mikrocirculationens

The microcirculation encompasses the smallest blood vessels in the circulatory system—arterioles, capillaries, and venules—that supply all tissues and organs. It forms a dense capillary network that connects arterial blood flow to venous drainage and is organized into functional units called microvascular beds.

Its primary role is exchange of gases, nutrients, and waste between blood and tissues. Red blood cells travel slowly through capillaries, increasing transit time for diffusion; capillaries provide a large surface area to support diffusion and convection. Regulation of perfusion ensures matching of supply to metabolic demand.

Regulation occurs at multiple levels. Endothelial cells release vasodilators such as nitric oxide and prostacyclin and vasoconstrictors like endothelin. Local metabolic factors (CO2, H+, adenosine), shear stress, and neural and hormonal inputs modulate arteriolar tone and capillary recruitment.

Clinical relevance includes microcirculatory dysfunction in sepsis, shock, diabetes, and ischemia-reperfusion injury, where perfusion becomes heterogeneous and tissue hypoxia can occur. Assessment methods include intravital or sidestream dark-field videomicroscopy, capillaroscopy, laser Doppler flowmetry, and near-infrared spectroscopy, which measure capillary density, blood flow, and flow heterogeneity.

A detailed understanding of the microcirculation supports therapeutic strategies to optimize perfusion, including careful fluid management, vasomodulatory drugs, and anti-inflammatory approaches aimed at preserving capillary patency and reducing edema.