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In contrast to regular venules, high endothelial venules are a special type of venule where the endothelium is made up of simple cuboidal cells. Lymphocytes exit the blood stream and enter the lymph nodes via these specialized venules when an infection is detected. Compared with arterioles, the venules are larger with much weaker muscular coat.
Naïve T cells express CCR7 receptor and adhesion molecules L-selectin and LFA-1. [5] As naïve T cells move through the circulation, they 'roll' over the endothelial cells in the vessel walls. The rolling mechanism helps the L-selectin molecules on the surface of naive T cells to weakly interact with GlyCAM-1 and CD34 molecules on HEV cells.
Most vessels of the microcirculation are lined by flattened cells of the endothelium and many of them are surrounded by contractile cells called pericytes.The endothelium provides a smooth surface for the flow of blood and regulates the movement of water and dissolved materials in the interstitial plasma between the blood and the tissues.
The venous system apart from the post-capillary venules is a high volume, low pressure system. Vascular smooth muscle cells control the size of the vein lumens, and thereby help to regulate blood pressure. [31] The post-capillary venules are exchange vessels whose ultra-thin walls allow the ready diffusion of molecules from the capillaries. [10]
In general, arteries and arterioles transport oxygenated blood from the lungs to the body and its organs, and veins and venules transport deoxygenated blood from the body to the lungs. Blood vessels also circulate blood throughout the circulatory system. Oxygen (bound to hemoglobin in red blood cells) is the most critical nutrient carried by ...
It is very thin in veins and venules. [1] In elastic arteries such as the aorta, which have very regular elastic laminae between layers of smooth muscle cells in their tunica media, the internal elastic lamina is approximately the same thickness as the other elastic laminae that are normally present. [2]
Communication between endothelial cells and pericytes is vital. Inhibiting the PDGF pathway leads to pericyte deficiency. This causes endothelial hyperplasia, abnormal junctions, and diabetic retinopathy. [36] A lack of pericytes also causes an upregulation of vascular endothelial growth factor (VEGF), leading to vascular leakage and hemorrhage ...
Cellular factors include reduced number and function of bone-marrow derived endothelial progenitor cells. [25] and reduced ability of those cells to form blood vessels. [26] Formation of additional capillaries and larger blood vessels (angiogenesis) is a major mechanism by which a cancer may help to enhance its own growth.