Operational Medicine Medical Education and Training

The Gastrointestinal System

CORRESPONDENCE COURSE

U.S. ARMY MEDICAL DEPARTMENT CENTER AND SCHOOL

SUBCOURSE MD0581 EDITION 100

THE GASTROINTESTINAL SYSTEM

In this subcourse, you will study the gastrointestinal system. This system processes food so that it can be used by the body.

Chemical reactions occur in each body cell. Some chemical reactions synthesize new enzymes, cell structures, bone, and other components of the body. Other chemical reactions release energy needed for the building processes. The foods we eat are usually too large to pass through the membranes of the body's cells.

The organs of the gastrointestinal system break down food molecules for use by the cells of the body and eliminate the waste products the body cannot use. Knowledge of the gastrointestinal system is vitally important to most medical MOSs.

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Length: 145 Pages

Estimated Hours to Complete: 15

Format: PDF file

Size: 2.2 MB

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Anyone may take this course. However, to receive credit hours, you must be officially enrolled and complete an examination furnished by the Nonresident Instruction Branch at Fort Sam Houston, Texas. Enrollment is normally limited to Department of Defense personnel. Others may apply for enrollment, but acceptance is not guaranteed.

Stomach Anatomy

Basic Human Anatomy

Distance Learning Course
145 Pages
Est. 15 Hours
2.2 MB pdf file

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TABLE OF CONTENTS

 

INTRODUCTION

1 ANATOMY AND PHYSIOLOGY OF THE DIGESTIVE SYSTEM

Section I. Anatomy of the Digestive System

Section II. Functions and Stages of the Digestive Process

Exercises

2 PHYSICAL ASSESSMENT OF THE DIGESTIVE SYSTEM

Exercises

3 DISEASES AND DISORDERS OF THE GASTROINTESTINAL SYSTEM

Section I. Diseases/Disorders of the Upper Gastrointestinal System

Section II. Hernias

Section III. Diseases/Disorders of the Lower Gastrointestinal System

Section IV. Diseases/Disorders of the Accessory Organs

Exercises

4 INGESTED POISONS

Exercises

5 NASOGASTRIC INTUBATION

Section I. Preliminary Steps

Section II. Procedure for Inserting the Nasogastric Tube

Section III. Procedure for Removing the Nasogastric Tube

Exercises

6 ABDOMINAL TRAUMA

Exercises

7 HEPATITIS

Exercises

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LESSON 1

ANATOMY AND PHYSIOLOGY OF THE DIGESTIVE SYSTEM

Section I. ANATOMY OF THE DIGESTIVE SYSTEM

1-1. INTRODUCTION

a. Food is Essential to Life. Food is necessary for the chemical reactions that take place in every body cell; for example, formation of new enzymes, cell structures, bone, and all other parts of the body that give the energy to supply the body's needs.

Most of the foods we eat are just too large to pass through the plasma membranes of the cells. The process of breaking down food molecules for the body's cells to use is called digestion, and the organs which work together to perform this function are termed the digestive system.

b. Regulation of Food Intake. How much food we eat is regulated by two sensations--hunger and appetite. When we crave food in general, we are experiencing hunger, and when we want a specific food, the correct term is appetite. The stronger of the two sensations is hunger which is accompanied by a stronger feeling of discomfort.

The hypothalamus is the control center for food intake. There are a cluster of nerve cells in the lateral hypothalamus (the appetite center) which send impulses causing a person to want to eat. Another cluster of nerve cells tell the person he has had enough.

These cells are located in the medial hypothalamus and called the satiety center. A person's food intake must be regulated to prevent the digestive tract from becoming too full. The upper digestive tract expands to let food enter the tract. Receptors in the walls of the digestive tract are stimulated and send signals to the satiety center, signals that tell the person he is full. He stops taking in food, and the contents of the digestive tract are digested.

c. Digestive Processes. Five basic activities help the digestive system prepare for use by the cells. These activities are ingestion, peristalsis, digestion, absorption, and defecation.

(1) Ingestion. Taking into the body of food, drink, or medicines by mouth.

(2) Peristalsis. Alternating contraction and relaxation of the walls of a tubular structure by which food is move along the digestive tract.

(3) Digestion. The processes by which food is broken down chemically and mechanically for the body's use. In chemical digestion, catabolic reactions break down protein, lipid, and large carbohydrate molecules we have eaten into smaller molecules which can be used by the body's cells. Mechanical digestion refers to the various movements which aid chemical digestion. Examples of such movements are the chewing of food by teeth and the churning of food by the smooth muscles of the stomach and the small intestine.

(4) Absorption. The taking up of digested food from the digestive tract into the cardiovascular and lymphatic systems for distribution to the body's cells.

(5) Defecation. The discharge of indigestible substances from the body.

d. Organization of Digestive Organs. The digestive organs are commonly divided into two main groups: the gastrointestinal (GI) tract (also called the alimentary canal) and the accessory structures.

(1) The gastrointestinal (GI) tract. The gastrointestinal tract is a continuous tube which extends from the mouth to the anus and which runs through the ventral body cavity. The tube is about 30 feet long in a cadaver and a little shorter in a living person because the tube's wall muscles are toned. From the time food is eaten until it is digested and eliminated, it is in the gastrointestinal tract. Muscular contractions in the walls of the GI tract churn the food breaking it into usable molecules. The organs which make up the gastrointestinal tract are the mouth, pharynx, esophagus, stomach, small intestine, and large intestine. These organs are sometimes referred to as the primary organs of the digestive system.

(2) Accessory structures. These structures include the teeth, tongue, salivary glands, liver, gallbladder, and pancreas. Except for the teeth and the tongue, all the structures lie outside the continuous tube which is the gastrointestinal tract. Secretions that aid in the chemical breakdown of food are produced and stored by these structures. Eventually, such secretions are released into the GI tract through ducts in the body.

(3) General histology (structure of tissues). The gastrointestinal wall has the same basic tissue arrangement from the mouth to the anus. There are four coats (also called tunics): the mucosa, submucosa, muscularis, and serosa (adventitia). The mucosa, the inner tissue layer, contains blood and lymph vessels which carry nutrients to other tissues and also protects the rest of the body against disease. The submucosa is made up of loose connective tissue and binds the mucosa to the next layer which is the muscularis. Skeletal muscle in the muscularis of the mouth, pharynx, and esophagus produce voluntary swallowing. The outer layer of tissue is the serosa.

NOTE: Remember that the GI tract carries food which often contains bacteria.

From The Gastrointestinal System

 

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