Blood vessel

A blood vessel is a tube that carries blood in the circulatory system. Blood vessels that take blood away from the heart are arteries. Blood vessels that take blood back to the heart are veins. Capillaries are between veins and arteries and they supply tissue with blood.

The heart plus all of the blood vessels in the body together are called the circulatory system. Blood is moved by the pumping of the heart and carries oxygen to the tissues.

The expansion of blood vessels is called vasodilation, it helps the body to get rid of heat energy (vas- in Latin means "container" or "vessel"^[1]). The constriction of blood vessels is called vasoconstriction, it prevents the body from losing warmth.

Originally, August Krogh estimated that there was 100,000 km (60,000 miles) of combined blood vessels in the human body. However, his figure was based off of incorrect assumptions assuming that the density of blood vessels in the human body was significantly more than what we know today. He based his calculations on the assumption of a 143kg body with 50kg of pure muscle, an unrealistic body, leading to unrealistic estimations. A new study^[2] determined that the actual is somewhere between 9,000 km - 19,000 km (5,600 miles - 11,800 miles).

Growing new blood vessels is called angiogenesis.

1. ↑ Harper, Douglas (2001–2016). "Online Etymology Dictionary". Online Etymology Dictionary. Retrieved March 8, 2016.
2. ↑ Poole, David C.; Kano, Yutaka; Koga, Shunsaku; Musch, Timothy I. (2021-03-01). "August Krogh: Muscle capillary function and oxygen delivery". Comparative Biochemistry and Physiology. Part A, Molecular & Integrative Physiology. 253: 110852. doi:10.1016/j.cbpa.2020.110852. ISSN 1531-4332. PMC 7867635. PMID 33242636.