Third graders should know about the brain, the heart, the lungs and the stomach, according the Texas Department of State Health Services. These organs make up the main parts of the circulatory, digestive, respiratory and nervous systems.
The brain is the organ that allows humans to do all voluntary and involuntary actions, such as moving, feeling and thinking. It sends messages to the rest of the body on what to do and how to act, and it is where all ideas and movements originate. It is the most important organ, and the main organ of the central nervous system.
The heart is part of the circulatory system that pumps blood throughout the body, allowing all parts to get oxygen. The heart is made up of four separate chambers, and the blood is pumped to and from the heart through veins and arteries. The oxygen is taken from the respiratory system that is made up mostly of the lungs. The lungs take in air and expand, then extract oxygen and push out carbon dioxide.
The stomach is part of the digestive system, and it takes in everything humans consume. Once food reaches the stomach, the stomach uses acids to break down the food and take all the nutrients that the body needs.