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7.3.6Unit 6: Practical Skills in Biology II

Hormones in Osmoregulation — IAL Edexcel Linear Revision Notes & Topical Questions

5 min read 4 parts Lesson 33 of 48 Unit quiz

📚 IAL Edexcel Linear Hub / Topical Revision
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Part 1 of 4Detecting Changes

7.3.6 Hormones in Osmoregulation
Osmoregulation
  • The control of the water potential of body fluids, which is part of homeostasis.
Osmoreceptors
  • Receptor cells in the hypothalamus monitor the water potential of the blood.
Posterior pituitary
  • Stimulated by impulses from the hypothalamus to release the hormone ADH into the blood.
ADH
  • Antidiuretic hormone, carried in the blood to the kidney where it affects the distal tubule and collecting duct.
Causes of low water
  • Sweating, diarrhoea or reduced water intake cause the blood water potential to fall.

Part 2 of 4When Water Potential Falls

1
The hypothalamus detects the fall in water potential and causes the posterior pituitary to secrete more ADH.
2
ADH binds to receptors on the cells of the distal convoluted tubule and collecting duct, starting a signalling cascade.
3
Vesicles containing aquaporins move to the cell surface membrane facing the lumen and fuse with it.
4
More aquaporins increase membrane permeability to water, so more water is reabsorbed by osmosis into the concentrated medulla.
5
A small volume of concentrated urine is produced and the blood water potential rises back to normal.

Part 3 of 4When Water Potential Rises

When Water Potential Rises
Detection
  • The hypothalamus detects the high water potential and the pituitary releases less ADH.
Membrane
  • Aquaporins are removed from the membrane, so the collecting duct becomes less permeable to water.
Result
  • A large volume of dilute urine is produced and the blood water potential falls.
Feedback
  • The changes restore the normal level, which is an example of negative feedback.
FeatureLow blood waterHigh blood water
ADHIncreasesDecreases
AquaporinsMoreFewer
UrineSmall, concentratedLarge, dilute

Part 4 of 4Exam Checklist & Tips

7.3.6 – Key Points for the Exam

  • Osmoregulation Control of the water potential of body fluids.
  • Osmoreceptor A receptor that detects changes in blood water potential.
  • ADH A hormone that increases the permeability of the collecting duct to water.
  • Aquaporin A channel protein that allows water to cross a membrane.
  • Posterior pituitary The gland that releases ADH into the blood.

Common Mistakes

  • Saying ADH makes the kidneys produce more water; it makes them reabsorb more.
  • Stating that ADH is secreted when the blood is too dilute.
  • Forgetting the aquaporins and describing only a change in permeability.
  • Mixing up the sitesADH acts on the distal tubule and collecting duct.

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