Cardiovascular

4. valve positioned between the right ventricle and the pulmonary artery (two words)
6. flow of blood from the heart to the lungs and back to the heart (two words)
7. one of two pairs of vessels carrying oxygenated blood from the lungs to the left atrium of the heart (two words)
9. thin-walled vessel that carries blood from body tissues and lungs back to the heart.
10. muscular middle layer of the heart
12. innermost lining of blood vessels
13. largest type of blood vessel
14. one of two upper chambers of the heart
15. valve between the left atrium and the left ventricle (two words)
17. inner lining of the heart
18. largest artery in the body
19. one of two lower chambers of the heart
20. specialized nervous tissue in the right atrium that begins the heartbeat

1. located between the right atrium and the right ventricle (two words)
2. double-layered membrane surrounding the heart
3. smallest type of blood vessel
5. largest vein in the body (two words)
6. artery carrying oxygen-poor blood from the heart to the lungs (two words)
8. small vein
11. small artery
16. structure in begins or in the heart that temporarily closes an opening so that blood flows in only one direction
20. beat of the heart as felt through the walls of the arteries