Mikroverenkiertoon

Mikroverenkiertoon (microcirculation) refers to the component of the circulatory system consisting of the smallest blood vessels—the arterioles, capillaries, and venules—that supply and drain tissues. It lies between the larger arteries and veins and is the primary site of the exchange of gases, nutrients, and wastes between blood and surrounding cells.

Anatomy and function: The microcirculatory network includes precapillary arterioles, metarterioles, capillary beds, and postcapillary venules, often supported by pericytes on capillaries. Capillary walls are thin, formed by endothelial cells with a basement membrane, allowing rapid diffusion of oxygen, carbon dioxide, glucose, and other solutes. Thickness and density of the capillary network determine tissue perfusion and exchange capacity.

Regulation: Blood flow through the microcirculation is locally regulated to match tissue demand. Autoregulation involves myogenic responses of arterioles, while metabolic control uses mediators such as nitric oxide, adenosine, carbon dioxide, and pH changes. Neural and hormonal inputs modulate vascular tone, and precapillary sphincters can dynamically open or close to direct flow to active regions. The regulation of flow also influences capillary hydrostatic and oncotic forces, affecting interstitial fluid balance.

Clinical relevance: Microcirculatory dysfunction is implicated in many conditions, including diabetes mellitus, sepsis, shock, peripheral ischemia, and aging. Assessment methods include nailfold capillaroscopy, laser Doppler flowmetry, and measurements of capillary density and perfusion. Therapeutic approaches aim to improve endothelial function, promote adequate capillary perfusion, and minimize tissue hypoxia, with ongoing research into targeted interventions and better diagnostic tools.