CHAPTER 14: THE DIGESTIVE SYSTEM
Overview of the Digestive System
Two groups of organs compose the digestive tract:
1) The Gastrointestinal (GI) Tract includes mouth, pharynx, esophagus, stomach, small intestine, large intestine & rectum. This is continuous tube extending from the mouth to the anus. Amature horse’s GIT is ~ 103 ft long! 2) Accessory Digestive Organs : teeth, tongue, salivary glands, liver, and pancreas. Only the teeth and tongue come in direct contact with food.
Overall, the digestive system performs 6 basic processes:
1) Ingestion : taking foods and liquids into the mouth (eating)
2) Secretion : cells within the walls of the GI tract secrete water, acid, buffers, and enzymes into the lumen of the tract. 3) Mixing and Propulsion : alternating contractions/relaxation of smooth muscle in the walls of the GI tract mix food and secretions and propel them toward to the anus (Motility). 4) Digestion : mechanical and chemical processes that break down ingested food into small molecules. There are 2 types: Mechanical : teeth cutting and grinding food before it is swallowed; smooth muscles of the stomach and small intestine churning the food. Chemical : large carbohydrate, lipid, protein, and nucleic acid molecules in food are split into smaller molecules by hydrolysis. Digestive enzymes produced by the salivary glands, tongue, stomach, pancreas, and small intestine catalyze the catabolic reactions. Some substances in food do not require chemical digestion. They are vitamins, ions, cholesterol, and water.
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