Artery

From ArticleWorld

An artery is a tubular structure that, in connection with many other arteries, carries oxygen-rich blood from the heart, via many branches of decreasing caliber, to the smaller arteries, called arterioles, and finally, to the capillaries, which are where oxygen transfer takes place. The only arteries that do not carry oxygen-rich blood are the pulmonary arteries that carry oxygen-depleted blood from the right ventricle of the heart to the pulmonary vascular system in the lungs.

Structure

Arteries, as mentioned, have the thickest walls among all blood vessels. A cross-section of an artery would reveal that it consists of a lumen, through which blood flows, and a surrounding wall. The inner layer of the wall is called the tunica intima (or just “intima”). It is made up of a specific cell-type called the endothelial cell. Endothelial cells form the innermost layer of many tubular structures in the body.

Outside of the intima layer is the tunica media (or just “media”), made up of connective tissue and smooth muscle cells. The smooth muscle cells are connected to nerve endings which control whether or not the smooth muscle should contract or constrict the flow of blood. This smooth muscle layer can help direct blood flow toward or away from certain body areas.

The outer layer of an artery is called the tunica adventitia (or just “adventitia”). The adventitial layer is composed primarily of connective tissue that is stiff enough to keep an artery from collapsing even if the pressure inside it becomes low.

Arterial Blood Pressure

It is through the arteries that the measurement of blood pressure is obtained. The blood pressure can be determined by inserting a needle into the artery and measuring the rise and fall of the pressure in the artery during a heartbeat. This is often done on extremely ill patients in a hospital setting.

Measuring the blood pressure, in most clinical settings, is done using a blood pressure cuff and a device that can detect the pressure inside the artery by listening to characteristic sounds an artery makes at different pressures. While usually done on the arm, the blood pressure of the leg can be determined as well.

The blood pressure of the arterial system is described as having two different stages even though the pressure inside an artery is changing all the time. The systolic blood pressure reading (or the “top” number) measures the peak pressure in the artery—the pressure that is generated by the pumping pressure of the heart. The diastolic blood pressure reading (or the “bottom” number) represents the amount of pressure (in millimeters of mercury) left over in the artery after the heart has pumped and while it is temporarily at rest.

The blood pressure reading has many clinical applications and, in situations where an individual has what is considered a “high” blood pressure (or hypertension), medications to control it are often used.