When you apply the brakes, brake fluid is forced under pressure into the wheel cylinder, which in turn pushes the brake shoes into contact with the machined surface on the inside of the drum. When the pressure is released, return springs pull the shoes back to their rest position.
Normally, protein is not removed when the kidneys filter waste from the blood. However, when the kidneys are damaged, protein leaks through the damaged filters and is removed from the body in the urine, along with the waste products.
Today, we often put them on a diet that is not necessarily very low in protein, but instead contains protein that is more digestible (therefore producing fewer nitrogen by-products). These diet changes are made merely because damaged kidneys may not be able to handle the excess nitrogen efficiently.