Anatomy & Physiology

Anatomy & Physiology Study Guide

Chapter 23: The Digestive System The digestive tract (GI) tract or alimentary canal, consists of a muscular tube and a variety of other organs. The oral cavity (mouth), pharynx, esophagus, stomach, small intestine, and large intestine make up the digestive tract. Accessory digestive organs include the teeth, tongue, and various glandular organs, such as the salivary glands, liver, and pancreas, which secrete their products into ducts emptying into the digestive tract. Food enters the digestive tract and passes along its length. 23.1 Functions of the Digestive System The digestive system is the system in the human body that is responsible for acquiring all the nutrients needed to survive and passing those nutrients through the body. The digestive system works in a series of necessary steps: • Ingestion occurs when materials enter the digestive tract via the mouth. • Mechanical processing is crushing and shearing materials, making it easier to propel along the digestive tract. • Digestion is the chemical breakdown of food into smaller fragments making it suitable for absorption by the gastrointestinal epithelium. • Secretion is the release of water, acids, enzymes, buffers, and salts by the epithelium of the digestive tract and by glandular organs. • The movement of essential substrates, electrolytes (inorganic ions), vitamins, and water across the digestive epithelium and into the interstitial fluid of the gastrointestinal tract is known as absorption . • Excretion is defined as the removal of waste products from body fluids. The ejection of materials from the digestive tract, a process called defecation, or egestion, eliminates materials as feces. The lining of the digestive tract also plays a protective role by safeguarding surrounding tissues against the corrosive effects of digestive acids and enzymes, mechanical stresses, such as abrasion, and bacteria that either is swallowed with food or reside in the digestive tract. The gastrointestinal epithelium and its secretions provide a nonspecific defense against these bacteria. When bacteria reach the underlying layer of areolar tissue, the lamina propria, macrophages, and other cells of the immune system attack them. 23.2 The Digestive Organs and the Peritoneum The abdominopelvic cavity contains the peritoneal cavity , which is lined by a serous membrane consisting of a superficial mesothelium covering a layer of areolar tissue. The serous membrane is divided into two layers: visceral peritoneum (or serosa ) and the parietal peritoneum . The visceral peritoneum covers the organs in the peritoneal cavity and continuously produces peritoneal fluid, also called the gastrointestinal

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