Mikrovascular

Mikrovascular refers to the small-blood-vessel network that forms the microcirculation, comprising arterioles, capillaries, and venules, including postcapillary venules. The endothelium lines the lumen, supported by pericytes along capillaries and a surrounding basement membrane. The glycocalyx, a gel-like layer on the luminal surface, participates in barrier function and mechanotransduction.

This microvascular bed is the principal site of exchange between blood and tissue. Oxygen and nutrients diffuse through capillary walls, while carbon dioxide and waste products move into the blood. Fluid exchange is governed by Starling forces and modulated by capillary permeability, which is influenced by the endothelium and glycocalyx. The lymphatic system helps return excess interstitial fluid.

Regulation of microvascular tone and flow is achieved by autoregulation, autonomic nerves, metabolic signals, and endothelium-derived mediators such as nitric oxide and endothelin. Pre-capillary sphincters and arteriolar resistance determine capillary perfusion, while capillary recruitment adjusts perfused surface area according to tissue demand.

Clinical relevance: microvascular dysfunction is implicated in diabetes mellitus–related retinopathy and nephropathy, hypertension, sepsis, and aging. Microvascular leakage and rarefaction can contribute to edema and impaired tissue healing. In cancer, abnormal microvasculature supports tumor growth; in critical illness, capillary leak can lead to hypotension and organ dysfunction.

Assessment approaches include nailfold capillaroscopy, capillary refill time, and imaging methods such as intravital microscopy in research or noninvasive perfusion imaging; in practice, biomarkers of endothelial function and microvascular compliance may be used.