Sinusoids

Sinusoids are small blood vessels found in the liver, bone marrow, spleen, and lymph nodes. They are a type of capillary similar to venules, but have a larger diameter and are more permeable, allowing larger molecules and even cells to pass through. Sinusoids are lined with endothelial cells, which have gaps between them, and are surrounded by pericytes.

Structure

Sinusoids are unique in structure compared to other blood vessels. They are larger in diameter and have a discontinuous endothelium, meaning there are gaps between the endothelial cells. These gaps, or fenestrations, allow for the exchange of larger molecules and even cells between the blood and the surrounding tissue. The endothelial cells are also unique in that they lack a basement membrane, a thin layer of extracellular matrix that underlies the endothelium in most other blood vessels.

The walls of sinusoids are supported by pericytes, a type of cell that wraps around the endothelial cells. Pericytes are involved in many functions, including regulation of blood flow, immune response, and tissue repair.

Function

The primary function of sinusoids is to facilitate the exchange of materials between the blood and the surrounding tissue. This is particularly important in the liver, where sinusoids allow for the exchange of nutrients, waste products, and metabolites between the blood and the liver cells.

In the bone marrow, sinusoids allow for the migration of mature blood cells from the marrow into the bloodstream. In the spleen, they facilitate the removal of old and damaged red blood cells from the circulation.

Clinical significance

Due to their unique structure and function, sinusoids are involved in several diseases. In liver disease, such as cirrhosis, the sinusoids can become damaged, leading to impaired liver function. In certain types of cancer, tumor cells can invade the sinusoids, facilitating their spread to other parts of the body.

See also

• Capillary
• Endothelium
• Pericyte
• Cirrhosis

References

Sinusoids Resources
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