Arteries are blood vessels which carry blood away from the heart. All of which, with the exception of the pulmonary artery, carry oxygenated blood. The most widely known artery within the human body is the Aorta.
This is the largest of all blood vessels and transports blood away from the left ventricle of the heart where it then branches into smaller arteries. As the arteries divide further they become smaller and smaller, until they are classed as arterioles. Arterioles continue to branch into smaller and smaller vessels which, once they have decreased in size below 10 micrometers in diameter are known as capillaries.
The pulmonary artery is classed as an artery as it carries blood away from the heart, however, it carries deoxygenated blood. The blood it carries has travelled around the body and back to the heart where it is pumped, via the pulmonary artery, to the lungs to release waste products and pick up more oxygen.
The artery walls consist of three layers:
- Tunica Adventitia: This is the strong outer covering of arteries and veins which consists of connective tissues, collagen, and elastic fibres.
- Tunica Media: This is the middle layer and consists of smooth muscle and elastic fibres. This layer is thicker in arteries than veins.
- Tunica Intima: This is the inner layer which is in direct contact with the blood flowing through the artery. It consists of an elastic membrane and smooth endothelial cells. The hollow centre through which blood flows is called the lumen.
Smaller arteries and arterioles contain more smooth muscle tissue in order to control the changing pressure of the blood flow. This change in pressure is a direct effect of the pumping of the heart. During the diastolic phase blood pressure is low due to the rest period of the heart. In the systolic phase the heart contracts, forcing blood through the arteries and subsequently increasing the pressure. This change in pressure within an artery is what you can feel when you take a pulse.