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GI System - The stomach is bathed in very strong HCl The...

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The stomach is bathed in very strong HCl . - The stomach is constantly churning - Helicobacter pylori can thrive in the stomach’s acidic environment: it is usually associated with the development of peptic ulcers : can be treated with proper drug treatment. - We have developed protective mechanisms against autodigestion : if these mechanisms fail, then we develop raw patches known as peptic ulcers . - Peptic ulcers penetrate through the walls of the GI tract, causing the development of “holes.” Primary function of the GI tract – to move nutrients, water, and electrolytes from the external environment into the body’s internal environment - Must also match input with output - Example : diarrhea is excessively watery feces: it can become an emergency if so much water is excreted that the ECF volume decreases to a point where the CV system is unable to maintain adequate BP. Autodigestion – a condition in which the enzymes associated with the GI system cause digestion of the GI tract itself Digestion – chemical/mechanical breakdown of foods into smaller units that can be transferred across the epithelium - Takes place in the lumen Absorption – active or passive transfer of substances from the GI lumen into the ECF Motility – movement of material within the GI tract itself as a result of muscle contraction - Regulated - Smooth muscle contracts spontaneously . Tonic contractions – sustained for minutes or hours Phasic contractions – sustained for seconds. Slow wave potentials – spontaneous cycles of depolarization and repolarization - How it happens there are spontaneous depolarizations that occur in GI smooth muscle cells: with each slow wave, it does not necessarily reach a threshold : when it does reach a threshold, it becomes an action potential . - A slow wave that does not reach threshold will not cause a contraction in the muscle fiber. - When it does reach threshold, it will contract via a similar mechanism as in myocardial pacemaker cells (Calcium is released into the muscle cell, initiating contraction) - Recall: muscle contraction is regulated by MLCK activity, regulating myosin ATPase (which hydrolyzes ATP, allowing contraction of the muscle cell) Sidenote: In between meals, the GI tract initiates a series of contractions that pass from the stomach eventually to the large intestine – each series of contractions takes approximately 90 minutes to reach the large intestine – this is a housekeeping function that sweeps food remnants and bacteria out of the upper GI tract and into the large intestine.
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During a meal, peristalsis involves progressive waves of contraction that move from one section of the GI tract to the next. - Similar to the rippling of a wave caused by a crowd of people at a football stadium.
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