Arterial System

Arterial System

The arterial system consists of the aorta and the left and right pulmonary arteries. The aorta sends oxygenated blood to the various body systems, whereas the pulmonary arteries carry deoxygenated blood to the lungs. Arteries are grouped based on whether they are elastic or muscular. Smaller arteries are called arterioles.

Elastic Arteries

Elastic arteries are located near the heart and havethick walls. They include the aorta and its primary branches. They are the arteries of largest diameter in the body and the most elastic. The elastic arteries range between 2.5 and 1 cm in diameter, with large lumens. The size of their lumens causes them to be low-resistance pathways for blood as it moves from the heart to the medium-sized arteries. Elastic arteries are also known as conducting arteries.

There is more elastin in the elastic arteries than in the other types of arteries. Elastin is found in all three tunics, with the tunica media being the most elastic. In the tunica media, the elastin has holes and is found between layers of smooth muscle cells. When ­atherosclerosis and similar conditions cause the blood vessels to lose elasticity, the blood flows through with more difficulty, raising the blood pressure. Arteriosclerosis accounts for 50 percent of deaths in the United States.

Muscular Arteries

The smaller, distal muscular arteries, also known as distributing arteries, deliver blood to body organs. Theyhave the thickest tunica media of all blood vessels, in proportion to their size. A muscular artery’s diameter is 0.4 cm. The tunica media of muscular arteries, in com-parison with elastic arteries, have relatively more smooth muscle and less elastic tissue. Because of this, they have more vasoconstrictive actions but are less able to stretch.

Arterioles

The arterioles are the smallest of all arteries. The diameter of their lumens is between 0.3 mm and 10 μm. The largest arterioles have three tunics, whereas the smallest­ arterioles are basically a single layer of smooth muscle cells circled around an endothelial lining. The tunica media of larger arterioles is mostly made up of smooth muscle, with a small amount of elastic fibers in various areas. Arterioles have a poorly defined tunica externa. The smaller arterioles lead directly into the capillary beds. With resistance describing the force that opposes blood flow, arterioles are also called resis-tance vessels because more pressure is needed to pushblood through them than arteries. This is because they are more constricted.

1. Compare vasoconstriction with vasodilation.

2. Identify the three layers of a blood vessel.