Endothelial glycocalyx: longitudinal cross section of blood vessels with endothelial cells adherent to the endothelial basement membrane. The endothelial glycocalyx is secreted by the underlying endothelial cells and projects 0.5–1.2 μm into the blood vessel lumen forming a negatively charged meshwork of glycosaminoglycan branches that interact and form a barrier to the overlying albumin, macromolecules, and red blood cells alike. The most numerous components of the glycocalyx are the anchoring proteoglycan syndecan-1 with its attached glycosaminoglycans, namely, heparan sulphate (represented by the blue rectangles and lines) and chondroitin sulphate (not drawn). Another structural component is hyaluronan, which occurs in chains, of several million dalton in size, attached to the underlying endothelium by the glycoprotein CD44 (represented by the green triangles and lines). The glycocalyx interacts with other endothelial structures such as intracellular adhesion molecule-1 (ICAM-1; represented by the green T’s) by acting as a physical barrier and preventing leucocytes from reaching these much shorter glycoprotein adhesion molecules. Shown also are the adherent plasma proteins that interact with the glycocalyx, providing vital endothelial functions such as haemostasis by binding von Willebrand factor (vWF; represented by the magenta objects) and antithrombin (represented by the grey circles). In addition, binding extracellular superoxide dismutase (EC-SOD; represented by the gold triangles) and endothelial nitric oxide synthase (eNOS; represented by the yellowish green cylinders), the glycocalyx contributes to protection from free radical injury and mechanotransduction, respectively.