
Answer: A) Increased bicarbonate excretion The primary renal response to metabolic alkalosis is increased bicarbonate excretion to normalize pH. 2
Question 94
Which of the following best describes the primary cardiovascular response to exercise? A) Decreased cardiac output B) Increased peripheral vascular resistance C) Decreased stroke volume D) Increased heart rate and cardiac output E) Decreased venous return
Answer: D) Increased heart rate and cardiac output Exercise increases sympathetic activity and decreases parasympathetic activity, leading to increased heart rate and cardiac output. 2
Question 95
Which of the following best describes the primary response to high altitude exposure? A) Decreased ventilation B) Decreased erythropoietin production C) Increased 2,3-diphosphoglycerate (2,3-DPG) in erythrocytes D) Decreased pulmonary vasoconstriction E) Decreased hemoglobin affinity for oxygen
Answer: C) Increased 2,3-diphosphoglycerate (2,3-DPG) in erythrocytes High altitude exposure leads to increased 2,3-DPG in erythrocytes, which shifts the oxygen-hemoglobin dissociation curve to the right, facilitating oxygen unloading to tissues. 2
Question 96
Which of the following best describes the primary response to dehydration? A) Decreased ADH secretion B) Decreased thirst C) Increased urine output D) Increased ADH secretion E) Decreased aldosterone secretion
Answer: D) Increased ADH secretion Dehydration increases plasma osmolality, stimulating ADH secretion to increase water reabsorption in the collecting ducts. 2
Question 97
Which of the following best describes the primary response to a meal high in carbohydrates? A) Decreased insulin secretion B) Increased glucagon secretion C) Increased insulin secretion D) Decreased GLP-1 secretion E) Increased cortisol secretion
Answer: C) Increased insulin secretion A high-carbohydrate meal increases blood glucose, stimulating insulin secretion from pancreatic beta cells. 2
Question 98
Which of the following best describes the primary response to severe hypoxemia? A) Decreased cerebral blood flow B) Increased cerebral blood flow C) No change in cerebral blood flow D) Decreased pulmonary blood flow E) Increased coronary blood flow only
Answer: B) Increased cerebral blood flow Severe hypoxemia causes cerebral vasodilation, increasing cerebral blood flow to maintain oxygen delivery to the brain. 2
Question 99
Which of the following best describes the primary response to severe acidosis? A) Increased cardiac contractility B) Decreased cardiac contractility C) No effect on cardiac contractility D) Increased peripheral vascular resistance only E) Decreased heart rate only
Answer: B) Decreased cardiac contractility Severe acidosis decreases cardiac contractility by affecting calcium binding to troponin C and other cellular mechanisms. 2
Question 100
Which of the following best describes the primary response to severe hyperkalemia? A) Cardiac excitability B) Decreased cardiac excitability followed by increased excitability C) No effect on cardiac excitability D) Initial increased excitability followed by decreased excitability E) Effects limited to skeletal muscle
Answer: D) Initial increased excitability followed by decreased excitability Severe hyperkalemia initially increases cardiac excitability by partially depolarizing cell membranes, but eventually leads to decreased excitability and conduction abnormalities as potassium levels continue to rise. 1