34 practice MCQs on osmoregulation, excretion, the kidney and nephron, urine formation and thermoregulation. Every question has the correct answer and an explanation.
Start free — 20 questionsHomeostasis is part of the MDCAT Biology syllabus. This page collects Homeostasis MCQs in the style of past MDCAT papers — below are 12 of them with answers and explanations, and the full set of 34 questions is in the HighYield MDCAT QBank.
This chapter covers: osmoregulation, excretion, the kidney and nephron, urine formation and thermoregulation.
Correct answer: D. Loop of Henle
Water reabsorption via the countercurrent multiplier mechanism occurs in the loop of Henle, which establishes the medullary concentration gradient.
Correct answer: B. Abdomen
In peritoneal dialysis, dialysis fluid is introduced directly into the abdominal (peritoneal) cavity, using the peritoneum as the filtering membrane.
Correct answer: B. Proximal tubule
Most reabsorption of filtered substances, including glucose, amino acids, water and ions, occurs in the proximal tubule of the nephron.
Correct answer: C. Distal and collecting ducts
The distal convoluted tubule and collecting duct are the nephron segments whose water permeability is regulated by antidiuretic hormone (ADH).
Correct answer: D. Na+
Active reabsorption of sodium ions (Na+) in the thick ascending limb of the loop of Henle is driven mainly by the Na-K-2Cl transporter, distinct from aldosterone's site of action in the distal nephron.
Correct answer: A. Juxtamedullary nephrons
Juxtamedullary nephrons, with their long loops of Henle extending deep into the medulla, are responsible for producing highly concentrated urine.
Correct answer: B. Posterior pituitary lobe
Antidiuretic hormone (ADH) is synthesized in the hypothalamus but stored in and released from the posterior pituitary lobe.
Correct answer: A. Loop of Henle
The countercurrent multiplier mechanism operates in the loop of Henle, establishing the osmotic gradient that allows urine concentration.
Correct answer: D. Ammonia
Ammonia is the most toxic nitrogenous excretory product, requiring rapid dilution or conversion (e.g. to urea) to prevent toxicity.
Correct answer: D. Posterior pituitary
Vasopressin (ADH) and oxytocin are synthesized in the hypothalamus but released from the posterior pituitary gland.
Correct answer: A. Uric acid
Ammonia, urea and uric acid are the major forms of nitrogenous wastes excreted by the animals. Ammonia is the most toxic form and requires large amount of water for its elimination, whereas uric acid, being the least toxic, can be removed with a minimum loss of water.
Correct answer: C. Normal health
Health is a state of complete physical, mental and social well-being and not merely the absence of disease or infirmity and the steady state of hemostasis is also known as normal health.
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