Sinusoids

Sinusoids
Liver sinusoid with fenestrated endothelial cells. Sinusoidal width is about 5 microns. Credit: Edward Harris / Cell Image Library

Sinusoids

Organs such as the liver, spleen, and bone marrow contain blood vessel structures called sinusoids instead of capillaries. Like capillaries, sinusoids are composed of endothelium. The individual endothelial cells, however, do not overlap as in capillaries and are spread out. Fenestrated sinusoid endothelium contains pores to allow small molecules such as oxygen, carbon dioxide, nutrients, proteins, and wastes to be exchanged through the thin walls of the sinusoids.

This type of endothelium is found in the intestines, kidneys, and in organs and glands of the endocrine system. Discontinuous sinusoid endothelium contains even larger pores that allows blood cells and larger proteins to pass between the vessels and surrounding tissue. This type of endothelium is found in the sinusoids of the liver, spleen, and bone marrow.

Sinusoid Size

Sinusoids range in size from about 30-40 microns in diameter. By comparison, capillaries measure in size from about 5-10 microns in diameter.