Blood vessels carry nutrients (like glucose) and oxygen to the muscle cells that need them. Blood vessels take away carbon dioxide and waste from muscle cells.
The brain checks up on the amount of carbon dioxide in the blood and adjusts the rate of breathing. The brain “communicates” with the lungs using nerves from the brain to lungs.
Blood vessels carry red blood cells to the lungs, to get rid of carbon dioxide and pick up oxygen that has been breathed in. The heart pumps red blood cells carrying oxygen from lungs to all cells in the body and back to the lungs once the oxygen has been used up.
Blood vessels deliver nutrients and oxygen for all the intestinal cells to function. Blood in blood vessels picks up nutrients absorbed by the intestines and carries them away to other parts of the body that need them.
Nerves send messages to muscles to tell them how and where to move. Nerves check up on the body’s need for oxygen in the muscles and adjust breathing rate and heart rate as needed.
The brain tells the stomach, intestines, and liver when to be active and when to rest. Messages to and from the brain decide when it’s time to process food.