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ABU Qualifying Exam practice questions

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Question 1Physiology, immunology, molecular biology, hypertension, transplantation, sexual dysfunction, voiding dysfunction

Which hormone is released from the posterior pituitary and directly increases water reabsorption in the collecting duct?

  1. Antidiuretic hormone Correct answer.
  2. Parathyroid hormone
  3. Aldosterone
  4. Atrial natriuretic peptide

Explanation

Antidiuretic hormone (vasopressin) binds V2 receptors on collecting duct principal cells, increasing aquaporin-2 insertion into the apical membrane and raising water permeability. Aldosterone acts on sodium transport, ANP promotes natriuresis, and PTH regulates calcium and phosphate.

Question 2Physiology, immunology, molecular biology, hypertension, transplantation, sexual dysfunction, voiding dysfunction

Renin is secreted by which cells of the kidney?

  1. Mesangial cells
  2. Podocytes
  3. Macula densa cells
  4. Juxtaglomerular cells Correct answer.

Explanation

Renin is stored and released by juxtaglomerular (granular) cells in the wall of the afferent arteriole in response to reduced renal perfusion, reduced sodium delivery, or sympathetic beta-1 stimulation. The macula densa senses sodium chloride but does not secrete renin.

Question 3Physiology, immunology, molecular biology, hypertension, transplantation, sexual dysfunction, voiding dysfunction

A patient with a renal artery stenosis develops hypertension. Which mechanism best explains the rise in blood pressure?

  1. Suppressed sympathetic outflow to the kidney
  2. Primary hyperaldosteronism independent of renin
  3. Increased renin release with angiotensin II-mediated vasoconstriction Correct answer.
  4. Excess atrial natriuretic peptide secretion

Explanation

Reduced renal perfusion pressure lowers afferent arteriolar stretch and distal sodium delivery, increasing renin release. Angiotensin II then raises blood pressure through vasoconstriction and by stimulating aldosterone, which expands volume.

Question 4Physiology, immunology, molecular biology, hypertension, transplantation, sexual dysfunction, voiding dysfunction

Which class of antihypertensive drug most commonly causes dry cough as an adverse effect?

  1. Thiazide diuretics
  2. Alpha-1 receptor blockers
  3. Dihydropyridine calcium channel blockers
  4. Angiotensin-converting enzyme inhibitors Correct answer.

Explanation

ACE inhibitors reduce bradykinin degradation, and bradykinin accumulation in the airway produces a persistent dry cough in a subset of patients. Switching to an angiotensin receptor blocker usually avoids this effect.

Question 5Physiology, immunology, molecular biology, hypertension, transplantation, sexual dysfunction, voiding dysfunction

A 58-year-old man has resistant hypertension despite three agents including a diuretic. Which secondary cause is most consistent with hypokalemia and a suppressed renin level?

  1. Pheochromocytoma
  2. Renal artery stenosis
  3. Primary aldosteronism Correct answer.
  4. Coarctation of the aorta

Explanation

Primary aldosteronism produces aldosterone excess that is autonomous of renin, so renin is suppressed while aldosterone drives sodium retention and potassium wasting. The combination of hypertension, hypokalemia, and low renin points to this diagnosis.

Question 6Physiology, immunology, molecular biology, hypertension, transplantation, sexual dysfunction, voiding dysfunction

Which immunoglobulin isotype is the first to be produced in a primary humoral immune response?

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

Explanation

Naive B cells initially express IgM, and IgM is the earliest antibody class secreted during a primary response before class switching occurs. IgG dominates later and on secondary exposure.

Question 7Physiology, immunology, molecular biology, hypertension, transplantation, sexual dysfunction, voiding dysfunction

Which cell presents processed antigen on MHC class II molecules to CD4+ T cells?

  1. CD8+ cytotoxic T cell
  2. Red blood cell
  3. Dendritic cell Correct answer.
  4. Platelet

Explanation

Dendritic cells are professional antigen-presenting cells that load exogenous peptides onto MHC class II for recognition by CD4+ helper T cells. MHC class II expression is restricted largely to professional antigen-presenting cells.

