ABSTRACT
The microcirculation consists of the arteriolar inflow to the capillary network, the capillary network and the venous outflow. Arterioles and venules have smooth muscle. Capillaries consist of only endothelial cells. Blood flow from the arterial supply of an organ to its capillary bed is determined by the amount of constriction or dilatation of the small muscular arteries and arterioles. A capillary wall consists of a single layer of endothelial cells. Exchange is facilitated by the very high surface area to volume ratio in the capillary bed. Metarterioles are shunt vessels. Other names are "thoroughfare channel" and "arteriovenous anastomosis." They are present in certain specialized areas. The biconcave Red blood cells (RBC) must fold and slide through the capillary lumen. This minimizes diffusion distance from RBC to the interstitium. The flow is intermittent and dependent on arteriolar or precapillary sphincter control.
