Structure & Function of Blood Vessels

Function

There are three types of blood vessels in the human body: arteries, veins and capillaries. Arteries carry blood from the heart to the rest of the body. Veins return blood to the heart. Capillaries connect arteries and veins. Blood carries oxygen and nutrients throughout your body, and disposes of the waste products of metabolism, such as carbon dioxide. Your blood circulates in two systems: the pulmonary circulatory system and the systemic circulatory system. The pulmonary circulatory system sends oxygen-poor blood from the right side of the heart to the lungs. Here, your alveoles, or tiny air sacs, transfer oxygen to your red blood cells. The freshly oxygenated blood travels from the left side of the heart throughout the body via the systemic circulatory system.

Structure

Blood vessels have three layers of tissue, according to North Seattle Community College. The innermost layer, called the tunica interna, is a smooth surface. This provides a low-friction wall through which blood can flow. The middle layer, the tunica media, consists of smooth muscle tissue. This muscle controls contraction and relaxation of the blood vessels. The outer wall, or tunica adventia, consists of connective tissue. It keeps blood from seeping into the body and from losing oxygen and vital nutrients.

How Blood Vessels Work

Blood vessels work because their structure is suitable to the mechanical stress placed on them by the blood pumping through them. The blood vessels have some pressure even when there is no blood present; when blood is present, the internal pressure causes the blood to keep flowing in the proper direction. According to the University of Michigan, blood vessels are more elastic near the heart, because the force of the blood being pumped is stronger and the arteries have to accommodate for that fact.

References

• Lecture Slides From North Seattle Community College
• University of Michigan College of Engineering