In preparation ...
Next haematuria, and it has different music
Unlike proteinuria, haematuria can come from anywhere in the urinary tract, and indeed more commonly comes from below the kidney. However here we're looking at how blood gets from the glomerular capillary into the urinary space. Red cells are big, so the GBM has to be broken. (Two examples of how this can happen.)
First example Alport
On the left is a segment of a normal glomerular capillary wall, capillary below, urinary spaceabove, GBM the grey line from Left to Right. One the right is a similar view from a patient with Alport syndrome, in which one of the three specialised type IV collagen chains that make up the GBM is mutated. The GBM degenerates, causing renal failure that comes on in teens or twenties, typically associated with progressive deafness as similar changes occur in the cochlea. This is usually an X-linked recessive disease so the disease is most common in young men. Not surprisingly, haematuria is a feature. Alport syndrome is the second most common inherited cause of renal failure , after polycystic kidney disease.
And here is an acquired mechanism. On the left we're looking down on a rat glomerulus from which Bowman's capsule and all the podocytes that would usually cover the GBM have been removed. On the right, the same view after the GBM has been attacked by an immune response generated by anti-GBM antibodies. You can see that holes have been blown in the capillary walls allowing blood cells and components to escape into Bowman's space.
Reider 1898 pic of red cell casts
As the red cells pass down the nephron, they may form red cell casts which will appear in urine like this.
Collar 2001 EM of rbc squeezing through a gap
Most holes are more subtle than the ones you just saw, and as the cells are squeezed through cracks the take a bit of a beating.
Glom rbc Fogazzi
This can be useful diagnostically, as the fragments and misshapen cells on the right show, but the requirement for high quality microscopes and skilled operators have prevented the widespread adoption of this as a quick diagnostic technique.
We've touched on proteinuria and haematuria, which leaves fluid and function, and we're just going to touch on each of those.