Schematic representation of microcirculation components. The microcirculation is a network of small blood vessels, including arterioles, venules and capillaries. Blood flows from the arteries into the arterioles and then pass into the venules across true capillaries or throughfare channels and metarterioles (arteriovenous bypass). The precapillary sphincter, made of smooth muscle cells, controls blood flow into the true capillaries. As blood travels through the capillaries, plasma proteins and fluid enter the interstitial space according to hydrostatic and osmotic pressure gradients. Most of the fluid is reabsorbed into the post-capillary venules, while a fraction enters to the lymphatic circulation for its return to the blood circulation.