Question 8Physiology, immunology, molecular biology, hypertension, transplantation, sexual dysfunction, voiding dysfunction

A transplant recipient develops fever, rising creatinine, and a donor-specific antibody response several years after transplantation. Which process is most likely occurring?

  1. Acute cellular rejection
  2. Graft-versus-host disease
  3. Chronic antibody-mediated rejection Correct answer.
  4. Hyperacute rejection

Explanation

Chronic antibody-mediated rejection results from donor-specific antibodies that develop over months to years and cause progressive graft injury with rising creatinine. Hyperacute rejection occurs within minutes, and acute cellular rejection is T-cell mediated and typically earlier.

Question 9Physiology, immunology, molecular biology, hypertension, transplantation, sexual dysfunction, voiding dysfunction

Which immunosuppressant acts by inhibiting calcineurin and thereby blocking interleukin-2 transcription in T cells?

  1. Prednisone
  2. Sirolimus
  3. Mycophenolate mofetil
  4. Tacrolimus Correct answer.

Explanation

Tacrolimus binds FKBP and inhibits calcineurin, preventing dephosphorylation of NFAT and blocking interleukin-2 gene transcription. This reduces T-cell activation and proliferation.

Question 10Physiology, immunology, molecular biology, hypertension, transplantation, sexual dysfunction, voiding dysfunction

Which finding is required to establish brain death before organ procurement in a potential deceased donor?

  1. Serum creatinine above a fixed threshold
  2. Presence of brainstem reflexes
  3. Spontaneous respiratory effort
  4. Absence of cerebral and brainstem function with apnea confirmed Correct answer.

Explanation

Brain death requires irreversible loss of cerebral and brainstem function, including absence of brainstem reflexes and a positive apnea test in the absence of confounding factors. Organ function parameters such as creatinine are not part of the neurologic determination.

Question 11Physiology, immunology, molecular biology, hypertension, transplantation, sexual dysfunction, voiding dysfunction

In the male sexual arousal pathway, which enzyme converts guanosine triphosphate to cyclic guanosine monophosphate in cavernosal smooth muscle?

  1. Cyclooxygenase
  2. Adenylate cyclase
  3. Guanylate cyclase Correct answer.
  4. Phosphodiesterase type 5

Explanation

Nitric oxide released from cavernous nerves activates soluble guanylate cyclase, which converts GTP to cGMP and relaxes cavernosal smooth muscle to enable erection. Phosphodiesterase type 5 then degrades cGMP to terminate the signal.

Question 12Physiology, immunology, molecular biology, hypertension, transplantation, sexual dysfunction, voiding dysfunction

A man taking a phosphodiesterase type 5 inhibitor develops severe hypotension after taking a nitrate. What is the mechanism of this interaction?

  1. Direct alpha-adrenergic blockade
  2. Increased sympathetic outflow
  3. Enhanced nitric oxide scavenging
  4. Reduced cGMP degradation with additive vasodilation Correct answer.

Explanation

Nitrates increase nitric oxide and cGMP production, while PDE5 inhibitors block cGMP breakdown. The combined rise in cGMP produces profound smooth muscle relaxation and hypotension.

Question 13Physiology, immunology, molecular biology, hypertension, transplantation, sexual dysfunction, voiding dysfunction

Which structure must be intact for psychogenic erection mediated by visual and imaginative stimuli?

  1. Thoracolumbar sympathetic outflow and pelvic plexus Correct answer.
  2. Somatic pudendal nerve alone
  3. Sacral parasympathetic reflex arc only
  4. Cauda equina dorsal roots exclusively

Explanation

Psychogenic erection depends on descending pathways that reach the thoracolumbar sympathetic outflow and pelvic plexus, which supply the cavernosal tissue. This pathway is distinct from the sacral reflex-mediated erection.

Question 14Physiology, immunology, molecular biology, hypertension, transplantation, sexual dysfunction, voiding dysfunction

A 62-year-old man reports poor erections and reduced early-morning erections. Which test best helps distinguish organic from psychogenic erectile dysfunction?

