Regulation of Water Balance Flashcards
What is the relative blood pressure of a patient with renal failure? Why?
High because the kidney cannot excrete excess fluid
What is insensible fluid loss?
Water lost through evaporation off the skin, or respiration
What is the daily intake of water relative to the daily output?
Equal
True or False: Kidneys control water excretion independently of Na+, K+, and urea
True
On which surface of the proximal tubule cells is AQP1 expressed? How many molecules of water can be transported at once?
Both apical and BL membranes; 4 H2O
Which part of the loop of Henle is permeable to water but impermeable to salt?
Thin descending limb
Where are AQP3 and 4 expressed within the nephron?
Constitutive expression on the BL membrane of prinicipal cells of the collecting duct
What are the two mechanisms of ADH secretion?
Osmoreceptors in the brain sense increases in plasma osmolarity; arterial baroreceptors detect increased MABP/ volume and signal to hypothalamus to release AVP
Which of the two stimulatory mechanisms of ADH release is more sensitive? Which is more powerful?
Osmoreceptors are more sensitive but the volume receptors are more powerful
Where and when is AQP2 expressed?
Expressed on the apical membrane of principal cells of the CD in response to ADH stimulation
How does ADH stimulate AQP2 insertion into the membrane?
Binds to V2 receptor, which is a GsPCR– increased cAMP– phosphorylation of vesicles containing AQP2– exocytosis and fusion
True or False: When circulating ADH levels fall there are signals for endocytic retrieval of AQP2 resulting in lysosomal degradation
False- no degradation
How does AVP increase renal medullary interstitial osmolarity?
Increases urea reabsorption, and NaCl reabsorption
What is the countercurrent mechanism?
The mechanism by which urine is concentrated
What is the countercurrent mechansim dependent on?
Unique solute transport processes and specific anatomical arrangemet of loops of Henle and vasa recta
What are the parts of the countercurrent system?
Countercurrent flow, countercurrent exchange, and countercurrent multiplication
What is meant by countercurrent flow?
The movement of fluid and blood down the descending loop of Henle and vasa recta is opposite the movement of fluid/blood up the ascending LoH or vasa recta
What is countercurrent exchange, and what is its purpose?
The passive diffusion of solutes and water in both directions across vasa recta capillary walls; restores isotonic plasma and maintains hyperosmotic medullary interstitium
True or False: The ascending vasa recta carry away more water and solute than enters
True
What determines how concentrated urine is?
The length of the Loop of Henle
What are the countercurrent multipliers? What is the purpose?
The loops of Henle; establishes hyperosmotic medullary interstitium
What physical characteristics allows the Loop of Henle to be the countercurrent multiplier?
The dtLoH is salt impermeable and water permeable and the TAL is H2O impermeable and salt permeable
What is the driving force of H2O reabsorption in the tdLOH and CD?
Medullary ISF osmotic pressure
What dictates the maximal urine concentration?
ISF osmolality
