Skip to main content
Biology LibreTexts

18: Digestive System

  • Page ID
    22577
  • This chapter outlines the structure and function of the gastrointestinal tract and accessory organs of digestion. It explains the processes of peristalsis, mechanical and chemical digestion of food, and absorption of nutrients. The chapter also describes several disorders of the gastrointestinal tract.

    • 18.1: Case Study: Food Processing
      Angela and Mariah are college students who met in physics class. They decide to study together for their upcoming midterm, but first they want to grab some lunch. Angela says there is a particular restaurant she would like to go to because they are able to accommodate her dietary restrictions. Mariah agrees and they head to the restaurant.
    • 18.2: Introduction to the Digestive System
      If you’re an ice cream lover, then just the sight of this yummy ice cream cone may make your mouth water. The “water” in your mouth is actually saliva, a fluid released by glands that are part of the digestive system. Saliva contains digestive enzymes among other substances important for digestion. When your mouth waters at the sight of a tasty treat, it’s a sign that your digestive system is preparing to digest food.
    • 18.3: Digestion and Absorption
      Digestion of food is a form of catabolism, in which the food is broken down into small molecules that the body can absorb and use for energy, growth, and repair. Digestion occurs when food is moved through the digestive system. It begins in the mouth and ends in the small intestine. The final products of digestion are absorbed from the digestive tract, primarily in the small intestine. There are two different types of digestion that occur in the digestive system: mechanical digestion and chemica
    • 18.4: Upper Gastrointestinal Tract
      Besides the esophagus, organs of the upper gastrointestinal (GI) tract include the mouth, pharynx, and stomach. These hollow organs are all connected to form a tube through which food passes during digestion. The only role in digestion played by the pharynx and esophagus is to move food through the GI tract. The mouth and stomach, in contrast, are organs where digestion, or the breakdown of food, also occurs. In both of these organs, food is broken into smaller pieces and broken down chemically.
    • 18.5: Lower Gastrointestinal Tract
      This photomicrograph shows some of the cells of what has been called “the last human organ to be discovered.” This “organ” weighs about 200 grams (0.44 lb.) and consists of a hundred trillion cells, yet scientists are only now beginning to learn everything it does and how it varies among individuals. What is it? It’s the mass of bacteria that live in our lower gastrointestinal tract.
    • 18.6: Accessory Organs of Digestion
      Did you ever hear of a person looking at something or someone with a “jaundiced eye”? It means to take a negative view, such as envy, maliciousness, or ill will. The expression may be based on the antiquated idea that liver bile is associated with such negative emotions as these, as well as the fact that excessive liver bile causes jaundice, or yellowing of the eyes and skin. Jaundice is likely to be a sign of a liver disorder or blockage of the duct that carries bile away from the liver. Bile c
    • 18.7: Disorders of the Gastrointestinal Tract
      If you had a skin rash like the one shown in this photo, you probably wouldn’t assume that it was caused by a digestive system disease. However, that’s exactly why the individual in the picture has a rash. He has a gastrointestinal (GI) tract disorder called Crohn’s disease.
    • 18.8: Case Study Celiac Conclusion and Chapter Summary
      The garlic bread stuffed with spaghetti shown above may or may not look appetizing to you, but for people with celiac disease, it is certainly off limits. Bread and pasta are traditionally made with wheat, which contains proteins called gluten. As you learned in the beginning of the chapter, even trace amounts of gluten can damage the digestive system of people with celiac disease. When Angela and Mariah met for lunch, Angela chose a restaurant that she knew could provide her with gluten-free fo

    Thumbnail: Scheme of digestive tract, with esophagus marked. Image used with permission ( CC BY-SA 2.5; Olek Remesz).