Capillary

Capillaries ( /ˈkæpɨlɛri/) are the smallest of a body's blood vessels and are parts of the microcirculation. Their endothelial linings are only one cell thick. These microvessels, measuring 5-10 μm in diameter, connect arterioles and venules, and enable the exchange of water, oxygen, carbon dioxide, and many other nutrients and waste chemical substances between blood and surrounding tissues. During embryological development, new capillaries are formed by vasculogenesis, the process of blood vessel formation occurring by a de novo production of endothelial cells and their formation into vascular tubes. The term angiogenesis denotes the formation of new capillaries from pre-existing blood vessels.