Basics of blood vessels

Blood vessels, as its name suggests, are vessels that carry blood to different parts of the human body. These intricate ducts act as the conduit of blood so that oxygen and nutrients can be delivered to the tissues. Without the complex networks of blood vessels, blood circulation necessary to sustain human life would be an impossible feat. Some of the basic facts about blood vessels will be tackled in this article.

The human circulatory system can be compared to an elaborate plumbing system with the heart acting as the central pump. As the heart contracts (pumps), oxygenated blood is forced through the blood vessels and carried to every tissue of the body. The blood vessels that carry oxygenated blood away from the heart are called arteries. Veins carry deoxygenated blood back to the heart. Other blood vessels include the capillaries, arterioles and venules.


Arteries are muscular and elastic tubes that are composed of three layers. Tunica intima is the innermost layer of the artery and consists of a lining of fine network of connective tissue and elastic fibers. The middle layer, tunica media, is composed of smooth muscle cells and elastic fibers. The outermost layer is composed of tough collagen fibers and is called tunica adventitia.

The largest artery of the body is called aorta. It is connected to the left ventricle of the heart. When the heart pumps, oxygenated blood is forced out of the heart through a valve and travels the aorta and then to different arteries of the body. All arteries, with the exception of the pulmonary artery, carry oxygen and nutrients from the heart to other parts of the body. As arteries are farther from the heart, their sizes also become smaller, and the smallest of the arteries are called arterioles.


These are vessels that carry oxygen depleted blood back to the atrium of the heart. From the veins, deoxygenated blood is transported back to the heart via the superior or inferior vena cava. The pulmonary veins are the only veins that carry oxygenated blood from the lungs to the left atrium of the heart. The smallest of the veins are called venules.

Just like the arteries, they are also composed of three layers namely: tunica intima, tunica media and tunica adventitia. These ducts differ from arteries because many veins have valves that prevent the backflow of blood and they have thinner walls. Arteries are fewer and veins are more numerous in the body.


Capillaries are small networks of blood vessels where exchange of oxygen, nutrients and waste between the blood and tissues occur. From the arteries, the final destination of blood carrying nutrients and oxygen are the capillary network of the tissues. After oxygen and nutrients are absorbed by the tissues, wastes and deoxygenated blood are carried back to the heart.  

Blood vessels and old age

As a person advances in age, the blood vessels also undergo certain changes. Changes in the connective tissues of the vessel walls cause the aorta to become thicker, making it stiffer and less flexible. Also, excess cholesterol and fat deposits build up as plaque in the arteries causing the blood vessels to become narrow. The plaque deposits in the arteries, a condition called atherosclerosis, can lead to elevated blood pressure, and increase the risk of stroke and heart disease.

Furthermore, receptors responsible for monitoring and maintaining of blood pressure, called baroreceptors, become less sensitive with age. These changes cause orthostatic hypotension, a condition where are a person becomes dizzy after positional changes because of low blood pressure.

These are some of the few changes of the blood vessels when a person grows old. Young and old, the importance of blood vessels in the body remain the same. They serve as pathways so that oxygen, nutrients and other substances can be delivered to specific tissues. They also serve as sewer systems where carbon dioxide and other body wastes are eliminated from the body.