NHM 101- Week 3 Notes
NHM 101- Week 3 Notes NHM101
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This 3 page Class Notes was uploaded by Matt Cutler on Sunday February 7, 2016. The Class Notes belongs to NHM101 at University of Alabama - Tuscaloosa taught by Lebo Tan in Winter 2016. Since its upload, it has received 18 views. For similar materials see NHM101-002 in Nutrition and Food Sciences at University of Alabama - Tuscaloosa.
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Date Created: 02/07/16
Ch 3- Digestion, Absorption, and Transport Monday, February 1, 2016 9:01 AM • Digestion- the process by which food (mostly macronutrients: carbs, proteins, lipids) is broken down into absorbable smaller units • Absorption- the uptake of nutrients by the cells of the small intestine for transport into either the blood or the lymph system. • Gastrointestinal (GI) tract: the digestive tract ○ A flexible, muscular tube that runs from the mouth to the anus ○ Lumen- the inner space within the GI tract and is continuous from one end to the other. 1. Digestion system a. Anatomy b. Mouth i. Functions 1) Chewing and crushing food pieces 2) Secretion from salivary glands blend with food for easy swallowing 3) Carbohydrate digestion begins here (Salivary amylase: enzyme that helps digest starch) □ Food enters the esophagus as the upper esophageal sphincter opens ii. What is a sphincter? 1) A circular muscle surrounding, and able to close, a body opening. 2) Sphincters muscles open and close periodically, controlling the pace of food contents move through the GI tract. 3) Keeps the flow of food in one direction. 4) Multiple throughout the GI tract: a) Upper esophageal sphincter (esophagus to stomach) b) Lower esophageal sphincter (esophagus to stomach) c) Pyloric sphincter (stomach to small intestine) d) Ileocecal valve (small intestine to large intestine) e) Two sphincters of the anus c. Esophagus: NO DIGESTION OCCURS Upper esophageal sphincter opens and food enters into the esophagus. Food moves through the esophagus Lower esophageal sphincter opens to allow food into the stomach d. Stomach Strongest muscle of the GI tract and thickest walls i. Food slowly transfers from the upper portion to the lower portion 1) Juices released by stomach walls are added to the food and ground into a semi-liquid mass called chyme 2) Digestion of protein and fat begin in stomach a) Using the enzymes pepsin for protein and lipase for fats 3) Pyloric sphincter opens about 3 times per minute to allow chyme into the small intestine. e. Small Intestine 10 feet i. 3 segments i. 3 segments 1) Duodenum a) Has an opening from the common bile duct which can secrete fluids from the gall bladder(responsible for storage of bial: required for fat digestion) and the pancreas(produces many digestion enzymes that can drip in to small intestine; can also produce hormones) 2) Jejunum a) Main part where most digestion and absorption takes place 3) Ileum Most digestion occurs in the Small intestine Almost ALL absorption occurs in SI Chyme bypasses the opening of the common bile duct, which drips fluid from the gallbladder and the pancreas f. Large Intestine (Colon) (5-7ft) i. Remaining contents enter the large intestine through the ileocecal valve ii. Large intestine withdraws water as intestinal contents pass through the rectum 1) Leaves a semisolid waste iii. Rectum and anal muscles hold back waste until rectal muscles relax and 2 anal sphincters open. ○ How does food move through the GI tract? Muscular action of GI tract □ GI tract is ringed with circular muscles surrounding the rings are longitudinal muscles Circular muscles tighten and long muscles relax= tube is constricted Circular muscles relax and long muscles tighten= tube bulges □ Peristalsis- wavelike muscular contractions of the GI tract that move the food along, occurs continuously. □ Sphincters muscles open and close periodically controlling the pace of food contents moving through the GI tract. 2. Secretions of Digestion a. Digestion requires secretions from 5 different organs i. Salivary glands (breaks down carbs in mouth) ii. Stomach iii. Pancreas iv. Gallbladder v. Small intestine b. Secretions bring in an abundance of water and a variety of digestive enzymes i. Enzymes are proteins that facilitate a chemical reaction ii. Digestive enzymes break down large nutrient molecules into smaller pieces iii. Identified by the organ they come from and the nutrient they breakdown 1) Ex: gastric lipase vs. pancreatic lipase c. Salivary glands i. Saliva contains water, salts, mucus, and enzymes ii. Moisten food; breaks down starches in food via salivary amylase iii. Initiates carbohydrate digestion d. Stomach i. Gastric glands secrete gastric juice ii. Pepsin is enzyme in stomach that breaks down proteins. iii. Gastric juices contain water, enzymes and hydrochloric acid. iv. Stomach contents is highly acidic (pH of 2) e. Small Intestine i. Pancreatic juice is secreted by the pancreas into the duodenum 1) Pancreatic juice contains enzymes that act on all 3 macronutrients 2) It contains sodium bicarbonate which helps to neutralize the chyme that has entered from the stomach ii. Bile is secreted by gallbladder into the duodenum 1) Liver continuously produces bile and it is stored in the gallbladder 2) Bile is an emulsifier(a food additive used to stabilize processed foods), not an enzyme, it helps the lipid digestion iii. Cells of the intestinal wall also produce digestive enzymes 1) Lactase is produced by the cells of the small intestine and is used to break down lactose (milk sugar) 3. Absorption 3. Absorption ○ Most absorption occurs in the small intestine ○ Villi: fingerlike projections of the small intestinal wall Absorptive cells on the surface of villi ○ Microvilli: tiny, hair like projections on each cell of every villus that can trap nutrient particles and transport them into the cells 4. Diffusion a. Simple diffusion- does not require a carrier b. Facilitated and active transport require a carrier and active requires energy. 5. Circulatory System and Nutrients ○ Nutrient molecule crosses the absorptive cell on the villi ○ Then, enter either the vascular system (bloodstream) or the lymphatic system. Both supply vessels to each villus a. Bloodstream • Macronutrients ○ Carbs and proteins enter blood i. Water-soluble nutrients are released directly into the bloodstream ii. Then, go to the liver first where their fate and destination will be determined. Lipids go to lymphatic system b. Lymphatic system • Micronutrients ○ Minerals and water soluble i. Fats and fat-soluble vitamins (A, B, E, K) ii. Due to being insoluble in water and the bloodstream is primarily water vitamins enter blood iii. Initially bypass liver; goes to the liver last ○ Fat and soluble vitamins enter lymphatic system ○ Fibers are not absorbed and continue into the large intestine Carry some minerals, bile, additives, and contaminants out of the body Helps exercise GI muscles and keep them strong to perform peristalsis ○ Intestinal bacteria ferment some fibers producing water, gas and small fragments of fat in the large intestine. 6. Health of GI Tract a. GI Bacteria i. 10 trillion ii. Prevalence of bacteria depends on pH, peristalsis, diet, etc iii. Large intestine iv. Primarily beneficial bacteria (flora) b. Beneficial bacteria i. Probiotics (beneficial bacteria found in the gut) 1) Bacteria found in foods and supplements that are beneficial to our health 2) Alleviate diarrhea, constipation, ulcers, allergies, IBS (irritable bowel symptom) ii. Prebiotics: non digestible carbohydrates(such as Fiber) 1) Food/Fuel for probiotics 2) Encourage the growth and activity of bacteria.
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