loop of henle Flashcards
2 functions of the loop of Henle
- 25% reabsorption of NaCl, H2O, HCO3-, K+
- Concentrates or dilutes urine
Are there more cortical or juxtamedullary nephrons? Which one has the longer loop of Henle?
More cortical nephrons, but juxtamedullary ones have the longer loop.
Characterise the 3 parts of the loop of Henle
-
Thin descending limb:
- No active NaCl transport
- Permeable to water, urea, or solutes (NaCl)
-
Thin ascending limb: diluter
- No active NaCl transport
- Permeable to to urea or solutes (NaCl)
- NOT permeable to water
-
Thick ascending limb: diluter
- NaCl reabsorption!
- NOT permeable to H2O
A & B only
Everything but glucose
What are teh permeability and transport activityof the thin ascending limb? (Select all that apply)
- Impermeable to urea
- Permeable to NaCl
- Little if any active NaCl transport
- Impermeable to H2O
Permeable to NaCl
Little if any active NaCl transport
Impermeable to H2O
What are the permeability adn ransport activity of the thick ascending limb ( selecta all that apply)?
- Totally impermeable to water
- Permeable to solutes
- Active NaCl transport
- Active urea reabsorption
Totally impermeable ot water
Permeable to solutes
Active NaCl transport
Active transport in the thick ascending limb is performed by what transporter?
What drives it?
Na, K, 2Cl-cotransporter brings in the Na+ after the Na,K-ATPase pumped Na+ out of the cell to decrease [Na]intracellular
Furosemide (Lasix)
High-ceiling diuretic that inhibits the apical Na, K, 2Cl-cotransporter
–> large increases in urine flow & natriuresis
What happens to K+ in the thick ascending limb?
- K+ enters the cell both via the Na,K, 2Cl-contransporter and the Na,K-ATPase
- Some of the K+ is secreted back into the tubular fluid via apical membrane K+ channels, generating a lumen-positive transepithelial gradient
What is the driving force for passive Na+ reabsorption along the paracellular pathway in the thick ascending limb?
The recycling of K+ from the cell back into the lumen generates a positive lumen that drives Na+ out paracellularly towards the blood.
This is ~50% of Na+ reabsorption in the thick ascending limb
For every ATP used by the Na,K-ATPase, what happens to Na+?
1 Na+ is sent out transcellularly by the ATPase
Another Na+ is sent out paracellularly because the K+ put inside the cell by the ATPase is secreted into the lumen, where it generates the electrical gradient for the Na+ to leave. (50%)
Why is the thick ascending limb the “diluting segment”?
It reabsorbs NaCl but not water
Corticomedullary interstitial osmotic gradient
As you go down from the cortex into the medulla, the interstitium becomes more concentrated because the ascending limbs are sending NaCl into it
Going down the descending limb, the tube gets more ____
Going up the ascending limb, the tube gets more ___
Going down = concentrated
Going up = diluted
Why does the tubular fluid at the hairpin turn have the same osmolality as the surrounding interstitium?
The corticomedullary interstitial gradient (becuase of the ascending limbs) makes the interstitium more concentrated as you go down.
This causes water to get reabsorbed in the descending limb.
If there is no ADH, then what happens to tubular fluid after the loop of Henle?
It gets a bit more dilute as the collecting duct reabsorbs some Na+.
Very diluted for excretion
How do you concentrate urine (countercurrent mechanism)?
ADH makes the late distal tubule & collecting duct permeable to water.
This causes the dilute distal tubule fluid to passively send out water into the interstitium (which, due to the corticomedually interstitial gradient, is very concentated)
Single effect
Thick ascending limb pumps out NaCl –> hyperosmotic interstitium & diluted tubular fluid in ascending limb
Max = 200 mOsm/kg
Describe countercurrent multiplication after “single effect”
- Flow: Descending limb fluid (concentrated by equilibrating w the more hyperosmotic interstitium) enters the ascending limb.
- Concentrate: Now impermeable to water, fluid in the ascending limb continues pumping NaCl out into the interstitium to dilute itself.
- Flow: The interstitium is now even more concentrated, which promotes passive reabsorption of water in the descending limb.
The thin descending limb is highly permeable to water. Why is there still a high interstitial osmolality in the medulla?
- The thick ascending limb pumps NaCl into the interstitium
- Urea is reabsorbed by the inner medullary collecting duct
- Countercurrent exchange by the vasa recta
Vasa recta
Blood vessels that course down with the loops of Henle
At the vasa recta, all movement of water and solute is ___
PASSIVE ONLY
this is blood
Explain countercurrent exchange in vasa recta
Descending vasa recta is surrounded by increasingly concentrated interstitium as it goes down–> send out water –> vasa recta fluid concentrates
Ascending vasa rect is surrounded by increasingly dilute interstitium as it goes up –> take in water –> vasa recta fluid dilutes, interstitium concentrates even more
What effect does ADH have on the late distal tubule vs the collecting duct?
Late distal tubule: Increase permeability to H2O, but not urea –> [urea]lumen increases as water leaves
Collecting duct: Increase permeability to both –> all that concentrated urea in the fluid is reabsorbed and [urea]lumen decreases
Passive countercurrent multiplication
Urea is reabsorbed by ADH at the inner medullary collecting duct, constributing to the osmolality of the interstitium
–> driving passive reabsorption of NaCl at the ascending limb (diluting segment).
