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Development of the Urinary System Quiz
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Which statement best describes the role of the mesonephros during human embryonic development?
- A It is a non-functional vestigial structure with no excretory role You picked ✕
- B It develops from endoderm and drains directly into the ureter You picked ✕
- C It is a temporary excretory system that contributes to the male genital tract You picked ✓
- D It persists as the primary kidney throughout postnatal life You picked ✕
- E It forms the definitive kidney responsible for lifelong urine production You picked ✕
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Incorrect
The answer is C: It is a temporary excretory system that contributes to the male genital tract
Explanation
Why C is correct
See Mesonephros. Option C is correct: the mesonephros is the second of the three embryonic kidney systems, and it acts as a temporary excretory system (one that removes waste) for the embryo from about weeks four to eight. Its tubules receive a tuft of capillaries from the aorta, so blood is filtered, and the filtrate drains into the mesonephric duct. Most of the tubules have regressed by the end of the second month, once the definitive kidney, the metanephros, begins to take over. The system leaves something behind, though. In males, testosterone (the hormone made by the testes) keeps the mesonephric duct, which forms the efferent ductules (the tubes that carry sperm out of the testis), the epididymis (the coiled tube where sperm are stored and mature), the vas deferens and the seminal vesicles. In females, without testosterone, the duct degenerates and leaves only a vestigial remnant (Gartner's duct). The mesonephric duct also sprouts the ureteric bud, which triggers the metanephros to form. The memory aid is that the mesonephros is the middle kidney, a stand-in that works for a few weeks, but its duct stays on as the male genital plumbing.
- Role: The mesonephros is a temporary excretory system for about weeks four to eight.
- Duct: The mesonephric duct drains it and sprouts the ureteric bud.
- Male fate: With testosterone the duct forms the epididymis, vas deferens and seminal vesicles.
Why the other options are incorrect
- A. It is a non-functional vestigial structure with no excretory role: This describes the pronephros, which is never functional in humans and regresses by the end of the fourth week. The mesonephros does filter blood and drains it into the mesonephric duct. This statement would be correct for the pronephros. Your answer
- B. It develops from endoderm and drains directly into the ureter: Two details are wrong: the mesonephros arises from intermediate mesoderm, not endoderm, and its tubules drain into the mesonephric duct, not straight into the ureter. The ureter instead develops from the ureteric bud, an outgrowth of that duct. Your answer
- D. It persists as the primary kidney throughout postnatal life: The mesonephros does not persist as a working kidney, and the metanephros supplies kidney function from about 12 weeks of gestation onwards. What persists in males is the mesonephric duct and some tubules as genital structures, which is the likely source of this confusion. Your answer
- E. It forms the definitive kidney responsible for lifelong urine production: The definitive kidney is the metanephros, which forms when the ureteric bud meets the metanephric mesenchyme. The mesonephros is only a temporary stand-in that comes before it. This statement would be correct as a description of the metanephros. Your answer
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More questions from this set. Start the quiz to answer them and see each explanation.
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1
Which embryological structure gives rise to the permanent (definitive) kidney in humans?
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2
Which embryological structure gives rise to the collecting system of the definitive kidney?
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