Pericytes, sometimes referred to as Rouget cells, are cells that wrap around the endothelial cells of capillaries. These cells play an important role in angiogenesis, the process of formation of new blood vessels. Monocytes are macrophages of the immune system, Purkinje fibers are found in the heart, and allow conductance of electricity to the cardiomyocytes, Schwann cells are glial cells in the peripheral nervous system that myelinate axons.

Capillaries have the largest total cross sectional and surface area. They are thin-walled and consist of a single layer of endothelial cells surrounded by basal lamina. Capillaries are the site of exchange of nutrients, water, and gases.

Arteries are thick-walled, with extensive elastic tissue and smooth muscle. Arteries are under high pressure.

At any given moment, the majority of blood in the human body can be found in the venous network. Veins contain 64% of the body's blood, making it the largest reservoir of blood in the body. Capillary networks contain the largest surface area of blood, however, not the largest percentage of blood volume.

The walls of arteries, arterioles, veins, and venules are all much too thick to allow for the diffusion of substances. However, capillaries only have simple squamous endothelial cells lining their walls, without muscular and/or elastic tissue surrounding them. Their walls are thin enough to allow for diffusion of substances into the interstitium.

Fluid movement into and out of capillaries is mainly dependent on two forces: hydrostatic pressure and osmotic pressure. Hydrostatic pressure is determined by fluid volume and the pressure of the fluid against the capillary walls. Osmotic pressure is determined by osmotic gradient, pulling water in the direction of higher protein concentration. Osmotic pressure is largely directed into the capillary due to the high concentration of albumin in the plasma. The osmotic pressure outside of the capillary remains relatively constant, however, as the capillary moves from the arteriole end to the venule end the hydrostatic pressure drops significantly. Eventually, the osmotic pressure in the interstitium becomes greater than the hydrostatic pressure in the capillary, and fluid returns to the capillaries.