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14.1.614-15 · Homeostasis and Control

Osmoregulation — Cambridge AS & A Level Biology 9700 Revision Notes & Topical Questions

5 min read 8 parts Lesson 7 of 31 1 quiz

📚 Cambridge AS & A Level Biology 9700 Hub / Topical Revision
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Lesson summary

14.1.6 Osmoregulation — CAMBRIDGE AS & A LEVEL BIOLOGY 9700 — REVISION NOTES notes: Explain how ADH controls water reabsorption in the collecting duct.Definition — the control of the water potential of body fluids.Role — a key part of homeostasis.Osmoreceptors — sensory neurones …

  • Aquaporins
  • Water movement
  • Permeability
  • Posterior pituitary
  • Osmoreceptors — sensory neurones in the hypothalamus that monitor the water potential of the blood
  • Osmoreceptors detect a decrease in water potential

Part 1 of 6Osmoregulation

Definition
  • Definition the control of the water potential of body fluids.
Role
  • Role a key part of homeostasis.
Osmoreceptors
  • Osmoreceptors sensory neurones in the hypothalamus that monitor the water potential of the blood.

Part 2 of 6Response to low blood water potential

1
Osmoreceptors detect a decrease in water potential.
2
Impulses pass along sensory neurones to the posterior pituitary gland.
3
The posterior pituitary releases antidiuretic hormone (ADH).
4
ADH enters the blood and travels to the kidneys.
5
The kidneys reabsorb more water, reducing water loss in urine.

Part 3 of 6How ADH acts on the collecting duct

1
ADH binds to receptor proteins on the collecting duct cells.
2
A signalling cascade phosphorylates aquaporin molecules.
3
Vesicles with aquaporins fuse with the luminal membrane.
4
The membrane becomes more permeable to water.
Vesicles
  • Vesicles collecting duct cells contain vesicles with many aquaporins in their membranes.
Aquaporins
  • Aquaporins water-permeable channels, increased in number in the luminal membrane.

Part 4 of 6Result of ADH

Water movement
  • Water movement water leaves the collecting duct by osmosis into the medulla tissue fluid and blood.
Filtrate
  • Filtrate becomes more concentrated as it loses water.
Urine
  • Urine a small volume of concentrated urine is produced.
Route
  • Route urine flows to the bladder through the ureters.

Part 5 of 6When blood water potential is high

Impulses
  • Impulses none are sent to the posterior pituitary.
ADH
  • ADH none is released.
Aquaporins
  • Aquaporins are removed from the luminal membrane.
Permeability
  • Permeability collecting duct cells are no longer permeable to water.
Urine
  • Urine a large volume of dilute urine is produced.

Part 6 of 6More from the specification

1Hepatic deamination of amino acids
  • Hepatic deamination of amino acids deamination of excess amino acids in the liver produces urea, which causes osmotic water regulation demands.
2Ultrafiltration in the Renal Corpuscle
  • High hydrostatic pressure in the glomerular capillaries forces blood plasma fluid across the basement membrane into the Bowman's capsule of the nephron, creating glomerular filtrate free of large proteins and blood cells.
3Selective Reabsorption in the Convoluted Tubule
  • Epithelial cells of the proximal convoluted tubule actively reabsorb essential solutes from filtrate back into peritubular capillaries,
  • including 100% of filtered glucose and amino acids via sodium cotransport.
4Hormonal Regulation and Glucose Homeostasis
  • Pancreatic insulin ensures normal blood plasma glucose levels;
    • in untreated diabetes mellitus, glomerular filtrate contains excess glucose exceeding tubule carrier transport maximums,
  • leading to glucose in urine.
5Gradient
  • A difference in concentration.
6Negative feedback
  • A mechanism in which a change from the set point triggers a response that returns the factor to the set point.
7Epithelial cell
  • A cell forming a covering or lining layer of tissue.
8Amino acid
  • The unit from which proteins are made; the sequence decides the protein's shape and function.
9Selective reabsorption
  • Return of useful substances from the filtrate to the blood.
10Glucose oxidase
  • Enzyme oxidising glucose to gluconic acid and hydrogen peroxide.
11Basement membrane
  • Collagen and glycoprotein filter layer.
12Target cells
  • Cells that respond to a particular hormone.
13Glucose
  • A simple sugar; the unit that starch, glycogen and cellulose are built from.
14Capsule
  • Protective outer layer on some bacteria.
15Capillary
  • Vessel one cell thick where exchange takes place.
16Insulin
  • A pancreatic hormone that lowers blood glucose.
17Nephron
  • Kidney tubule that filters blood and forms urine.
18Plasma
  • The liquid part of blood.
19Glomerulus
  • A knot of capillaries inside the Bowman's capsule.
20Cause
  • A factor that directly produces an effect through a known mechanism.

Key terms

TermMeaning
OsmoregulationControl of water potential of body fluids.
OsmoreceptorCell detecting changes in blood water potential.
ADHAntidiuretic hormone, increasing water reabsorption.
AquaporinChannel protein allowing water to cross a membrane.
Posterior pituitaryGland releasing ADH.
Collecting ductTube where ADH acts on water reabsorption.

Avoid these mistakes

1
Saying ADH is made in the kidney — it is released from the posterior pituitary.
2
Saying ADH makes the duct less permeable — it increases aquaporins and permeability.
3
Saying osmoreceptors are in the kidney — they are in the hypothalamus.
4
Saying high water potential increases ADH — ADH release stops.

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