Regulation of Body Fluid Osmolarity - Rao Flashcards
What does increased osmolarity stimulate in the hypothalamus?
Increased intracellular Ca -> AVP secretion
Increased thirst
What is the mechanism of AVP/ADH?
Vasoconstrict (V1)
V2 receptors -> Increase cAMP in collecting duct cells -> translocation of AqP-2 to lumen
Where is AVP degraded?
Liver
Proximal tubule
What is the threshold concentration for thirst?
280mOsm
What is nocturia a symptom of?
Decreased ability to concentrate urine
What is the equation of osmolar clearance?
UF * Uosm / Posm
*Normal = 2 ml/min
What is the equation for free water clearance?
UF * (1 - Uosm / Posm)
What is signified by a free water clearance = 1?
> 0 - dilute urine and concentrate plasma
< 0 - concentrate urine and dilute plasma
Is the kidney more efficient at clearing or conserving water?
More efficient at clearing water
What contributes 40% of osmolarity in the medullary ISF?
Urea
What features contribute to the preservation of medullary interstitial hyperosmolarity?
Low medullary blood flow (1-2% of renal flow)
Countercurrent exchanges via vasa recta
What causes a deficiency in the kidney’s ability to concentrate or dilute urine?
Defecting in AVP secretion
Defect in response to AVP (at CD)
Defect in medullary osmolarity gradient
What are the types of diabetes insipidus?
Central
Nephrogenic
What is the mechanism of central diabetes insipidus?
Pituitary gland fails to release AVP
What is the mechanism of nephrogenic diabetes insipidus?
No response to AVP at CD
V2 receptor mutation
AqP-2 mutation
Drugs (lithium, tetracycline)
