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The Digestive System

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Western University
Physiology 1021
Sarah Mc Lean

Module 15 The Digestive SystemIntroductionThe main function of the digestive system is to break down organic nutrients so that they can be absorbed into the body These organic nutrients can be carbohydrates proteins fats water vitamins and minerals We will discuss how the digestive system performs this function as it applies to a relatively common but not necessarily nutritious meala hamburger fries and a soda The Digestive Systemthe MealThe meat within the hamburger assuming it is lean hamburger is made up of mostly protein with a little fat lipid The hamburger bun and fries are made up of carbohydrates fries also contain fat The soda will consist mostly of water carbohydrates and some other dissolved substances Anatomy and Basic FunctionThe basic functions of the structures are summarized below 1 In the mouth food is broken up by chewing mastication and is mixed with saliva2 The salivary glands produce saliva to moisten and begin digesting some food particles3 The esophagus is a straight muscular tube that connects the mouth and pharynx not shown to the stomach4 The stomach stores mixes and digests some food and delivers food to the small intestine5 The liver has many functions but for digestion it produces and secretes bile6 The gallbladder stores and concentrates bile7 The pancreas secretes digestive enzymes hormones and bicarbonate8 The small intestine allows digestion and absorption of most food particles 9 The large intestine stores and concentrates undigested material and absorbs salt and water10 The rectum is the site where the defecation reflex is triggeredBasic ProcessesThe basic processes of the digestive system include the following Secretion involves the release of digestive fluids into the lumen of the digestive tract This fluid may include water mucus acid electrolytes enzymes bile salts and digestive enzymesDigestion is the process whereby food is broken down into smaller molecules by the digestive enzymes so they can be taken up by the bodyAbsorption is the process whereby these small molecules are taken up by the circulatory system and are distributed throughout the bodyMotility is the movement of the food through the digestive system by the contraction of smooth muscle that lines the walls of the tractExcretion is the removal of the unwanted waste products from the body after almost all of the wanted material is absorbed The MouthDigestion of your meal begins in the mouth where it is broken down by chewing or mastication and is mixed with saliva to form a bolus The saliva consists mostly of water 995 with ions and proteins 05 and is secreted by three glands shown at right These glands parotid submandibular and sublingual can produce up to 2 liters 05 gallon of saliva each day Saliva helps to lubricate the bolus of food and begins digesting carbohydrates because it contains the enzyme amylase The production and secretion of saliva is under the control of the autonomic nervous system SwallowingOnce the bolus of food has been formed and sufficiently lubricated with the saliva it will be pushed to the back of the mouth by the tongue and the swallowing reflex will be initiated The uvula of the soft palate closes over the nasopharynx The larynx is lifted by muscles in the neck and the epiglottis bends back over the glottis covering the larynx The bolus moves down the esophagus through the
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