| A | B |
|---|
| cardiovascular system | The body system that consists of the heart, blood vessels, and blood; also called the circulatory system. |
| heart | A hollow, muscular organ that pumps blood throughout the body. |
| atrium | Each of the two upper chambers of the heart that receives blood that comes into the heart. |
| ventricle | Each of the two lower chambers of the heart that pumps blood out of the heart. |
| valve | A flap of tissue in the heart or a vein that prevents blood from flowing backward. |
| aorta | The largest artery in the body; receives blood from the left ventricle. |
| coronary artery | An artery that supplies blood to the heart itself. |
| pulse | The alternating expansion and relaxation of an artery wall as blood travels through an artery. |
| lymph node | A small knob of tissue in the lymphatic system that filters lymph, trapping bacteria and other microorganisms that cause disease. |
| pacemaker | A group of cells located in the right atrium that sends out signals that make the heart muscle contract and that regulates heart rate. |
| artery | A blood vessel that carries blood away from the heart. |
| capillary | A tiny blood vessel where substances are exchanged between the blood and the body cells. |
| vein | A blood vessel that carries blood back to the heart. |
| lymph | The fluid that the lymphatic system collects and returns to the bloodstream. |
| lymphatic system | A network of veinlike vessels that returns the fluid that leaks out of blood vessels to the bloodstream. |
| plasma | The liquid part of blood. |
| red blood cell | A cell in the blood that takes up oxygen in the lungs and delivers it to cells elsewhere in the body. |
| hemoglobin | An iron-containing protein that binds chemically to oxygen molecules, makes up most of red blood cells. |
| white blood cell | A blood cell that fights disease. |
| platelet | A cell fragment that plays an important part in forming blood clots. |
| diffusion | The process by which molecules move from an area of higher concentration to an area of lower concentration. |
| blood pressure | The pressure that is exerted by the blood against the walls of blood vessels. |
