What does this phrase refer to/ mean?
and the increase in osm in the medullar interstitum affects the osmosis out of the collecting ductThe loop of Henle is responsible for concentrating urine through the countercurrent multiplier. Basically, the descending portion is permeable to water, but the ascending portion isn't. As solute is reabsorbed in the ascending limb, it pulls water out in the descending limb. This leads to a high concentration of solute in the medullary interstitium which helps water reabsorption and the formation of concentrated urine.
Yes, and the other key thing to remember is that the deeper you go into the medulla (longer loop of henle) the more concentrated it gets. So JM nephrons produce more concentrated urine than cortical nephrons.
The ascending loop has Na/K ATPase pumps that pump sodium out, so the ascending loop is more dilute, especially at the cortex side. (also called the single effect)
Yes, the concentration increases towards the medulla, and decreases towards the cortex. And yes the descending loop runs counter current with the ascending loop of Henle.
The descending loop is permeable to both water and ions (ions move in, increasing the concentration as it moves down the loop of Henle).
The collecting duct has variable permeability which is controlled by ADH. More ADH, more aquaporin channels = more reabsorption of water and more concentrate urine.
Less ADH, fewer aquaporin channels = less reabsorption of water and more dilute urine.
The collecting duct also moved countercurrent to the ascending loop... Increasing the concentration of solutes as it moves towards the inner medulla.
I'm pretty sure the descending loop is permeable only to water.
I'm pretty sure the descending loop is permeable only to water.
No.Descending only permeable to water & Ascending portion only permeable to salt
No.
The thin descending limb is permeable to both water and ions (NaCl). IIRC, it's also permeable to urea. The thick ascending limb is permeable to NaCl, but impermeable to water.
Hope this helps.
No.
The thin descending limb is permeable to both water and ions (NaCl). IIRC, it's also permeable to urea. The thick ascending limb is permeable to NaCl, but impermeable to water.
Hope this helps.
It's how I learned it here in med school and that's what is stated in major physio books, like Guyton and Costanzo. Directly from Guyton's (bolded mine):No, MedPR is right. While it is permeable to urea, the descending limb is virtually impereable to ions, especially Na and Cl.
It's how I learned it here in med school and that's what is stated in major physio books, like Guyton and Costanzo. Directly from Guyton's (bolded mine):
"The descending part of the thin segment is highly permeable to water and moderately permeable to most solutes, including urea and sodium. The function of this nephron segment is mainly to allow simple diffusion of substances through its walls."
I think, for MCAT purposes, you'll be fine thinking of the descending limb as only permeable to water.
No.
The thin descending limb is permeable to both water and ions (NaCl). IIRC, it's also permeable to urea. The thick ascending limb is permeable to NaCl, but impermeable to water.
Hope this helps.
Technically this is correct; the descending limb is very slightly permeable to ions. To put this in perspective, we think of our internet firewall as being impermeable to viruses because it keeps the vast majority of them out, but we all certainly know it is not a perfect security system. The same is true for the descending limb and ions.
For the MCAT, though, the descending limb is permeable to water and the ascending permeable to ions.
Maybe our classification should be more focused on understanding where in the kidney active and passive water transport occurs?
So passive transportation of Na+ Cl- solutes only occurs in the thin ascending limb, whereas every where else active transportation of Na+ causes the passive diffusion of H2O (can anyone verify this to make sure that's correct?)
I think this is why Kaplan notes that water is not usually pumped at all. Instead the kidney move ions (mostly Na+ and Cl-) by active transport to create gradients that water will follow by osmosis.
I think you guys are going way too in-depth for MCAT purposes. Keep it simple and think of the general concepts of what happens at each segment of the nephron (ex. most reabsorption occurs in the proximal tubule, the loop of Henle is designed to concentrate the ECF in the medulla, the late distal tubule/collecting duct is where urine is concentrated/diluted, etc). For the most part, that should get you through the renal questions that show up. And, if it gets more detailed than that, it's likely going to be passage-based rather than a discrete. Renal physiology is very tough. They're unlikely to ask you discrete questions on the details of renal physio.Active transport only occurs in the ascending loop.
Na/K ATPase pumping ions out.
Everything else occurs via osmosis/diffusion via electrochemical gradients and osmotic gradients.
EK states
Proximal Tubule is where most reabsorption occurs.
Solute exchange and
-secretion
-(Na H antiporter)
-urea
-bile pigments
-antibitotics
-other drugs
-absorption
-permeable to water
-apical membrane secondary active transport responsible for reabsorption of nearly all glucose, most proteins, and other solutes
NET result of PT is to reduce the amount of filtrate in the nephron while changing the solute composition without changing the osmolarity
Descending Loop of Henle
-fxn to increase solute concentration, and thus osmotic pressure, of the medulla (?? when the say medulla are they referring to the ECF or the lumen of the nephron in the medulla...pretty sure its the latter just want to double check)
-has avery low permeability to salt so filtrate osm goes up
Great question.I'm still don't quite understand why the filtrate is more concentrated. If water leaves in the descending limb and salt leaves in the ascending limb, then both water and salt decrease, so shouldn't concentration stay the same?