The circulatory or cardiovascular system is composed of the heart, arteries, capillaries, venules and veins.
The arteries are strong, flexible blood vessels that carry blood away from the heart. Their strenght helps maintain
blood pressure while the heart is between beats. Smaller arteries and arterioles have muscular walls that can adjust
their diameter to increase or decrease bloodflow to a particular area, depending on the body's needs.
The vessels that return blood to the heart.
The smallest blood vessels in the circulatory system. Capillaries have thin walls that facilitate the transfer of
oxygen and glucose into a cell and waste products such as carbon dioxide back out into the blood stream
to be carried away and taken out of the body via the lungs. They act as the bridge between arteries, carrying blood
away from the heart, and veins, carrying blood back to the heart.
Excessive relaxation or dilation of the blood vessel walls. The resulting low blood pressure causes an
supply to body cells, which can result in shock (blood pressure too low to sustain life).
Causes of excessive dilation
include head injury, liver failure, poisoning, drug overdoses and severe bacterial infection.