DIGESTIVE SYSTEM AND DIGESTION

I   Overview

            A.  Muscular tube

            B.  Function

                        1.  digestion : chemical and mechanical

                        2.  absorption

II   Nutrient molecules and absorption size*  (review for final)

            A.   Carbohydrates --> polysaccharides --> monosaccharide (glucose)*

            B.   Lipids --> --> glycerol *  +   fatty acids*

            C.   Proteins --> polypeptides --> amino acids*

            D.   Nucleic acids

III  Regions of gastrointestinal tract

            A.  Mouth

                        1.  mechanical digestion

                        2. chemical digestion: salivary amylase breaks down carbohydrates and starches

            B.  Pharynx (throat)

            C.  Esophagus                                           

                        1.  peristalsis

            D.  Stomach

                        1.  regions:   cardiac, fundus, body, pyloric and rugae

                        2.  chemical digestion :  gastric glands

                                    a.  hydrochloric acid (HCl) : breaks down connective tissue and pepsinogen

                                    b.  pepsinogen �> pepsin :  breaks proteins to amino acids

                        3.  mechanical digestion

                                    a.  peristalsis (three layers of muscle in the wall)

                        4.  absorption is minimal

            E.  Small intestine:  major site of digestion and absorption                           

                        1.  regions : duodenum, jejunum, ileum

                        2.  chemical digestion

                                    a.  bile (liver and gall bladder) : breaks up lipids

                                    b.  pancreatic enzymes :  pancreatic amylase, trypsin, lipase

                                    c.  intestinal enzymes :  amylases, proteases

                        3.  mechanical digestion :  segmentation

                        4.  absorption

                                    a. increased surface area by foldings

                                                1.  plica circulares --> villi --> microvilli (brush border)

            F.  Large intestine

                        1.  regions : cecum, ascending, transverse, descending, and sigmoid colon, rectum

                        2.  reabsorption

At the end of this unit you should be able to:

    -  distinguish between digestion and absorption

    -  distinguish between mechanical and chemical digestion

    -  list the four groups of nutrient molecules and the units they must be broken into to be absorbed

    -  identify the six major regions of the digestive tube

    -  describe the types of digestion that occur in the mouth

    -  locate and distinguish between pharynx, larynx, and esophagus

    -  explain gastro-esophageal "acid reflux"

    -  identify the regions of the stomach

    -  discuss the chemical and mechanical digestion in the stomach

    -  locate the three major regions of the small intestine

    -  identify the accessory structures which add digestive juices to the duodenum

    -  discuss the chemical digestion that occurs in the duodenum

    -  compare peristalsis and segmentation

    -  discuss the structures of absorption in the small intestine

    -  identify and locate the regions of the large intestine

    -  state the function of the large intestine

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