Week 1 NUTR 221 Essential Concepts PDF

NUTR 221 Advanced Nutrition Micronutrients Essential concepts Dr. Christine M. Mills, RD, MPH, PhD (she/her) Slides cannot be shared or reproduced without permission Adapted from slides by Dr. Brian Bandy, PhD Dr. Mills Registered dietitian with work experience in primary care, community healt...

NUTR 221 Advanced Nutrition Micronutrients Essential concepts Dr. Christine M. Mills, RD, MPH, PhD (she/her) Slides cannot be shared or reproduced without permission Adapted from slides by Dr. Brian Bandy, PhD Dr. Mills Registered dietitian with work experience in primary care, community health, public health Provost’s Interdisciplinary Postdoctoral Fellow at the University of Waterloo Ph.D. in Aging & Health from Queen’s University M.P.H. in Nutrition & Dietetics from University of Toronto B.A.Sc. in Applied Human Nutrition and B.Eng. in Biological Engineering from University of Guelph Dr. Mills Military spouse Owned by Sphynx cats Runner Group fitness instructor Learning Objectives Identify the organs of the digestive tract and their roles/functions in nutrient digestion and absorption. Describe the secretions released by the digestive tract organs, including accessory organs, and factors influencing the release of these secretions. Describe the structural features of the small intestine that facilitate nutrient absorption. Describe the roles of the nervous system and regulatory peptides in regulation of the digestive process. Structures of the Digestive Tract and the Digestive and Absorptive Process Digestive tract structures Main structures: Oral cavity Esophagus Stomach Small and large intestines Digestive tract structures Accessory Organs: Pancreas Liver Gallbladder © Cengage Learning Inc. Layers of the Lumen Mucosa: Mucosal membrane Lamina propria Muscularis mucosa Layers of the Lumen Submucosa: Connective tissue Blood Lymphatic vessels Lymphoid tissue Submucosal plexus Layers of the Lumen Muscularis externa Layers of the Lumen Serosa: Flat mesothelial cells © Cengage Learning Inc. The Oral Cavity Mouth and pharynx Salivary glands: Parotid Submandibular Sublingual Enzymes in saliva © Cengage Learning Inc. The Esophagus Moves bolus from oral cavity to stomach Swallowing: Voluntary, pharyngeal, esophageal Peristalsis Gastroesophageal sphincter Selected disorders of the esophagus: GERD The Stomach Four main regions: Cardia region Fundus Body Antrum or distal pyloric The Stomach Stomach muscles mix food with gastric juices to form chime: Gastric juices facilitate digestion. Gastric glands: Cardiac glands Oxyntic glands Pyloric glands Regulation of Gastric Secretions Three phases: Before food reaches the stomach: Acetylcholine, gastrin Once food is in the stomach: Stomach distension enhances gastric secretions. After food has left the stomach: Reduction in chyme volume and pH trigger release of somatostatin Accessory Organs The Pancreas Ductless endocrine cells that secrete hormones into the blood Digestive enzymes produced by acinar exocrine cells Pancreatic juice contains the following: Water Electrolytes Bicarboante Pancreatic digestive enzymes © Cengage Learning Inc. The Liver Consists of lobes made of lobules Portal circulation Bile canaliculi Bile synthesis and function: Bile composed of bile acids and salts, cholesterol, phospholipids and bile pigments in alkaline solution Bile acts like detergent to emulsify. The Liver © Cengage Learning Inc. The Gallbladder Concentrates and stores bile Selected disorders of the gallbladder: Gallstones The recirculation and excretion of bile: Most bile salts are reabsorbed. Bile circulation and hypercholesterolemia The Absorptive Process Absorption begins in the duodenum and continues throughout the jejunum and ileum. Absorption is rapid — few hours Absorption methods: Diffusion, facilitated diffusion, active transport or pinocytosis/endocytosis © Cengage Learning Inc. © Cengage Learning Inc. © Cengage Learning Inc. The Colon (Large Intestine) Contracts to mix materials Proximal colonic mucosal cells absorb sodium and water: Influenced by hormones Materials dehydrated Colonic secretions: Goblet cells secrete mucus. Bicarbonate © Cengage Learning Inc. Coordination and Regulation of the Digestive Process Neural Regulation and Regulatory Peptides Neural regulation: Myenteric plexus: peristalsis, motility Submucosal plexus: secretions, local blood flow Regulatory peptides: Hormones Paracrines Selected Regulatory Hormones/Peptides of the Gastrointestinal Tract © Cengage Learning Inc. Hormone/Peptide Main Production Sites Selected Function(s) Gastrin Stomach and small intestine Stimulates gastric acid secretion Stimulates pepsinogen secretion Cholecystokinin Small intestine and enteric nerves Stimulates gallbladder contraction Stimulates sphincter of Oddi relaxation Stimulates pancreatic enzyme secretion Secretin Small intestine Stimulates pancreas juice secretion Diminishes gastric emptying Diminishes gastric acid secretion Motilin Stomach and intestines Stimulates gastric and intestinal motility between meals Glucose-dependent insulinotropic Small intestine Stimulates insulin secretion peptide May diminish gastric acid secretion Peptide YY Small and large intestines Diminishes gastric acid secretion Diminishes gastric emptying Somatostatin Pancreas, stomach, and small intestine Diminishes gastric acid secretion Diminishes gastric emptying Diminishes pancreatic enzyme secretions Inhibits gallbladder contraction Glucagon-like peptides Small and large intestines Stimulates insulin secretion Reduces digestive tract motility Reduces gastric secretions Pancreatic polypeptide Pancreas Decreases gastric emptying Reduces pancreatic exocrine secretions Regulation of Gastric Motility and Gastric Emptying Peristaltic waves propel digestive contents: Basic electrical rhythm is initiated by pacemaker cells. Gastric emptying is affected by factors in stomach and duodenum. Dietary fat intake has an inhibitory effect on gastric emptying. Regulatory Peptides Paracrine-acting substances Neurocrine peptides Other Hormones: Ghrelin Leptin CRH Summary Factors influencing digestion and absorption: Dispersion and mixing of ingested food Quantity and composition of gastrointestinal secretions Enterocyte integrity Expanse of intestinal absorptive area Transit time of intestinal contents Adequate nourishment depends on a normally functioning gastrointestinal tract. Dietary Reference Intakes Phillips SM, Paddon-Jones D, Layman DK. 2020 NUTR 120 “DRI Diagram” is useful to show how EAR is used to set RDA but does not explain “risk” of inadequacy and risk of excess. The RDA = EAR + 2SD DRI Diagram: “risk” of “inadequacy” “excess” 1 2 3 1 3 2 RISK 1 (EAR) = 50% 2 (RDA) = 2.5% 3 (UL) = 0 40 The Development of the DRIs 1994-2004 Lessons Learned and New Challenges. 2008