chapter 023

The Human Body in Health and Illness, 4th edition

Barbara Herlihy

Chapter 23:Digestive System

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Lesson 23-1 Objectives

• List four functions of the digestive system.• Describe the four layers of the digestive tract.• Describe the structure and functions of the

organs of the digestive tract.• Describe the structure and functions of the

accessory organs of the digestive tract.

Copyright © 2011, 2007 by Saunders, an imprint of Elsevier Inc. All rights

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Functions of the Digestive System

• Ingest food• Digest it

– Mechanical– Chemical

• Absorb nutrients• Excrete waste


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Overview of the Digestive System

• Mouth• Pharynx• Esophagus• Stomach• Small intestine• Large intestine• Rectum, anus• Accessory organs


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Four Layers of the Digestive Tract

• Mucosal layer• Submucosal layer• Muscle layer

- Circular and longitudinal - Mixing, mashing action - Peristaltic action

- Enteral nervous system• Serosal layer

- Peritoneal membranes


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Peristalsis

• Waves of muscle contraction, relaxation

• Pushes food from mouth toward anus

• Peristaltic movements differ from organ to organ


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Oral Cavity

• Teeth: Mastication• Tongue: Swallowing• Salivary glands

- Parotid - Submandibular - Sublingual


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Eating and Swallowing

• Mouth

• Pharynx

• Esophagus - Esophageal sphincters

Pharyngoesophageal Lower esophageal


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Functions of the Stomach

• Regulates rate of gastric emptying• Secretes gastric juice, including HCl• Secretes gastric hormones and intrinsic factor• Digests limited amount of food• Absorbs limited substances


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Parts of the Stomach

• Fundus• Body• Pylorus• Pyloric sphincter• Lesser curvature• Greater curvature• Rugae


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Muscles of the Stomach

• Longitudinal• Oblique• Circular

• Mixing and mashing chyme

• Peristalsis


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Stomach Structure: Mucosa

• Mucous cells• Parietal cells

- HCl - Intrinsic factor

• Chief cells - Digestive enzymes


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Clinical Conditions: Stomach

• Gastric ulcer• Hiatal hernia• Nasogastric tube• Gastrostomy tube• Gastric resection• Pyloric stenosis• Vagolytic effects


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Small Intestine: Parts and Functions

• Parts– Duodenum– Jejunum– Ileum

• Functions– Digests– Absorbs– Secretes hormones and

digestive enzymes


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Duodenum: Villi and Microvilli

• Folds increase area for absorption

• Inside composed of capillaries and lacteals

• End products of digestion delivered to hepatic portal system and lymphatics

Copyright © 2011, 2007 by Saunders, an imprint of Elsevier Inc. All rights reserved. 15

Large Intestine

• Cecum– Vermiform appendix

• Colon– Ascending– Transverse– Descending– Sigmoid

• Rectum and anus


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Functions of the Large Intestine

• Absorption of water and electrolytes• Synthesis of vitamins by intestinal bacteria• Temporary storage of waste• Elimination of waste (feces) and gas (flatus)


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Clinical Conditions: Large Intestine

• Intestinal obstruction

• Colostomy• Hemorrhoids• Enema


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Accessory Digestive Organs

• Liver

• Gallbladder

• Pancreas


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Liver Functions

• Synthesis of bile salts and secretion of bile• Synthesis of plasma proteins• Storage of glucose, fat-soluble vitamins• Detoxification

– Main organ for drug detoxification• Excretion of bilirubin, cholesterol, drugs• Metabolism of carbohydrates, protein, fats• Phagocytosis (Kupffer cells, macrophages)


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Hepatic Portal System

• End products of digestion flow through portal vein to liver

• Liver processes end products of digestion, discharging blood through hepatic veins and into IVC


