March 12 Lecture - March 12, 2009 The Digestive System...

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March 12, 2009 The Digestive System Secretions of the Digestive Processes - Pancreatic Juices (enzymes electrolytes and sodium bicarbonate) - Liver Secretions (bile, either constantly secreted or stored in the gall bladder) Lining of the Intestine Secretions The Intestine - Functions o Receives food from the stomach o Movements propel the material alogn the length of the tube - Various Types of Movement exist which function to o Mix the chyme with the digestive juices o Bring chyme into contact with the small intestine in order to bring the food to areas where absorption can occur o Moves material along the length of the intestinal tract o Movements tend to enhance the flow of blood through the wall of the intestine o Enhances the flow of lymph These are the way through which nutrients are picked up and moved around the body o Main type of movement which occurs within the small intestine is known as sementation movement As the small intestine becomes distended it brings about dilation of the tube which causes the tube to contract back, so a series of ring-like processes are initiated along the length of the tube The rings tend to displace the chyme into adjacent regions, which will become more distended The distended regions will then constrict, moving the chyme toward its original sites This process repeats so adjacent sites also distend and compress Continuous movement of chyme slightly laterally and then back into its original position The column of chyme becomes very segmented along the length of the tube (continuous division and subdivision) Not propulsive movement, but rather a movement that aids in the mixing of the chyme with the secretions of the small intestine o Another type of movement which is observed in the small intestine are known as pendular movements These are weak contractile waves which originate and travel relatively short distances They travel back and forth along the wall of the gut (relatively short distances) Relatively slow moving waves (1-2 cm/sec)
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This is superimposed on the sementation movement (they occur at the same time and in the same portions of the gut) Purpose of pendular movement is similar to that of segmentation, which is to ensure mixing of the material, as opposed to propelling the content along the length of the tube o Peristaltic rush is another form of movement, it is a form of peristalsis Ring of relaxation followed by a ring of contraction Travels along a length of the small intestine (30-40 cm) Moves at a rate of 5-6 cm/sec These may occur infrequently, several may take place within a 24 hour period Purpose is to move the material along the length of the tube (in a caudal direction) - The small intestine is said to be polarized , movements tend to occur much more readily in one direction than they do in the other o The caudal direction will occur much more easily than the reverse - This is used to a clinical benefit o Individuals who have lost a portion of the small intestine often have a relatively
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March 12 Lecture - March 12, 2009 The Digestive System...

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