Chapter 3 Digestions and Absorption Kin 110 Chapter 3 Digestions and Absorption

Overview of Digestion and Absorption Chapter 3 Gastrointestinal tract Overview of Digestion (details discussed with each nutrient lecture) Mechanical Chemical Overview of Absorption (details discussed with each nutrient lecture) Circulation of nutrients Regulation and influences on Digestion and Absorption

The Gastrointestinal Tract Organization Mouth  anus Accessory organs Salivary glands, liver, pancreas, gallbladder Functions Ingestion Transport Secretion Digestion Absorption Elimination

The Digestive Tract Wall

Mouth: chews and mixes food with saliva Salivary Glands: secrete enzymes & mucous Pharynx & Esophagus: passages for food Stomach: adds acid & enzymes mixes, churns and grinds food regulates entry of food into small intestine Liver: manufactures bile (required for fat digestion) ES Pancreas: secretes enzymes and buffers secretes hormones Gallbladder: stores and releases bile Pyloric Sphincter Small Intestine: primary site of digestion and absorption Large Intestine: reabsorbs water and minerals contains bacteria which digest some food and synthesize some vitamins

Overview of Digestion Digestion - the mechanical and chemical breakdown of foods into smaller units that can be taken across the intestinal epithelium into the body Physical movement Peristalsis Waves of muscle contraction propelling food forward Segmentation Mixing contractions that do not propel food forward

Chemical Digestion: Enzymes Definition proteins that act as CATALYSTS to facilitate (speed up) chemical reactions change molecules while remaining unchanged themselves digestive enzymes break down molecules into smaller components via HYDROLYSIS “hydro” = water “lysis” = to burst or break apart ENZYME

Chemical Digestion: Enzymes cont. Examples prefix indicates molecule the enzymes acts on suffix “ase” indicates an enzyme amylase sucrase lactase maltase pepsin trypsin peptidase lipase digest proteins digest carbohydrates digests lipids

Secretions of the Digestive Tract Salivary Secretions water, mucous, enzymes, buffers, lysozyme Stomach (gastric) Secretions hydrochloric acid, intrinsic factor, pepsinogen, gastric lipase, mucous, HCO3-, hormones (gastrin) Liver & Gallbladder bile

Secretions cont. Pancreatic Secretions Small Intestine exocrine: enzymes & buffers (HCO3-) endocrine: insulin, glucagon, & secretin, others Small Intestine exocrine: enzymes, mucous endocrine & paracrine: CCK, motilin, others

Absorption - movement of small units of food particles (after digestion) from the interior of the gut (lumen) into the blood stream or lymphatic system. - Requires particles to be broken down by digestion, a large surface area to interact with particles and in some cases specialized transportation mechanisms to move particles across cell membranes

Large surface area facilitates absorption

Mechanisms of Absorption passive (simple) diffusion the unassisted movement of substances in or out of cells down a concentration gradient

Mechanisms of Absorption facilitated diffusion carrier proteins (transporters) in the cell membrane help move substances in or out of cells down a concentration gradient

Mechanisms of Absorption cont. active transport the movement of molecules into or out of cells against a concentration gradient using a transport protein requires energy (ATP)

Mechanisms of Absorption cont. endocytosis the uptake of material by a cell through indentation and pinching off of part of the membrane to form a vesicle

Circulation of Nutrients Vascular system Lymphatic system

Transport of Nutrients blood direct absorption of glucose, fructose, galactose, & proteins, and small lipid molecules travels directly to the liver lymph larger lipid molecules are too large to enter the blood directly absorbed first into the lymph enter the blood at the inferior vena cava

Transport of nutrients Some nutrients travel freely in the blood (e.g. glucose, proteins). Others are bound to protein transporters (e.g. lipids, vitamins, and minerals)

Regulation of GI Activity Nervous system Regulates GI activity Local system of nerves Central nervous system Hormonal system Increases or decreases GI activity

Regulation of GI Activity cont. Endocrine (Hormonal) System

Influences on Digestion & Absorption Psychological taste, smell, presentation of food Cephalic phase (see next slide) Chemical processing of foods and food preparation, medications Bacterial some may cause gastris, ulcers; others are beneficial

Cephalic Phase Responses

Nutrition and GI Disorders Constipation Hard, dry, infrequent stools Reduced by high fiber, fluid intake, exercise Diarrhea Loose, watery, frequent stools Symptom of diseases/infections Can cause dehydration Diverticulosis Pouches along colon High fiber diet reduces formation