Osmoregulation
Introduced| English | Meaning |
|---|---|
| osmoregulation/ˌɒzmɔːɡjʊˈleɪʃn/ | The control of water balance and dissolved solute concentrations in an organism. |
| hypothalamus/ˌhaɪpəʊˈθælæməs/ | A brain region that helps regulate homeostasis and links nervous control with hormonal signalling. |
| pituitary gland/pɪˈtjuːɪtəri ɡlænd/ | An endocrine gland beneath the hypothalamus that releases hormones involved in growth, reproduction and control of other endocrine organs. |
| antidiuretic hormone/ˌæntɪˌdɪjuːˈretɪk ˈhɔːməʊn/ | A hormone that increases water reabsorption in the kidneys, helping regulate body water balance. |
| collecting duct/kəˈlektɪŋ dʌkt/ | A kidney tube receiving fluid from several nephrons, where further water and ion regulation helps determine urine composition. |
| aquaporin/ˈækwəpɔːrɪn/ | A membrane channel protein that allows water molecules to pass through. |
Balancing the body's water
- Osmoregulation 渗透调节 controls the water content of the blood.
- It is run by the brain, using a hormone called ADH.
- It is a clear example of negative feedback.
The hormone that controls water reabsorption in the kidney is ______.
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ADH makes the collecting duct more permeable to water.
The ADH pathway
- The hypothalamus 下丘脑 detects the water potential of the blood.
- When the blood is too concentrated, the pituitary gland 垂体 releases antidiuretic hormone 抗利尿激素 (ADH).
- ADH makes the collecting ducts 集合管 more permeable to water by adding water channels (aquaporins 水通道蛋白).
- More water is reabsorbed into the blood, so less, more concentrated urine is made.
Osmoregulation by ADH (negative feedback)
The ADH pathway
Step through it. When the blood gets too concentrated, ADH makes the kidney save water — classic negative feedback.
Which part of the brain detects the water potential of the blood?
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The hypothalamus monitors blood water potential and triggers ADH release from the pituitary.
ADH increases water reabsorption by:
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ADH inserts aquaporins into the collecting duct membranes, so more water is reabsorbed.
When the blood is too concentrated, the body:
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More ADH means more water returned to the blood, restoring its water content (negative feedback).
Put the ADH response to concentrated blood in order.
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Detect → release ADH → reabsorb water → return to the set point. Negative feedback.
Negative feedback in action
- Too concentrated → more ADH → more water reabsorbed → blood water restored.
- Too dilute → less ADH → less water reabsorbed → more dilute urine.
- Either way, the change is corrected — negative feedback.
Osmoregulation by ADH is an example of negative feedback.
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A change in blood water triggers a response that returns it to normal — classic negative feedback.
When water balance fails
- Too little water → blood is concentrated → more ADH → small volume of concentrated urine.
- Too much water → blood is dilute → less ADH → large volume of dilute urine.
You've got it
- osmoregulation controls blood water content
- the hypothalamus detects water potential; the pituitary releases ADH
- ADH adds aquaporins to the collecting ducts → more water reabsorbed → concentrated urine
- it works by negative feedback (more ADH when blood is too concentrated)