Gastrointestinal System



Gastrointestinal System


Common diseases of the esophagus, the stomach, and the small and large intestines include functional disorders, inflammation, infections, and tumors.





Nontumorous Diseases of the Small and Large Intestines


Congenital disorders of the intestines are uncommon and are discussed in Table 4-1 and malabsorption syndromes in Table 4-4.



Infectious enterocolitis (IEC) and food poisoning are diseases of worldwide prevalence characterized by diarrhea and (gastro)intestinal inflammation with increased intestinal secretion and reduced absorption. Mucosal necrosis, hemorrhage, and ulceration develop according to local or systemic toxic influences of the causative agent. Loss of fluid and toxic side effects are especially dangerous for children and the elderly. Etiologic agents frequently identified in acute IEC are viruses (rotavirus, Norwalk agent) and bacteria (enterotoxic Escherichia coli); however, in up to 50% of cases, no organism is identified. In the United States, the most common causative agents in fatal IEC, in order of frequency, are Salmonellae, Listeria, Toxoplasma, Norwalk agent, E. coli, and Campylobacter.


The most common vascular lesions of the small and large bowel are phlebectases (hemorrhoids) and ischemic and thrombotic disorders; less common are local vasculitis accompanying systemic vasculitis and collagen-vascular diseases as well as angiodysplasia.



Tumors of the Small and Large Intestines


Benign tumors of the intestines are most often epithelial in nature and are referred to clinically as polyps. They usually are rare in the small intestine but frequent in the large intestine (colonic polyps increase in frequency from approximately 20% before the age of 40 years to 50% beyond the age of 60 years). The clinical entity polyp is subclassified pathologically into polyps as such (i.e., reactive lesions, such as hyperplastic, hamartomatous, or inflammatory polyps) and adenomas (i.e., benign neoplastic lesions, such as tubular or villous adenomas). The pathologic entity polyp does not possess malignant potential, whereas adenomas (also referred to as adenomatous polyps) do. Depending on their size, there is a 10% to 15% risk of cancer development within 5 years in tubular adenomas and a 30% to 40% risk in villous adenomas. The risk of malignancy increases with the number of adenomas; especially prone for malignant change are familial polyposis syndromes (e.g., Gardner syndrome) in which the occurrence of cancer approaches 100% by midlife.


Other more infrequent benign lesions of the intestines are lipomas, leiomyomas, neurofibroma, and hemangioma, which may also impress clinically as polyps and rather rarely may cause complications (e.g., erosion, bleeding and anemia, obstruction, or intussusception).


Malignant tumors of the small intestine account for less than 0.1% of tumors diagnosed at autopsy, or less than 5% of all gastrointestinal (GI) tumors. They consist primarily of adenocarcinomas, malignant lymphomas, and carcinoid tumors (CTs). Even less frequent are stromal tumors, such as leiomyosarcoma and gastrointestinal stromal tumors (GIST). By contrast, adenocarcinomas of the colon and the rectum are among the most common malignant tumors in the Western world, accounting for approximately 15% of all cancer deaths in the United States (approximately 150,000 new cases diagnosed every year, with a peak incidence at the age of 60-70 years). Other malignant tumors of the large bowel include CTs and, rarely, malignant lymphomas and (anal) melanomas. As in the small intestine, stromal tumors occasionally occur.





TABLE 4-4


PATHOGENESIS OF MALABSORPTION SYNDROMES*








































Major Cause of MAS Specific Disturbance
Defective intraluminal digestion Deficiency in bile or pancreaticenzymes or both
Inactivation of pancreatic enzymes by excess gastric acid
Disturbed resorption by bacterial overgrowth
Defective intestinal digestion Deficiency in hydrolytic enzymes and peptidases secondary to bacterial overgrowth with mucosal atrophy
Defective transepithelial transport Abetalipoproteinemia
Reduction in resorptive surface Gluten-sensitive enteropathy (celiac sprue)
Crohn disease
After surgery (gastrectomy, bypass, short bowel)
Specific infections Whipple disease
Tropical sprue
Parasitic infestations
Tuberculosis
Malignancies Intestinal lymphoma (IPSID)


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*IPSID indicates immunoproliferative small intestinal disease; MAS, malabsorption syndrome.





Jun 28, 2017 | Posted by in PATHOLOGY & LABORATORY MEDICINE | Comments Off on Gastrointestinal System
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