The glycocalyx is present as soon as blood flow is initiated and is required for normal vascular development

► The glycocalyx is present at as early as 14 somites in the avian embryo. ► The endothelial surface layer is visible at developmental stages of 25 and 35 somites. ► Vessel branching is altered by selective degradation of the glycocalyx. ► Hyaluronan is the main glycocalyx component affecting vascular barrier function. ► Angiogenic and shear-induced gene expressions are affected by selective degradation.