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NPLEX II practice questions

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Question 1Part I – Biomedical Science

A patient with a lesion of the left optic nerve before the optic chiasm presents with which visual field defect?

  1. Bitemporal hemianopia
  2. Right homonymous hemianopia
  3. Total blindness in the right eye
  4. Total blindness in the left eye Correct answer.

Explanation

A lesion anterior to the chiasm interrupts axons from the ipsilateral retina only, so the entire left eye loses vision. The right eye is unaffected because its fibers travel in the right optic nerve. Chiasmal and retrochiasmal lesions produce the other patterns.

Question 2Part I – Biomedical Science

Deficiency of which vitamin impairs the gamma-carboxylation of glutamate residues in clotting factors II, VII, IX, and X?

  1. Folate
  2. Vitamin C
  3. Vitamin K Correct answer.
  4. Thiamine

Explanation

Vitamin K is the cofactor for the gamma-glutamyl carboxylase that converts glutamate to gamma-carboxyglutamate on factors II, VII, IX, and X. This modification is required for calcium-dependent binding to phospholipid membranes. Deficiency prolongs prothrombin time.

Question 3Part I – Biomedical Science

Which segment of the nephron is the primary site of regulated water reabsorption under the control of antidiuretic hormone?

  1. Glomerular capillary
  2. Thick ascending limb of the loop of Henle
  3. Collecting duct Correct answer.
  4. Proximal convoluted tubule

Explanation

Antidiuretic hormone inserts aquaporin-2 channels into the apical membrane of collecting duct principal cells, allowing regulated water reabsorption. The proximal tubule reabsorbs most water but does so constitutively and is not the ADH-regulated site. The thick ascending limb is water-impermeable.

Question 4Part I – Biomedical Science

A patient develops muscle weakness, hypertension, and metabolic alkalosis with hypokalemia. Which adrenal abnormality best explains this presentation?

  1. Primary hyperaldosteronism Correct answer.
  2. Addison disease
  3. Cushing disease
  4. Pheochromocytoma

Explanation

Excess aldosterone increases sodium reabsorption and potassium secretion in the distal nephron, producing hypertension, hypokalemia, and metabolic alkalosis. Aldosterone also causes mild sodium retention and volume expansion. The other disorders have different electrolyte and hemodynamic profiles.

Question 5Part I – Biomedical Science

Which immunoglobulin isotype is the first produced in a primary humoral response and is most efficient at activating the classical complement pathway?

  1. IgG
  2. IgA
  3. IgM Correct answer.
  4. IgE

Explanation

IgM is the first antibody isotype produced in a primary response and, as a pentamer, is highly efficient at binding C1q and activating the classical complement cascade. IgG also activates complement but is less efficient per molecule. IgA and IgE do not efficiently activate the classical pathway.

Question 6Part I – Biomedical Science

A tumor in the region of the sella turcica compresses the optic chiasm. Which visual field defect is most likely?

  1. Binasal hemianopia
  2. Total monocular blindness
  3. Bitemporal hemianopia Correct answer.
  4. Left homonymous hemianopia

Explanation

The optic chiasm contains crossing fibers from the nasal retina of each eye, which subserve the temporal visual fields. Compression of these decussating fibers produces loss of both temporal fields, called bitemporal hemianopia. This pattern is characteristic of pituitary adenomas and other sellar masses.

Question 7Part I – Biomedical Science

Which enzyme catalyzes the rate-limiting step of cholesterol biosynthesis?

  1. Carnitine palmitoyltransferase I
  2. Lipoprotein lipase
  3. Acetyl-CoA carboxylase
  4. HMG-CoA reductase Correct answer.

Explanation

HMG-CoA reductase converts HMG-CoA to mevalonate and is the rate-limiting enzyme of cholesterol synthesis. It is the target of statin drugs. The other enzymes participate in fatty acid synthesis, lipid hydrolysis, or fatty acid transport.

