Question at position 16 Dehydration stimulates the release of __________ from the pituitary gland, which stimulates water reabsorption in the kidneys and results in a small volume of more concentrated urine.oxytocinantidiuretic hormone (ADH)growth hormone (GH)luteinizing hormone (LH)Clear my selection单项选择题
A
oxytocin
B
antidiuretic hormone (ADH)
C
growth hormone (GH)
D
luteinizing hormone (LH)

Question

Question at position 16 Dehydration stimulates the release of __________ from the pituitary gland, which stimulates water reabsorption in the kidneys and results in a small volume of more concentrated urine.oxytocinantidiuretic hormone (ADH)growth hormone (GH)luteinizing hormone (LH)Clear my selection单项选择题

A

oxytocin

B

antidiuretic hormone (ADH)

C

growth hormone (GH)

D

luteinizing hormone (LH)

BlackTom AI · Accepted Answer

Antidiuretic hormone (ADH), also called vasopressin, is the hormone released in response to dehydration and is the correct choice.

1. Relevant knowledge points and concepts
- Body water balance is regulated by plasma osmolarity and blood volume.  
- Osmoreceptors in the hypothalamus detect increased plasma osmolarity (dehydration).  
- ADH is synthesized in the hypothalamic supraoptic and paraventricular nuclei and released from the posterior pituitary (neurohypophysis).  
- ADH acts on V2 receptors in the renal collecting ducts to increase cAMP-mediated insertion of aquaporin-2 channels, raising water reabsorption and concentrating urine.  
- Other pituitary hormones (oxytocin, growth hormone, luteinizing hormone) have distinct functions unrelated to direct water reabsorption.

2. Step-by-step reasoning process
- Dehydration increases plasma osmolarity and/or reduces blood volume.  
- Hypothalamic osmoreceptors sense this change and trigger action potentials to posterior pituitary terminals.  
- The posterior pituitary releases stored ADH into the bloodstream.  
- ADH binds to V2 receptors on principal cells of the renal collecting duct.  
- Intracellular cAMP signaling causes aquaporin-2-containing vesicles to fuse with the apical membrane, increasing water permeability.  
- More water is reabsorbed from the filtrate back into blood, producing a smaller volume of urine with higher osmolarity.

3. Intermediate steps (mechanistic detail)
- Increased plasma osmolarity → hypothalamic osmoreceptor activation → ADH secretion.  
- ADH → V2 receptor → Gs protein → adenylate cyclase → ↑cAMP → PKA-mediated trafficking of aquaporin-2 to apical membrane → increased water reabsorption.

4. Why the correct answer is correct
ADH directly mediates renal water reabsorption in response to dehydration, causing concentrated, low-volume urine. This matches the physiological description in the question.

5. Why other options are incorrect
- Oxytocin: released from posterior pituitary but primarily causes uterine contraction and milk ejection, not water reabsorption.  
- Growth hormone (GH): anterior pituitary hormone that stimulates growth and metabolic effects, not acute regulation of renal water handling.  
- Luteinizing hormone (LH): anterior pituitary gonadotropin that triggers ovulation and sex steroid production, unrelated to urine concentration.

6. Conclusion
Therefore, the hormone released during dehydration that stimulates renal water reabsorption and produces a small volume of concentrated urine is antidiuretic hormone (ADH), which matches the provided correct answer.