The ADH trap
A free TEAS® anatomy & physiology explainer with an original practice question
ADH, antidiuretic hormone, helps the body keep water. It makes the collecting ducts of the kidney more permeable to water, so more water moves back into the blood.
More ADH therefore means less urine, and the urine is more concentrated. Less ADH means more, dilute urine. The name is a clue: a diuretic increases urine, and antidiuretic works against that.
The trap is linking more hormone with more output. Follow the water instead: if more water is recovered from the same fluid, less is left to leave as urine.
Try a sample question
In a model with fixed collecting-duct water input and other conditions held constant, more ADH action occurs. What change is expected in water leaving the duct as urine?
- A.It increases
- B.It remains unchanged
- C.It increases because recovery decreases
- D.It decreases
Show the answer
D. It decreases
"It decreases" because greater ADH action recovers more water from the same input. An increase is a trap: greater recovery leaves less water in fluid exiting as urine.
Why the other answers tempt:
- A. Greater ADH action promotes water recovery, leaving less water for urine.
- B. When recovery rises from the same input, less water remains in the duct.
- C. Greater ADH action promotes, rather than decreases, water recovery.
ADH helps the body recover water.
Checked against OpenStax Anatomy and Physiology 2e, 25.9 Regulation of Fluid Volume and Composition. Original question, not from a real test.
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