Question 8Part I – Biomedical Science

A patient with type 1 diabetes develops ketoacidosis. Which metabolic change most directly drives hepatic ketone body production?

  1. Increased insulin-mediated fatty acid synthesis
  2. Increased mitochondrial fatty acid oxidation with high acetyl-CoA Correct answer.
  3. Decreased glucagon-stimulated gluconeogenesis
  4. Increased pyruvate dehydrogenase activity

Explanation

Insulin deficiency and glucagon excess promote lipolysis and hepatic fatty acid oxidation, flooding the liver with acetyl-CoA. When acetyl-CoA exceeds the capacity of the citric acid cycle, it is converted to ketone bodies. This process is enhanced by low oxaloacetate availability.

Question 9Part I – Biomedical Science

Which structure is most directly responsible for the resting membrane potential of a typical neuron?

  1. Sodium-potassium ATPase acting alone
  2. Voltage-gated sodium channels
  3. Potassium leak conductance with the sodium-potassium ATPase Correct answer.
  4. Ligand-gated chloride channels

Explanation

Resting membrane potential is set primarily by potassium leak conductance, which allows potassium to approach its equilibrium potential, with the sodium-potassium ATPase maintaining the ionic gradients. Voltage-gated channels open during action potentials rather than at rest. Ligand-gated channels produce synaptic potentials.

Question 10Part I – Biomedical Science

A patient has a lesion of the right cranial nerve XII. Which finding is expected?

  1. Loss of taste on the anterior tongue
  2. Deviation of the tongue to the right on protrusion Correct answer.
  3. Deviation of the tongue to the left on protrusion
  4. Loss of the gag reflex

Explanation

The genioglossus muscle, innervated by cranial nerve XII, protrudes the tongue. When the right nerve is weak, the unopposed left genioglossus pushes the tongue toward the weak right side. Taste and the gag reflex are mediated by other cranial nerves.

Question 11Part I – Biomedical Science

Which hormone is secreted by the zona glomerulosa of the adrenal cortex?

  1. Dehydroepiandrosterone
  2. Epinephrine
  3. Cortisol
  4. Aldosterone Correct answer.

Explanation

The zona glomerulosa produces aldosterone under the regulation of angiotensin II and potassium. Cortisol comes from the zona fasciculata, and adrenal androgens come from the zona reticularis. Epinephrine is produced by the adrenal medulla.

Question 12Part I – Biomedical Science

Which of the following best describes the Frank-Starling relationship in the heart?

  1. Increased end-diastolic volume increases stroke volume within physiologic limits Correct answer.
  2. Increased heart rate always increases stroke volume
  3. Increased afterload increases stroke volume
  4. Decreased venous return increases stroke volume

Explanation

The Frank-Starling law states that increased ventricular filling stretches cardiac muscle and increases contractile force, raising stroke volume within physiologic limits. Excessive filling eventually produces overstretch and reduced efficiency. Afterload and heart rate changes have different effects.

Question 13Part I – Biomedical Science

A patient with chronic obstructive pulmonary disease has an elevated bicarbonate level with a normal pH. What is the most likely acid-base interpretation?

  1. Uncompensated metabolic alkalosis
  2. Uncompensated respiratory alkalosis
  3. Compensated metabolic acidosis
  4. Compensated respiratory acidosis Correct answer.

Explanation

Chronic carbon dioxide retention from hypoventilation raises carbonic acid, and the kidneys compensate by retaining bicarbonate. When compensation is complete, pH returns toward normal despite elevated carbon dioxide and bicarbonate. A normal pH with high bicarbonate and high carbon dioxide indicates compensated respiratory acidosis.

Question 14Part I – Biomedical Science

Which of the following is the principal function of the sarcoplasmic reticulum in skeletal muscle?