  1. Nocturnal penile tumescence testing Correct answer.
  2. Bulbocavernosus reflex latency
  3. Cystometry
  4. Serum prostate-specific antigen

Explanation

Nocturnal penile tumescence testing assesses erections during sleep, when psychogenic inhibition is reduced. Preserved nocturnal erections suggest a psychogenic component, whereas their absence favors an organic vascular or neurologic cause.

Question 15Physiology, immunology, molecular biology, hypertension, transplantation, sexual dysfunction, voiding dysfunction

Detrusor overactivity with involuntary contractions during bladder filling is most characteristic of which condition?

  1. Urinary fistula
  2. Urge incontinence Correct answer.
  3. Overflow incontinence
  4. Stress incontinence

Explanation

Urge incontinence results from involuntary detrusor contractions during filling, producing a sudden strong desire to void with leakage. Stress incontinence instead results from urethral sphincter weakness with increased abdominal pressure.

Question 16Physiology, immunology, molecular biology, hypertension, transplantation, sexual dysfunction, voiding dysfunction

A patient reports leakage of urine with coughing and sneezing but no urgency. Which mechanism best explains this finding?

  1. Detrusor underactivity with retention
  2. Involuntary detrusor contraction during filling
  3. Bladder neck obstruction
  4. Urethral hypermobility and sphincter weakness Correct answer.

Explanation

Stress urinary incontinence occurs when increased intra-abdominal pressure overcomes a weakened sphincter mechanism, often due to urethral hypermobility or intrinsic sphincter deficiency. Leakage with coughing in the absence of urgency is typical.

Question 17Physiology, immunology, molecular biology, hypertension, transplantation, sexual dysfunction, voiding dysfunction

Which measure reflects detrusor contractility during a pressure-flow study?

  1. Post-void residual volume
  2. Maximum detrusor pressure during voiding Correct answer.
  3. Bladder capacity at first sensation
  4. Maximum urethral closure pressure

Explanation

Maximum detrusor pressure during voiding, interpreted against flow rate, reflects the strength of detrusor contraction. Post-void residual and capacity describe emptying and storage rather than contractile force.

Question 18Physiology, immunology, molecular biology, hypertension, transplantation, sexual dysfunction, voiding dysfunction

Which molecular technique amplifies a specific DNA segment using primers and a thermostable polymerase?

  1. Western blotting
  2. Southern blotting
  3. Northern blotting
  4. Polymerase chain reaction Correct answer.

Explanation

The polymerase chain reaction uses sequence-specific primers and a thermostable DNA polymerase through repeated denaturation, annealing, and extension cycles to amplify DNA exponentially. The blotting techniques detect nucleic acids or proteins without amplification.

Question 19Physiology, immunology, molecular biology, hypertension, transplantation, sexual dysfunction, voiding dysfunction

In a family, a disease is present in every generation and affects about half of the offspring of an affected parent, with male-to-male transmission observed. Which inheritance pattern is most likely?

  1. Autosomal recessive
  2. Mitochondrial
  3. X-linked recessive
  4. Autosomal dominant Correct answer.

Explanation

Vertical transmission through successive generations with roughly 50% affected offspring and male-to-male transmission is characteristic of autosomal dominant inheritance. Male-to-male transmission excludes X-linked inheritance.

Question 20Physiology, immunology, molecular biology, hypertension, transplantation, sexual dysfunction, voiding dysfunction

Which type of mutation most commonly produces a premature stop codon and a truncated protein?

  1. Missense mutation
  2. Silent mutation
  3. Nonsense mutation Correct answer.
  4. Frameshift insertion of three nucleotides

Explanation

A nonsense mutation changes a codon into a stop codon, terminating translation early and producing a truncated protein. Silent mutations do not change the amino acid, and missense mutations substitute one amino acid.

Question 21Physiology, immunology, molecular biology, hypertension, transplantation, sexual dysfunction, voiding dysfunction

During DNA replication, which enzyme relieves supercoiling ahead of the replication fork?

