Sinusoids are chambers within the liver where deoxygenated blood from the gut (containing products of digestion) and oxygenated blood from the heart, mix. Sinusoids are lined with liver cells (hepatocytes) which are able to remove, or return substances into the blood. This allows the concentrations of the components of the blood to be regulated, an example of this is Kupffer cells- these are macrophages that break down and recycle old blood vessels. Furthermore, the hepatocytes themselves are able to add or remove substances where necessary, due to their specialised structure. Hepatocytes are cuboidal to increase surface area of contact to the blood, they also contain many organelles that are necessary for synthesis/degradation of substances in the blood, which include ribosomes (for protein synthesis) and lysosomes (for protein degradation).