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Across 5. Vessels allowing for diffusion between blood and tissue cells. 7. The muscle under the lungs that assists in breathing. 9. Electric impulses that are produced by the pacemaker can be detected by an... 12. Iron deficiency in the blood. 13. The respiratory system of fish. 15. Chemical that carries information from one neuron to another. 19. sets the beat of the heart. 20. Prevent the back flow of blood; mostly present in veins. 21. the bundle of nerve fibers inside of the spinal cord. 22. Largest part of the brain. 23. the voluntary carrying of signals to the skeletal muscles. 24. layers of connective tissues in the brain for protection. 25. Anything that causes a nerve signal to start.

Down 1. The master control center of the body. 2. Voice box 3. Molecules on red blood cells that carry oxygen. 4. The brain and the spinal cord. 6. Clusters of air sacs where the gases are exchanged with blood vessels. 8. A rhythmic stretching of the arteries caused by the pressure of forced blood in the arteries during systole. 10. The rapid, long distance internal transport system that facilitates the exchange of materials. 11. A long, single fiber, that conducts signals towards another neuron or body part. 14. Neurotransmitters are released into this gap. 16. Chronic cardiovascular disease. 17. This part of the brain is responsible for hearing and smelling. 18. The rhythmic contractions and relaxations of the heart; diastole and systole