Osmolarity throughout the nephron?

[velocitous]

Hi,

Can anyone explain to me how osmolarity changes in the different parts of the nephron tubule, how it compares to the cortical/medullary interstitial fluid’s osmolarity, and the osmolarity of the blood? Why is the osmolarity of the glomerular filtrate the same as the filtrate in the blood despite the presence of proteins in the plasma?

Also, why doesn’t the osmolarity in the proximal convoluted tubule change when solutes are actively secreted into it?

Thanks

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[shefv]

Glomerulus filtrate is made up of the fluids and small components from the blood that have passed through the glomerulus into the Bowman's Capsule, so it has the same osmolarity as the blood. Most of the components from the filtrate are reabsorded from the PCT. You can think of the filtrate becoming more and more concentrated as it passes through the nephron. In the descending loop of henle, the membrane is more permeable to water and water moves out, this water is carried away by the vasa recta, to help maintain the osmotic gradient. The thin ascending loop of henle is where the ions are selectively reabsorded and the thick ascending loop of henle is where the salts are reabsorbed. When the filrate reaches the DCT, it can be concentrated or diluted based on what body needs to conserve and what it needs to get rid of. This is also the point where hormones act (aldosterone). Once the filtrate reaches the collecting ducts, it is now called urine and depending on the body's conditions and needs, this urine can be highly concentrated or diluted. This is also where the hormones (ADH) act.

I don't think that solutes are secreted into the proximal convoluted tubule, it is secreted or reabsorbed into the distal convoluted tubule.

 

[burritobowl60]

All of the following will result in kaliuresis (high excretion of potassium) in ALL except?
A. Increased sympathetic activity
B. Hypovolemia
C. Hyperaldosteronism
D. Acidosis.
E. Increased renal perfusion
Torn between A or B. What do you guys think?

 

[shefv]

I am thinking A (sympathetic NS decreases excretory activity so it cannot lead to higher excretion of potassium). What's the correct answer?

For B, I am thinking that hypovolemia (low blood volume) will lead to high water retention, not affecting potassium excretion.

 

[muddyphud]

I think its acidity (takes K out of cells)

ABC all cause increased aldo which dumps K. increased perfusion will simply filter and excrete more K.

 

[burritobowl60]

Sorry for the extremely late response but I think it's B. I checked with my professor.


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