The human body has three types of blood vessel:
- Arteries which carry blood away from the heart.
- Veins which carry blood back towards the heart.
- Capillaries which connect arteries and veins, and are the smallest blood vessels.
The blood vessels form a closed loop network of tubular channels connected to the heart, whose function is to carry blood to and from the organs and tissues in the body.
They vary in diameter from around 2 centimeters for the aorta, the largest artery, down to 3 micrometers for the finest capillaries.