TH1.H1.3 Arteries
Arteries:
- Arteries are the distributing tubes of the cardiovascular system
- They have a thick tunica media composed of smooth muscle
- There are two main types of artery - elastic and muscular arteries
- Elastic arteries have sheets of elastic fibres interspersed between the smooth muscle cells of the tunica media
- The aorta, and the proximal parts of "great vessels" are elastic arteries
- At systole when blood is forced into the great vessels at high pressure, the elastic arteries stretched due to the presence of the elastic fibres
- In diastole, the elastic recoil from the elastic fibres helps to maintain a high blood pressure within the arterial system and smooths the pressure variation which would otherwise exist between systole and diastole
- Muscular arteries have a thick tunica media containing several layers of smooth muscle cells
- They have only a single layer of elastic fibres which lies between the tunica intima and the tunica media
- The smooth muscle cells are usually found orientated circularly around the blood vessel wall
- By contracting, the diameter of the artery, and the amount of blood flowing to the region of the body supplied by that artery, will be reduced
- A small number of arteries have both a circular and a longitudinal layer of smooth muscle cells
- These are specialised to act either as a peristaltic pump, as in the umbilical arteries or in sites where the lumen has to be occluded for periods of time, as in (some) arteries supplying the erectile tissue of the penis or clitoris
