Fall in water potential response

• A rise in solute concentration lowers the water potential of the blood. This can be caused by three different occurrences : 1. too much water being consumed, 2. lots of sweat occurring, 3. large amounts of ions being taken in.
• When the blood water potential falls, this is detected by osmoreceptor cells in the hypothalamus. This is because water will leave the osmoreceptor cells via osmosis, causing them to shrink. This causes the hypothalamus to release ADH.
• ADH stands for anti-diuretic hormone.
• ADH is released from the hypothalamus, then travels to the posterior pituitary gland where it enters the capillaries. Once it arrives at the kidneys, it binds to receptors on the surface of the collecting duct, activating the phosphorylase enzyme.
• Due to the activation of the phosphorylase enzyme, vesicles containing aquaporins fuse with the cell surface membrane. This increases the permeability of the membrane to water and urea. Consequently, urea leaves the collecting duct, causing water to leave and be reabsorbed by the blood.