The gastrointestinal tract extends from the pharynx to the esophagus, stomach, intestines, and rectum. Each anatomic segment of the gastrointestinal tract has specialized functions, which serve to either conduct, store, or digest food.

The esophagus is a 20 cm tube that delivers food to the stomach via peristalsis. The stomach is a muscular organ that secrets acids and enzymes (e.g., pepsin) that help to breakdown complex foods into essential building blocks (e.g., amino acids and simple sugars). The adult stomach holds a volume of about one liter. With the aide of pancreatic secretions, the small intestine serves to solubilize and extract (absorb) nutrients into the bloodstream. Loops of the small bowel (duodenum, jejunum, ileum) fill most of the abdominal cavity. The large intestine serves to concentrate fecal material and absorb water. Resident bacteria contribute to the digestive process.

Diseases of the gastrointestinal tract may be broadly categorized as congenital, nutritional, inflammatory, vascular, or neoplastic. Major diseases of the esophagus include hiatal hernia, reflux esophagitis, Barrett esophagus, esophageal varices, and esophageal cancer. Major diseases of the stomach include acute erosive gastritis, chronic nonerosive gastritis, peptic ulcer disease, and stomach cancer. Major diseases of the large intestine include pseudomembranous colitis, diverticulosis, Crohn disease, ulcerative colitis, ischemic colitis, benign adenomatous polyps, adenomatous polyposis coli, and adenocarcinoma of the colon.

Here are the Key Points:

1. Failure of muscular function in the esophagus causes difficult in swallowing (dysphagia).

2. Achalasia is characterized by the absence of peristalsis in the body of the esophagus, associated with the lack of ganglion cells in the myenteric plexus.

3. Hiatal hernia represents a herniation of the stomach through an enlarged esophageal hiatus (opening) in the diaphragm. It is a common acquired condition of unknown cause.

4. Reflux esophagitis refers to esophageal injury caused by regurgitation of gastric contents. It is commonly seen in association with sliding hiatal hernia.

5. Barrett esophagus represents columnar metaplasia of squamous epithelium in response to injury produced by chronic gastroesophageal reflux. The majority of patients with Barrett esophagus regularly drink alcohol and smoke tobacco. As might be expected, Barrett esophagus carries a serious risk of malignant transformation to adenocarcinoma.

6. Esophageal varices are dilated veins immediately beneath the mucosa, which are prone to rupture and hemorrhage. They arise in the lower third of the esophagus, virtually always in patients with portal hypertension, secondary to liver cirrhosis.

7. Most cancers of the esophagus are histologically identified as squamous cell carcinomas. Environmental factors are thought to contribute to the development of this disease.

8. Congenital pyloric stenosis represents a narrowing of the pyloric canal that obstructs the outlet of the stomach. It is the most common cause of abdominal surgery in the first 6 months of life. It is four times more common in males than in females.

9. Acute erosive gastritis is the presence of focal necrosis of the mucosa in an otherwise normal stomach. It is most commonly associated with the intake of aspirin, other nonsteroidal anti-inflammatory agents, and excess alcohol. However, any serious illness that is accompanied by profound physiologic alterations renders the gastric mucosa more vulnerable to erosive gastritis. For example, severe trauma, shock, sepsis, or debilitating chronic disease predisposes to the development of acute erosive gastritis.

10. Chronic nonerosive gastritis refers to chronic inflammation that ranges from mild superficial involvement to severe atrophy. Categories of chronic gastritis include autoimmune, idiopathic (unknown cause), and infectious. Persons with atrophic gastritis have a high incidence of cancer of the stomach.

11. Infectious gastritis is caused by Helicobacter pylori. It is the most common type of chronic gastritis in the United States. H. pylori infection is also associated with peptic ulcer disease of the stomach and duodenum.

