Introduction to the Digestive System

Learning Objectives

By the end of this section, you will be able to:

  1. Identify the six major organs of the alimentary canal and the six accessory digestive organs.
  2. Describe the location and function of the peritoneal membranes, cavity and fluid.
  3. Identify the four basic layers of the alimentary canal. Describe their basic location, structure, and functions.
  4. Describe the structure and functions of the tongue.
  5. Describe the location and function of the extrinsic salivary glands and the major functions of saliva.
  6. Describe the basic digestive processes that occur in the mouth.
  7. Describe the function of the esophagus.
  8. Describe the location and function of the cardiac and pyloric sphincters.
  9. Describe the basic functions of the stomach.
  10. Describe gastric pits and gastric glands and the four main types of gastric gland cells. Identify the secretory products of gastric glands and describe their function.
  11. Identify and describe the phases of gastric secretion.
  12. Describe the function of the small intestine. Include its secretory, digestive, motility and endocrine roles.
  13. Identify the digestive function and nondigestive functions of the liver.
  14. Describe the structure and function of the liver lobule as well as the basic composition and function of bile.
  15. Describe the functions of the gallbladder and control of its activity.
  16. Describe the primary exocrine function of the pancreas.
  17. Define pancreatic islets and describe their primary function.
  18. Describe the function of secretin and cholecystokinin as well as the trigger for their release.
  19. Identify the primary functions of the large intestine.
  20. Discuss how the histology of the large intestine differs from that of the small intestine and how it relates to their respective functions.
  21. Describe the motility of the large intestine.
This photograph shows two women eating apples.

Figure 1. Eating may be one of the simple pleasures in life, but digesting even one apple requires the coordinated work of many organs. (credit: “Aimanness Photography”/Flickr)

The digestive system is continually at work, yet people seldom appreciate the complex tasks it performs in a choreographed biologic symphony. Consider what happens when you eat an apple. Of course, you enjoy the apple’s taste as you chew it, but in the hours that follow, unless something goes amiss and you get a stomachache, you don’t notice that your digestive system is working. You may be taking a walk or studying or sleeping, having forgotten all about the apple, but your stomach and intestines are busy digesting it and absorbing its vitamins and other nutrients. By the time any waste material is excreted, the body has appropriated all it can use from the apple.

In short, whether you pay attention or not, the organs of the digestive system perform their specific functions, allowing you to use the food you eat to keep you going. This chapter examines the structure and functions of these organs, and explores the mechanics and chemistry of the digestive processes.