QUIZ: Kidney structure and function

Test your understanding of nephron structure and kidney physiology with these five quiz questions.

1. A 52-year-old woman presents with oedema and frothy urine. Urinalysis reveals heavy proteinuria, but no haematuria. Her serum albumin is low.
   Which of the following best describes the role of the glomerulus in the nephron?
   A) Reabsorption of glucose and amino acids
   B) Active secretion of potassium ions
   C) Filtration of blood plasma into Bowman's capsule
   D) Concentration of urine via water reabsorption
   E) Synthesis of renin
   Explanation: The glomerulus filters blood plasma into Bowman’s capsule. This is the first step in urine formation, where water and small solutes are filtered from the blood into the nephron.


2. A 35-year-old man is recovering from acute dehydration. Blood tests reveal a mild elevation in creatinine, but urine sodium is low and urine osmolality is high.
   Which part of the nephron is most responsible for bulk reabsorption of filtered sodium and water?
   A) Secretion of antidiuretic hormone (ADH)
   B) Reabsorption of approximately 65% of filtered sodium and water
   C) Filtration of large proteins from the blood
   D) Concentration of urine through passive water reabsorption
   E) Generation of the corticomedullary gradient
   Explanation: The PCT reabsorbs around 65% of filtered sodium and water, as well as nearly all glucose, amino acids, and bicarbonate. This is crucial for maintaining homeostasis.


3. A 24-year-old man is lost in the desert for two days with minimal water intake. His kidneys activate mechanisms to conserve water while still clearing solutes.
   In the Loop of Henle, the descending limb is permeable to _____, while the ascending limb actively transports _____ out of the filtrate.
   A) Sodium; water
   B) Water; sodium, potassium, and chloride ions
   C) Glucose; amino acids
   D) Urea; bicarbonate
   E) Bicarbonate; water
   Explanation: The descending limb is permeable to water, while the ascending limb actively transports sodium, potassium, and chloride. This creates a gradient used for urine concentration.


4. A 68-year-old woman with congestive heart failure is prescribed spironolactone. On review, her potassium level is elevated.
   Which hormone is most responsible for increasing sodium reabsorption and potassium secretion in the distal nephron?
   A) Antidiuretic hormone (ADH)
   B) Parathyroid hormone (PTH)
   C) Aldosterone
   D) Atrial natriuretic peptide (ANP)
   E) Erythropoietin
   Explanation: Aldosterone acts on the distal tubule and collecting duct to increase sodium reabsorption and potassium secretion. It is part of the renin-angiotensin-aldosterone system (RAAS).


5. A 76-year-old man with long-standing heart failure is admitted with hyponatraemia and low serum osmolality. His urine remains concentrated despite low sodium.
   Which of the following best explains how his kidneys can still concentrate urine?
   A) Initiating the filtration of blood
   B) Reabsorbing glucose and amino acids
   C) Creating a concentration gradient in the medulla to concentrate urine
   D) Stimulating aldosterone release
   E) Generating renin from the juxtaglomerular cells
   Explanation: Countercurrent multiplication in the Loop of Henle establishes a hyperosmotic medullary interstitium, allowing water reabsorption in the collecting duct and concentration of urine.

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