1. Mechanical and chemical digestion

2. What is Mechanical Digestion?  Mechanical digestion : the movement and breakdown of food (for example, tearing, smashing).  There are two basic types of mechanical digestion.  Mastication : chewing begins the process of breaking down food into nutrients.  Peristalsis : is the involuntary contractions responsible for the movement of food through the esophagus and intestinal tracts.

3. Watch this video clip  http://highered.mheducation.com/sites/0072495855/student_view0/ chapter26/animation__organs_of_digestion.html http://highered.mheducation.com/sites/0072495855/student_view0/ chapter26/animation__organs_of_digestion.html

4. What is Chemical Digestion?  enzymes are needed to chemically digest the large molecules: carbohydrates  monosaccharides lipids  fatty acids & glycerol proteins  amino acids  once digested, the nutrients can be absorbed  the other types of nutrients (vitamins, minerals, water) can be absorbed directly without being digested

5. The mouth- salivary glands  secrete saliva  saliva contains: mucins for lubrication  amylase for digesting starch  the chewed bolus is pushed into the pharynx and swallowed

6. Stomach  the stomach is lined with millions of gastric glands  parietal cells:  secrete hydrochloric acid (pH = 1 to 2)  The acid kills some bacteria, denatures protein, breaks down tissue, activates the enzyme pepsin  chief cells:  secrete pepsinogen – which is activated by the acid to form the enzyme pepsin  pepsin digests proteins into smaller polypeptide chains

7. Small intestine  long, thin, muscular tube (7 m long)  three major sections:  duodenum – receives secretions from pancreas and liver  jejunum – most digestion occurs here; some absorption  ileum – most absorption occurs here

8. Duodenum bile: produced in liver, stored in gall bladder composed of salts, pigments and cholesterol (NOT an enzyme!) emulsifies fats: physically breaks down large fat droplets into smaller fat droplets digestive enzymes: produced in the pancreas and sodium bicarbonate: from pancreas neutralizes acid, raises pH to 8 activates intestinal enzymes

9. Jejunum & Ileum  secrete more digestive enzymes from intestinal glands  also is the major site for nutrient absorption

10. How Long Does it Take to Digest Food?  In healthy adults, this process can range from 24-72 hours but the average is about 36.  Typically, after ingestion, food remains in the stomach and small intestine from 6-8 hours.  The large intestine is capable of holding undigested food waste for days.