High endothelial venules

High Endothelial Venules (HEVs) are a type of venule that allow lymphocytes to exit the bloodstream and enter the lymph nodes. They are found in the paracortex of lymph nodes and are characterized by their high, cuboidal endothelial cells.

Structure

HEVs are small blood vessels that are part of the microcirculation system. They are lined by a single layer of endothelial cells that are taller than those found in other venules, giving them their characteristic "high" appearance. These cells are also known as cuboidal cells due to their cube-like shape.

Function

The primary function of HEVs is to facilitate the migration of lymphocytes from the bloodstream into the lymph nodes. This is a critical step in the immune response, as it allows lymphocytes to encounter and respond to antigens that have been captured by dendritic cells in the tissues and transported to the lymph nodes.

Clinical significance

HEVs are of particular interest in the field of immunology due to their role in lymphocyte trafficking. They are also involved in various diseases, including autoimmune diseases, infections, and cancer. For example, in rheumatoid arthritis, HEVs can be found in the inflamed synovium, where they contribute to the recruitment of lymphocytes.

See also

• Lymphocyte
• Lymph node
• Endothelial cell
• Venule
• Microcirculation