Malabsorption

pathology subject that contains some diseases that can cause malabsorption

1. MALABSORPTION

2. Definition: Defective absorption of fats, fat- and water-soluble vitamins, proteins , carbohydrates, electrolytes and minerals and water

3. Characterize by: weight loss, anorexia, abdominal distention, borborygmi , muscle wasting steatorrhea

4. Types of diarrhea Secretory diarrhea is characterized by isotonic stool and persists during fasting. Osmotic diarrhea, e.g in lactase deficiency , due to osmotic forces exerted by unabsorbed luminal solutes. Malabsorptive diarrhea caused by inadequate nutrient absorption is associated with steatorrhea . Exudative diarrhea is due to inflammatory disease and characterized by purulent, bloody stools that continue during fasting.

5. Malabsorption results from disturbance in ( 1) I ntraluminal digestion , in which proteins, carbohydrates, and fats are broken down into absorbable forms. ( 2) T erminal digestion , which involves the hydrolysis of carbohydrates and peptides by disaccharidases and peptidases, in the brush border of the small intestinal mucosa. ( 3) T ransepithelial transport , in which nutrients, fluid, and electrolytes are transported across and processed within the small intestinal epithelium. ( 4) L ymphatic transport of absorbed lipids .

6. Cystic Fibrosis Defects in intestinal and pancreatic ductal chloride ion secretion. Leads to interference with bicarbonate, sodium & water secretion resulting in defective luminal hydration. Meconium ileus, which is present in up to 10% of newborns with cystic fibrosis. Intraductal concretions Obstruction , lowgrade chronic autodigestion of the pancreas exocrine pancreatic insufficiency .

7. Celiac Disease celiac disease is often associated with anemia (due to iron deficiency and B12 and folate deficiency), diarrhea, bloating , and fatigue. silent celiac disease: positive serology and villous atrophy without symptoms. latent celiac disease: positive serology is not accompanied by villous atrophy.

8. Pathogenesis

9. Microscopy affecting the proximal more than the distal small intestine ? The histopathologic picture is characterized by increased numbers of intraepithelial CD8+ T lymphocytes, with intraepithelian lymphocytosis , crypt hyperplasia, and villous atrophy. increased numbers of plasma cells, mast cells, and eosinophils , especially within the upper part of the lamina propria . increase in the number of intraepithelial lymphocytes particularly within the villus, is a marker of mild forms of celiac disease.

10. Environmental (Tropical) Enteropathy syndrome of stunted growth and impaired intestinal function that is common in developing countries. Many pathogens are endemic in these communities, but no single infectious agent has been linked to these diarrheal episodes. histologic features are more similar to those of severe celiac disease. a cycle of mucosal injury, malnutrition, infection , and inflammation.

11. Lactase ( Disaccharidase ) Deficiency lactase, are located in the apical brush border membrane of the villous absorptive epithelial cells . the defect is biochemical, biopsies are generally unremarkable.

12. types: Congenital lactase deficiency is an autosomal recessive disorder caused by a mutation in the gene encoding lactase. explosive diarrhea with watery, frothy stools and abdominal distention after milk ingestion. Symptoms abate when exposure to milk and milk products is terminated, • Acquired lactase deficiency is caused by downregulation of lactase gene expression. Onset of acquired lactase deficiency is sometimes associated with enteric viral or bacterial infections

13. Abetalipoproteinemia autosomal recessive disease characterized by an inability to secrete triglyceride-rich lipoproteins. An example of a transepithelial transport defect . Mutation in the microsomal triglyceride transfer protein renders enterocytes unable to export lipoprotein and free fatty acids. As a result, monoglycerides and triglycerides accumulate within the epithelial cells. Lipid vacuoles in small intestinal epithelial cells particularly after a fatty meal. Abetalipoproteinemia manifests in infancy, and the clinical picture is dominated by failure to thrive, diarrhea, and steatorrhea . leads to deficiencies of fat-soluble vitamins, and lipid defects in plasma membranes acanthocytic red cell (spur cells) in peripheral blood smears.

14. Burr cell

15. Irritable Bowel Syndrome Chronic and relapsing abdominal pain, bloating, and changes in bowel habits including diarrhea and constipation. The pathogenesis is poorly defined but involves psychologic stressors , diet, and abnormal gastrointestinal motility. No gross or microscopic abnormalities are found . between 20 and 40 years of age, more in female. Diagnosis by exclusion. The prognosis for IBS is most closely related to symptom duration, with longer duration correlating with reduced likelihood of improvement.

16. Microscopic Colitis Microscopic colitis encompasses two entities, collagenous colitis and lymphocytic colitis. Both of these idiopathic diseases manifest with chronic, non bloody , watery diarrhea without weight loss. Findings on radiologic and endoscopic studies typically are normal.

17. Collagenous colitis, Seen in middle-aged and older women. characterized by the presence of a dense subepithelial collagen layer, increased numbers of intraepithelial lymphocytes and a mixed inflammatory infiltrate within the lamina propria .

18. Lymphocytic colitis Histologically similar , but the subepithelial collagen layer is of normal thickness and the increase in intraepithelial lymphocytes. Lymphocytic colitis is associated with celiac and autoimmune diseases, including thyroiditis, arthritis , and autoimmune or lymphocytic gastritis.

19. Graft-Versus-Host Disease Graft-versus-host disease occurs after allogeneic hematopoietic stem cell transplantation. The small bowel and colon are involved in most cases . Due to targeting of antigens on the recipient’s epithelial cells by donor T cells ,. however the lymphocytic infiltrate in the lamina propria is typically sparse. histologic finding :epithelial apoptosis , particularly of crypt cells. Intestinal graft-versus-host disease often manifests as a watery diarrhea.

20. Whipple disease Rare systemic infection. involve any organ of the body but principally affects the intestine, CNS, and joints. Cause by a gram-positive, Tropheryma whippelii . more in males in the fourth to fifth decades of life. causes a malabsorptive syndrome occasionally accompanied by lymphadenopathy, hyperpigmentation, polyarthritis, and central nervous system complaints. Response to antibiotic therapy is usually prompt. relapses are common.

21. The hallmark of Whipple disease is a small intestinal mucosa laden with distended periodic acid-Schiff-positive macrophages in the lamina propria .