The liver is composed of five major cell types. Hepatocytes comprise approximately 70% of the liver cell population and are responsible for most metabolic and hormonal processes. The other four cell types, collectively known as hepatic non-parenchymal cells, consist of resident macrophages called Kupffer cells, stellate cells, liver sinusoidal endothelial cells, and cholangiocytes. These cells serve to support the liver structure, transport molecules in and out, and communicate with the immune system.