Microcirculation

The microcirculation is the circulation of the blood in the smallest blood vessels, the microvessels of the microvasculature present within organtissues. The microvessels include terminal arterioles, metarterioles, capillaries, and venules. Arterioles carry oxygenated blood to the capillaries, and blood flows out of the capillaries through venules into veins.

In addition to these blood vessels, the microcirculation also includes lymphatic capillaries and collecting ducts. The main functions of the microcirculation are the delivery of oxygen and nutrients and the removal of carbon dioxide (CO₂). It also serves to regulate blood flow and tissue perfusion, thereby affecting blood pressure and responses to inflammation which can include edema (swelling).

Most vessels of the microcirculation are lined by flattened cells of the endothelium and many of them are surrounded by contractile cells called pericytes. The endothelium provides a smooth surface for the flow of blood and regulates the movement of water and dissolved materials in the interstitial plasma between the blood and the tissues. The vascular endothelium also plays an important regulatory role in microcirculatory function. Endothelial cells respond to biochemical and mechanical stimuli and regulate vascular tone through the release of vasoactive mediators such as nitric oxide, prostacyclin, and endothelin.

The microcirculation contrasts with macrocirculation, which is the circulation of blood to and from the organs.