  1. Transmission of action potentials from the motor neuron
  2. Storage and release of calcium ions Correct answer.
  3. Production of ATP through oxidative phosphorylation
  4. Synthesis of actin and myosin filaments

Explanation

The sarcoplasmic reticulum stores calcium and releases it through ryanodine receptors during excitation-contraction coupling. Calcium binds troponin and permits crossbridge cycling. Contractile proteins are synthesized in the cytosol, and ATP production occurs in mitochondria.

Question 15Part I – Biomedical Science

A patient with a mutation causing loss of function of the cystic fibrosis transmembrane conductance regulator develops viscous secretions. Which ion transport defect underlies this?

  1. Increased chloride secretion and decreased sodium reabsorption
  2. Increased chloride reabsorption and increased sodium reabsorption
  3. Decreased chloride secretion and increased sodium reabsorption Correct answer.
  4. Decreased potassium secretion and decreased sodium reabsorption

Explanation

CFTR normally secretes chloride and inhibits the epithelial sodium channel. Loss of CFTR function reduces chloride secretion and, through loss of inhibition, increases sodium and water reabsorption, thickening secretions. This produces the viscous mucus characteristic of cystic fibrosis.

Question 16Part I – Biomedical Science

Which neurotransmitter is released at the neuromuscular junction to activate skeletal muscle?

  1. Gamma-aminobutyric acid
  2. Dopamine
  3. Norepinephrine
  4. Acetylcholine Correct answer.

Explanation

Motor neurons release acetylcholine at the neuromuscular junction, where it binds nicotinic receptors on the motor end plate. This depolarizes the sarcolemma and initiates contraction. The other neurotransmitters act elsewhere in the nervous system.

Question 17Part I – Biomedical Science

A tumor compressing the posterior pituitary most likely produces which hormonal abnormality?

  1. Graves disease
  2. Central diabetes insipidus Correct answer.
  3. Primary hyperaldosteronism
  4. Syndrome of inappropriate antidiuretic hormone secretion

Explanation

The posterior pituitary stores and releases antidiuretic hormone and oxytocin. Compression or damage reduces antidiuretic hormone release, causing central diabetes insipidus with polyuria and dilute urine. The other disorders arise from different glands.

Question 18Part I – Biomedical Science

Which of the following best explains why a patient with severe liver disease develops edema?

  1. Decreased plasma albumin with reduced oncotic pressure Correct answer.
  2. Increased lymphatic return
  3. Increased plasma oncotic pressure
  4. Increased arterial blood pressure alone

Explanation

The liver synthesizes albumin, which maintains plasma oncotic pressure. In severe liver disease, hypoalbuminemia lowers oncotic pressure and favors fluid movement into the interstitium, producing edema and ascites. Portal hypertension contributes in ascites but not through oncotic pressure.

Question 19Part I – Biomedical Science

Which of the following is the primary site of iron absorption in the gastrointestinal tract?

  1. Ileum
  2. Colon
  3. Stomach
  4. Duodenum Correct answer.

Explanation

Iron is absorbed primarily in the duodenum and proximal jejunum, where enterocytes take up heme and non-heme iron. Absorption is regulated by hepcidin and body iron stores. The ileum absorbs vitamin B12 and bile acids, while the colon absorbs water and electrolytes.

Question 20Part I – Biomedical Science

A patient with a mutation in the LDL receptor has markedly elevated LDL cholesterol. Which mechanism best explains this finding?

  1. Increased conversion of LDL to bile acids
  2. Increased biliary excretion of cholesterol
  3. Impaired receptor-mediated clearance of LDL Correct answer.
  4. Increased hepatic uptake of LDL

Explanation

LDL receptors on hepatocytes mediate clearance of LDL from plasma. Loss of receptor function reduces uptake and prolongs the half-life of LDL, raising plasma levels in familial hypercholesterolemia. Biliary excretion and bile acid conversion are separate pathways.

Question 21Part I – Biomedical Science

Which of the following describes the primary role of surfactant in the alveoli?

