digestive - Digestive system Needed for intake and...

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Digestive system Needed for intake and processing of foods, which become both fuel and building blocks of the body. Comprised of gastrointestinal (GI) tract: oral cavity, pharynx, esophagus, stomach, small intestine, large intestine; and accessory organs: teeth, tongue, glandular organs (pancreas, liver, salivary glands) GI tract- long muscular tube which carries food from one end to other. Along the route, glandular organs secrete substances into the tube which assist in digestion and absorption 6 functions of the digestive system: 1. ingestion – taking in of foods into the mouth. Involves conscious processes/thought. 2. mechanical processing – crushing and shearing to make food easier to move along digestive tract. Involves teeth and tongue in the mouth, as well as churning in the stomach and intestines 3. digestion – chemical breakdown of food into smaller organic fragments that can be absorbed 4. secretion – release of substances by accessory organs 5. absorption – movement of nutrients across digestive epithelium into interstitial fluid of digestive tract 6. excretion – removal of waste products after absorbing everything useful, also, may be removal of waste that has been secreted into digestive tract (defecation) Since the digestive tract is continuous with the outside world it must play a role in nonspecific defense – physical barrier against bacteria; acidic environment (epithelium is also constructed to keep corrosive acid and enzymes away from underlying tissues); and macrophages in underlying tissue. Movement of materials in digestive tract is due to rhythmic contraction of smooth muscle cells, triggered by pacesetter cells that trigger waves of contraction through muscle layer. These contractions control 2 processes: - peristalsis, movement of materials from one area to another. Waves of muscular contractions that will move bolus (small mass of food) along the tract. Circular muscles behind bolus first, while those in front relax, pushing food forward. Then longitudinal muscles contract, shortening the segment, and helping propel food forward. - Segmentation, contraction that holds a bolus in one place to churn and fragment it. Oral cavity: The beginning of processing – in the mouth. - analysis of food before swallowing - mechanical processing - lubrication - beginning of digestion (carbohydrates and lipids)
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Internal structure designed to help process food. Tongue: mechanical compression, manipulation to assist in chewing, sensory input (taste, temperature, touch), and secretion of mucus and enzymes. Salivary glands:
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This note was uploaded on 04/17/2008 for the course BIO 121 taught by Professor Short during the Fall '07 term at Finger Lakes Community College.

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digestive - Digestive system Needed for intake and...

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