Regulation of body osmolarity Flashcards
Rise in osmolarity has what effect on the hypothalamus?
In in osmolarity activates the supraoptic and paraventricular nuclei. Axons from the supraoptic nucleus carry and impulse to the posterior pituitary gland. Causes a rise in intracellular calcium (needed for AVP vesicle to fuse with plasma membrane) and secretion of AVP.
Osmoreceptors initiate cell shrinkage.
Also activates osmoreceptors in the thirst center. So…there are two responses.
What part of the nephron doesvasopressin act on>
Collecting duct
What effect does vasopressin have and how does it do this?
It increases water reabsorption by inserting aquaporin 2 into the epithelium of the collecting duct. These aquaporins are not activated when vasopressin is low.
Where does AVP come from and what stimulates this
Comes from the posterior pituitary, the post pituitary is stimulated to realease AVP by the hypothalamus which sends nerve impuls from the supraoptic nucleus.
What is the osmolarity threshold for AVP release?
270mOsm/L
What is the threshold for hte Thirst Center?
280mOsm/L
How do you measure the ability of the kidney to concentrate urine?
Measure the osmolar clearance
What is the equation for osmolar clearance?
( Urine flow x urine osmolarity)/ plasma osmolarity
What part of the nephron is permeable to urea?
Inner medullary region of the collecting duct
Regarding impairments in urinary concentration and dilution, what are the three major causes?
- )defect in production or regulation of AVP.
- ) Inability of collecting ducts to respond to AVP
- ) Failure to form medullary osmolarity gradient
Mechanism of disease in diabetes insipidous?
Pituitary gland doesnt release AVP, patients don’t absorb water and get dehydrated
What is nephrogenic diabetes insipidous
Collecting ducts do not respond to AVP
Diabetes insipidous is simply…
A condition where the kidneys are unable to conserve water.
