Bodily Defenses Image Map
Can you imagine having a 30-foot-long tube running from your mouth to your anus? That is exactly what you have in your digestive system. Food contains nutrients, proteins, carbohydrates, and fats that the cells in our body use as energy. The process of digestion involves breaking down the food so that cells can use its components to fuel our body and keep it functioning. This module explains how organisms digest, absorb, and utilize food to obtain the materials they need for their cells to sustain life, grow, and multiply.

Usually in biological science, we learn most of what we know from studies of animals. But some of our first notions of what happens in digestion comes from the study of a live human patient who had an unhealed wound that led from the stomach to the outside. Read the interesting Story Time of Dr. Beaumont and his patient.

After completing this lesson, the student should be able to: 

  • Explain what we mean by "digestion" and how it occurs.
  • Explain how absorption occurs and where in the digestive tract various nutrients are absorbed.
  • Identify how the digestive system protects the body from bacteria and other harmful toxins.
  • Summarize what we know about ulcers and food poisoning


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