Olivia is a science teacher, and today she is explaining the human body to her class. She says that our body is like a very smart and beautiful machine. Inside us, different organs and systems work together every minute of the day. First, she points to a picture of the heart in the chest. The heart is the engine of the circulatory system because it pumps blood. Next, she explains the respiratory system and how we use our two lungs. Our lungs take in fresh air and oxygen when we breathe every day. Then, Olivia talks about the stomach and the digestive system in our body. The stomach breaks down food to give energy to our legs and arms. Finally, she explains the nervous system and the power of the human brain. The brain is the computer of the body because it controls everything. Olivia thinks that understanding our main body systems helps us live a healthy life.