  1. Increasing surface tension to prevent overexpansion
  2. Increasing airway resistance
  3. Reducing oxygen diffusion distance
  4. Reducing surface tension to prevent alveolar collapse Correct answer.

Explanation

Surfactant, produced by type II pneumocytes, reduces alveolar surface tension according to Laplace's law, preventing small alveoli from collapsing at end-expiration. This stabilizes alveoli of differing sizes. It does not change diffusion distance or airway resistance.

Question 22Part I – Biomedical Science

A patient with a cerebellar lesion is most likely to demonstrate which finding?

  1. Loss of pain and temperature sensation
  2. Resting tremor
  3. Intention tremor Correct answer.
  4. Spastic hemiparesis

Explanation

The cerebellum coordinates voluntary movement and smooths motor output. Its lesions produce intention tremor, dysmetria, and ataxia, which worsen as the limb approaches a target. Resting tremor, spasticity, and sensory loss localize elsewhere.

Question 23Part I – Biomedical Science

Which of the following best explains why a patient with a severe deficiency of pyruvate dehydrogenase develops lactic acidosis?

  1. Impaired conversion of pyruvate to acetyl-CoA with pyruvate shunting to lactate Correct answer.
  2. Increased fatty acid oxidation with reduced pyruvate production
  3. Increased conversion of pyruvate to acetyl-CoA
  4. Enhanced gluconeogenesis from lactate

Explanation

Pyruvate dehydrogenase converts pyruvate to acetyl-CoA for entry into the citric acid cycle. When this enzyme is deficient, pyruvate accumulates and is reduced to lactate by lactate dehydrogenase, producing lactic acidosis. Enhanced gluconeogenesis would consume lactate rather than accumulate it.

Question 24Part I – Biomedical Science

Which of the following describes the primary effect of parathyroid hormone on the kidney?

  1. Decreased water reabsorption and increased urea reabsorption
  2. Decreased calcium reabsorption and increased phosphate reabsorption
  3. Increased sodium reabsorption and increased potassium secretion
  4. Increased calcium reabsorption and decreased phosphate reabsorption Correct answer.

Explanation

Parathyroid hormone increases renal calcium reabsorption in the distal tubule and inhibits phosphate reabsorption in the proximal tubule, producing hypercalcemia and hypophosphatemia. It also stimulates 1-alpha-hydroxylase to increase calcitriol production. The other renal effects are not mediated by parathyroid hormone.

Question 25Part I – Biomedical Science

A patient has a lesion of the right optic tract. Which visual field defect is expected?

  1. Left homonymous hemianopia Correct answer.
  2. Total blindness in the right eye
  3. Right homonymous hemianopia
  4. Bitemporal hemianopia

Explanation

The right optic tract carries fibers from the temporal retina of the right eye and the nasal retina of the left eye, which subserve the left visual field. A lesion therefore produces a left homonymous hemianopia. Prechiasmal and chiasmal lesions produce different patterns.

Question 26Part I – Biomedical Science

A 58-year-old man has a fasting serum calcium of 8.2 mg/dL and an albumin of 2.5 g/dL. Which adjusted calcium value is most consistent with these results?

  1. 7.0 mg/dL
  2. 8.2 mg/dL
  3. 9.4 mg/dL Correct answer.
  4. 10.6 mg/dL

Explanation

Corrected calcium adds 0.8 mg/dL to measured calcium for every 1 g/dL that albumin falls below 4 g/dL. Here albumin is 1.5 g/dL low, so 1.2 mg/dL is added to 8.2, giving 9.4 mg/dL. Using the measured value without correction underestimates the physiologically active calcium.

Question 27Part I – Biomedical Science

Which laboratory pattern is most characteristic of an anion-gap metabolic acidosis?

