The Question
A person has a disorder where she is unable to secrete ADH. It is most likely that …
A the renal tubules will become more permeable to water.
B the blood will have a higher volume of water.
C large volumes of urine will be produced.
D more water is reabsorbed by the renal tubules.
Details
💡 Hint
What is the primary function of ADH in the kidneys? If this hormone is absent, what would be the direct opposite effect on water reabsorption and urine production?
📝 Solution Steps
- Step 1: Recall the normal function of ADH in the human body, specifically its effect on the kidneys and water reabsorption.
- Step 2: Consider the physiological consequences if ADH is *not* secreted.
- Step 3: Evaluate each given option against these consequences to find the most likely outcome.
📚 Explanation
ADH (Antidiuretic Hormone) plays a crucial role in osmoregulation by increasing the permeability of the renal tubules (specifically the collecting ducts and distal convoluted tubules) to water. This allows more water to be reabsorbed from the filtrate back into the blood, leading to a smaller volume of concentrated urine.
If a person is *unable to secrete ADH*:
* The renal tubules will become *less permeable* to water (the opposite of ADH’s effect).
* Less water will be reabsorbed from the filtrate.
* This will result in a *large volume of dilute urine* being produced.
* Consequently, the blood volume would tend to decrease, and the blood would become more concentrated (higher solute concentration).
Let’s check the options:
* **A the renal tubules will become more permeable to water**: Incorrect. Lack of ADH makes them *less* permeable.
* **B the blood will have a higher volume of water**: Incorrect. Less water reabsorption means more water is lost in urine, leading to lower blood volume.
* **C large volumes of urine will be produced**: Correct. Without ADH, water is not reabsorbed effectively, leading to excessive urine production.
* **D more water is reabsorbed by the renal tubules**: Incorrect. Less water will be reabsorbed.
✅ Answer
C
⚠️ Common Mistakes
- Confusing the effect of ADH with the effect of its absence.
- Incorrectly linking ADH to blood glucose regulation (which is insulin/glucagon).
- Misinterpreting the impact on urine volume or blood volume.