Arteries and veins are essential components of the vascular systems of animals. They are in charge of moving blood around the body.
If you had to write one structural difference between the composition of artery and veins, it would be that the tunica media, the middle layer of the wall of the vein or artery, is thicker in arteries than in veins.
Arteries have the task of moving oxygenated blood from the heart to the body. There are three types of arteries that are differentiated by the construction of their vein walls: elastic, muscular and arteriole.
An elastic artery is found closer to the heart. Muscular arteries distribute blood around the body to the arterioles, which move blood into capillary beds.
Elastic arteries contain a lot of durable elastic fibers to give them some flexibility and help them withstand the pressure of blood flow from the heart. Muscular arteries have less tunica media and more tunica adventitia (this is the external layer of the artery or vein) to help with vasoconstriction to move blood around the body.
Arterioles are the smallest arteries found in the body and move blood into the capillary beds so it can fuel cells.
Veins move de-oxygenated blood away from the body and back to the heart. Veins are thinner than arteries as veins don't have the pressure of the heart pumping blood behind them. Unlike arteries, veins have valves that prevent blood from moving backward in the body. There are four different kinds of veins:
- Deep veins
- Superficial veins
- Pulmonary veins
- Systemic veins
Deep veins are associated with an artery and found in the muscle tissues. Superficial veins are close to the surface of the skin and not associated with an artery. As the name suggests, the pulmonary veins move blood to and from the lungs for oxygenation. Systemic veins are found across the entire body and move blood back to the heart.
Artery Walls vs. Vein Walls
Arteries and veins have a similar wall structure. They have an outer layer called the tunica adventitia or externa, a middle layer called the tunica media and the inner layer called the tunica intima.
Each layer functions similarly in arteries and veins, but the proportions change depending on the type of artery or vein. Loose connective tissues and elastic membranes are also included to help the veins and arteries do their work.
The tunica adventitia is primarily composed of collagen with some elastic fibers and smooth muscle fibers. The elastic allows the artery or vein to stretch a little.
The smooth muscle is typically thicker in veins than in arteries. As the outer layer, its purpose is to maintain the vein or artery's form under pressure from blood flow and prevent the vein or artery's movement within body tissues.
This middle section is made up of smooth muscles and elastic fibers layered into circular sheets. At the outer edge of this section, on top of the circular muscle sheets, are longitudinal muscles that help with vasoconstriction and vasodilation.
This layer is much thicker in arteries due to the need for arteries to pump blood around the body.
This section is also made of connective and epithelial tissues. The tunica intima endothelium is made up of simple squamous epithelium cells.
As the innermost section, it plays a vital role in keeping the lumen of the vein or artery open for healthy blood flow. Other duties include assisting with changing blood flow and regulating capillary exchange.
Artery Structure vs. Vein Structure
Despite being constructed of similar tissue types, the overall structure of arteries and veins is different. Arteries are round with thick muscular walls. In contrast, veins can have an irregular shape and are more likely to collapse as they have thinner walls.