  1. High pH, high bicarbonate, elevated anion gap
  2. Low pH, low bicarbonate, elevated anion gap Correct answer.
  3. Low pH, low bicarbonate, normal anion gap with elevated chloride
  4. High pH, low bicarbonate, normal anion gap

Explanation

An anion-gap acidosis reflects accumulation of unmeasured anions such as lactate or ketones, producing a low pH and low bicarbonate with a widened gap. The gap is calculated as sodium minus the sum of chloride and bicarbonate. A normal-gap acidosis instead shows a rise in chloride as bicarbonate falls.

Question 28Part I – Biomedical Science

A 24-year-old woman has fatigue, weight gain, cold intolerance, and a TSH of 14 mIU/L with a low free T4. Which site of dysfunction best explains these findings?

  1. Hypothalamus
  2. Thyroid gland Correct answer.
  3. Adrenal cortex
  4. Pituitary gland

Explanation

A high TSH with a low free T4 indicates primary hypothyroidism, in which the thyroid gland fails to produce hormone and the pituitary responds with elevated TSH. The clinical features of fatigue, weight gain, and cold intolerance fit hypothyroidism. A pituitary or hypothalamic cause would produce a low or inappropriately normal TSH.

Question 29Part I – Biomedical Science

Which renal structure is primarily responsible for creating the medullary osmotic gradient that permits concentrated urine formation?

  1. Macula densa
  2. Loop of Henle Correct answer.
  3. Proximal convoluted tubule
  4. Glomerulus

Explanation

The loop of Henle operates as a countercurrent multiplier, with active salt reabsorption in the thick ascending limb and water permeability in the descending limb generating a hypertonic medullary interstitium. This gradient allows the collecting duct to reabsorb water under ADH influence. The other structures listed do not generate the gradient.

Question 30Part I – Biomedical Science

A 46-year-old man has a resting tremor, bradykinesia, and rigidity. Loss of which neuronal population best explains these findings?

  1. Ventral horn motor neurons
  2. Substantia nigra pars compacta dopaminergic neurons Correct answer.
  3. Cerebellar Purkinje cells
  4. Caudate nucleus GABAergic neurons

Explanation

Parkinson disease results from degeneration of dopaminergic neurons in the substantia nigra pars compacta, reducing striatal dopamine and disinhibiting the indirect basal ganglia pathway. This produces the classic triad of tremor, bradykinesia, and rigidity. The other cell populations produce different clinical syndromes.

Question 31Part I – Biomedical Science

A patient sustains a spinal cord hemisection at T8 on the right side. Which combination of findings is most expected below the lesion?

  1. Bilateral loss of proprioception with preserved pain and temperature
  2. Bilateral loss of pain and temperature with preserved vibration sense
  3. Contralateral loss of proprioception and ipsilateral loss of pain and temperature
  4. Right-sided loss of proprioception and contralateral loss of pain and temperature Correct answer.

Explanation

Brown-Séquard syndrome interrupts the dorsal columns, which carry ipsilateral vibration and proprioception, and the spinothalamic tract, which carries contralateral pain and temperature. Corticospinal fibers are also interrupted, giving ipsilateral spastic weakness. This produces the characteristic dissociated sensory loss.

Question 32Part I – Biomedical Science

Which immunoglobulin isotype is the first produced in a primary humoral immune response and is most efficient at activating complement?

  1. IgG
  2. IgE
  3. IgM Correct answer.
  4. IgA

Explanation

IgM is the first antibody produced in a primary response and, because of its pentameric structure, is highly efficient at complement activation. IgG dominates secondary responses and also activates complement but less avidly per molecule. IgA and IgE serve mucosal and allergic functions respectively.

Question 33Part I – Biomedical Science

A 30-year-old woman develops hives, wheezing, and hypotension minutes after a penicillin infusion. Which mechanism best explains this reaction?

  1. IgG-mediated complement fixation on erythrocytes
  2. T-cell–mediated delayed hypersensitivity
  3. Immune complex deposition in vessel walls
  4. IgE-mediated mast cell degranulation Correct answer.

