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Lecture

Jan 27 what happens to the food we eat.doc

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Department
Nutrition
Course
NUTR100
Professor
Sabina Valentine
Semester
Winter

Description
Jan 27 –Ch3 What Happens to the food we eat? Digestion: The Mouth • Digestion begins in the mouth • Chewing is the mechanical digestion that breaks food into smaller pieces • Some chemical digestion takes place • Salivary amylase is an enzyme produced by the salivary glands that begins the chemical digestion of carbs • The epiglottis covers the opening to the trachea during swallowing • Food travels from the mouth to the stomach through the esophagus • Peristalsis is the muscular contractions moving food through the GI tract • In chewing, the epiglottis is open, the esophagus is closed Swallowing • In swallowing, the soft palata rises to close opening to nasal passages • The epiglottis bends to close off trachea and open esophagus • Bolus of food is moved through the esophagus to the stomach by peristalsis • No digestive enzymes are secreted by the esophagus Digestion: Stomach • The gastroesophageal sphincter seperates the esophagus from the stomach Digestion in the stomach includes: • Extensive mechanical digestion to mix food with gastric juice • Chemical digestion of proteins and fats Gastric juice contains: • Hydrochloric acid (HCI) – to denature proteins and activate pepsin • Pepsin – an enzyme to digest protein • Gastric lipase – an enzyme to digest fat • Mucus – to protect the stomach lining • Chyme: semi-solid product of mechanical and chemical digestion in the stomach • Mechanical digestion occurs when peristattic waves mix contents of stomach • Gastric juic is secreted by stomach • Pepsin initiates protein digestion • Gastric lipase initiates a small amount of fat digestion • Small amounts of water, some fatty acids, drugs, and alcohol are absorbed Digestion: Small Intestine • From the stomach, chyme is slowly released through the pyloric sphincter to the small intestine • Chemical digestion continues in the small intestine using pancreate enzymes and bile Digestion: Accessory Organs Accessory organs of the GI tract include • Liver – produces bile which emulsifies fats • Pancreas: produces many digestive enzymes, produces bicarbonate to neutralize chyme • Gall bladed – stores bile • Bile from the gallbladder emulsifies fat to aid digestion • Pancreatic lipase digests fats • Pancreatic amylase digests carbs • Proteases digest protein • Bicarbonate secreted by the small intestine neutralizes acidic chyme coming from the stomach into the small intestine Absorption • Absorption: the process of taking molecules across a cell membrane and into cells of the body • A small amount of absorption occurs in the stomach (ex. Water, alcohol) • Most absorption of nutrients occurs in the small intestines • The lining of the GI tract has special structures to facilitate absorption • Villi are folds in the lining that are in close contact with nutrient molecules • The brush border is composed of microvilli which greatly increase the surface area Elimination • Undigested food components move through a sphincter called the ileocecal valve to the large intestine In the large intestine: • Bacteria ferment undigested food particles • Material is stored 12-24 hours prior to elimination while water and some nutrients are absorbed • Intestinal bacteria ferment undigested food particles • Water and chemicals are absorbed into the bloodstream • Nondigestible matter forms feces, which are help in the rectum and excreted through the anus Disorders Related to Digestion • The lining of the stomach is designed to cope with HCl acid but other egions of the GI tract aren’t • Heartburn is caused by HCl acid in the esophagus • GERD, or gastroesophageal, reflux disease, is painful, persistent heartburn • Peptic ulcers are regions of the GI tract that have been eroded by HCL and pepsin • The bacterium Helicobacter pylori contributes to the production of both gastric and duodenal ulcers Celiac disease • Complete intolerance for gluten, a protein found in wheat, rye, triticale, and barley • Can damage the small intestine leading to poor absorption of nutrients • Requires a diet lacking wheat, rye, triticale, and barley • There may be a genetic component to the disease Inflammatory bowel disease (IBD) includes two diseases causing inflammation: • Crohn’s disease affects the small intestine and interferes with absorption • Ulcerative colitis affects the colon and results in bloody diarrhea • In either case, surgery may be needed to remove damaged intestine Irritable bowel syndrome (IBS) is a disorder that interferes with normal colon function Symptoms of IBS include • Abdominal cramps and bloating • Diarrhea and/or constipati
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