The glomerular capillary walls is a filtration system of 3 sieves:
- The first one with the largest holes, letting most things through into the Bowman’s Capsule
- REMEMBER: things in the Bowman’s Capsule are on the path for excretion (ie will become urine)
- This is then further sorted out through the second and third layers by size
Layer 1: Endothelium
- General definition: endothelium
- Relatively large pores, through which solutes, plasma proteins, and fluids can pass through, but blood cells cannot
- This is why blood in urine is not a great sign - it’s the first thing that the body makes sure isn’t excreted
Layer 2: Basement membrane
- Made up of 3 layers
- You do NOT need to know the 3 layers of the basement membrane, BUT if you’re curious:
- Prevent plasma proteins from being filtered out
If you’re keeping track, what’s left is solutes and fluids
Layer 3: Epithelium
- Contains cells called podocytes
- Not all of it attaches to the basement membrane, only extensions called foot processes
- This leaves thin slits in between the processes called filtration slits
- A thin diaphragm between the slits acts as a final filtration barrier
“2613 Podocytes.jpg” by OpenStax College, licensed under CC BY 3.0, via Wikimedia Commons.
Source: https://commons.wikimedia.org/wiki/File:2613_Podocytes.jpg
Only allows smallest proteins and small solutes like glucose, ions, and urea.
Next step: The Nephron