A-LEVEL BIOLOGY AQA NOTES
control of blood water potential
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The Role of the Kidneys in Osmoregulation
- Osmoregulation is maintaining a constant water potential of the blood, despite changes in the level of water and salt intake.
- The kidneys are made if nephrons which help filter the blood. The blood undergoes ultrafiltration at the glomerulus due to the smaller diameter of the efferent arteriole than the afferent arteriole, creating high hydrostatic pressure
- The filtrate passes into the Bowman’s capsule and travels around the entire nephron, where certain ions and water are reabsorbed into the blood whilst the remaining filtrate is excreted as urine.
- Sodium is actively transported out of the proximal convoluted tubule and into the blood
- Glucose & amino acids are co-transported out of the proximal convoluted tubule via sodium ions diffusing into the epithelial cells
The Role of the Hypothalamus in Osmoregulation
- The hypothalamus contains osmoreceptors which signal to specialised neurosecretory cells. A fall in water potential causes the release of antidiuretic hormone (ADH) from the pituitary gland.
- ADH travels in the blood to the kidneys, attaching to ADH receptors, activating the intracellular enzyme phosphorylase. This causes vesicles containing aquaporins to fuse with the plasma membrane, reducing water loss by increasing the permeability of the collecting duct and distal convoluted tubule