  1. DNA ligase
  2. Helicase
  3. DNA polymerase
  4. Topoisomerase Correct answer.

Explanation

Topoisomerases cut and rejoin DNA strands to relieve torsional stress generated ahead of the advancing replication fork. Helicase separates strands, polymerase synthesizes DNA, and ligase joins fragments.

Question 22Physiology, immunology, molecular biology, hypertension, transplantation, sexual dysfunction, voiding dysfunction

Which feature distinguishes MHC class I from MHC class II molecules?

  1. Class II presents lipid antigens to natural killer cells
  2. Class I presents to CD4+ T cells and is restricted to antigen-presenting cells
  3. Class II is expressed on red blood cells
  4. Class I presents to CD8+ T cells and is expressed on nearly all nucleated cells Correct answer.

Explanation

MHC class I molecules are expressed on nearly all nucleated cells and present endogenous peptides to CD8+ cytotoxic T cells. MHC class II expression is largely limited to professional antigen-presenting cells and presents to CD4+ T cells.

Question 23Physiology, immunology, molecular biology, hypertension, transplantation, sexual dysfunction, voiding dysfunction

A kidney transplant recipient is prescribed a drug that inhibits inosine monophosphate dehydrogenase to suppress lymphocyte proliferation. Which drug is this?

  1. Cyclosporine
  2. Mycophenolate mofetil Correct answer.
  3. Basiliximab
  4. Azathioprine

Explanation

Mycophenolate mofetil inhibits inosine monophosphate dehydrogenase, depleting guanosine nucleotides and preferentially blocking proliferation of lymphocytes, which rely on de novo purine synthesis.

Question 24Physiology, immunology, molecular biology, hypertension, transplantation, sexual dysfunction, voiding dysfunction

Which change in the nephron occurs in response to volume depletion and helps restore blood pressure?

  1. Increased sympathetic tone with afferent arteriolar constriction Correct answer.
  2. Increased atrial natriuretic peptide release
  3. Reduced angiotensin II formation
  4. Increased sodium delivery to the macula densa

Explanation

Volume depletion increases sympathetic outflow, which constricts the afferent arteriole and stimulates renin release, supporting blood pressure. Reduced renal perfusion and distal sodium delivery also activate the renin-angiotensin system.

Question 25Physiology, immunology, molecular biology, hypertension, transplantation, sexual dysfunction, voiding dysfunction

A man with a spinal cord injury above the sacral level develops reflexogenic erections but not psychogenic erections. Which explanation best fits this pattern?

  1. The sacral reflex arc is intact while descending psychogenic pathways are disrupted Correct answer.
  2. Both sacral and thoracolumbar pathways are destroyed
  3. Cavernosal smooth muscle is unresponsive to nitric oxide
  4. The pudendal nerve is bilaterally transected

Explanation

Upper motor neuron lesions above the sacral cord preserve the sacral parasympathetic reflex arc that mediates reflexogenic erection while interrupting descending psychogenic input. This produces reflex erections without psychogenic erections.

Question 26Physiology, immunology, molecular biology, hypertension, transplantation, sexual dysfunction, voiding dysfunction

Which immunoglobulin isotype is most abundant in human serum and crosses the placenta to provide passive immunity to the fetus?

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

Explanation

IgG is the most abundant serum immunoglobulin and is actively transported across the placenta via the neonatal Fc receptor, conferring humoral immunity to the newborn. IgM is largely intravascular and does not cross the placenta; IgA is secreted into mucosal fluids; IgE mediates type I hypersensitivity.

Question 27Physiology, immunology, molecular biology, hypertension, transplantation, sexual dysfunction, voiding dysfunction

Which receptor on the surface of a cytotoxic T lymphocyte binds to MHC class I molecules on a target cell?

  1. CD40 ligand
  2. CD8 Correct answer.
  3. CD28
  4. CD4

Explanation

CD8 acts as a co-receptor that binds the alpha-3 domain of MHC class I, allowing the T-cell receptor to engage peptide presented on class I molecules. CD4 instead binds MHC class II; CD28 and CD40 ligand provide costimulatory signals.

Question 28Physiology, immunology, molecular biology, hypertension, transplantation, sexual dysfunction, voiding dysfunction

Which cytokine is the principal stimulus for differentiation of naive CD4+ T cells into the Th1 subset?

