The Digestive System

Dr. Ali Ebneshahidi

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings



Functions of the Digestive System

ingestion – the oral cavity allows food to enter the digestive tract and have mastication (chewing) occurs , and the resulting food bolus is swallowed .

Digestion:

Mechanical digestion – muscular movement of the digestive tract (mainly in the oral cavity and stomach) physically break down food into smaller particles .

chemical digestion – hydrolysis reactions aided by enzymes (mainly in the stomach and small intestine) chemically break down food particles into nutrient molecules , small enough to be absorbed . .

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Secretion ▪

– enzymes and digestive fluids secreted by the digestive tract and its accessory organs facilitate chemical digestion .

Absorption – passage of the end – products (nutrients) of chemical digestion from the digestive tract into blood or lymph for distribution to tissue cells .

Elimination – undigested material will be released through the rectum and anus by defecation .

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Organization of The Digestive System

Organs of the digestive system are divided into 2 main group : the gastrointestinal tract (GI tract) and accessory structures .

GI tract is a continuous tube extending through the ventral cavity from the mouth to the anus – it consists of the mouth , oral cavity , oropharynx , esophagus , stomach , small intestine , large intestine , rectum , and anus .

Accessory structures include the teeth, tongue (in oral cavity) , salivary glands , liver , gallbladder , and pancreas .

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Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Figure 23.1



Muscular movement of the GI tract

Peristalsis – wavelike movement that occurs from the oropharynx to the rectum , allowing GI tract to push food particles toward the anus .

Mixing—mixing motion in the oral cavity and stomach that allows the GI tract to repeatedly break down food into smaller particles , using mechanical digestion .

Segmentation – regions of the small intestine contracting and relaxing independently , allowing the small intestine to digestive and absorb more efficiently .

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings



Histology of the Alimentary Canal

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Figure 23.6



Peristalsis and Segmentation

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Figure 23.3



Regulation of GI Tract Activities

Autonomic nervous system

- parasympathetic nerves stimulate GI tract activities .

- sympathetic nerves inhibit GI tract activities .

Hormonal control

- hormones from endocrine gland and from GI tract itself help regulate GI tract activities .

Reflex mechanism

- regions of the GI tract (especially the stomach and small intestine) use reflexes to stimulate or inhibit one another .

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Nervous Control of the GI Tract

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings