AQA · A-Level · Biology
Course version: 7402 · Version from Sept 2016
The roles of the hypothalamus, posterior pituitary and antidiuretic…
Full specification wording
Control of blood water potential (A-level only): The roles of the hypothalamus, posterior pituitary and antidiuretic hormone (ADH) in osmoregulation.
Osmoregulation controls blood water potential.
Checked against the AQA 7402 specification (opens in a new tab) on .
- Point 2 of 3
- 4 key terms
Study notes
From the checked teaching notes for this specification point.
The idea
Osmoregulation controls blood water potential. If it falls, water leaves osmoreceptors in the hypothalamus by osmosis, causing them to shrink. This stimulates the hypothalamus to produce more ADH, which moves to the posterior pituitary gland for release into the blood. ADH travels to the kidneys, binding to complementary receptors on the cell-surface membranes of the distal convoluted tubule and collecting duct. This activates a second messenger, causing vesicles containing aquaporins to fuse with the membrane. This increases membrane permeability to water. More water is reabsorbed into the blood by osmosis, producing a smaller volume of concentrated urine and restoring blood water potential.
What earns the marks
- Osmoreceptors in the hypothalamus detect a decrease in the water potential of the blood.
- Water leaves the osmoreceptors by osmosis, causing them to shrink and stimulate ADH production.
- ADH is produced in the hypothalamus and secreted into the blood by the posterior pituitary gland.
- ADH binds to receptors with a complementary tertiary structure on the cell-surface membranes of the distal convoluted tubule and collecting duct.
- More water is reabsorbed into the blood by osmosis down the water potential gradient, producing a smaller volume of concentrated urine.
Common mistakes and how to put them right
Stating the pituitary gland produces ADH.
Put it right: The hypothalamus produces ADH; the posterior pituitary only stores and secretes it.
Explaining ADH binding using enzyme terminology like 'active site'.
Put it right: Use receptor terminology, stating the receptor has a specific tertiary structure complementary to the ADH molecule.
Forgetting to mention osmosis when describing water reabsorption.
Put it right: State that water moves back into the blood by osmosis down a water potential gradient.
Exam tips
- Clearly distinguish between the roles of the hypothalamus (detects water potential changes, produces ADH) and the posterior pituitary (secretes ADH).
- When explaining how ADH increases water reabsorption, explicitly mention the fusion of vesicles containing aquaporins with the cell-surface membrane.
Try the lesson
The start of the Control of blood water potential (A-level only): The roles of the hypothalamus, posterior pituitary and antidiuretic hormone (ADH) in osmoregulation. lesson, made from checked teaching notes for this specification point.
Have a go first
Which structure detects a fall in the water potential of the blood and triggers the release of antidiuretic hormone (ADH)?
Listen
Osmoregulation controls blood water potential. If it falls, water leaves osmoreceptors in the hypothalamus by osmosis, causing them to shrink. This stimulates the hypothalamus to produce more ADH, which moves to the posterior pituitary gland for release into the blood. ADH travels to the kidneys, binding to complementary receptors on the cell-surface membranes of the distal convoluted tubule and collecting duct. This activates a second messenger, causing vesicles containing aquaporins to fuse with the membrane. This increases membrane permeability to water. More water is reabsorbed into the blood by osmosis, producing a smaller volume of concentrated urine and restoring blood water potential. A strong answer earns marks for these points. Osmoreceptors in the hypothalamus detect a decrease in the water potential of the blood. Water leaves the osmoreceptors by osmosis, causing them to shrink and stimulate ADH production. ADH is produced in the hypothalamus and secreted into the blood by the posterior pituitary gland. ADH binds to receptors with a complementary tertiary structure on the cell-surface membranes of the distal convoluted tubule and collecting duct. A common slip: Stating the pituitary gland produces ADH. Instead, The hypothalamus produces ADH; the posterior pituitary only stores and secretes it. Exam tip: Clearly distinguish between the roles of the hypothalamus (detects water potential changes, produces ADH) and the posterior pituitary (secretes ADH).
Key words
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Osmoregulation
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Antidiuretic hormone (ADH)
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Hypothalamus and posterior pituitary
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Aquaporins
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See every definition
- Osmoregulation
- Controls blood water potential; if it falls, water leaves osmoreceptors in the hypothalamus by osmosis, causing them to shrink.
- Antidiuretic hormone (ADH)
- Produced in the hypothalamus and secreted into the blood by the posterior pituitary gland, travelling to the kidneys.
- Hypothalamus and posterior pituitary
- The hypothalamus detects water potential changes and produces ADH, while the posterior pituitary secretes it into the blood.
- Aquaporins
- Contained in vesicles that fuse with the membrane, increasing membrane permeability to water.
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