The microcirculation is the business end of the cardiovascular system. It is in this branching network of microvessels that transport and exchange of heat, respiratory gases, nutrients, waste products, water and hormones occurs between blood and the body’s tissues (1,2). Blood flowing in the microvasculature also carries leukocytes and lymphocytes to their tissue targets, and it is here that trafficking of these inflammatory and immune cells takes place between blood and tissue (3,4). Microvessels also importantly contribute to peripheral vascular resistance (5), vascular capacitance (6), and blood pressure regulation (5), and they are the effectors responsible for the control of blood flow to, and within the body’s tissues and organs (1,5,7,). Microvascular smooth muscle cells (1,5,7), or related pericytes (8–12), participate directly or indirectly in all of the listed functions of the microcirculation by controlling vessel diameter and hence local microvascular hemodynamic resistance, pressure, and luminal fluid flow.
William F. Jackson, Microcirculation, Muscle, 2012