Sinusoid

A sinusoid (vas sinusoideum) is a specialized, low-pressure vascular channel found in certain organs, most notably the liver. Sinusoids are distinct from typical capillaries in that they are wider, have a discontinuous or fenestrated endothelial lining, and lack a well-defined basal lamina. This unique structure allows for efficient exchange of nutrients, oxygen, and macromolecules between the blood and adjacent parenchymal cells. In the liver, sinusoids facilitate the delivery of blood from the portal vein and hepatic artery to hepatocytes and drain into the central vein. The sinusoidal wall is composed of endothelial cells, Kupffer cells (resident macrophages), and hepatic stellate cells, with the space of Disse separating the endothelium from hepatocytes.

Sinusoids are formed by the subdivision of larger vascular spaces during organ development and are closely associated with the surrounding parenchymal tissue. Their permeability and cellular composition are critical for organ-specific functions, such as hepatic metabolism, immune surveillance, and regeneration.