This preview shows page 1. Sign up to view the full content.
Unformatted text preview: Nutrition: Digestion and Absorption
Introduction to Human Nutrition BHSU105
Ellen R. Glovsky, PhD, RD Judith M. Richman, MS, RD, LDN Northeastern University
DIGESTION: The breaking apart of foods into smaller and smaller units... small enough to be transported into the body ABSORPTION: The movement of those units from the gut into the bloodstream or lymphatic system for circulation 2 Digestion Cephalic Phase: preabsorptive responses to sensory stimulation Body primes it's resources to better absorb and utilize anticipated nutrients Chemosenses: olfactory cells (smell) gustatory cells (taste) common chemical sense (sensations) Recognize flavors through sense of smell
3 4 (Alimentary Canal) Definition: The Gastrointestinal Tract The connected series of organs and structures used for digestion of food and absorption of nutrients One long tube! Starts at mouth, ends at rectum Food is not considered inside the body while in the GI Tract 5 Functions The Gastrointestinal Tract Ingestion : eating Transport: movement through the system Secretion of digestive enzymes
Enzymes, acid, mucous and bile 6 The Gastrointestinal Tract Functions Absorption: process of taking nutrients that result from digestion into the cells of body Movement of undigested materials Elimination: transport, storage and excretion of waste products
7 The Gastrointestinal Tract Specific parts of the tube: Mouth Esophagus Stomach Small intestine Rectum Large intestine 8 The Gastrointestinal Tract Assisting parts Liver Gallbladder Salivary glands Sphincters: "valves" to control flow of food Materials flow in just one direction! Located throughout the intestinal tract
9 Pancreas 10 11 Digestion: 2 Types of Processes are Involved: Physical & Chemical 1) The physical movement of food
nutrients along the GI tract Longitudinal muscle: propelling action Peristaltic contractions transport food and Segmentation: the pushing of a mass of partially digested food (chyme) intestine (see next slide) May move forward and backward in the small 12 Circular muscle: squeezing action Physical Processes: Peristalsis and Segmentation 13 Chemical Breakdown of Food Purpose is to divide foods into smaller units to facilitate absorption Digestive enzymes: enzymes that catalyze the reactions that break apart nutrients. Protein compounds that can speed up chemical reactions but are not altered in the process Commonly end in ase, such as lactase, sucrase Other fluids secreted into GI tract for total volume of 67 quarts/day!
14 Salivary Glands: 3 pair Moisten food 1.5 quarts/day! Digestion: Assisting Organs Begins process of digestion Liver: Bile Emulsifier: breaks up globs of fat to smaller pieces, increasing surface area and allowing fat and water to blend Detoxifies harmful substances
15 Digestion: Assisting Organs Gallbladder Pancreas Stores bile Releases bile when stimulated by ingestion of fat (about 500 ml of bile/d released into SI) Fat ingestions stimulates a hormone, CCK, which causes contraction of gallbladder One of the most important organs in the digestion and use of food Secretes enzymes that affect digestion and absorption (about 1500 ml/d) Insulin, glucagon (regulate Blood sugar levels) 16 Nutrient Digestion and Absorption Mouth: Saliva: amylase and lingual lipase Saliva and mucus combine with food to soften Stomach enzymes and function Kills many harmful bacteria and create a bolus of food Hydrochloric acid (HCl): very acidic (pH 2) Aids in protein digestion: allows breakup into amino acids Pepsin, gastric lipase, gastrin, Intrinsic Factor 17 18 Muscular Structure of the Stomach 19 Nutrient Digestion and Absorption Stomach (cont): By the time the chyme is ready to leave the stomach, digests 3040% of carbohydrate, 1020% of protein and less than 10% of fat Very little absorption Empties in 2 4 hours Carbs fastest, followed by Pro and Fat 20 Nutrient Digestion and Absorption Small Intestine: 10' Long Duodenum, Jejunum, Ileum Digestive secretions from Pancreas & Gallbladder received in SI Most digestion occurs here Food stays in SI 310 hours Absorptive Structures Wrinkled into folds, tripling absorptive area Carpeted with fingerlike projections called villi that further increase surface area Trap food stuffs to enhance absorption
21 Villi on Surface of Small Intestine Each villus contains blood vessels and a lymph vessel which transport nutrients through the body Absorption along entire length of small intestine Villi on surface of intestinal folds increase area of intestine 10X Microvilli on surface of villus cells increase area of intestine another 20X Surface area of SI is 600X that of 22 Nutrient Absorption: Four Roads
Passive diffusion: no NRG required Facilitated Diffusion: use of special carriers (proteins) to transport Active Transport: requires NRG for the transport (works against concentration gradient) Endocytosis: Absorptive membrane engulfs the particles or fluid ("cell eating") 23 Nutrient Digestion and Absorption (cont) Large Intestine: No further digestion, but bacterial action (can digest small amounts of fiber and forms Vit K and B12) Absorption of water, sodium, chloride, potassium, some Vitamin K Food travels 28 24 hours along the L.I. Lactose Intolerance (Increased gas due to bacteria)
24 Nutrition Digestion/Absorption (cont) Circulation of Nutrients: Vascular system or blood Network of veins and arteries thru which the blood carries nutrients Lymphatic system: fatsoluble nutrients circulated Bypasses the liver before delivery to the bloodstream 25 Metabolism Next step once food is absorbed: What happens in the cells Conversion of chemical energy from food sources into a form usable by cells Chemical reactions in cells converts end products of carbohydrates, fats and sugars into products of metabolic reactions and transfer of Energy to a form that cells can use ATP: Energy currency of the body
26 Summary of Nutrient Digestion and Absorption
27 Psychological Influences Influences on Digestion and Absorption Taste, smell, presentation of food, expectations that food tastes good, environment Chemical Influences Bacterial Influences
intestine Preparation of food, digestibility, temperature Amount of stomach acid, microbes in large 28 GI Disorders Constipation Stool moves through system too slowly or not bulky enough Too much water removed Stool is hard and small Stool moves too rapidly for sufficient water to be removed (increased peristalsis) May be a variety of reasons/causes 29 Diarrhea GERD GI Disorders Gastroesophageal Reflux Disease "Heartburn" Symptoms: Crampy abdominal pain with constipation or diarrhea Cause unknown Small pouches develop along the large intestine May become infected May be chronic condition (worsened by lowfiber diets)
30 Irritable Bowel Syndrome: Diverticulosis 31 ...
View Full Document
This note was uploaded on 04/07/2008 for the course BHS 105 taught by Professor Richmann during the Fall '07 term at Northeastern.
- Fall '07