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Digestive Physiology - notes (continued) .doc

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BIOL 153
Paul Hewitt

Bio 155 OrgansThe alimentary canal also called the gastrointestinal tract consists of the mouth pharynx esophagus stomach small intestine and large intestineThe accessory digestive organs are the teeth tongue salivary glands liver gallbladder and pancreasDigestive ProcessesIngestion Propulsion peristalsis Mechanical digestion physically preparing food for chemical digestion Chemical digestion enzymatic breakdown of foodAbsorption into blood or lymph from small intestineDefecation elimination of wasteDigestive ActivityA range of mechanical and chemical stimuli provokes digestive activityVarious receptors located in the GI tract respond to several stimuli such as stretching of the wall by food osmolarity and pH and presence of substratesWhen receptors are stimulated theyInitiate reflexes that either activate or inhibit glands that secrete digestive juices andor hormonesMix lumen contents and moves them along by stimulating smooth muscle of GI tract wallsControls of digestive activity are both extrinsic and intrinsicThe entire GI tract is lined with nerve plexuses that result in two reflexesThe short reflexes are mediated by the local enteric plexuses in response to GI tract stimuliLong reflexes are initiated by stimuli arising within or outside the GI tractThey involve the CNS centers and extrinsic autonomic nervesThe stomach and small intestine also contain hormoneproducing cells that reach their target cells through the bloodWhen stimulated their contents contribute to secretory or contractile activity
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