Digestion, Digestion, Absorption, and Absorption, and

TransportTransport

Chapter 3Chapter 3

DigestionDigestion

• Breaking down foods into nutrients• Prepare for absorption

• Challenges of digestion• Tasks of the mouth• Diaphragm• Steady movement• Lubrication of food• Digestive enzyme functions• Excretion of waste

Anatomy of the Digestive TractAnatomy of the Digestive Tract

• Gastrointestinal (GI) tract• Flexible and muscular• Path

• Mouth → esophagus → stomach → small intestine → large intestine → rectum → anus

• Lumen• Continuous

The Gastrointestinal TractThe Gastrointestinal Tract

Anatomy of the Digestive TractAnatomy 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 TractAnatomy of the Digestive Tract

• Esophagus• Two sphincters

• Upper esophageal sphincter

• Lower esophageal sphincter

• Stomach• Movement of bolus• Chyme• Pyloric sphincter

Anatomy of the Digestive TractAnatomy 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

Transverse colon

Ascending colon

Descending colon

Sigmoid colonAnus

Rectum

Appendix

Opening from small intestine to large intestine

End of small intestine

Stepped Art

Figure 3-2 p72

Transverse colon

Ascending colon

Descending colon

Sigmoid colonAnus

Rectum

Appendix

Opening from small intestine to large intestine

End of small intestine

Stepped Art

Fig. 3-2, p. 72

Muscular Action of DigestionMuscular 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

Stomach MusclesStomach Muscles

Muscular Action of DigestionMuscular 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

An Example of a Sphincter An Example of a Sphincter MuscleMuscle

Secretions of DigestionSecretions of Digestion

• Five organs• Salivary glands, stomach, pancreas, liver,

small intestine

• Secretions• Water • Enzymes

• Protein facilitator of chemical reactions

• Hydrolysis

Secretions of DigestionSecretions of Digestion

• Saliva• Moisten food for easy passage• Protective role• Carbohydrate digestion

• Gastric juice• Protein digestion• Mucus• pH units

The Salivary Glands

Secretions of DigestionSecretions of Digestion

• Pancreatic juice and intestinal enzymes• Released via ducts into duodenum• Enzymes act on all three energy nutrients• Sodium bicarbonate

• Bile• Liver• Gallbladder

Summary of Digestive Secretions & Their Major Actions

The Final StageThe Final Stage

• Undigested residues• Exercise intestinal muscles• Retention of water

• Colon• Intestinal bacteria• Recyclable materials

• Water and dissolved salts

AbsorptionAbsorption

• Small intestine• Majority of absorption• Ten feet long

• Surface area

• Absorption techniques• Simple diffusion

• Facilitated diffusion

• Active transport

Carrier loads nutrient on outside of cell . . .

Carrier loads nutrient on outside of cell . . .

Outside cell

Cell membrane

. . . and then releases it on inside of cell.

. . . and then releases it on inside of cell.Inside

cellFACILITATED

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.

Stepped Art

Some nutrients (such as water and small lipids) are absorbed by simple diffusion. They cross into intestinal cells freely.

SIMPLE DIFFUSION

Figure 3-8 p77

Carrier loads nutrient on outside of cell . . .

Carrier loads nutrient on outside of cell . . .

Outside cell

Cell membrane

. . . and then releases it on inside of cell.

. . . and then releases it on inside of cell.Inside

cellFACILITATED

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.

Stepped Art

Some nutrients (such as water and small lipids) are absorbed by simple diffusion. They cross into intestinal cells freely.

SIMPLE DIFFUSION

Fig. 3-9, p. 78

Anatomy of the Absorptive Anatomy of the Absorptive SystemSystem

• Villi• Select and regulate nutrients absorbed

• Microvilli• Enzymes and “pumps”

• Crypts• Secretion of intestinal juices

• Goblet cells• Mucus secretion

A Closer Look at the Intestinal A Closer Look at the Intestinal CellsCells

• Villi cells• Regulate nutrient absorption based on needs

• Microvilli• Enzymes and ‘pumps’

• Specialized cells • Food combining

• Enhanced use in the body

A Closer Look at the Intestinal Cells

• 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 SystemThe Vascular System

• Closed system of vessels• Heart pump

• Blood• Delivers oxygen and nutrients• Removes carbon dioxide and wastes• Blood flow

• Special routing for digestive system

• Liver

The Vascular SystemThe Vascular System

The LiverThe Liver

The Lymphatic SystemThe Lymphatic System

• One-way route• No pump• Circulation between cells

• Entry into bloodstream• Subclavian vein

• Nutrients in lymphatic vessels• Bypass liver at first

Health and Regulation of the GI Health and Regulation of the GI TractTract

• Gastrointestinal bacteria – flora • Most are not harmful

• Benefits of gastrointestinal bacteria

• Factors influencing bacteria presence• Diet – probiotics

• Prebiotics • Others

• Digestion of fibers and complex proteins• Vitamin production

Gastrointestinal Hormones and Gastrointestinal Hormones and Nerve PathwaysNerve Pathways

• Homeostatic regulation• Endocrine system• Nervous system• Feedback mechanisms

• Examples

• GI hormones• Gastrin

• Secretin

• Cholecystokinin (CCK)

An Example of a Negative An Example of a Negative Feedback LoopFeedback Loop

The Primary actions of The Primary actions of Selected GI Hormones Selected GI Hormones

The System at Its BestThe 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 Common Digestive ProblemsProblems

Highlight 3Highlight 3

ChokingChoking

• Food slips into trachea• Cuts off breathing

• International sign for choking• Heimlich maneuver

• Foods commonly associated with choking• Prevention of choking

Normal Swallowing and Normal Swallowing and ChokingChoking

First Aid for ChokingFirst Aid for Choking

VomitingVomiting

• Vomiting• Adaptive mechanism of the body• Medical treatment

• Dehydration

• Self induced

Diarrhea

• Diarrhea• Symptom of medical conditions & treatments

• Irritable bowel syndrome (IBS)

• Colitis

• Treatment

Irritable Bowel Syndrome and Colitis

• Irritable bowel syndrome• Characterization• Cause

• Unknown

• Triggers

• Colitis• Inflammation of large intestine

Celiac Disease

• Autoimmune disease• Inflammation of small intestine

• Gluten-containing foods• Symptoms• Treatment

• Rehydration

ConstipationConstipation

• Not a disease• Symptoms of constipation• Causes

• Lifestyle• Side effect of medications

• Prevention• Fiber and water• Physical activity

Constipation

• Hemorrhoids• Diverticulosis• Laxatives• Harmful practices

• Colonic irrigation

Belching and GasBelching and Gas

• Belching• Swallowed air• Prevention

• Intestinal gas• Consumption of certain foods

• Individually determined

Heartburn and Heartburn and ““Acid Acid IndigestionIndigestion””

• Gastroesophageal reflux (heartburn)• Causes• Prevention

• Indigestion• Causes• Antacids and acid controllers

• Damage to esophagus• Barrett’s esophagus

Gastroesophageal Reflux

UlcersUlcers

• Peptic ulcers• Gastric ulcers• Duodenal ulcers

• Causes• Bacterial infection• Anti-inflammatory drugs• Excessive gastric acid secretion

• Ulcer treatment regimen

Strategies to Prevent or Alleviate Common GI Problems