How the Heart Works

Page: 1 2 3 (of 3)	Previous

the circulatory system

The heart would be useless without the intricate system of blood vessels that make up the circulatory system. The human body has more than 60,000 miles of blood vessels, enough to circle the earth more than twice. There are three types of blood vessels in the circulatory system:

• Arteries: These vessels take oxygen-rich blood from the heart to the rest of the body. Arteries get smaller as they reach their targets. The largest artery is the aorta.
• Veins: These vessels take oxygen-poor blood from the body back to the heart. Veins get larger as they get closer to the heart. The largest veins are the inferior vena cava (which accepts blood from the lower body) and the superior vena cava (which directs blood from the upper body).
• Capillaries: These tiny vessels connect arteries and veins. They have very thin walls, which allow the exchange of oxygen and nutrients to the body’s cells, as well as help cart away waste products.

SOURCES: National Heart, Lung, and Blood Institute, Advocacy Health Care, WebMD, Human Physiology (McGraw-Hill, 7th edition), and Human Anatomy (McGraw-Hill, 5th edition).