Timmy

2. The middle, muscular layer of the heart responsible for its contractions.
4. Blood vessels that carry oxygenated blood from the lungs to the left atrium of the heart.
6. A lubricating fluid found in the pericardial cavity between the layers of the pericardium, which reduces friction as the heart beats.
7. The blood vessel that carries oxygen-poor blood from the right ventricle to the lungs.
8. Tiny thin-walled blood vessels where exchange of oxygen and carbon dioxide occurs between the blood and tissues.
10. The innermost layer of the heart, composed of smooth endothelial cells that line the heart and valves.
11. A valve between the right ventricle and pulmonary artery that prevents blood from flowing back into the ventricle when it contracts.
13. One of the two upper chambers of the heart, which receive blood from the veins.
14. A sac-like structure that surrounds and protects the heart, composed of two layers (visceral and parietal pericardium).
15. A valve between the right atrium and right ventricle that prevents blood from flowing back into the atrium when the ventricle contracts.

1. A partition or wall that separates the chambers of the heart.
3. A valve between the left ventricle and aorta that prevents blood from flowing back into the ventricle when it contracts.
5. A valve between the left atrium and left ventricle that prevents blood from flowing back into the atrium when the ventricle contracts.
9. The largest artery in the body that carries oxygenated blood from the left ventricle to the rest of the body.
12. One of the two lower chambers of the heart, responsible for pumping blood out to the body or lungs.