  1. Interleukin-5
  2. Interleukin-12 Correct answer.
  3. Interleukin-10
  4. Interleukin-4

Explanation

Interleukin-12 produced by activated dendritic cells and macrophages drives STAT4 signaling and expression of T-bet, committing CD4+ T cells to the Th1 lineage. Interleukin-4 drives Th2 differentiation, and interleukin-10 is an anti-inflammatory cytokine.

Question 29Physiology, immunology, molecular biology, hypertension, transplantation, sexual dysfunction, voiding dysfunction

A 24-year-old man has recurrent bacterial infections and is found to have absent B cells and very low serum immunoglobulins, while T-cell numbers and function are normal. Which diagnosis is most likely?

  1. Severe combined immunodeficiency
  2. Complement C3 deficiency
  3. Chronic granulomatous disease
  4. X-linked agammaglobulinemia Correct answer.

Explanation

X-linked agammaglobulinemia results from mutations in Bruton tyrosine kinase (BTK), causing arrest of B-cell development and profound hypogammaglobulinemia with intact T-cell immunity. SCID would also affect T cells; chronic granulomatous disease impairs phagocyte killing; C3 deficiency causes recurrent pyogenic infections but immunoglobulins are normal.

Question 30Physiology, immunology, molecular biology, hypertension, transplantation, sexual dysfunction, voiding dysfunction

Which process describes the covalent attachment of ubiquitin to a protein, targeting it for proteasomal degradation and subsequent presentation on MHC class I molecules?

  1. Ubiquitination Correct answer.
  2. Phosphorylation
  3. Acetylation
  4. Glycosylation

Explanation

Ubiquitination tags intracellular proteins for recognition and degradation by the proteasome, generating peptides that are transported into the endoplasmic reticulum and loaded onto MHC class I. Glycosylation, phosphorylation, and acetylation are post-translational modifications that do not directly target proteins to the proteasome for antigen presentation.

Question 31Physiology, immunology, molecular biology, hypertension, transplantation, sexual dysfunction, voiding dysfunction

In the kidney, which segment of the nephron is the primary site of action of aldosterone?

  1. Cortical collecting duct Correct answer.
  2. Thin descending limb of the loop of Henle
  3. Distal convoluted tubule
  4. Proximal convoluted tubule

Explanation

Aldosterone binds mineralocorticoid receptors in principal cells of the cortical collecting duct, increasing expression of epithelial sodium channels and Na+/K+-ATPase to promote sodium reabsorption and potassium secretion. The proximal tubule, thin descending limb, and distal convoluted tubule are not the main aldosterone targets.

Question 32Physiology, immunology, molecular biology, hypertension, transplantation, sexual dysfunction, voiding dysfunction

Which change in renal sodium handling is expected in a patient with primary hyperaldosteronism?

  1. Decreased sodium reabsorption with volume depletion
  2. Increased sodium reabsorption with hypertension and hypokalemia Correct answer.
  3. Decreased sodium reabsorption with hypotension and hyperkalemia
  4. Increased sodium excretion with metabolic acidosis

Explanation

Excess aldosterone increases sodium reabsorption in the collecting duct, expanding plasma volume and raising blood pressure, while enhancing potassium secretion and causing hypokalemia. The other options describe states of aldosterone deficiency or tubular dysfunction.

Question 33Physiology, immunology, molecular biology, hypertension, transplantation, sexual dysfunction, voiding dysfunction

Which of the following best defines the term 'immunological synapse' in T-cell activation?

  1. The junction between a T cell and an antigen-presenting cell where the T-cell receptor engages peptide-MHC Correct answer.
  2. The site of antibody production within germinal centers
  3. The contact area between a cytotoxic T cell and a target cell during apoptosis
  4. The region where complement proteins assemble on a bacterial surface

Explanation

The immunological synapse is the organized interface between a T lymphocyte and an antigen-presenting cell, where the T-cell receptor binds peptide-MHC and costimulatory and adhesion molecules cluster to sustain signaling. It is not a site of antibody production, complement assembly, or the lytic synapse of a cytotoxic T cell.

