Measurable Outcomes

• Label the anatomical structures of the digestive system on available models.
• Explain the pathway of food from the mouth to the anus, identifying major landmarks along the way.
• Deduce the pathway of major arteries and veins that supply the organs of the digestive system.
• Identify the histology of the digestive organs on microscope slides.
• Demonstrate an adequate understand of the material in this section.

Background

The digestive system consists of the gastrointestinal tract (also known as the alimentary canal), a hollow muscular tube extending from the mouth to the anus, and accessory organs, including the liver and pancreas.  Technically, until food is absorbed in the intestines it is considered to be outside of the body. To promote absorption, the intestines have villi which contain hair-like structures called microvilli. Like the alveoli of the lungs, microvilli substantially increase the surface area of the intestines to between 180 to 300 m² (the size of the average American home).  Major structures of the gastrointestinal tract include the oral cavity, pharynx, esophagus, stomach, small intestine, large intestine, rectum, and anus. These structures and organs form a  hollow space from mouth to anus and function to chemically and mechanically catabolize and absorb nutrients. Along the way organs such as the salivary glands, liver, gallbladder and pancreas release enzymes to aid digestion and are known collectively as accessory structures.

The organs of the GI tract are made from four layers, the inner lining or mucosa, the submucosa containing blood vessels and lymphatics, the muscularis or smooth muscle layer, and the outermost layer or serosa/adventitia. Each layer plays a vital role in the digestive system ranging in their capacity to form a protective barrier from the highly acidic contents of the stomach to supplying hormones, producing muscle contractions and draining lymph. Furthermore, specialized cells such as the foveolar, chief cells of the stomach are supporting cells which produce a protective layer of mucus and gastric acid for digestion. Other supporting cells, such as the gastric parietal cells of the stomach and the ductal and acinar cells of the pancreas release zymogens, inactive forms of digestive enzymes.

The peritoneum is a large serous membrane which lines the abdominal cavity and coverers most of the digestive organs. some organs are only partially covered by the peritoneum while others are entirely uncovered. These organs are referred to as being retroperitoneal. Formed by the double folding of the peritoneum is a continuous set of tissues known as the mesentery. This organ was relatively recently reclassified as an organ after discovering its complex constitution. The mesentery houses lymphatic vessels as well as providing a conduit for the blood vessels for the small and large intestines.

Vocabulary for Digestive System can be found on page(s) 165-166.