Arteries: Moving Blood Away from the Heart
Your heart is responsible for circulating blood throughout your body via arteries. The aorta and pulmonary arteries are large vessels, but their branches (and branches of those branches) gradually get smaller in diameter until they reach the tiny capillaries. No matter their size, all arteries are hollow tubes with walls made up of three layers called tunics:
Tunica intima: The thin innermost lining of the arteries, containing endothelium and connective tissue
Tunica media: A middle layer of smooth muscle
Tunica adventitia: The outer layer of connective tissue, made of collagen fibers
The thick tunica media of the large elastic arteries contains smooth muscle and several sheets of elastic layers that give the large arteries plenty of flexibility to expand each time the heart beats. This expansion helps to maintain fairly even blood pressure and blood flow. Following are examples of large elastic arteries:
Aorta: This artery leaves the left ventricle of the heart.
Pulmonary artery: This artery runs from the heart to the lung.
Common carotid artery: This artery travels through the neck.
Right subclavian artery: This artery is also in the neck.
The medium muscular (or distributing) arteries have less elastic tissue than the large elastic arteries because the main component of the tunica media is smooth muscle. The body has many medium muscular arteries, including the following:
Radial and ulnar arteries: These arteries are in the forearm and wrist.
Brachial artery: This artery travels through the arm.
Femoral artery: The femoral is the major artery of the thigh.
Anterior tibial and fibular arteries: These arteries course through the leg.
Dorsalis pedis artery: This artery is in the foot.
The walls of the small arteries and arterioles are thick because they have a lot of smooth muscle, but they have small lumen (the open part inside the arteries). These little blood vessels regulate the amount of pressure in the arteries (blood pressure). When the smooth muscles contract, the blood flow is restricted and blood pressure goes up. When they relax, the blood pressure goes down.
Hypertension (high blood pressure) is a condition in which blood pressure remains elevated over time. Having high blood pressure increases the risk of heart disease, stroke, and kidney disease. Hypertension is referred to as the silent killer because high blood pressure has no symptoms and damage can be done to the heart, kidneys, and blood vessels before the person notices anything. Hypertension is treated in a variety of ways, including lifestyle changes (diet and exercise) and medication.
Anastomoses are connections formed between the branches of an artery. This type of connection allows for collateral circulation that ensures blood will reach the desired destination even if one of the branches is blocked or occluded. The circle of Willis (which is in the brain) is an arterial anastomosis.