They regulate blood flow by their contractile activity and secrete extracellular matrix, prostaglandins, and cytokines.

Mesangial cells also have phagocytic activity, removing proteins and other molecules trapped in the glomerular basement membrane or filtration barrier.

The Bowman's capsule has an outer parietal layer composed of simple squamous epithelium.

The lamina densa is the central layer consisting of type IV collagen and laminin.

This layer acts as a selective macromolecular filter, preventing the passage of large protein molecules into Bowman's space.

This layer contains heparan sulfate, a negatively charged glycosaminoglycan that contributes to the electrostatic barrier of the glomerular filter.