Final answer:
Glomerular filtration involves three layers: the endothelium of the capillary with fenestrations for small substances, the basement membrane to restrict medium-to-large proteins, and the podocytes with filtration slits that allow small molecules to pass. Charge also plays a role, with negatively charged proteins repelling similar charges. Mesangial cells can regulate the glomerular filtration rate resulting in filtrate without cells or large proteins.
Step-by-step explanation:
Glomerular Filtration Layers and Permeability
The glomerular filtration process in the kidneys is critical for filtering blood and it involves three layers:
- The endothelium of the capillary, which features fenestrations that prevent filtration of blood cells or large proteins, allowing other constituents to pass through.
- The basement membrane, which restricts the passage of medium-to-large proteins such as globulins.
- Podocytes and filtration slits, where the extensions of podocytes create slits, forming a barrier that allows smaller molecules to pass.
Substances can pass through these layers if they are less than 4 nm in size, and most pass freely up to 8 nm in size. Additionally, the charge of molecules affects their filtration; negatively charged proteins associated with the pores tend to repel similarly charged substances, facilitating the passage of positively charged substances.
Mesangial cells within the filtration membrane also play a role in regulating filtration by contracting to adjust the glomerular filtration rate (GFR). The result of these layers working together is a filtrate that excludes cells or large proteins and is slightly richer in positively charged substances.
The first function of the nephron is to take blood and form a primary filtrate that is later modified into urine through processes of reabsorption and secretion. The renal corpuscle, including the glomerulus and Bowman's capsule, is where this filtration takes place.