NHM 101 Lecture 3 notes
NHM 101 Lecture 3 notes NHM 101-001
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This 6 page Class Notes was uploaded by Adriana McGhee on Friday February 5, 2016. The Class Notes belongs to NHM 101-001 at University of Alabama - Tuscaloosa taught by Denise DeSalvo in Fall 2016. Since its upload, it has received 65 views. For similar materials see Intro To Human Nutrition in Nutrition and Food Sciences at University of Alabama - Tuscaloosa.
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Date Created: 02/05/16
Lecture Chapter 3 (1116): Digestion, Absorption, and Transport DEFINITIONS Digestion: process by which food is broken down Absorption: uptake of nutrients by the cells of the small intestine for transport into either the blood or lymph system Gastrointestinal tract: the digestive tract o Flexible, muscular tube that extends from mouth to anus o Lumen the inner space within the GI tract and is continuous from one end to another ANATOMY OF DIGESTIVE TRACT Mouth Esophagus Stomach Small intestine Large intestine (colon) Rectum (anus) MOUTH Process of digestion begins here o Chewing and crushing food pieces o Fluids from food/beverages and from salivary glands blend with food for easy swallowing Food is swallowed then passes through pharynx (the short tube shared by both digestive and respiratory system) then epiglottis closes off the airway and lastly food enter the esophagus as the upper esophageal sphincter opens Carbohydrate digestion begins here WHAT IS A SPHINCTER? A circular muscle surround and able to close a body opening Keeps food flow in one direction There are multiple throughout the GI tract that regulate the flow of food particles o Upper esophageal sphincter (mouth/pharynx to esophagus) o Lower esophageal sphincter (esophagus to stomach) o Pyloric sphincter (stomach to small intestine) o Ileocecal valve (small intestine to large intestine) o Two sphincters of the anus ESOPHAGUS Upper esophageal sphincter opens and food enters into the esophagus o Sphincter muscle at each end of esophagus Food moves through the esophagus and passes through a hole in the diaphragm Lower esophageal sphincter opens to allow food into stomach STOMACH Food particles enter stomach upon the opening of the lower esophageal sphincter Food slowly transfers from the upper portion of stomach to lower portion o At the same time, juices are added to the food and ground into a semi liquid mass called chyme Chyme is released as the pyloric sphincter opens and goes into small intense Strongest mucle in the GI tract Thickest walls Stomach wall releases gastric juices until chyme is liquefied Pyloric sphincter opens about 3 times per minute to allow chyme into small intestine Digestion of carbs continue in the stomach and digestion of proteins and fats begin in the stomach SMALL INTESTINE 10 feet of tubing Chyme enters into the small intestine as the pyloric sphincter opens o the pyloric sphincter only allows a small amount of food at one time to pass Chyme bypasses the opening of the common bile duct which drips fluids o the fluid is from the gallbladder and the pancreas Chyme travles through the 3 segments o duodenum o jejunum o ileum Most digestion occurs in the SI LARGE INTESTINE (COLON) Remaining contents enter the large intestine through the ileocecal valve Large intestine withdraws water as intestinal contents pass to the rectum o Leaves semisolid waste Rectum and anal muscles hold back waste until rectal muscles relax and 2 anal sphincters open HOW DOES FOOD MOVE THROUGH THE GI TRACT? Peristalsis: wavelike muscular contractions of the GI tract that push the contents o Peristalsis occurs continuously GI tract is ringer with circular muscles and surrounding the rings are longitudinal muscles o Circular muscles tighten and long muscles relax (tube is constricted) o Circular muscles relax and long muscles tighten (tube bulges) o Stomach has third layer of diagonal muscles Sphincters muscles open and close periodically SECRETIONS OF DIGESTION Secretions of digestion are required from 5 different organs o Salivary glands o Stomach o Pancreas o Gallbladder o Small intestine Secretions bring in an abundance of water and a variety of enzymes o Enzymes are proteins that facilitate a chemical reaction o Identified by the organ they come from and the nutrient breakdown (ex: gastric lipase) o Enzymes in digestion facilitate hydrolysis o Hydrolysis: the addition of water to break a molecule into small pieces Salivary glands o Squirt enough saliva to moisten food o Saliva contains water, salt, mucus, and enzymes o Initiates carb digestion Stomach gastric juices o Gastic glands secrete gastric juice o Gastric juices contain water, enzymes, and hydrochloric acid o Stomach contents is highly acidic (pH of 2) o Stomach wall protects itself from the acidic juices by secreting mucus Small intestine Pancreatic juice (pancreatic lipase) enters into the digestive process in the duodenum o Pancreatic juice contains enzymes that act on all 3 macronutrients o Contains sodium bicarbonate which helps to neautralize the chyme that has entered from the stomach o Chyme remains neutral or slightly basic from this point forward Bile also enters into the digestive process in the duodenum o Liver continuously produces bile and its stored in the gallbladder o Bile is an emulsifier not an enzyme Cells of the intestinal wall also have digestive enymes ABSORPTION Most absorption occurs in the small intestine Fibers are not absorbed and continue through the digestive tract o Carry some minerals, bile, additives, and contaminants out of the body o Helps exercise GI mucles and keeps them strong to perfume peristalsis Intestinal bacteria ferment some fibers producing water, gas and small fragments of fat in the large intestine Large intestine retrieves material that it can use o Water and dissolved salts Blood continuously comes by the surface of the SI and carries nutrients away Nutrient molecules are trapped in the microvilli (tiny, fingerlike projections on each cell villi) Nutrient molecules are digested further by enzymes on the microvilli and then absorbed into the cell Absorption typically occurs by diffusion DIFFUSION CIRCULATORY SYSTEM AND NUTRIENTS Nutritent molecule crosses the cell of a virus (diffusion) Then, enter either the vascular system (bloodstream) or the lymphatic system Bloodstream o Watersoluable vitamins and smaller products of fat digestion o Then, go to the liver Lymphatic system o Fatsoluable vitamins and larger fats o Due to being insoluable in water and the bloodstream is primarily water o Initially bypass liver BLOODSTREAM Artery carries blood from heart to the digestive system Hepactic portal vein carries blood away from the digestive system o Blood goes to liver Hepatic vein carries blood from liver to heart Liver is the first organ to receive nutrients digested in the GI tract HEALTH OF GI TRACT GI bacteria o 100 trillion microbes o prevalence of bacteria depends on pH, peristalsis, diet, etc o primarily beneficial bacteria (flora) Beneficial bacteria Probiotics o Bacteria found in foods and supplements are beneficial to health o Alleviate diarrhea, constipation, IBS, ulcers, allergies Prebiotics o Food for probiotics
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