Explanation

Anaphylaxis is a type I hypersensitivity reaction in which antigen cross-links IgE on mast cells, triggering degranulation and release of histamine and other mediators. This produces urticaria, bronchospasm, and vasodilatory shock. The other mechanisms correspond to types II, IV, and III hypersensitivity.

Question 34Part I – Biomedical Science

A tumor produces excessive erythropoietin. Which change in the oxygen-hemoglobin dissociation curve is most expected as a compensatory response to the resulting erythrocytosis?

  1. Decreased temperature shifting the curve to the left
  2. Increased fetal hemoglobin shifting the curve to the left
  3. Increased 2,3-BPG shifting the curve to the right Correct answer.
  4. Decreased 2,3-BPG shifting the curve to the left

Explanation

Erythrocytosis increases red cell mass and raises 2,3-BPG, which binds deoxyhemoglobin and shifts the dissociation curve to the right, facilitating oxygen unloading at tissues. A rightward shift lowers hemoglobin oxygen affinity. The other options describe leftward shifts that increase affinity and impair unloading.

Question 35Part I – Biomedical Science

Which vitamin deficiency most directly impairs the carboxylation of glutamate residues in clotting factors II, VII, IX, and X?

  1. Vitamin B12
  2. Vitamin C
  3. Vitamin K Correct answer.
  4. Vitamin B1

Explanation

Vitamin K is the cofactor for gamma-glutamyl carboxylase, which carboxylates glutamate residues on factors II, VII, IX, and X and on proteins C and S. Without carboxylation these factors cannot bind calcium and phospholipid membranes effectively. This is why warfarin, which blocks vitamin K recycling, prolongs the prothrombin time.

Question 36Part I – Biomedical Science

A 62-year-old man has a blood pressure of 168/102 mmHg and hypokalemia. Which hormonal abnormality most likely underlies this presentation?

  1. Primary hyperaldosteronism Correct answer.
  2. Diabetes insipidus
  3. Pheochromocytoma
  4. Cushing syndrome

Explanation

Primary hyperaldosteronism causes sodium retention, hypertension, and renal potassium wasting, producing hypokalemia. Aldosterone excess also suppresses renin. The combination of hypertension with hypokalemia is the classic clue to this diagnosis.

Question 37Part I – Biomedical Science

Which statement best describes the role of the Na+/K+-ATPase in maintaining the ionic gradient across a resting cell membrane?

  1. It imports three sodium ions while extruding two potassium ions per ATP hydrolyzed
  2. It extrudes three sodium ions while importing two potassium ions per ATP hydrolyzed Correct answer.
  3. It moves sodium and potassium in equal one-to-one exchange
  4. It passively equilibrates sodium and potassium without ATP consumption

Explanation

The Na+/K+-ATPase pumps three sodium ions out and two potassium ions in for each ATP consumed, maintaining high extracellular sodium and high intracellular potassium. This electrogenic pump contributes to the resting potential and sustains the gradients used for action potentials. Passive leak channels alone cannot restore gradients after signaling.

Question 38Part I – Biomedical Science

A 70-year-old woman has a serum sodium of 122 mEq/L after several days of poor oral intake and excessive free water drinking. Which initial approach is most appropriate?

  1. Rapid correction of sodium to normal within 6 hours
  2. Free water restriction alone with no monitoring
  3. Administration of hypotonic fluids to dilute the sodium further
  4. Slow correction with hypertonic saline only if she has severe neurologic symptoms Correct answer.

Explanation

Symptomatic hyponatremia requires cautious correction, generally limiting the rise to about 8 to 10 mEq/L in 24 hours to avoid osmotic demyelination. Hypertonic saline is reserved for severe symptoms such as seizures or obtundation. Asymptomatic or mildly symptomatic cases are managed with fluid restriction and treatment of the cause.

Question 39Part I – Biomedical Science

Which of the following best describes the role of the juxtaglomerular apparatus in blood pressure regulation?

