Urinary Concentration And Dilution Flashcards
In the Loop of Henle, is sodium reabsorbed actively or passively?
Actively
In the loop of henle, is water reabsorbed actively or passively?
Passively, solute linked
What is the counter current multiplier?
Its a large gradient of increasing osmolarity in the interstitial fluid down the descending loop of henle, and then decreasing osmolarity along the length of the ascending loop of henle
(Runs from the corticomedullary border to the tip of the papilla)
In the descending limb of the LOH, what is entering/leaving the lumen?
TONS of water is leaving the lumen due to the very high osmolarity of the interstitium and the presence of many aquaporins
(NO active transport of NaCl)
Which is more permeable to water:
Descending limb or ascending limb
Descending by far
Is the ascending limb permeable to water?
No
Does the ascending limb reabsorb NaCl actively or passively?
Actively
Where is the urine most concentrated in the loop of henle?
At the bottom (1200 mOsm)
Why is urine get progressively more dilute along the ascending limb?
Due to ions getting actively transported into the ISF
What is the largest osmotic gradient that can be maintained across the wall of the ascending limb?
200 mOsm
What is the essential component of the countercurrent multiplier?
ACTIVE TRANSPORT***
What transporter is blocked by Lasix?
the NKCC2 cotransporter in the thick ascending limb
Prevents reabsorption of Na+, 2Cl-, and K+, so they will stay in the urine
What transporter is stimulated by ADH?
NKCC2 in the ascending limb
What happens to the blood in the vasa recta as it flows down the hairpin loop?
NaCl diffuses into the blood
Water diffuses out
(Blood gets more concentrated)
What happens to the blood in the vasa recta as it come up the hairpin loop?
NaCl diffuses out
Water diffuses in
(Blood gets more dilute)
What is the effect of the blood in the vasa recta getting more concentrated as it descends and more dilute as it ascend?
Protects the ISF gradient (countercurrent multiplier)
As blood in the vasa recta gets more concentrated and then more dilute, is there active transport?
No, the entire process is entirely passive. Diffusion only
(Descending: salt in, water out
Ascending: salt out, water in)
What controls the permeability of the collecting duct to urea?
ADH
Which means that without ADH you can’t concentrate urine well
Where is urea recycled?
In the medulla of the kidneys
Watch the osmosis video for this
What happens to the urine when it gets to the Early DCT?
The NCC transporter reabsorbs NaCl
No water is moving in/out, so the urine gets DILUTED
What transporter is affected by thiazide diuretics?
The NCC (NaCl) transporter in the early DCT
(Reason why thiazide diuretics are not as powerful as loop diuretics….this is in the cortex and does no contribute to the corticopapillary gradient)
Is there an NKCC2 transporter in the Early DCT?
NO
What are the 2 types of cells in the Late DCT and Collecting duct?
Principal Cells
α-Intercalated cells
What do principal cells do?
Reabsorb Na+
Secrete K+
(Done via two separate channels: ENaC (epithelial Na channel) and then a K+ channel that doesn’t have a fun name)
What kind of transporters are in principal cells?
ENaC (apical surface) reabsorbs
K+ channel for secretion (apical surface)
Na-K-ATPase (basal surface)
What does aldosterone do?
Targets the Principal cells in the late DCT and Collecting duct: Increases the number of ENaC channels and increases the Na-K-ATPase activity
=increased Na+ reabsorption and increased K+ secretion
What do the α-intercalated cells do?
Secrete H+ into the lumen (via H+ ATPase and H-K+ ATPase
Reabsorb K+
What kind of transporters are in α-intercalated cells?
H+ ATPase (secretes H+)
H+, K+ ATPase (secretes one H+ and absorbs one K+)
What controls the permeability of the collecting duct to water and urea?
ADH
If there is no ADH, will water or urea leave the collecting duct?
No
How does ADH increase water permeability in the collecting duct?
It causes the insertion of aquaporins into the apical membranes of CD cells
If you are very dehydrated, a lot of water will be reabsorbed out of the collecting duct and late DCT. What 2 mechanisms allow this?
- ADH made the aquaporins
2. Concentration gradient made by the Loop of Henle
In the ascending limb of the LOH, is the urine hyperosmotic or hyposomotic?
Hyposmotic (slightly)
In the early distal tubule, is the urine hyperosmotic or hyposmotic?
Hyposmotic
No water reabsorption in early DCT with some NaCl reabsorption
In the late DCT and collecting ducts, Na+ reabsorption is regulated by ___________
Aldosterone
In the presence of ADH, is urine hypersomotic or hyposmotic
Hyperosmotic
What does amiloride do?
It blocks the ENaC channel in the late distal tubule and collecting duct.
(prevents the reabsorption of Na+)
