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Module 15- The Digestive System Good notes, organized by colour, great diagrams, all the material you need to know for this module

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Western University
Physiology 1021
Tom Stavraky

Physiology: Module 15 March 2011 The Digestive System 1. Mouth: food masticated & mixed with saliva 2. Salivary glands produce saliva to moisten & begin digesting some food 3. The esophagus is a straight muscular tube that connects the mouth and pharynx to the stomach. 4. Stomach: stores, mixes, and 5. Liver: produces and secretes bile. digests some food and delivers food to the small intestine. 6. Gallbladder stores and concentrates bile 7. Pancreas secretes digestive enzymes, hormones, and bicarbonate 8. Small intestine: allows digestion and absorption of most food particles. 9. Large intestine: stores and concentrates undigested material and absorbs salt and water. 10. Rectum: site where defecation reflex is triggered Digestion is the process whereby food Secretion involves the release of digestive fluids (water, is broken down into mucus, acid, electrolytes, enzymes, bile salts, and smaller molecules by digestive enzymes) into the lumen of the digestive tract. the digestive enzymes so they can be taken up by the body. Motility is the movement of Excretion is the removal of the Absorption is the process unwanted waste products from the "food" through the digestive whereby these small molecules system by the contraction of the body after almost all of the are taken up by the circulatory wanted material is absorbed. smooth muscle that lines the system and are distributed walls of the tract. throughout the body. 1 | P a g e March Physiology: Module 15 2011 Saliva: water (99.5%) with ions & proteins (0.5%); secreted by 3 glands (parotid, submandibular, sublingual) *can produce up to 2 L (0.5 gallon) of saliva each day Saliva helps to lubricate the bolus of food and begins digesting carbohydrates (contains amylase). The production & secretion of saliva is under the control of the autonomic nervous system (ANS). Digestion Begins in the mouth; food is broken down by chewing (or mastication) & mixed with saliva to form a bolus. Swallowing 1. Bolus is pushed to the back of the mouth with the tongue and the swallowing reflex is initiated. 2. The uvula over the soft palate closes over the nasopharynx. 3. The larynx is lifted by muscles in the neck. 4. The epiglottis bends back over the glottis, covering the larynx. 5. The bolus moves down the esophagus through the cardiac orifice (lower esophageal sphincter) & into the stomach by a wave of smooth muscle contraction (peristalsis). The Stomach 3 general regions of the stomach: 1. Fundus (dome-shaped; upper region) 2. Body (largest part of thestomach ; middle region) 3. Antrum (pyloric region; lower part) Pyloric sphincter (located at the distal porti:n) regulates the emptying of the stomach into the duodenum (the first part of the small Peristaltic contraction of the stomach walls begin at the fundus and end at the antrum; they mix *Most digestion & chyme, help move it through the pyloric absorption takes sphincter & into the small intestine. Proteins place in the small begin to be digested in the stomach by pepsin (enzyme). intestine* *only alcohol and aspirin can cross the lining of the stomach (to be absorbed into the bloodstream) Substances secreted by the stomach Mucus -secreted by cells in -protects the lining of the stomach from the extremely the body & antrum acidic environment produced by HCl HCl -secreted by cells in -begins to unfold (denature) the complex protein & the body connective tissue found in protein; kills bacteria; converts the pepsinogen (inactive) to pepsin (active) Pepsinogen -produced by the -begins to digest large protein molecules when converted cells in the body to pepsin (active) Gastrin -secreted by cells in -stimulates the secretion of HCl the antrum Intrinsic -helps with the absorption of vitamin B12 Factor 2 | P a g ePhysiology: Module 15 March 2011 The Pancreas The pancreas produces and secretes: -amylase (carbohydrate-digesting enzyme) -trypsin, chymotrypsin & proteases (protein-digesting enzymes) -lipase (fat-digesting enzyme) -sodium bicarbonate (into the duodenum to neutralize the acid from the stomach) The Small Intestine The stomach contents empty through the pyloric sphincter into the small intestine and ends at the ileocecal sphincter where it empties into the ascending colon of the large intestine. Three segments of the small intestine: 1. Duodenum (first segment & is the *Almost all digestion & shortest) absorption 2. Jejunum (second segment & is the takes place longest; makes up 50% of the small here * ) intestine * Longest section of the digestive tract; 9m (30 ft) 3. Ileum Inner wall of the small Epithelial cells intestine is thrown into folds; 1. Villus containing microvilli': the folds, contain villi; this secrete digested results in a large surface area
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