Osmoregulation Flashcards
What is negative feedback?
mechanisms to restore any deviations from normal in a system back to its original state
Why is osmoregulation important?
-HYPERTONIC: too much water leaves cells, crenation, chemical reactions etc, cant occur
- HYPOTONIC: water moves into cells, so cells burst, lysis.
What is hypertonic?
blood has too low water potential (less water more ions)
What is hypotonic?
blood has too high water potential (more water less ions)
What might cause blood to be hypertonic?
- lots of ions in food
- not enough water
- sweating
What might cause blood to be hypotonic?
- too much water
- not enough ions
What detects change in water potential?
osmoreceptors in the hypothalamus
Where is ADH produced?
osmoreceptors in the hypothalamus
What stimulates MORE ADH to be produced?
water leaves osmoreceptor cells, stimulating ADH to be produced
Where is ADH released?
posterior pituitary gland
What effect does ADH have?
- increases the permeability of the walls of the distal convoluted tubule and collecting ducts
- so more water is reabsorbed
What happens when ADH reaches the kidneys?
- ADH binds to complementary receptors on the cell membranes of epithelial cells of the collecting duct
What happens when ADH binds to receptors?
activates phosphorylase enzyme in the cells
What does phosphorylase cause to happen?
- vesicles containing aquaporins
- fuse to cell membranes, integrating more aquaporins into the membrane
What are aquaporins?
channel proteins that allow water to pass through
What is the effect of ADH on the collecting ducts?
- more channel proteins
- membrane is more permeable to water
- water moves into blood by osmosis
How does the loop of Henle reabsorb water from glomerular filtrate? (5 points)
- ascending limb, Na+ actively transported out
- ascending limb impermeable to water
- Na+ diffuse in to descending limb
- water moves out of descending limb to the medulla, which has a lower water potential, by osmosis
- longer loop = lower WP in medulla
What causes osmoreceptors to release ADH?
- low water potential in the blood
- water moves out by osmosis
- cell shrivels, ADH secreted
How does ADH allow water to enter the blood?
- ADH binding causes vesicles containing aquaporins to fuse to the membrane
- water can move into epithelial cells by osmosis
- water then moves into the capillary
