Final answer:
The structures on a podocyte are essential for the filtration of blood plasma within the kidneys, keeping out blood cells and large proteins while forming a filtrate that is the initial step in urine production.
Step-by-step explanation:
The foot processes and negatively charged filtration slits of a podocyte in the glomerular capsule wall serve a very specific function in the kidney's process of forming urine. These structures are crucial for the filtration of blood plasma. As blood flows through the glomerular capillaries under pressure, water, salts, and small molecules are filtered out while blood cells and large proteins are kept within the blood vessels. The negative charge of the proteins associated with the pores repels negatively charged substances and preferentially allows positively charged substances to pass more easily. This selective filtration forms a filtrate that is free from cells and large proteins, initiating the urine formation process.