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Biliary Tree

• Ducts connect liver, gallbladder, pancreas to duodenum

• Hepatic ducts• Cystic duct• Common bile duct

– Ampulla of Vater– Sphincter of Oddi


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Bile

• Formed from blood in the liver lobules

• Assists in digestion of fat

• Stored in gallbladder• Composition

– Water– Cholesterol– Bile pigments, salts


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Gallbladder

• Pear-shaped sac on the underside of the liver– Concentrates and stores bile

• Attached to common bile duct by cystic duct• Fat in the duodenum stimulates release of the

hormone cholecystokinin (CCK)– CCK causes gallbladder to contract, eject bile into

common bile duct and duodenum


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Path of Pancreatic Digestive Enzymes

Pancreatic acinar cells

Main pancreatic duct

Base of common bile duct

DuodenumCopyright © 2011, 2007 by Saunders,

an imprint of Elsevier Inc. All rights reserved.

25

Clinical Conditions

• Gallstones • Bleeding

– Loss of clotting factors (liver failure)

• Esophageal varices• Ascites

– Paracentesis

• Acute pancreatitis


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Lesson 23-2 Objectives

• Explain the physiology of digestion and absorption.

• Describe the effects of amylases, proteases, and lipases.

• Describe the role of bile in the digestion of fats.

• Describe five categories of nutrients.


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Carbohydrates: Digestion and Absorption

• Polysaccharides– Digested by amylases to

disaccharides

• Disaccharides– Digested by disaccharidases to

monosaccharides

• Monosaccharides– Simple sugars, end products of

digestion absorbed by villi


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Proteins: Digestion and Absorption

• Gastric HCl unravels strands of protein

• Proteases digest protein into amino acids, which are absorbed into villi

• Common proteases– Pepsin, stomach– Trypsin, pancreas– Chymotrypsin, pancreas– Enterokinase, duodenum


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Fats: Digestion and Absorption

• Fats are insoluble in water.• Emulsification

– Bile splits big fat globules into small ones.

– Bile salts make fat water-soluble.

• Digestion– Accomplished by lipases– End products : Fatty acids and

glycerol, absorbed by lacteals


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Digestion and Absorption: Summary

• Trace the flow of food from the mouth to the anus.

• Point out entrance of each accessory organ into the digestive tract.


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Nutrition: Concepts to Know

• Nutrition: Study of the relationship of food to body function

• Five categories of nutrients– Carbohydrates– Proteins– Lipids– Vitamins– Minerals


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Nutrition Concepts: Carbohydrates

Simple Sugars

• Monosaccharides• Disaccharides

Complex Carbohydrates

• Polysaccharides• Consist primarily of

starch and fiber• Most carbohydrate

consumption should be in this form.


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Nutrition Concepts: Proteins

• Essential amino acid: Not synthesized by the body; must be consumed

• Nonessential amino acid: Synthesized in the body; not essential to consume

• Complete protein: Contains all the essential amino acids

• Incomplete protein: Does not contain all essential amino acids


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Nutrition Concepts: Fats

• Saturated fatty acid: Solid at room temperature

• Unsaturated fatty acid: Oil; liquid at room temperature

• Essential fatty acid: Not synthesized by the body and must be consumed; linoleic acid is an important component of cell membranes


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Nutrition Concepts: Vitamins

• Small organic molecules that help regulate cell metabolism

• Fat-soluble vitamins– Vitamins A, D, E, and K– Can be stored in the body

• Water-soluble vitamins– Vitamins B and C– Most are not stored by the body


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Nutrition Concepts: Minerals

• Inorganic substances needed for normal body function

• Sodium, chloride• Potassium• Calcium, phosphorus, magnesium• Iron• Iodine• Trace elements


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Appetite Control

• Hypothalamus– Feeding center– Satiety center

• Theories of satiety– Glucostat hypothesis– Lipostat hypothesis


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chapter 023

Health & Medicine

imprint of elsevier

digestive enzymes copyright

organ copyright

digestive system1

macrophages copyright

ivc copyright

stomach structure

gastric hormones