  1. It filters plasma and directly reabsorbs glucose
  2. It senses distal tubular sodium chloride delivery and releases renin Correct answer.
  3. It concentrates urine through countercurrent exchange
  4. It secretes erythropoietin in response to hypoxia

Explanation

The juxtaglomerular apparatus includes the macula densa, which senses sodium chloride delivery to the distal tubule, and granular cells that release renin. Renin initiates the renin-angiotensin-aldosterone cascade, raising blood pressure and sodium retention. This feedback links tubular salt delivery to systemic vascular tone.

Question 40Part I – Biomedical Science

A 3-year-old child has recurrent sinopulmonary infections and absent tonsils, and blood tests show markedly low levels of all immunoglobulin classes. Which diagnosis is most likely?

  1. Severe combined immunodeficiency
  2. X-linked agammaglobulinemia Correct answer.
  3. Common variable immunodeficiency
  4. Chronic granulomatous disease

Explanation

X-linked agammaglobulinemia results from a BTK mutation that blocks B-cell maturation, causing near-absent B cells and low levels of all immunoglobulin isotypes. Boys present after maternal IgG wanes with recurrent bacterial sinopulmonary infections and absent tonsils. T-cell function remains intact, distinguishing it from SCID.

Question 41Part I – Biomedical Science

Which of the following best describes the primary effect of insulin on adipose tissue?

  1. Inhibition of glucose transporter translocation
  2. Stimulation of hormone-sensitive lipase
  3. Stimulation of lipoprotein lipase and glucose uptake Correct answer.
  4. Promotion of ketogenesis

Explanation

Insulin promotes storage by stimulating lipoprotein lipase, which liberates fatty acids from circulating lipoproteins for uptake, and by increasing glucose transport into adipocytes. It simultaneously inhibits hormone-sensitive lipase, reducing lipolysis. These actions favor fat storage in the fed state.

Question 42Part I – Biomedical Science

A 55-year-old man with cirrhosis has a prolonged prothrombin time, low platelets, and elevated bilirubin. Which additional finding best supports impaired synthetic function rather than vitamin K deficiency alone?

  1. Increased reticulocyte count
  2. Prolonged bleeding time
  3. Elevated D-dimer
  4. Low serum albumin Correct answer.

Explanation

Albumin is synthesized exclusively by hepatocytes, so a low albumin supports impaired hepatic synthetic capacity. Vitamin K deficiency prolongs the prothrombin time but does not lower albumin. In liver disease, factor and albumin synthesis both decline, whereas vitamin K deficiency spares albumin.

Question 43Part I – Biomedical Science

Which of the following best describes the mechanism by which a loop diuretic such as furosemide increases urine output?

  1. Inhibition of carbonic anhydrase in the proximal tubule
  2. Blockade of aldosterone receptors in the collecting duct
  3. Inhibition of the Na-Cl cotransporter in the distal convoluted tubule
  4. Inhibition of the Na-K-2Cl cotransporter in the thick ascending limb Correct answer.

Explanation

Loop diuretics block the Na-K-2Cl cotransporter in the thick ascending limb, reducing medullary solute reabsorption and the concentrating gradient. This produces the most powerful natriuresis among diuretic classes. The other options describe thiazide, potassium-sparing, and carbonic anhydrase inhibitor mechanisms.

Question 44Part I – Biomedical Science

A patient inherits a defect in the enzyme that converts phenylalanine to tyrosine. Which clinical feature is most expected if the disorder is untreated from birth?

  1. Hemolytic anemia with jaundice
  2. Intellectual disability with musty urine odor Correct answer.
  3. Corneal clouding with joint stiffness
  4. Proximal muscle weakness with lactic acidosis

Explanation

Phenylketonuria results from deficiency of phenylalanine hydroxylase, causing phenylalanine accumulation and neurotoxicity with intellectual disability if untreated. Phenylalanine metabolites give the urine a musty odor. Dietary restriction of phenylalanine prevents the neurologic damage.

Question 45Part I – Biomedical Science

Which of the following best explains why a patient with an obstructing ureteral stone develops a rising creatinine?

