The basic functional unit of the kidney is referred to as the renal unit. The renal unit is mainly composed of renal tubules and tubules, which can be divided into glomeruli and capsules. The glomerulus is commonly understood to be composed of capillaries, and the filtration membrane of the glomerulus mainly performs the function of filtration. The filtration membrane of the glomerulus can be divided into three layers, mainly composed of capillary walls, into endothelial, basal and epithelial layers. The glomerular filtration membrane can excrete toxic substances from the blood and leave what is needed in the body, such as protein, in the body. This is similar to the sieve commonly used in real life, which sifts unwanted toxic waste out of the body and leaves useful things inside the sieve. Therefore, the glomerulus can also be called as the filter of blood.