Filtration barrier at kidney

[scilearner]

 

Red-capillary Purple- Basement membrane Blue-podocyte

 

Hello everyone, Now my question is after something if filtered from the capillary how does it go to the podocyte. The basement membrane looks too thick with no pores to me, it seems to be blocking the passage of molecules. Thanks

Edited February 27, 2011 by scilearner

[SMF]

Basement membranes are made of a fibrous material (mostly charged glycosaminoglycans and type 4 collagen) that, along with the capillary fenestrae and podocyte filtration slits, make the ultrafiltration membrane. SM

[scilearner]

Thanks but wouldn't this collagen ect block the diffusion of substance by being a mechanical barrier.

[SMF]

No, it makes a nice filter that allows fluids and small molecules through, but excludes larger proteins. Many of the smaller molecules are allowed through and then some are transported back into the blood by specific mechanisms for this. By this process wastes are eliminated while nutrients and necessary ions are retained by bringing them back in. This in-out transport is a topic in renal physiology. One more anatomical question, regarding this mechanism, is how is the filter kept clean. The janitorial crew in charge of cleaning the ultra-filtration membrane in the kidney consists of the mesangial cells. They extend pseudopods into the basement membrane space between capillaries and podocytes and phagocytose molecules, mostly proteins, that get filtered out by the basement membrane. I really need some of these guys to take care of my coffee filters.Below is one of my drawings showing the relationship between capillaries, podocytes, their common basement membrane filter, and mesangial cells