| myocardium | thick middle muscle layer of the heart; pumps blood through the circulatory system |
| atrium | upper chamber of the heart that receives and holds blood that is about to enter the ventricle |
| ventricle | lower chamber of the heart that pumps blood out of the heart |
| pulmonary circulation | pathway of circulation between the heart and the lungs |
| systemic circulation | pathway of circulation between the heart and the rest of the body except the lungs |
| valve | flap of connective tissue between an atrium and a ventricle, or in a vein, that prevents backflow of blood |
| pacemaker | small group of cardiac muscle cells in the right atrium that "set the pace" for the heart as a whole; also known as the sinoatrial node (SA) |
| aorta | large blood vessel in mammals through which blood travels after it leaves the left ventricle |
| artery | large blood vessel that carries blood from the heart to the tissues of the body |
| capillary | smallest blood vessel; brings nutrients and oxygen to the tissues and absorbs carbon dioxide and waste products |
| vein | a blood vessel that returns blood to the heart |
| atherosclerosis | condition in which fatty deposits called plaque build up on the inner walls of the arteries |
| plasma | straw-colored fluid that makes up about 55% of blood |
| hemoglobin | iron-containing protein in red blood cells that transports oxygen from the lungs to the tissues of the body |
| lymphocyte | type of white blood cell that produces antibodies that help destroy pathogens |
| platelet | cell fragment released by bone marrow that helps in blood clotting |
| lymph | fluid lost by the blood into surrounding tissue |
| pharynx | muscular tube at the end of the throat that connects the mouth with the rest of the digestive tract, and serves as a passageway for air and food |
| trachea | windpipe; tube through which air moves |
| larynx | structure in the throat containing the vocal cords |
| bronchus | passageway leading from the trachea to a lung |
| alveolus | tiny air sac at the end of a bronchiole in the lungs that provides surface area for gas exchange to occur |
| diaphragm | large, flat muscle at the bottom of the chest cavity that helps with breathing |
| nicotine | stimulant drug in tobacco that increases heart rate and blood pressure |
| emphysema | disease in which the tissues of the lungs lose elasticity, making breathing very difficult |
| aorta | brings oxygen-rich blood from the left ventricle to the body |
| superior vena cava | large vein that brings oxygen-poor blood from the upper part of the body to the right atrium |
| pulmonary veins | bring oxygen-rich blood from each of the lungs to the left atrium |
| right atrium | right upper chamber of heart; receives oxygen-poor blood |
| right ventricle | right lower chamber of heart; pumps blood out of the heart |
| septum | divides the right side of the heart from the left side |
| inferior vena cava | vein that brings oxygen-poor blood from the lower part of the body to the right atrium |
| pulmonary arteries | bring oxygen-poor blood to the right or left lung |
| left atrium | left upper chamber of heart; receives oxygen-rich blood from the pulmonary veins |
| left ventricle | left lower chamber of heart; pumps blood out of the heart |
| pulmonary valve | prevents blood from flowing back into the right ventricle after it has entered the pulmonary artery |