Artery

In human physiology, an artery is any of the vessels that, with the exception of the coronary arteries, transport oxygenated blood and nutrients from the heart to the body’s tissues. The pulmonary artery is an exception, as it transports oxygen-depleted blood to the lungs for oxygenation and elimination of excess carbon dioxide (see pulmonary circulation).

Arteries are muscular and elastic tubes that must transfer blood while being subjected to a high pressure generated by the heart’s pumping motion. The pulse, which may be felt near the skin’s surface over an artery, is caused by the arterial wall expanding and contracting alternately when the beating heart forces blood into the arterial system via the aorta. The aorta’s large arteries branch off to form smaller arteries until the level of the smallest arteries, or arterioles, is reached. The threadlike arterioles transport blood to networks of small vessels known as capillaries, which nourish and oxygenate the tissues and remove carbon dioxide and other metabolic waste products via the veins.

Structure

The anatomy of arteries can be divided into gross anatomy, which is visible at the macroscopic level, and microanatomy, which requires the use of a microscope to study. The human body’s arterial system is divided into systemic arteries, which transport blood from the heart to the rest of the body, and pulmonary arteries, which transport deoxygenated blood from the heart to the lungs.

The tunica externa, also known as tunica adventitia, is the outermost layer of an artery (or vein). It is formed of collagen fibres and elastic tissue, with the biggest arteries including vasa vasorum (small blood vessels that supply large blood vessels). While the majority of the layers have a distinct boundary, the tunica externa has an ill-defined boundary. Typically, its boundary is defined by the point at which it meets or contacts the connective tissue. The tunica media, or medium, is located within this layer and is composed of smooth muscle cells, elastic tissue (also known as connective tissue proper), and collagen fibres. The tunica intima, commonly referred to as the intima, is the innermost layer that comes into direct contact with the blood flow. The artery’s elastic nature enables it to bend and pass-through narrow passageways in the body. This layer is predominantly composed of endothelial cells (and a supporting layer of elastin rich collagen in elastic arteries). The lumen is the hollow internal cavity through which blood flows.

Development

Arterial development begins and finishes with the expression of arterial-specific genes by endothelial cells, such as ephrin B2.

Function

Arteries are a vital component of the circulatory system. They transport oxygenated blood that has been pumped from the heart. Additionally, the coronary arteries assist the heart in pumping blood by supplying oxygenated blood to the heart, which enables the muscles to operate. Except for the pulmonary arteries, which transport blood to the lungs for oxygenation, arteries convey oxygenated blood away from the heart to the tissues (usually veins carry deoxygenated blood to the heart but the pulmonary veins carry oxygenated blood as well). There are two distinct types of arteries. The pulmonary artery is responsible for transporting blood from the heart to the lungs, where it is oxygenated. It is unique in that the blood contained therein has not yet been “oxygenated” by the lungs. The umbilical artery, on the other hand, is unique in that it transports deoxygenated blood from a foetus to its mother.

Blood pressure in arteries is higher than in other regions of the circulatory system. Throughout the cardiac cycle, the pressure in arteries changes. It is at its maximum when the heart contracts and at its minimum when the heart relaxes. The pressure variation generates a pulse, which can be felt in several locations of the body, including the radial pulse. Arterioles collectively exert the largest influence on both local blood flow and systemic blood pressure. They are the principal “adjustable nozzles” in the blood system, as they are the locations of the greatest pressure drop. The relationship between heart output (cardiac output) and systemic vascular resistance, which refers to the collective resistance of all of the body’s arterioles, is the primary determinant of arterial blood pressure at any given time.

Arteries experience the greatest pressure and have the smallest lumen diameter. It is composed of three tunics: the medial, the intima, and the exterior.

The systemic arteries are the arteries (including the peripheral arteries) that comprise the systemic circulation, the portion of the circulatory system that transports oxygenated blood away from the heart and back to the heart. Systemic arteries are classified as muscular or elastic based on the ratio of elastic to muscle tissue in their tunica media, as well as their size and composition of the internal and external elastic lamina. Larger arteries (>10 mm in diameter) are often elastic, whereas smaller arteries (0.1–10 mm) are typically muscular. The systemic arteries transport blood to the arterioles and then to the capillaries, which exchange nutrients and gases.

Blood passes from the aorta through peripheral arteries into smaller arteries known as arterioles and finally to capillaries. Arterioles contribute to blood pressure regulation through varying contraction of their smooth muscle walls and supply blood to capillaries.

Conclusion

Systemic arterial pressures are generated by the left ventricle of the heart contracting violently. High blood pressure contributes to arterial injury. Healthy resting artery pressures are typically less than 100 mmHg (1.9 psi; 13 kPa) above surrounding air pressure (about 760 mmHg, 14.7 psi, 101 kPa at sea level). To withstand and adjust to internal pressures, arteries are surrounded by different thicknesses of smooth muscle with an abundance of elastic and inelastic connective tissues. The pulse pressure, defined as the difference between systolic and diastolic pressures, is principally governed by the volume of blood evacuated by each heartbeat, or stroke volume, in comparison to the volume and flexibility of the major arteries.

A blood squirt, also known as an arterial gush, is the result of increased arterial pressures when an artery is cut. Blood is spurted forth at a quick, irregular rhythm that corresponds to the heartbeat. Blood loss can be extensive, occur swiftly, and be life-threatening.