Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Human Digestion and Absorption Learning Outcomes • Outline the roles played by the gastrointestinal tract and the related accessory organs (liver, gallbladder, and pancreas) in digestion and absorption. • Describe how foods are moved along the digestive tract. • Explain the 4 main types of absorption. Learning Outcomes • Identify the key enzymes and hormones involved in digestion and absorption and their functions. • Identify major nutrition-related gastrointestinal diseases and disorders and typical approaches to prevention and treatment. • Explain why diarrhea represents a serious health challenge to infants and young children around the world. Organization of the Human Body • Chemical Level – Atoms combine to form molecules • Cell Level – Molecules form organelles – Use ATP • Tissue Level – Similar cells make up tissues • Organ Level – Different tissues combine to form organs • Organ System Level – Organs make up an organ system • Organism Level – Organ systems make up an organism Human Tissues • Epithelial – Cells that cover surfaces inside and outside of the body • Connective – Support and protect the body by holding structures together • Muscle – Contract and relax to permit movement • Nervous – Transmit nerve impulses Digestive Organ System • GI tract – Mouth, esophagus, stomach, small intestine, large intestine • Liver, pancreas and gall bladder Digestive System Overview • Digestion – Process of breaking down foods into a form the body can use • Absorption – Uptake of nutrients from the GI tract into the blood or lymph • Excretion of waste matter • Immune system function Anatomy of the GI Tract • GI tract = the alimentary canal – 15’ long, hollow, muscular tube • Four layers – Mucosa • Innermost layer: forms hollow area of the lumen – Submucosa • Contains blood vessels (carry nutrients), nerves, and glands – Muscle (as double layers) • Moves food forward – Serosa • Outside layer;-protects the tract Sphincters • Ring like muscles that control the flow of contents in the GI tract – – – – – Lower esophageal sphincter Pyloric sphincter Sphincter of Oddi Ileocecal sphincter Anal sphincter GI Motility: Mixing and Propulsion • Peristalsis – Contractions • Segmentation – Back and forth movement • Mass movements – Peristalsis over widespread area • Elimination • Vomiting Digestive System Secretions • • • • • • • Saliva Mucus Digestive enzymes Hydrochloric acid Bile Bicarbonate ions Hormones Mouth (Oral Cavity) • Chewing increases surface area • Mixed with saliva food becomes a bolus • Saliva – Lysozyme • Breaks down bacteria – Mucus • Lubricates and hold bolus together – Amylase • Breaks down starch – Enhances perception of flavor Taste and Smell • Taste buds on the tongue and soft palate – contain taste-receptor cells – – – – – Salty Sour Sweet Bitter Umami • Olfactory cells in nose (smell) – Stimulated with chewing Esophagus • Swallowing – Moves bolus from the mouth to the esophagus • Epiglottis – Prevents food from entering the trachea – Closes over the larynx Stomach • Food bolus enters stomach through lower esophageal sphincter • Holding & mixing tank – Mixed with stomach secretions food becomes chyme Stomach Secretions • Parietal Cells – Hydrochloric Acid • • • • Inactivates proteins Destroys bacteria and viruses Dissolves minerals to aid in absorption Converts pepsinogen into pepsin – Pepsinogen • Protein digesting enzyme • Gastrin – Hormone that controls release of HCl and pepsinogen Other Stomach Secretions • Chief cells – Gastric lipase • Mucus – Protects the stomach from being digested – Production relies on prostaglandins Small Intestine • Most digestion and absorption occurs here • Pyloric sphincter allows chyme into the small intestine – Gastric inhibitory peptide (hormone) slows release of chyme • Sections – Duodenum, jejunum and ileum Small Intestine (2) • Circular folds • Villi – lined with: – Goblet cells - make mucus – Endocrine cells - produce hormones – Enterocytes - produce digestive enzymes and absorb nutrients • Contain a brush border of microvilli covered with glycocalyx Liver, Gallbladder and Pancreas • Liver – Provides bile – Enterohepatic circulation (recycling of bile) • Gallbladder – Bile storage • Pancreas – Produces sodium bicarbonate, lipases, proteases and pancreatic amylase Hormones of the GI Tract • Gastrin – Stomach release of HCl and pepsinogen • Cholescystokinin (CCK) – Release of bile • Secretin – Release of pancreatic bicarbonate • Gastric Inhibitory Peptide – Limits release of gastric juices Absorption • Primarily occurs in small intestine • Passive diffusion – Concentration gradient • Facilitated diffusion – Concentration gradient + carrier protein • Active – Carrier protein + energy (regardless of concentration) • Endocytosis – Engulfment of compounds or liquids Moving Nutrients around the Body • Cardiovascular System – Includes heart, blood vessels and blood – Water-soluble nutrients transported via capillaries in villi to portal vein • Lymphatic System – Includes lymph – Fat-soluble nutrients and large particles transported via lacteals into the lymph vessels to thoracic duct Large Intestine • Ileocecal valve • Colon – Cecum, ascending colon, transverse colon, descending colon and sigmoid colon • Rectum • Anus Functions of Large Intestine • Absorption of water and electrolytes • Formation and expulsion of feces • Housing of bacteria (microbiota) Microbiota (bacterial flora) • Beneficial bacteria – Control pathogenic bacteria – Synthesize Vitamin K and Biotin – Aid lactose digestion and fermentation of dietary fibers • Probiotics – Live bacteria in food and supplements – Health benefits • Prebiotics – Non digestible carbohydrates in food that promote the growth of bacteria– E.g. inulin, resistant starch When Digestive Processes Go Awry • Heartburn and Gastroesphogeal reflux disease (GERD) – Foods that increase reflux: • Citrus, caffeine, chocolate, fatty foods, spicy foods, onion, garlic and tomato based foods • (Peptic) Ulcers – Causes: H. pylori and NSAID medications – Treatment: • Medications • Avoid foods that increase symptoms When Digestive Processes Go Awry (2) • Food Intolerances • Intestinal Gas (Flatulence) • Constipation – Fiber, fluid and exercise – Laxative use • Diarrhea – Replace fluid and electrolytes • Irritable Bowel Syndrome (IBS) – Cause unknown • Inflammatory Bowel Disease (IBD) – Ulcerative colitis and Crohn’s disease • Hemorrhoids • Gallstones Celiac Disease • Intolerance to gluten • 1 in 133 people affected – Many undiagnosed • Can affect many body systems – GI and others • Gluten-free diet for life – Corn, rice, quinoa, and buckwheat OK