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Reabsorption, ADH and urine
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After filtration, the nephron takes back what the body needs. The hormone ADH controls how much water is reabsorbed.
Selective reabsorption of glucose
All the glucose in the filtrate is reabsorbed into the blood in the proximal convoluted tubule.
This is selective reabsorption: glucose is needed for respiration, so none is wasted in urine.
This is selective reabsorption: glucose is needed for respiration, so none is wasted in urine.
Water and ADH
Water is reabsorbed into the blood from the collecting duct.
If the blood is too concentrated (for example after sweating), the pituitary gland releases more ADH (antidiuretic hormone).
ADH makes the collecting duct more permeable to water, so more water is reabsorbed. A small volume of concentrated urine is made.
If the blood is too dilute, less ADH is released: less water is reabsorbed and a large volume of dilute urine is made.
If the blood is too concentrated (for example after sweating), the pituitary gland releases more ADH (antidiuretic hormone).
ADH makes the collecting duct more permeable to water, so more water is reabsorbed. A small volume of concentrated urine is made.
If the blood is too dilute, less ADH is released: less water is reabsorbed and a large volume of dilute urine is made.
Urine and other hormones
Urine contains water, urea and ions. Healthy urine contains no glucose and no protein.
The pituitary also releases FSH (causes an egg to mature in the ovary and stimulates oestrogen release) and LH (triggers ovulation).
The pituitary also releases FSH (causes an egg to mature in the ovary and stimulates oestrogen release) and LH (triggers ovulation).
On a hot day a student sweats a lot. Explain the effect on her urine.
- Sweating loses water, so the blood becomes more concentrated.
- The pituitary gland releases more ADH.
- The collecting ducts become more permeable and reabsorb more water.
Answer: She makes a smaller volume of more concentrated urine.
All glucose is reabsorbed in the proximal convoluted tubule. Water is reabsorbed from the collecting duct. When blood is too concentrated, the pituitary releases more ADH, more water is reabsorbed and urine is small in volume and concentrated. Urine contains water, urea and ions.
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