  1. Increased glomerular oncotic pressure raises filtration rate
  2. Decreased tubular sodium delivery stimulates renin release
  3. Increased hydrostatic pressure in the tubule reduces net filtration pressure Correct answer.
  4. Increased glomerular capillary permeability enhances filtration

Explanation

Urinary obstruction raises hydrostatic pressure in the tubular system and renal interstitium, which opposes glomerular filtration and reduces net filtration pressure. The resulting fall in GFR raises creatinine. Relieving the obstruction restores filtration if the process is reversed early.

Question 46Part I – Biomedical Science

A 40-year-old woman has a malar rash, photosensitivity, and joint pain, with a positive antinuclear antibody test. Which additional autoantibody is most specific for this condition?

  1. Anti-mitochondrial
  2. Anti-double-stranded DNA Correct answer.
  3. Anti-centromere
  4. Anti-histone

Explanation

Systemic lupus erythematosus is associated with anti-double-stranded DNA antibodies, which are highly specific and correlate with renal disease activity. Anti-Smith is also specific. Anti-histone, anti-centromere, and anti-mitochondrial antibodies characterize drug-induced lupus, limited scleroderma, and primary biliary cholangitis respectively.

Question 47Part I – Biomedical Science

Which of the following best describes the primary role of the complement membrane attack complex?

  1. Neutralization of viral particles by antibodies
  2. Cleavage of C3 into C3a and C3b
  3. Formation of pores in the target cell membrane Correct answer.
  4. Opsonization of bacteria for phagocytosis

Explanation

The membrane attack complex is assembled from C5b through C9 and inserts into the target membrane, creating pores that cause osmotic lysis. Opsonization is mediated by C3b, and anaphylatoxins arise from small cleavage fragments. These functions are distinct steps of complement activity.

Question 48Part I – Biomedical Science

A patient takes a drug that inhibits the enzyme converting angiotensin I to angiotensin II. Which change is most expected?

  1. Increased angiotensin II with decreased renin activity
  2. Increased aldosterone with sodium retention
  3. Decreased angiotensin II with increased renin activity Correct answer.
  4. Decreased bradykinin with vasoconstriction

Explanation

Angiotensin-converting enzyme inhibitors reduce angiotensin II formation, which lowers vasoconstriction and aldosterone release. The loss of negative feedback on renin release raises plasma renin activity. Because ACE also degrades bradykinin, inhibition increases bradykinin and can cause cough.

Question 49Part I – Biomedical Science

A 28-year-old man is found to have a hemoglobin of 10 g/dL with microcytic indices and a low ferritin. Which finding on peripheral smear most supports this diagnosis?

  1. Schistocytes with helmet cells
  2. Macroovalocytes with hypersegmented neutrophils
  3. Hypochromic microcytic red cells with increased red cell distribution width Correct answer.
  4. Normochromic normocytic cells with target forms

Explanation

Iron deficiency anemia produces hypochromic microcytic red cells with an elevated red cell distribution width reflecting variable cell sizes. Low ferritin confirms depleted iron stores. The other smear patterns suggest thalassemia trait, microangiopathy, or megaloblastic anemia.

Question 50Part I – Biomedical Science

Which mechanism best explains the accumulation of ammonia in a patient with advanced cirrhosis and hepatic encephalopathy?

  1. Reduced hepatic urea cycle capacity with portosystemic shunting Correct answer.
  2. Enhanced glutamine synthesis in the brain
  3. Excessive muscle uptake of ammonia with hyperammonemia
  4. Increased renal ammonia excretion with metabolic alkalosis

Explanation

The liver normally converts ammonia to urea through the urea cycle, and cirrhosis reduces this capacity while portosystemic shunting delivers ammonia directly to the systemic circulation. The resulting hyperammonemia impairs cerebral neurotransmission and astrocyte function. Lactulose and rifaximin target gut ammonia production.