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The Digestive System

Digestion is an important process that involves breaking down food and drink into small molecules that can be transported and used by the cells of the body. The digestive system consists of a one-way track, called the gastrointestinal (GI) tract, that food travels through. At various points of the GI tract, digestion, absorption, and elimination occur. Each portion has been structured to perform a specific function.

The GI tract includes the mouth, esophagus, stomach, small intestine, large intestine or colon, rectum, and anus. These organs contain a layer of tissue called the mucosa that is responsible for creating digestive juices, such as enzymes, that are capable of breaking down food. In addition to the mucosa layer there is also a tissue layer of smooth muscle that assists in moving food through the GI tract called the muscularis mucosae. The rhythmic contraction and relaxation of this smooth muscle layer is called peristalsis.

In addition to the GI tract, there are also two solid organs that

assist with digestion by creating and releasing substances into http://denverdigestive.com/art/DigestiveSystem.jpg the GI tract. The pancreas produces several digestive enzymes, while the liver is responsible for creating bile needed to break down fat. An additional accessory organ is the gallbladder that stores the bile produced by the liver.

The Process of Digestion

Step

Process

1Once food enters the mouth, salivary glands produce saliva that contains amylase. Amylase begins the digestion of starch and carbohydrates.

2From the mouth, food is pushed down the esophagus by swallowing. The food then passes through the

cardiac sphincter into the stomach. The cardiac sphincter prevents the contents of the stomach from moving back up the esophagus.

3Within the stomach, digestive glands within the lining of the stomach produce acid and pepsin to break

down proteins. A thick layer of mucus is also released to protect the stomach from the acid.

4The stomach is a muscular pouch that contracts and releases to “mix up” the food and digestive juices of the stomach much like a washing machine. Once the food is properly mixed, the stomach pushes the

contents through the pyloric sphincter into the first part of the small intestine, called the duodenum.

5The liver, pancreas, and gallbladder are attached to the duodenum through ducts and release additional digestive juices into the small intestine. These include bile to emulsify fats, amylase to further break down carbohydrates, lipase to break down lipids, and trypsin to further break down proteins.

6As the contents travel through the small intestine, they are absorbed through small projections on the surface of the intestines called villi. Each villi is connected to a capillary so, as molecules diffuse through the villi, they are transferred directly into the blood stream to be taken to the cells of the body.

7Eventually, any contents that are left and have not been absorbed by the small intestine are pushed through the ileocecal valve into the colon.

8As the contents move through the colon, water is removed and the leftover contents become feces that are expelled through the rectum and anus during a bowel movement.

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Digestive Disorders

There are many diseases and disorders associated with the digestive system. Some of the most important aspects of digestive disorders are the prevalence, healthcare costs, and mortality. Digestive disorders cost the U.S. approximately $141.8 billion dollars in 2004. The following chart summarizes the impact of the most common digestive disorders in the United States in 2004.

Digestive

Description

Diagnosis

Healthcare &

Annual

Disorder

Hospital Visits

Mortality

Prevalence

Rate

Constipation

Infrequent bowel movements

63 million

6.9 million

137

Diverticulitis

Inflammation of small pouches of the

3.2 million

2.2 million

3,372

intestines

Gallstones

Deposits that form in the gallbladder

20 million

2.4 million

1,092

Gastroesophageal

Stomach contents leak back up

60 million

21.4 million

1,150

Reflux (GERD)

through the esophagus

GI Infections

May be bacterial, viral, or fungal

211 million

2.7 million

4,396

Hemorrhoids

Swollen veins in the rectum or anus

75% 45+

3.5 million

14

Abdominal

Intestines protrude through the

4.7 million

3.7 million

1,663

Hernia

abdominal wall

Inflammatory Bowel

Inflammation of the intestinal lining

359,000

1.2 million

622

Disease (IBD)

Irritable Bowel

Irritation of the intestinal lining

15.3 million

3.2 million

20

Syndrome (IBS)

Liver Disease

Liver inflammation and tissue damage

2.6 million

3.1 million

36,090

Pancreatitis

Inflammation of the pancreas

1.1 million

454,000

3,480

Peptic Ulcers

Sores in the lining of the stomach

14.5 million

1.9 million

3,000

Colitis

Sores and inflammation of the colon

619,000

798,000

311

Viral Hepatitis

Inflammation of the liver caused by the

5.4 million

3.9 million

5,298

hepatitis virus

Diagnostic Tests for Digestive Disorders There are many diagnostic tests for digestive disorders. Biopsy samples, gastric juice samples, or stool samples can be used to recognize whether there may be a digestive source for a patient’s symptoms. Following lab tests that may signify a digestive disorder, imaging of the GI tract can be used. The

most effective diagnostic procedures involve using an endoscope to view portions of the GI tract with a camera. When this process is done through the rectum to view the colon, it is called a colonoscopy. When this process is done through the mouth to

view the esophagus, stomach, and/or duodenum, it http://www.merckmanuals.com/media/home/figures/GI_d

is called an EGD or an esophagogastroduodenoscopy.	igestive_tract_endoscope.gif

Upper and lower GI series can also create radiographic images of the GI tract using a contrast dye, such as barium. The images can show blockages, strictures, or other issues that may exist with the passage of food through the intestines. Using these imaging techniques, healthcare specialists are able to view and identify inflammation, ulcers, growths, and bleeding.

NIH. 2008. Your Digestive System and How it Works. National Institutes of Health (NIH), National Digestive Diseases Information Clearinghouse (NDDIC), NIH Publication No. 08-2681, http://digestive.niddk.nih.gov/ddiseases/pubs/yrdd/

NIH. 2010. Digestive Diseases Statistics for the United States. No. 10-3873,

http://digestive.niddk.nih.gov/statistics/statistics.aspx#ack

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