Question 34Physiology, immunology, molecular biology, hypertension, transplantation, sexual dysfunction, voiding dysfunction

A 45-year-old man has a blood pressure of 168/104 mmHg on three occasions. He reports no headache, chest pain, or visual changes. Which term best describes this presentation?

  1. Secondary hypertension
  2. Hypertensive emergency
  3. White-coat hypertension
  4. Hypertensive urgency Correct answer.

Explanation

Hypertensive urgency is severe elevation of blood pressure without acute target-organ damage. Emergency implies target-organ injury; white-coat hypertension is elevated pressure only in the clinic setting; secondary hypertension requires identification of an underlying cause.

Question 35Physiology, immunology, molecular biology, hypertension, transplantation, sexual dysfunction, voiding dysfunction

Which mechanism best explains the antihypertensive effect of an angiotensin-converting enzyme inhibitor?

  1. Inhibition of renin release from juxtaglomerular cells
  2. Blockade of angiotensin II type 1 receptors
  3. Reduction of angiotensin II formation and increased bradykinin levels Correct answer.
  4. Direct relaxation of vascular smooth muscle by opening potassium channels

Explanation

ACE inhibitors reduce conversion of angiotensin I to angiotensin II, lowering vasoconstriction and aldosterone secretion, and they also inhibit bradykinin degradation, which contributes to vasodilation. Receptor blockade describes angiotensin receptor blockers; renin inhibition describes direct renin inhibitors; potassium channel opening describes agents like minoxidil.

Question 36Physiology, immunology, molecular biology, hypertension, transplantation, sexual dysfunction, voiding dysfunction

A 58-year-old woman with resistant hypertension is found to have a low renin level and an elevated aldosterone-to-renin ratio. Which confirmatory test is most appropriate?

  1. Renal artery Doppler ultrasonography
  2. Plasma metanephrines
  3. Oral sodium loading with measurement of urinary aldosterone Correct answer.
  4. Adrenal vein sampling

Explanation

In primary aldosteronism, the aldosterone-to-renin ratio is a screening test. Confirmatory testing typically involves oral sodium loading or saline infusion; failure to suppress aldosterone confirms autonomous secretion. Adrenal vein sampling is used to distinguish unilateral from bilateral disease after confirmation.

Question 37Physiology, immunology, molecular biology, hypertension, transplantation, sexual dysfunction, voiding dysfunction

Which class of antihypertensive medication is most appropriate for a patient with hypertension and chronic kidney disease with proteinuria, assuming no contraindications?

  1. Angiotensin-converting enzyme inhibitor Correct answer.
  2. Alpha-blocker
  3. Beta-blocker
  4. Thiazide diuretic

Explanation

ACE inhibitors reduce intraglomerular pressure and proteinuria and slow progression of chronic kidney disease, making them preferred in proteinuric renal disease. Thiazides, beta-blockers, and alpha-blockers do not provide the same renoprotective effect.

Question 38Physiology, immunology, molecular biology, hypertension, transplantation, sexual dysfunction, voiding dysfunction

Which of the following is a recognized mechanism by which obesity contributes to hypertension?

  1. Decreased circulating angiotensinogen
  2. Increased leptin-mediated sympathetic activation Correct answer.
  3. Reduced renal sodium reabsorption
  4. Enhanced endothelial nitric oxide production

Explanation

Obesity increases leptin and insulin levels, activating the sympathetic nervous system and the renin-angiotensin-aldosterone axis, which raises blood pressure. Obesity also tends to increase renal sodium reabsorption and angiotensinogen while impairing nitric oxide bioavailability.

Question 39Physiology, immunology, molecular biology, hypertension, transplantation, sexual dysfunction, voiding dysfunction

A 32-year-old woman with end-stage renal disease receives a living-donor kidney transplant. Which immunosuppressive strategy is most commonly used for maintenance therapy to prevent acute rejection?

