smallbloodvessel

Small blood vessels, collectively the microvasculature, include arterioles, capillaries, and venules with diameters typically under 100 micrometers. They connect larger arteries and veins and are specialized for tissue perfusion and exchange. Capillaries, about 5–10 micrometers in diameter, are the principal sites of gas and nutrient exchange; arterioles regulate flow and pressure; postcapillary venules drain the capillary beds.

Anatomy: the vessels are lined by endothelial cells on a basement membrane. Capillaries may be continuous, fenestrated, or discontinuous depending on tissue needs. Pericytes accompany capillaries and small venules, contributing to stability and regulation of blood flow. The microvasculature interfaces with extracellular matrix and immune cells to support tissue homeostasis.

Function: exchange of oxygen, carbon dioxide, nutrients and wastes, maintenance of interstitial fluid balance, and leukocyte trafficking. Arterioles adjust regional perfusion and vascular resistance; capillary networks determine exchange surface area and diffusion distance.

Regulation and adaptation: local mediators such as nitric oxide and endothelin, along with metabolic cues, regulate vascular tone; neural input and circulating hormones modulate responses. The microvasculature can remodel during development, repair, or disease, guided by growth factors like VEGF to form new capillary networks when needed.

Clinical relevance: microvascular dysfunction is implicated in diabetic microangiopathy, hypertension-related small vessel disease, and cerebral or retinal microvascular disorders. Aging and chronic disease can reduce capillary density and autoregulatory capacity, affecting tissue perfusion. Diagnosis uses imaging modalities and functional tests of microvascular perfusion and reactivity.