Across
- 4. lymphatic tissue in the nasopharynx
- 6. The largest vein in the body
- 8. Windpipe
- 10. The contraction phase of the heartbeat
- 11. The smallest branches of the bronchi
- 14. breathing out
- 15. Muscular, middle layer of the heart
- 17. muscular pump
- 18. Double-layered membrane surrounding heart
Down
- 1. Inner lining of the heart
- 2. The largest type of blood vessel
- 3. the pacemaker of the heart
- 5. breathing in
- 7. The smallest blood vessel
- 9. One of two upper chambers of the heart
- 12. Voice box
- 13. gas that makes up 21% of air
- 16. Muscle separating the chest and abdomen