Chapter 5 · Question 20
How is the amount of urine produced regulated?
Q20
How is the amount of urine produced regulated?
Answer Revealed
Direct Answer:
The amount of urine is regulated by reabsorption of water in the collecting duct, controlled by the antidiuretic hormone (ADH) released by the pituitary gland.
Simple Explanation
Our brain releases a hormone called ADH that tells the kidneys how much water to keep or release. When you drink less water, more ADH is released so the kidneys save water and you produce less urine. When you drink more, less ADH is released and you produce more urine.
Exam-Ready Structure
The amount of urine produced is regulated through a feedback mechanism involving the hormone ADH (antidiuretic hormone or vasopressin). The process works as follows: 1. When the body has excess water, the blood becomes more dilute. Osmoreceptors in the hypothalamus detect this and signal the pituitary gland to release less ADH. 2. With less ADH, the walls of the collecting ducts in the kidneys become less permeable to water, so less water is reabsorbed from the filtrate back into the blood. More water remains in the filtrate and is excreted as dilute urine. 3. When the body is dehydrated, the blood becomes more concentrated. The pituitary releases more ADH, making the collecting duct walls more permeable to water. More water is reabsorbed into the blood, and a smaller volume of concentrated urine is produced. This is a negative feedback mechanism that maintains the body's water balance (osmoregulation).
Key Points
- ADH (antidiuretic hormone) controls water reabsorption
- More ADH → more water reabsorbed → less urine
- Less ADH → less water reabsorbed → more urine
- Osmoreceptors in hypothalamus trigger ADH release
Common Mistakes
- Saying urine production is controlled only by drinking water quantity
- Not naming ADH or the pituitary gland
Answer Sources
- Water reabsorption and urine controltextbook section | Science | Life Processes | Nephron function and urine formation | Pages 19-20