KMU Past Paper Practice

Question:

A 62-year-old man develops significant gastrointestinal blood loss. His plasma osmolality has not yet changed substantially, but vasopressin secretion increases. Which physiological stimulus best explains this response?

Correct Answer:
Reduction in effective circulating volume

Explanation: Vasopressin release is stimulated not only by increased osmolality but also by reduced effective circulating volume, helping conserve water during significant volume loss.

Question:

A hypothalamic lesion selectively damages the supraoptic and paraventricular nuclei. Which physiological function is most directly impaired?

Correct Answer:
Synthesis of vasopressin

Explanation: Vasopressin is synthesized mainly in the supraoptic and paraventricular nuclei of the hypothalamus before being transported to the posterior pituitary.

Question:

A suprasellar lesion interrupts the pituitary stalk while leaving vasopressin-producing hypothalamic neurons intact. The patient subsequently develops excessive dilute urine. Which step has most likely been disrupted?

Correct Answer:
Axonal transport and posterior-pituitary release of vasopressin

Explanation: Vasopressin synthesized in the hypothalamus travels down axons to the posterior pituitary. Stalk interruption can therefore prevent normal storage and release.

Question:

A 29-year-old woman has persistent water diuresis. Imaging shows no pituitary mass or recent trauma. Further evaluation suggests immune-mediated damage to vasopressin-producing neurons. Which etiological category best fits her disorder?

Correct Answer:
Autoimmune central diabetes insipidus

Explanation: Autoimmune or idiopathic injury to vasopressin-producing neurons is a recognized cause of central diabetes insipidus when structural causes are absent.

Question:

A boy has had marked polyuria and intense thirst since early childhood. Vasopressin production is preserved and the hypothalamic-pituitary region appears normal. A similar disorder is present in relatives. Which defect best explains the presentation?

Correct Answer:
Inherited abnormality of the V2 receptor or aquaporin-2 pathway

Explanation: Inherited nephrogenic DI may result from defects in the renal V2 receptor or aquaporin-2 system, causing poor renal response despite adequate hormone availability.

Question:

A patient with persistent potassium depletion develops increasing thirst and large-volume dilute urine. Vasopressin secretion is appropriate for his plasma state. Which mechanism best accounts for the urinary abnormality?

Correct Answer:
Acquired reduction in renal concentrating responsiveness

Explanation: Hypokalemia can impair renal concentrating ability and produce acquired nephrogenic DI despite appropriate endogenous vasopressin secretion.

Question:

A patient with chronic renal disease develops persistent water diuresis. Endogenous vasopressin is present, but urinary concentrating ability remains poor. Which abnormality is most likely responsible?

Correct Answer:
Impairment of the renal concentrating mechanism

Explanation: Renal disorders can cause nephrogenic DI by reducing the kidney’s ability to respond appropriately to vasopressin and concentrate urine.

Question:

A man with untreated diabetes insipidus passes large amounts of dilute urine but maintains a near-normal serum sodium concentration while working at home. Which factor most likely prevents a major rise in serum sodium?

Correct Answer:
Thirst-driven water intake matching urinary losses

Explanation: Intact thirst and unrestricted access to water can compensate for urinary free-water losses and maintain near-normal plasma sodium in DI.

Question:

A patient with established diabetes insipidus reports waking five to six times each night to pass urine. Which disturbance most directly explains this nocturnal symptom?

Correct Answer:
Persistent failure of renal water conservation

Explanation: Impaired antidiuretic action continues during sleep, so high-volume dilute urine production persists and produces nocturia.

Question:

A 36-year-old man presents with marked polyuria. Blood glucose is normal, urine contains no glucose, and the urine is very dilute. Which process best explains his excessive urine output?

Correct Answer:
Failure of normal renal free-water conservation

Explanation: DI produces a water diuresis rather than glucose-driven osmotic diuresis; urine is characteristically dilute because renal water conservation is impaired.

Question:

An 8-year-old child with persistent nocturnal enuresis is selected for desmopressin therapy after appropriate clinical assessment. Which therapeutic effect is being used in this setting?

Correct Answer:
Reducing overnight urine production

Explanation: Desmopressin enhances renal water reabsorption and can reduce nighttime urine production in appropriately selected patients with nocturnal enuresis.

Question:

A patient with von Willebrand disease is given desmopressin before a planned procedure. Which pharmacological effect contributes to improved hemostasis?

Correct Answer:
Release of von Willebrand factor and factor VIII from endothelial stores

Explanation: Desmopressin can increase circulating von Willebrand factor and factor VIII by promoting their release from endothelial stores in responsive patients.

Question:

A patient receiving desmopressin has satisfactory control of urine output and normal serum sodium but develops mild headache and nausea shortly after treatment. Which interpretation is most appropriate?

Correct Answer:
Headache and nausea can occur as adverse effects of desmopressin

Explanation: Headache and nausea are recognized adverse effects of desmopressin; normal sodium makes severe dilutional water intoxication less likely in this scenario.

Question:

Indomethacin is being considered as adjunctive therapy for nephrogenic diabetes insipidus. Which feature most limits its prolonged routine use?

Correct Answer:
Potential renal and gastrointestinal toxicity

Explanation: NSAIDs such as indomethacin can reduce polyuria, but renal and gastrointestinal toxicity limits prolonged routine use.

Question:

Vasopressin acts on a receptor subtype in the anterior pituitary and contributes to ACTH release. Which receptor mediates this effect?

Correct Answer:
V1b receptor

Explanation: V1b receptors participate in vasopressin-mediated ACTH release from the anterior pituitary, whereas V2 receptors mainly mediate renal antidiuresis.

Question:

A 44-year-old woman taking carbamazepine develops lethargy. Serum sodium and plasma osmolality are reduced, while urine remains more concentrated than expected. Which explanation best fits the clinical context?

Correct Answer:
Drug-associated inappropriate vasopressin activity

Explanation: Carbamazepine is a recognized drug-associated cause of SIADH, producing water retention with low plasma osmolality and inappropriate urine concentration.

Question:

A patient admitted with a significant pulmonary disorder develops low serum sodium and low plasma osmolality without evidence of excessive renal water loss. Which endocrine disturbance should be considered?

Correct Answer:
Pulmonary disease-associated SIADH

Explanation: Pulmonary disorders can stimulate inappropriate vasopressin secretion and therefore form an important etiological group for SIADH.

Question:

A patient develops hyponatremia following an inflammatory disorder affecting the central nervous system. There is no history of diuretic use or excessive gastrointestinal sodium loss. Which relationship best explains the endocrine abnormality?

Correct Answer:
Central nervous system disease disturbs regulation of vasopressin secretion

Explanation: CNS disorders can disrupt normal hypothalamic control of vasopressin, leading to inappropriate secretion and SIADH.

Question:

A patient receiving cyclophosphamide develops progressive hyponatremia. Plasma is hypo-osmolar, yet renal water excretion remains inappropriately limited. Which explanation is most appropriate?

Correct Answer:
Medication-related SIADH

Explanation: Cyclophosphamide is among the drugs associated with SIADH, in which inappropriate antidiuretic activity prevents normal free-water excretion.

Question:

A patient with SIADH develops a falling serum sodium concentration without a history suggesting major external sodium loss. Which process most directly produces the reduction in measured serum sodium?

Correct Answer:
Dilution of extracellular sodium by retained free water

Explanation: The characteristic hyponatremia of SIADH is primarily dilutional: inappropriate water retention increases body water relative to sodium concentration.