What a body cannot use has to leave

Not everything that goes in stays. Two things leave by different routes.

The idea

Blood carries carbon dioxide to the lungs. Carbon dioxide leaves into the air when we breathe out.

The gut is the long food tube. The anus is the way out for what the gut cannot digest. On the way, the large intestine takes back water and some salts. What remains is a semi-solid stool, which is thick but not hard. It waits in the rectum. The rectum is the last part of the large intestine. Then the stool leaves. That leaving is egestion.

Carbon dioxide leaves with the breath. Undigested food leaves through the anus. Only the second is egestion.

Try the lab to finish this lesson.