How many cellular layers are present in the glomerular filtration barrier?

The glomerular filtration barrier consists of three distinct cellular layers that work together to filter blood as it passes through the glomerulus in the kidney. These layers include:

1. Fenestrated Endothelium: This is the inner layer made up of endothelial cells that line the glomerular capillaries. The cells have small pores (fenestrations) that allow the passage of water and small solutes while preventing larger molecules like proteins and cells from passing through.

2. Glomerular Basement Membrane (GBM): The second layer is the glomerular basement membrane, a dense layer that provides structural support and plays a crucial role in the filtration process. The GBM has a negative charge that contributes to the selective permeability of the barrier, repelling negatively charged molecules such as proteins.

3. Podocytes: The outermost layer consists of podocytes, specialized epithelial cells that encapsulate the capillaries. These cells have foot-like processes (pedicels) that interdigitate, forming small filtration slits that further regulate the passage of substances based on size and charge.

Together, these three layers form an effective barrier that ensures that essential components of the blood, such as cells and large proteins