definition of osmoregulation
the control of the water potential of the body fluids
osmoregulation is a key part of
homeostasis
process of osmoregulation (1)
specialised sensory neurones ,(osmoreceptors) monitor the water potential of the blood
definition and location of osmoreceptors
specialised sensory neurones located in the hypothalamus part of the brain
process of osmoregulation (2)
if osmoreceptors detect a decrease in the water potential of the blood nerve impulses are sent along these sensory neurones to the posterior pituitary gland
process of osmoregulation (3)
nerve impulses stimulate the posterior pituitary gland to release antidiuretic hormone (ADH)
process of osmoregulation (4)
ADH molecules enter the blood and travel eventually to the kidneys causing them to reabsorb more water reducing water loss by urine
function of Antidiuretic hormone ADH
to stimulate the kidneys to reabsorb water in times of need
effect of ADH on the Kidneys (1)
ADH causes the luminal membranes of the collecting ducts cells to become more permeable to water
which area of the nephron does ADH affect
collecting ducts
effect of ADH on the Kidneys (2)
ADH does this by causing and increase in the number of aquaporins in the luminal membranes of the collecting duct
process of number of aquaporin increase (1)
collecting duct cells contain vesicles the membranes of which contain many aquaporins
what is an aquaporin
water permeable channel protein
effect of ADH on the Kidneys (2)
ADH molecules bind to receptor proteins activating a signalling cascade that leads to the phosphorylation of the aquaporin molecules
effect of ADH on the Kidneys (3)
aquaporins are activated causing the vesicles to fuse with the luminal membranes of the collecting duct cells which increases the permeability of the membrane to water
effect of ADH on the Kidneys (3)
as the filtrate in the nephron travels along the collecting duct, water molecules diffuse from the collecting duct of high water potential through the aquaporins and into the tissue fluid and blood plasma in the medulla of low water potential
effect of ADH on the Kidneys (4)
as the filtrate in the collecting duct loses water it becomes more concentrated
effect of ADH on the Kidneys (5)
resulting in a small volume of concentrated urine being produced
if there is an increase in the water potential of the body what happens
no ADH produced
NO stimulation of posterior pituitary gland
aquaporins remain unphosphorylated
aquaporins are removed from the luminar cell wall
more dilute urine produced