Loop of Henle Flashcards
How are lipid soluble and nonpolar substances reabsorbed in the tubules?
The active transport of Na which causes the transport of water creates a concentration gradient that forces lipid soluble substances across the membrane
What is absorbed in the proximal tubule?
- 65-75% of NaCl and water
- 100% of nutritionally important substances (glucose, AA’s, FA’s)
Why is the fluid that leaves the proximal tubule still isotonic with the plasma, despite the reabsorption of substrates?
- Because the substrate reabsorption always has equivalent water movement with it, keeping the concentrations the same
Where are the proximal and distal tubules of all nephrons located anatomically within the kidney?
The Cortex
What are the two types of nephrons? What is the difference between them?
- Cortical nephrons and juxtamedullary nephrons
- Juxtamedullary nephrons have a longer loop of Henle that penetrates deeper into the medulla than the short loops of the cortical nephrons
What is the maximum concentration of urine the human kidney can produce? How does it compare to plasma concentration? What is the minimum urine concentration?
1200-1400 mOsm/L
- Around 4x more concentrated than plasma
30-50 mOsm/L
Describe the permeability of the descending and ascending limbs of the loop of Henle
Descending: freely permeable to water, relatively impermeable to NaCl
Ascending: Impermeable to water, actively transports Na & Cl ions out of the tubule lumen into the interstitium
What is the mechanism that occurs in the loop of Henle of juxtamedullary nephrons called?
Counter-current multiplier mechanism
Describe the steps of by which the counter current mechanism is established in the loop of Henle
- The active transport pumps in the ascending limb move Na & Cl into the interstitium, until a limiting conc. gradient of 200 (300 interst., 100 tubule)
- Water in the descending limb follows salt to the interstitium, increasing conc. from 300 - 400
- Water moves from tissue into vasa recta (doesn’t dilute interstitium)
- Higher concentration of fluid flowing into the ascending limb allows more NaCl into interstitium, maintaining a conc. gradient of 200 (becomes 400 inter., 200 tubule)
- Once established the interstitium gradient goes from 300 at the top to 1200 at the bottom.
By what mechanism do drugs like frusemide inhibit the counter current mechanism? What is the consequence of this inhibition?
- They inhibit the active transport of Na out of the ascending limb
- Results in only isotonic urine being produced
What does the countercurrent mechanism acheive?
- Diluted urine enters the distal tubule
- About 15-20% of the initial filtrate is removed from the loop of Henle
- Established concentration gradient in the interstitium
Compared to plasma, how concentrated is the filtrate that enters the distal tubule after traversing the loop of Henle in a juxtamedullary nephron?
- Hypotonic to plasma, due to NaCl removal
Why is it that the vasa recta don’t just reabsorb the solute that is actively transported into the interstitium?
Because they are arranged in hairpin loops which slows blood flow, so any solutes reabsorbed into the blood have time to diffuse back into the interstitium
What is the purpose of the countercurrent mechanism in the loop of Henle?
To reabsorb water
- Without it only large volumes of isotonic urine would be produced, which would greatly increase water requirements
What are the functions of the vasa recta?
- Provide oxygen to the medulla
- Reabsorb water from the interstitium