12. Peptic ulcer disease refers to breaks in the mucosa of the stomach and proximal duodenum that are produced by the action of gastric secretions. Risk factors for peptic ulcer disease include cigarette smoking, increased gastric secretion of pepsin and hydrochloric acid, aspirin ingestion, chronic infection with Helicobacter pylori and genetic factors.

13. Stomach cancer is more common among persons who eat large amounts of smoked fish and picked vegetables. In this connection, benzpyrene, a potent carcinogen, has been detected in smoked foods. Many gastric cancers originate from epithelium that has undergone intestinal metaplasia.

14. Pseudomembranous colitis is an inflammatory disease of the colon caused by Clostridium difficile. The organism produces toxins that damage the colonic mucosa. Most cases of pseudomembranous colitis are today associated with antibiotic therapy. 15. Diverticulosis is an acquired herniation of the mucosa and submucosa through the muscular layers of the colon. Diverticulosis has been demonstrated in nearly one half of persons in the US older than the age of 60 years. Diverticulitis represents inflammation of a diverticulum caused by retention of fecal material. It is generally asymptomatic, but may present with episodic abdominal pain.

15. Crohn disease is a chronic, granulatomatus inflammatory disease of the bowel of unknown etiology. The disease usually appears in adolescents or young adults. The inflammation involves all layers of the bowel wall - transmural inflammation. The most frequent symptoms are abdominal pain, diarrhea and recurrent fever.

16. Ulcerative colitis is a disease of the large intestine characterized by chronic diarrhea and rectal bleeding, with a pattern of exacerbations and remissions. Ulcerative colitis usually extends from the most distal part of the rectum for a variable distance proximally. Persons with longstanding ulcerative colitis have a higher risk of developing colon cancer.

17. Ischemic colitis is most often caused by atherosclerosis. Thus, this disease usually occurs in persons older than age of 50 years.

18. Adenomatous polyps are adenomas of the colon that arise from the mucosal epithelium and project into the lumen of the gut. Most colon cancers are thought to arise in preexisting adenomatous polyps.

19. Adenomatous polyposis coli is inherited as an autosomal dominant trait. It is characterized by the progressive development of multiple adenomatous polyps of the colon. Carcinoma is inevitable unless a total colectomy is performed.

20. In the US and Western world, colorectal cancer is second in incidence only to carcinoma of the lung in men, and is third after breast and lung cancer in women.

The following images illustrate Key Morphological Concepts:

1. This is an example of ESOPHAGEAL CANCER arising in the distal esophagus. Risk factors for esophageal cancer include excessive consumption of alcohol, cigarette smoking, carcinogens (nitrosamines and aniline dyes), achalaia, and esophageal strictures. The large majority of esophageal cancers are identified as squamous cell carcinomas.

2. This is an example of a chronic GASTRIC PEPTIC ULCER. This patient experienced epigastric pain just after meals, with nausea and vomiting. His stool was positive for occult blood. On gross examination it is often difficult to distinguish a chronic peptic ulcer from an ulcerating gastric carcinoma.

3. This is an example of a DUODENAL PEPTIC ULCER. The most common serious complication of peptic ulcer disease is bleeding. Patients may present with iron deficiency anemia.

4. This is a histologic section through a DUODENAL PEPTIC ULCER. The surface is covered by a fibrinous exudate containing neutrophils, with hyperemic granulation tissue below. Perforation is life-threatening complication of active peptic ulcer disease, which occurs in about 5% of patients.

5. This is an example of ULCERATIVE COLITIS. This inflammatory bowel disease primarily affects the rectum and proximal colon. This patient had persistent bloody diarrhea for four weeks prior to admission, associated with cramps and fatigue.

6. This is an example of benign ADENOMATOUS POLYPS of the colon. Adenomatous polyps arise from the mucosal epithelium and project into the lumen of the gut. They are classified as either tubular (pedunculated) or villous (sessile) adenomas. Most colon cancers are thought to arise in preexisting adenomatous polyps.