GLOSSARY

Blood vessels are a network of closed tubes that carry blood from the heart to every tissue of the body and back to the heart, forming the cardiovascular system together with the heart.
The total length of an adult’s blood vessels is estimated at about 100,000 kilometres, most of which are capillaries.

Wall Structure (Three Layers)

• Inner layer (tunica intima): the endothelium, a smooth surface and active regulator.
• Middle layer (tunica media): smooth muscle and elastin, controlling vessel diameter.
• Outer layer (tunica externa/adventitia): connective tissue and collagen, for protection and anchorage.
• Capillaries: have only a single layer of endothelium.

Functions