Endothelium refers to the single layer of cells lining the inner surface of blood vessels, forming an interface between the blood and the vessel walls. However, this structure is not uniform throughout the entire vascular system. Instead, different types of endothelia that vary in structure and function are found, based on the vessel type and location within the body. Continuous endothelium is found in small- to medium-sized arteries, veins, and capillaries. It consists of tightly connected endothelial cells that form a continuous unbroken barrier. The cells are connected by both tight and adherens junctions, limiting the movement of molecules between cells. This endothelium allows for precise control over the movement of substances, such as nutrients and gases, between the bloodstream and surrounding tissues. Capillaries have very thin walls composed of just a single layer of endothelial cells in a continuous endothelium, facilitating efficient diffusion of substances. Fenestrated endothelium is found in certain specialized capillaries, such as those in the kidneys, endocrine glands, and intestines. This type of endothelium contains small pores (fenestrations) that allow for increased permeability to certain molecules. These fenestrations are covered by thin diaphragms that control the passage of larger molecules, whilst allowing for the rapid exchange of smaller molecules and fluids. Discontinuous endothelium, also known as sinusoidal endothelium, is found in large blood vessels called sinusoids, which are present in organs like the liver, spleen, and bone marrow. Here the endothelium has irregular gaps between cells, allowing the passage of large molecules and cells, including immune cells and platelets. This permeability is necessary for the movement of cells and substances in and out of these organs. Endothelium plays a critical role in maintaining vascular health and homeostasis. Its functions extend beyond forming a physical barrier and include: 1) Regulation of Vascular Tone. Endothelial cells produce vasodilators such as nitric oxide (NO) and vasoconstrictors like endothelin 1. These molecules help regulate blood vessel diameter and therefore blood pressure by influencing smooth muscle contraction; 2) Blood Coagulation and Anticoagulation. Endothelial cells secrete factors that regulate blood clotting, such as von Willebrand factor and tissue plasminogen activator (tPA), which breaks down clots. An imbalance in these factors can lead to thrombosis or bleeding disorders; 3) Inflammation. Endothelial cells are involved in immune responses by expressing adhesion molecules that help white blood cells adhere to vessel walls during inflammation. They also produce chemokines that attract such immune cells to sites of infection or injury. Endothelial cells principally regulate the movement of substances between the blood and surrounding tissues. They control the passage of nutrients, gases, and immune cells whilst preventing the leakage of large molecules. In response to certain signals, endothelial cells can proliferate and form new blood vessels, in a process known as angiogenesis. This is important during adult tissue repair, wound healing, and during development. Finally, endothelial cells produce hormones such as endothelin-1 and prostacyclin that influence vascular tone, blood clotting, and other processes. We provide a comprehensive product catalogue of research tools for studying endothelium, including Smad4 antibodies, PODXL antibodies, CD105 antibodies, Endothelin 1 ELISA Kits, and CD105 ELISA Kits. Explore our full endothelium product range below and discover more, for less.