Horm in osmo

• ·       Hormones such as antidiuretic hormone can adjust the permeability of the collecting duct to change how much water is leaving the body in the urine.
• ·       When the water potential of the blood is too low, osmoreceptors in the hypothalamus detect this, and the hypothalamus produces ADH, which increases the permeability to water of the cells in the wall of the distal convoluted tubule and collecting duct.
• ·       ADH binds to receptors on the surface on the cells, activating an enzyme called phosphorylase that causes vesicles within the cell to bind with the surface membrane, meaning the number of water channel proteins (aquaporins) is increased and the permeability of the walls to urea is increased, finally leading to more water leaving the collecting duct because of the lowered water potential in the surrounding fluid.
• ·       This process prevents blood water potential getting any lower, and once water potential increases (because of external reasons such as drinking more water) the hypothalamus sends less impulses to the pituitary gland, meaning that less ADH is produced.
• ·       When blood water potential is too high, the opposite process occurs and less water is reabsorbed from the collecting duct, meaning that urine becomes more dilute.