The Digestive System

by Karthik Gurumurthy

When you eat food, you chew, swallow, and stop thinking about it. You move on and do other things. Inside your body, however, your swallowed food is just beginning a long journey through your digestive system. Animals cannot use the food they eat until it has been digested, or broken down into its nutrients, so the digestive systems in animals is very important.

The bodies of some animals including jellyfish, sea stars, and octopuses, use the same opening in their bodies to take in food and get rid of waste. They have a “two-way” digestive system.

When they eat, the food goes into a large space, called central cavity. There the food is broken down into particles small enough to pass through the cell membranes. Once inside the cells, the food particles finish breaking down into useful nutrients. The unusable waste materials then take the reverse path that the food took. They travel out through the cell membrane and back into the central cavity, where they are pushed out the same hole through which the food came.

More complex animals, including humans, have a “one-way” digestive system. Food goes in one opening, the mouth, and waste leaves the body through another opening, the anus. Between these two openings is a long series of tubes and saclike organes where the food gets digested. Once digested, the nutrients are absorbed into the bloodstream, where they travel to the body’s cells.

Once nutrients reach a cell, they are processes and stored by special organelles, lysosomes and (in some animals) vacuoles. Chemicals in these organelles break down the food particles into their most basic componets, to be stored until they are needed.