  1. Calcineurin inhibitor plus an antimetabolite and corticosteroids Correct answer.
  2. Corticosteroids alone
  3. Sirolimus monotherapy
  4. Azathioprine plus intravenous immunoglobulin

Explanation

Standard maintenance immunosuppression after kidney transplantation combines a calcineurin inhibitor (tacrolimus or cyclosporine), an antimetabolite (mycophenolate or azathioprine), and corticosteroids. Monotherapy with steroids or sirolimus is inadequate, and azathioprine plus IVIG is not a standard maintenance regimen.

Question 40Physiology, immunology, molecular biology, hypertension, transplantation, sexual dysfunction, voiding dysfunction

Which finding on urinalysis is most suggestive of acute cellular rejection in a kidney transplant recipient?

  1. Hematuria with dysmorphic red cells
  2. Sterile pyuria with white blood cell casts Correct answer.
  3. Eosinophiluria
  4. Lipiduria with oval fat bodies

Explanation

Acute cellular rejection produces interstitial inflammation, leading to sterile pyuria and white blood cell casts without infection. Dysmorphic red cells suggest glomerular bleeding; eosinophiluria is associated with interstitial nephritis; lipiduria indicates nephrotic-range proteinuria.

Question 41Physiology, immunology, molecular biology, hypertension, transplantation, sexual dysfunction, voiding dysfunction

Which virus is the most common cause of opportunistic infection in the first six months after kidney transplantation and can cause colitis and retinitis?

  1. Herpes simplex virus type 1
  2. Cytomegalovirus Correct answer.
  3. BK polyomavirus
  4. Epstein-Barr virus

Explanation

Cytomegalovirus is the most frequent opportunistic viral infection after solid-organ transplantation, typically occurring within the first six months, and can cause pneumonitis, colitis, and retinitis. Epstein-Barr virus is associated with post-transplant lymphoproliferative disorder; herpes simplex causes mucocutaneous lesions; BK virus causes nephropathy.

Question 42Physiology, immunology, molecular biology, hypertension, transplantation, sexual dysfunction, voiding dysfunction

A kidney transplant recipient on tacrolimus develops tremor, confusion, and a rising creatinine. Tacrolimus trough level is 28 ng/mL (therapeutic range 5–15 ng/mL). Which management step is most appropriate?

  1. Reduce or hold tacrolimus and monitor levels Correct answer.
  2. Increase the tacrolimus dose
  3. Start high-dose corticosteroids for rejection
  4. Add a second calcineurin inhibitor

Explanation

The symptoms and elevated trough level indicate tacrolimus toxicity, which can cause neurotoxicity and nephrotoxicity. Reducing or holding the drug and monitoring levels is the appropriate first step. Increasing the dose or adding another calcineurin inhibitor would worsen toxicity.

Question 43Physiology, immunology, molecular biology, hypertension, transplantation, sexual dysfunction, voiding dysfunction

In the physiology of penile erection, which intracellular messenger directly mediates smooth muscle relaxation in the corpus cavernosum?

  1. Cyclic guanosine monophosphate Correct answer.
  2. Diacylglycerol
  3. Inositol triphosphate
  4. Cyclic adenosine monophosphate

Explanation

Nitric oxide released from cavernous nerves and endothelium activates guanylyl cyclase, raising cyclic guanosine monophosphate, which activates protein kinase G and lowers intracellular calcium, causing smooth muscle relaxation and erection. Cyclic adenosine monophosphate is a second messenger in other pathways; inositol triphosphate and diacylglycerol mediate contraction.

Question 44Physiology, immunology, molecular biology, hypertension, transplantation, sexual dysfunction, voiding dysfunction

A 60-year-old man with type 2 diabetes reports erectile dysfunction. Which underlying mechanism most likely contributes to his condition?

  1. Endothelial dysfunction and impaired nitric oxide bioavailability Correct answer.
  2. Elevated testosterone levels
  3. Enhanced cavernosal smooth muscle relaxation
  4. Increased penile arterial inflow

Explanation

Diabetes causes endothelial dysfunction, reducing nitric oxide production and bioavailability, which impairs cavernosal smooth muscle relaxation and erection. Increased arterial inflow, enhanced relaxation, and elevated testosterone would not cause erectile dysfunction.

