 In humans, HEVs are found in all secondary lymphoid organs (with the exception of spleen, where blood exits through open arterioles and enters the red pulp), including hundreds of lymph nodes dispersed in the body, tonsils and adenoids in the pharynx, Peyer's patches (PIs) in the small intestine, appendix, and small aggregates of lymphoid tissue in the stomach and large intestine.In contrast to the endothelial cells from other vessels, the high endothelial cells of HEVs have a distinctive appearance, consisting of a cuboidal morphology and with various receptors to interact with leukocytes (express specialized ligands for lymphocytes and are able to support high levels of lymphocyte extravasation).HEVs enable naïve lymphocytes to move in and out of the lymph nodes from the circulatory system.