Digestion, Absorption, and Transport Chapter 3

Digestion Breaking down foods into nutrients Challenges of digestion Prepare for absorption Challenges of digestion Tasks of the mouth Diaphragm Steady movement Lubrication of food Digestive enzyme functions

Anatomy of the Digestive Tract

Anatomy of the Digestive Tract Gastrointestinal (GI) tract Flexible and muscular Path Mouth → esophagus → stomach → small intestine → large intestine → rectum → anus Lumen Continuous

Anatomy of the Digestive Tract Mouth Process of digestion begins Mastication Four basic taste sensations Savory Aroma, texture, and temperature Pharynx Bolus

Anatomy of the Digestive Tract Esophagus Two sphincters Upper esophageal sphincter Lower esophageal sphincter Stomach Movement of bolus Chyme Pyloric sphincter

Anatomy of the Digestive Tract Small intestine Common bile duct Pancreas and gall bladder Three segments Large intestine (colon) Ileocecal valve Withdrawal of water Rectum and anus

Anatomy of the Digestive Tract

Opening from small intestine to large intestine Descending colon Transverse colon Ascending colon End of small intestine Opening from small intestine to large intestine Figure 3.2: The Colon. The colon begins with the ascending colon rising upward toward the liver. It becomes the transverse colon as it turns and crosses the body toward the spleen. The descending colon turns downward and becomes the sigmoid colon, which extends to the rectum. Along the way, the colon mixes the intestinal contents, absorbs water and salts, and forms stools. Descending colon Appendix Rectum Sigmoid colon Anus Stepped Art Fig. 3-2, p. 72

Muscular Action of Digestion Peristalsis Circular and longitudinal muscles working together Rate and intensity of contractions vary Factors that may interfere with peristalsis Stomach action Circular, longitudinal, and diagonal muscles Timing the release of chyme

Muscular Action of Digestion

Muscular Action of Digestion Segmentation Contraction of circular muscles in small intestine Mix chyme Promote contact with absorption cells Sphincter contractions Periodically open and close Control pace of GI tract contents

Muscular Action of Digestion

Muscular Action of Digestion

Secretions of Digestion Five organs Salivary glands, stomach, pancreas, liver, small intestine Secretions Water Enzymes Protein facilitator of chemical reactions Hydrolysis

Secretions of Digestion Saliva Moisten food for easy passage Protective role Carbohydrate digestion Gastric juice Protein digestion Mucus pH units

Secretions of Digestion Pancreatic juice Released via ducts into duodenum Enzymes act on all three energy nutrients Sodium bicarbonate Bile Liver Gallbladder

Secretions of Digestion

The Final Stage Vitamin and mineral absorption Undigested residues Exercise intestinal muscles Retention of water Colon Intestinal bacteria Recyclable materials Water and dissolved salts

Absorption Small intestine Majority of absorption Ten feet long Surface area Absorption techniques Simple diffusion Facilitated diffusion Active transport

Absorption

FACILITATED DIFFUSION Carrier loads nutrient on outside of cell . . . Carrier loads nutrient on outside of cell . . . Outside cell Energy Cell membrane . . . and then releases it on inside of cell. . . . and then releases it on inside of cell. Inside cell Some nutrients (such as water and small lipids) are absorbed by simple diffusion. They cross into intestinal cells freely. SIMPLE DIFFUSION FACILITATED DIFFUSION Some nutrients (such as the water-soluble vitamins) are absorbed by facilitated diffusion. They need a specific carrier to transport them from one side of the cell membrane to the other. (Alternatively, facilitated diffusion may occur when the carrier changes the cell membrane in such a way that the nutrients can pass through.) ACTIVE TRANSPORT Some nutrients (such as glucose and amino acids) must be absorbed actively. These nutrients move against a concentration gradient, which requires energy. Figure 3.9: Absorption of Nutrients. Absorption of nutrients into intestinal cells typically occurs by simple diffusion, facilitated diffusion, or active transport. Occasionally, a large molecule is absorbed by endocytosis—a process in which the cell membrane engulfs the molecule, forming a sac that separates from the membrane and moves into the cell. Stepped Art Fig. 3-9, p. 78

Anatomy of the Absorptive System Villi Select and regulate nutrients absorbed Microvilli Enzymes and “pumps” Crypts Secretion of intestinal juices Goblet cells Mucus secretion

Preparing Nutrients for Transport Transport pathways Bloodstream Water-soluble nutrients and smaller products of fat digestion Liver Lymphatic system Larger fats and fat-soluble vitamins Chylomicrons Bypass liver at first

The Vascular System Closed system of vessels Blood Heart pump Delivers oxygen and nutrients Removes carbon dioxide and wastes Blood flow Special routing for digestive system Liver

The Vascular System

The Vascular System

The Lymphatic System One-way route Entry into bloodstream No pump Circulation between cells Entry into bloodstream Subclavian vein Nutrients in lymphatic vessels Bypass liver at first

Health and Regulation of GI Tract Gastrointestinal bacteria – flora Most are not harmful Benefits of gastrointestinal bacteria Factors influencing bacteria presence Diet – probiotics Others Digestion of fibers and complex proteins Vitamin production

Health and Regulation of GI Tract Endocrine and nervous systems Homeostatic regulation Hormones and nerve pathways Stimulation and inhibition of digestive secretions Feedback mechanisms Examples GI hormones

Health and Regulation of GI Tract

Health and Regulation of GI Tract

The Digestive System at Its Best Sensitive and responsive to environment Immunity against intestinal diseases Defense against foreign invaders Health of digestive system Healthy supply of blood Lifestyle factors Types of foods eaten Balance, moderation, adequacy, and variety

Common Digestive Problems Highlight 3 Common Digestive Problems

Choking Food slips into trachea International sign for choking Cuts off breathing International sign for choking Heimlich maneuver Foods commonly associated with choking Prevention of choking

Choking

Choking

Vomiting and Diarrhea Vomiting Diarrhea Adaptive mechanism of the body Medical treatment Dehydration and projectile vomiting Diarrhea Symptom of medical conditions & treatments Irritable bowel syndrome (IBS) Colitis Treatment

Constipation Not a disease Symptoms of constipation Causes Prevention Lifestyle Side effect of medications Prevention Fiber and water Physical activity

Belching and Gas Belching Intestinal gas Hiccups Swallowed air Prevention Intestinal gas Consumption of certain foods Individually determined Hiccups

Heartburn and “Acid Indigestion” Gastroesophageal reflux (heartburn) Causes Prevention Indigestion Antacids and acid controllers Damage to esophagus Barrett’s esophagus

Ulcers Peptic ulcers Causes Ulcer treatment regimen Gastric ulcers Duodenal ulcers Causes Bacterial infection Anti-inflammatory drugs Excessive gastric acid secretion Ulcer treatment regimen