Copyright 2009, John Wiley & Sons, Inc. The Digestive System Digestive System - YouTube Copyright 2009, John Wiley & Sons, Inc.

2 groups of organs compose the digestive system Gastrointenstinal (GI) tract and glands or alimentary canal – mouth, most of pharynx, esophagus, stomach, small intestine, and large intestine Accessory digestive organs – teeth, tongue, salivary glands, liver, gallbladder, and pancreas Copyright 2009, John Wiley & Sons, Inc.

Organs of the digestive system Copyright 2009, John Wiley & Sons, Inc.

6 functions of the digestive system Ingestion Secretion of water, acid, buffers, and enzymes into lumen Mixing and propulsion Digestion Mechanical digestion churns food Chemical digestion – hydrolysis Absorption – passing into blood or lymph Defecation – elimination of feces Copyright 2009, John Wiley & Sons, Inc.

Copyright 2009, John Wiley & Sons, Inc. Mouth Oral cavity Formed by cheeks, hard and sot palates, and tongue Salivary glands release saliva Ordinarily, just enough is secreted to keep mouth and pharynx moist and clean When food enters mouth, secretion increases to lubricate, dissolve and begin chemical digestion Copyright 2009, John Wiley & Sons, Inc.

Structures of the mouth (oral cavity) Copyright 2009, John Wiley & Sons, Inc.

Copyright 2009, John Wiley & Sons, Inc. Saliva Saliva Mostly water 99.5% 0.5% solutes – ions, dissolved gases, urea, uric acid, mucus, immunoglobulin A, lysozyme, and salivary amylase (acts on starch) Not all salivary glands produce the same saliva Copyright 2009, John Wiley & Sons, Inc.

Copyright 2009, John Wiley & Sons, Inc. Tongue and Teeth Tongue Accessory digestive organ Maneuvers food for chewing, shapes mass, forces food back for swallowing Teeth or dentes 3 major regions – crown, root, and neck Dentin of crown covered by enamel 2 dentitions – deciduous and permanent teeth Copyright 2009, John Wiley & Sons, Inc.

A typical tooth and surrounding structures Copyright 2009, John Wiley & Sons, Inc.

Copyright 2009, John Wiley & Sons, Inc. Digestion in the mouth Mechanical digestion in the mouth Chewing or mastication Food manipulated by tongue, ground by teeth, and mixed with saliva Forms bolus Chemical digestion in the mouth Salivary amylase secreted by salivary glands acts on starches Copyright 2009, John Wiley & Sons, Inc.

Copyright 2009, John Wiley & Sons, Inc. Pharynx Food passes from the mouth in to the pharynx. Copyright 2009, John Wiley & Sons, Inc.

Copyright 2009, John Wiley & Sons, Inc. Esophagus Secretes mucous, transports food – no enzymes produced, no absorption Mucosa – protection against wear and tear Copyright 2009, John Wiley & Sons, Inc.

Deglutition (Swallowing) Act of swallowing Facilitated by secretions of saliva and mucus Involves mouth, pharynx, and esophagus 3 stages Voluntary – bolus passed to oropharynx Pharyngeal – involuntary passage through pharynx into esophagus Esophageal – involuntary passage through esophagus to stomach Peristalsis pushes bolus forward Copyright 2009, John Wiley & Sons, Inc.

Deglutition (swallowing) Copyright 2009, John Wiley & Sons, Inc.

Copyright 2009, John Wiley & Sons, Inc. Stomach Serves as mixing chamber and holding reservoir. Breaks down protein by gastric juice. Moves food mixture into the small intestine by the process of peristalsis. Copyright 2009, John Wiley & Sons, Inc.

Mechanical and Chemical Digestion Mechanical digestion – physically breaking down food into smaller substances. Chewing food is an example. Chemical digestion - occurs in the digestive tract, the chemicals secreted from the digestive gland break down the food into simple food molecules Copyright 2009, John Wiley & Sons, Inc.

Copyright 2009, John Wiley & Sons, Inc. Pancreas Secrete hormones glucagon and insulin. Copyright 2009, John Wiley & Sons, Inc.

Copyright 2009, John Wiley & Sons, Inc. Liver and gallbladder Liver is the heaviest gland of the body. Copyright 2009, John Wiley & Sons, Inc.

Copyright 2009, John Wiley & Sons, Inc. Gallbladder Copyright 2009, John Wiley & Sons, Inc.

Copyright 2009, John Wiley & Sons, Inc. Small intestine Churning and mixing of food. Prepares fat to be digested by secreting bile. Breaks down fats, proteins and carbohydrates by “using” juice secreted from the pancreas. Absorption of most nutrients Copyright 2009, John Wiley & Sons, Inc.

Histology of the small intestine Copyright 2009, John Wiley & Sons, Inc.

Copyright 2009, John Wiley & Sons, Inc. Large intestine Overall function to complete absorption, produce certain vitamins, and form and expel feces Copyright 2009, John Wiley & Sons, Inc.

Anatomy of the large intestine Copyright 2009, John Wiley & Sons, Inc.