To determine if a patient has hypertension, of course, you’ll measure his blood pressure. From his blood pressure measurements, you can determine his pulse pressure and mean arterial pressure (MAP). These measurements, in turn, can help you detect related disorders and understand the effects of certain hemodynamic factors on your patient’s blood pressure.
Arterial System
Arteries, the vessels through which blood travels away from the heart, all carry oxygenated blood, except for the pulmonary arteries, which carry oxygen-depleted blood from the heart to the lungs. The arterial system is made up of vessels of various sizes:
- large, usually elastic arteries, such as the aorta and the pulmonary trunk
- medium-sized arteries, which make up most of the arterial vasculature
- large and small arterioles.
Arteries have nerves bundled along their outer walls. Primarily derived from the sympathetic nervous system, these nerves cause the arteries to contract and relax, thus regulating the flow of blood to various parts of the body.
Arterial Walls
All arteries have three distinct layers. The outer layer (tunica adventitia or externa) is made of strong connective tissue with abundant elastic fibers. The middle layer (tunica media) consists of more elastic fibers than smooth-muscle fibers. The inner layer (tunica intima) is a transparent and highly elastic structure that has direct contact with the circulating blood.
The thickness of each of these layers varies depending on the location of the artery. For instance, large arteries like the aorta or pulmonary arteries typically have a thick tunica media with more elastic fiber than smooth muscle, enabling them to stretch as blood is ejected from the heart during systole and to recoil during diastole. However, arteries located farther away from the heart have less elastic tissue and more smooth muscle. These small-sized to medium-sized vessels are muscular arteries. Together, all arteries help to maintain blood pressure throughout the high-pressure, high-resistance, low-volume arterial system.
Arteries become arterioles when the diameter of the vessel is less than 0.5 mm. The thick smooth-muscle layer of the arterioles enables them to control the flow of blood through the systemic circulatory system by means of vasodilation and vasoconstriction and push the blood through finer arterial structures, the capillaries.