21. Countercurrent Mechanism Flashcards
Is the loop of Henle hypo or hyper osmotic?
Hyperosmotic
Is the DCT hypo or hyper osmotic?
Hyposmotic
What is the osmolarity in the PCT?
300 mOsmol
What happens to Na+ conc in the PCT?
Remains constant but mass decreases by 65%
What reabsorption happens in the early PCT?
HCO3- is reabsorbed with Na+
What reabsorption happens in the late PCT?
Na+ leaves by simple diffusion and bulk movement
Brings Cl- across with it
What is Na+ absorption controlled by in the DCT and CD?
Aldosterone
What is water absorption controlled by in the DCT and CD?
ADH
How does the loop of henle maintain a hypertonic interstitium?
Countercurrent multiplier system
What is the advantage of juxtamedullary nephrons?
Longer loops increase the ability to concentrate interstitium
What 3 things are essential for the countercurrent multiplier system?
Countercurrent flow
Descending limb is permeable to water
Ascending limb is impermeable to water and lined with salt pumps
What is countercurrent exchange?
Vessels are arranged so that flows are going in opposite directions
What is the countercurrent multiplier?
Arrangement of the Loop of Henle to concentrate the solute in the renal medulla
What are the steps in the countercurrent multiplier system?
- Everything begins at 300 mOsml
- Salt pump in ascending limb pumps NaCl out of lumen
- Water moves out of the descending limb until conc= interstitium
- Fluid moves around loop
- Concentration occurs again and a difference of 200 mOsml established at each level until reaching a maximum of 1200 at the bottom of the loop
What is the target of loop diuretics?
NKCC2
