| A | B |
|---|
| cardiovascular system | consists of the heart, blood vessels, and blood |
| heart | a hollow, muscular organ that pumps blood throughout the body |
| atria | upper chambers of the heart that receive blood |
| pacemaker | cells that send out signals to make the heart contract |
| ventricle | lower chambers of the heart that pump out blood |
| valve | a flap of tissue that prevents blood from flowing backward |
| arteries | blood vessels that carry blood away from the heart |
| capillaries | tiny, narrow blood vessels where substances are exchanged between the blood and body cells |
| veins | blood vessels that carry blood back to the heart |
| aorta | blood is pumped into it from the left ventricle; the largest artery in the body |
| coronary arteries | carry blood to the heart tissue |
| diffusion | the process by which molecules move from an area of higher concentration to an area of lower concentration |
| blood pressure | the force of blood against the walls of blood vessels |
