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

2. 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.

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

4. 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
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5. 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.

6. Structures of the mouth (oral cavity)
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7. 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.

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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
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9. A typical tooth and surrounding structures
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10. 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.

11. Copyright 2009, John Wiley & Sons, Inc.
Pharynx
Food passes from the mouth in to the pharynx.
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Esophagus
Secretes mucous, transports food – no enzymes produced, no absorption
Mucosa – protection against wear and tear
Copyright 2009, John Wiley & Sons, Inc.

13. 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.

14. Deglutition (swallowing)
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15. 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.

16. 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.

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Pancreas
Secrete hormones glucagon and insulin.
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Liver and gallbladder
Liver is the heaviest gland of the body.
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Gallbladder
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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.

21. Histology of the small intestine
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22. Copyright 2009, John Wiley & Sons, Inc.
Large intestine
Overall function to complete absorption, produce certain vitamins, and form and expel feces
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23. Anatomy of the large intestine
Copyright 2009, John Wiley & Sons, Inc.