Capillaries originate from the arteries and their origin is guarded by a precapillary sphincter, which is a flap of smooth muscle present around the structure to regulate the flow of blood into the capillary.Ĭapillaries don’t have any smooth muscle. This absence of tunica media and the gap in the inter-endothelial junctions contribute to the greater exchange of materials and increased permeability of the capillaries.Ĭapillaries are very thin. Unlike other blood vessels like arteries and veins, tunica media is completely absent in capillaries. These endothelial cells are joined together by inter-endothelial junctions between two adjacent cells. The cells are surrounded by a basement membrane, which is a layer of protein surrounding the capillary. Capillary walls are made up of a single layer of endothelial tissue This increases the surface area for a more rapid exchange of materials.
Morphology CapillaryĬapillaries form an extensive network through branching. Though the diameter of individual capillaries is very minimal, the large number of capillaries ensures that the capillaries have the largest cross-sectional surface area among all blood vessels in the body. All other cells in the body are in direct contact with the walls of the capillary. The products of metabolism and the substrate for metabolism can easily be exchanged between the cells and blood through a capillary wall.Ĭapillaries are present in almost all areas of the body except the lens and cornea of the eye. Capillaries are present close to all metabolically active cells. The constant supply of oxygen and nutrients is essential for the survival of tissues. Physiologically capillaries are of great importance. This is the region of exchange of nutrients, gases, water, and waste products. Only about 5% of the blood volume circulates in capillaries.Ĭapillaries are more commonly known as exchange vessels. The circulation of blood from arteries to venules through capillaries is called microcirculation.Ĭapillaries are also known as microvessels due to their small size and thin walls. Thus capillaries act as intermediary vessels between arteries and veins. From capillaries, this blood goes into venules and then into veins. These capillaries are present in almost every organ and it is in this vessel that gaseous exchange takes place, and the oxygenated blood in the capillaries becomes deoxygenated. The arteries divide and redivide to give smaller, thin branches like arterioles, meta-arterioles. They have thinner walls (less tunica media) with less smooth muscle and wider lumen.įor more details, read arteries and veins and their differences. They carry deoxygenated blood except for the pulmonary vein which carries oxygenated blood. Veins carry blood from other parts of the body back to the heart.