Renal 5 Flashcards
What is the osmolarity of the most dilute urine possible?
50 mOsm/L
What is the osmolarity of the most concentrated urine possible?
1200 mOsm/L
What is the osmolarity of typical urine under normal conditions?
500 mOsm/L
What does ADH do? What happens to aquaporin channels when there is low ADH?
Tells principal cells in the collecting duct to make aquaporin channels and reabsorb water.
When there is low ADH the aquaporin channels are endocytosed from the apical membrane.
What happens to the osmolarity of the filtrate as the filtrate travels down the descending loop of Henle?
The filtrate equilibrates with the osmolarity of the interstitium of the renal medulla through water reabsorption from the filtrate.
What happens as filtrate travels up the thick ascending loop of Henle? What is the osmolarity of the filtrate at the top of the loop with respect to plasma?
NaCl is actively reabsorbed, but water is not permeable –> hypotonic filtrate at the top of the loop
Can both solutes and water be reabsorbed in the distal tubule and collecting duct?
Yeah - but water is reabsorbed only in the presence of ADH
What is the maximum possible daily urine excretion? What percentage of total daily filtrate is this?
18L - 10% of total daily filtrate
What is diabetes insipidus?
Inability to make ADH, or lack of principal cell response to ADH –> lots of peeing, thirsty.
Explain why the minimum daily urine volume is 0.5L.
You need to secrete 600 mOsm of solutes per day, 40% of which is urea. Since the max osmolarity of urine is 1200 mOsm/L, you need to urinate 0.5 L to get rid of 600 mOsm.
How much urea do the kidneys clear per day? How much is excreted?
25-30 grams per day are cleared, 50% of that is excreted
Explain how the osmolarity of urea changes throughout the nephron.
As filtrate descends the descending loop of Henle, water is reabsorbed faster than urea, so the urea concentration increases. Further, urea concentration is high in the medullary interstitium so it diffuses into the filtrate. The thick ascending loop of Henle, DCT, and cortical CD are impermeable to urea, so its concentration in the filtrate remains high. In the lower CD, both water and urea are reabsorbed, but urea is reabsorbed at a slower rate, so urea is more concentrated than it was at the top of the CD by the time the filtrate gets to the end of the CD.
Why is the medullary interstitial osmolarity 600 mOsm/L at low ADH and 1200 mOsm/L at high ADH?
At low ADH, reduced permeability of medullary collecting duct –> less diffusion of urea from medulary collecting duct into interstitium –> more wash-out of urea in urine (hence urea contributes less to the osmolarity of the medullary interstitium).
Does the vasa recta “wash out” solutes in the renal medulla? Explain why or why not.
No, blood flow through the vasa recta is really slow, so diffusion limits how much solute is removed from the interstitium.
How does vasodilation of the vasa recta affect the kidney’s ability to make concentrated urine?
Increased vasodilation of the vasa recta will increase blood flow through the renal medulla, washing out solutes and decreasing its ability to make concentrated urine.
