Collecting Duct & ADH Flashcards
(3 cards)
Collecting Duct
Passes through a hypertonic region of the medulla
Anti Diuretic Hormone (ADH) controls the permeability of the collecting duct to water. When it is more permeable, more water is reabsorbed to the blood and less water is excreted as urine
When blood water potential is lower than the set point, osmoreceptors in the hypothalamus detect the change
The posterior pituitary gland releases ADH into the bloodstream
ADH attaches to receptors on the cells of the collecting duct. Aquaporins (vesicles with water channels) fuse with the membrane of the cells next to the lumen of the collecting duct
Water moves into the cells by osmosis and then passes from the cells into the bloodstream, raising the water potential of blood
A low volume of concentrated urine is produced
As the water potential of the blood increases, the production of ADH decreases. Less ADH leads to a less permeable membrane of the collecting duct. This will lead to the collecting duct losing less water by osmosis and the production of a large volume of dilute urine
This detection of a change away from normal conditions and consequent processes to move conditions back towards normal is called negative feedback.
If the kidneys fail a range of treatments are available…
-Medication can be used to control K+ and CA2- levels to help balance fluids
-A low protein diet can be used to reduce the number of excess amino acids and thus the urea made
-Drugs can be used to lower blood pressure
-A dialysis could be used to artificially remove urea from the blood
-A kidney transplant could be used to replace the kidney that is no longer functioning with a healthy one
Dialysis
A dialysis machine is effective for the following reasons:
-Temperature at 40degrees to increase the rate of diffusion and maintains patient body temperature
-A large number of strands of dialysis tubing increases the surface are where diffusion can take place
-Dialysis tubing in a semipermeable membrane with pores that only allow small molecules like urea, water and salt through
-Dialysis fluid has no urea to give a concentration gradient; water leaves by osmosis. There is no concentration gradient for glucose and so it doesn’t leave the blood
-Fresh dialysis fluid maintains a concentration gradient
-Counter current flow of blood and fluid maintains a concentration gradient
