Heart

1. / the fluid that circulates in the principal vascular system of human beings.
4. vein / a vein conveying oxygenated blood from the lungs to the left atrium of the heart.
6. / the two lower chambers on each side of the heart that receive blood from the atrium and in turn force it into the arteries.
9. / a hollow, pumplike organ of blood circulation.
11. / the two upper chambers on each side of the heart that receive blood from the veins and in turn force it into the ventricles.
12. cava / two large veins discharging blood into the right atrium of the heart.

2. / a colorless, odorless, gaseous element constituting about one-fifth of the volume of the atmosphere.
3. / small blood vessels that distribute oxygenated blood from the tissues to the body.
5. / a dividing membrane especially masses of soft tissue.
7. dioxide / a colorless, odorless, incombustible gas, present in the atmosphere and formed during respiration.
8. / the main trunk of the arterial system, conveying blood from the left ventricle of the heart to all of the body except the lungs.
10. / a membranous structure that controls the flow of the blood.