Question 45Physiology, immunology, molecular biology, hypertension, transplantation, sexual dysfunction, voiding dysfunction

Which medication is most commonly associated with erectile dysfunction through its antiandrogenic effects?

  1. Metformin
  2. Spironolactone Correct answer.
  3. Amlodipine
  4. Sildenafil

Explanation

Spironolactone has antiandrogenic activity, blocking androgen receptors and reducing testosterone synthesis, which can cause gynecomastia and erectile dysfunction. Sildenafil treats erectile dysfunction; amlodipine and metformin are not typically associated with antiandrogenic effects.

Question 46Physiology, immunology, molecular biology, hypertension, transplantation, sexual dysfunction, voiding dysfunction

A 55-year-old man presents with a painful erection lasting 4 hours without sexual stimulation. Which intervention is the initial step in management?

  1. Intracavernosal phenylephrine
  2. Immediate surgical shunt
  3. Corporal aspiration and irrigation with saline Correct answer.
  4. Oral tadalafil

Explanation

Priapism lasting more than 4 hours is a urologic emergency. Initial management is corporal aspiration and irrigation with saline to relieve compartment syndrome and remove stagnant blood; if this fails, intracavernosal phenylephrine is used. Surgical shunting is reserved for refractory cases.

Question 47Physiology, immunology, molecular biology, hypertension, transplantation, sexual dysfunction, voiding dysfunction

Which brainstem center coordinates detrusor contraction and external sphincter relaxation during normal voiding?

  1. Hypothalamic paraventricular nucleus
  2. Pontine micturition center Correct answer.
  3. Cerebellar vermis
  4. Medullary respiratory center

Explanation

The pontine micturition center (Barrington's nucleus) coordinates detrusor contraction with relaxation of the external urethral sphincter during voiding. The medullary respiratory center controls breathing; the paraventricular nucleus regulates autonomic and endocrine functions; the cerebellar vermis coordinates movement.

Question 48Physiology, immunology, molecular biology, hypertension, transplantation, sexual dysfunction, voiding dysfunction

A 70-year-old man has a post-void residual volume of 250 mL and an enlarged prostate. Which diagnosis is most consistent with these findings?

  1. Bladder outlet obstruction Correct answer.
  2. Overactive bladder without obstruction
  3. Stress urinary incontinence
  4. Detrusor overactivity

Explanation

An elevated post-void residual in the setting of an enlarged prostate suggests bladder outlet obstruction, often due to benign prostatic hyperplasia. Detrusor overactivity and overactive bladder typically present with urgency and frequency without a large residual; stress incontinence causes leakage with increased abdominal pressure.

Question 49Physiology, immunology, molecular biology, hypertension, transplantation, sexual dysfunction, voiding dysfunction

Which urodynamic finding is most characteristic of detrusor sphincter dyssynergia in a patient with a spinal cord injury?

  1. Absent detrusor contraction with normal sphincter tone
  2. Detrusor contraction with complete sphincter relaxation
  3. Detrusor contraction with simultaneous external sphincter contraction Correct answer.
  4. Low detrusor pressure with high urine flow

Explanation

Detrusor sphincter dyssynergia is defined by involuntary contraction of the external urethral sphincter during detrusor contraction, causing functional obstruction. Normal voiding involves sphincter relaxation; absent detrusor contraction indicates an acontractile bladder; low pressure with high flow suggests normal or reduced outlet resistance.

Question 50Physiology, immunology, molecular biology, hypertension, transplantation, sexual dysfunction, voiding dysfunction

Which neurotransmitter is primarily responsible for detrusor muscle contraction during voiding?

  1. Norepinephrine
  2. Dopamine
  3. Nitric oxide
  4. Acetylcholine Correct answer.

Explanation

Parasympathetic postganglionic neurons release acetylcholine, which activates muscarinic M3 receptors on detrusor smooth muscle to cause contraction. Norepinephrine mediates sympathetic relaxation and sphincter contraction; nitric oxide relaxes smooth muscle; dopamine is a central neurotransmitter.