Final answer:
The glomerular membrane functions to filter out most plasma proteins except the smallest ones, allowing for the formation of a filtrate that becomes urine while retaining larger plasma proteins in the blood.
Step-by-step explanation:
The function of the glomerular membrane in relation to plasma proteins is to filter out most plasma proteins except the smallest ones.
This filtration is possible because of the structural features of the membrane, including fenestrations in capillary endothelial cells, the negatively charged proteins associated with these pores, and the presence of the basement membrane which prevents the filtration of medium-to-large proteins such as globulins.
The glomerular filtration system is designed to let substances less than 4 nm in size pass readily and most substances up to 8 nm, while larger plasma proteins are filtered out. This maintains the plasma proteins within the blood while allowing other substances to pass through and form the filtrate which will eventually become urine.