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Malabsorption Syndromes

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					Malabsorption is characterized by suboptimal absorption of fats, fat-
soluble and other vitamins, proteins, carbohydrates, electrolytes and
minerals and water. At the most basic level, it is the result of
disturbance of at least one of the following normal digestive functions:
1.    Intraluminal digestion, in which proteins, carbohydrates, and fats
are broken down into assimilable forms. The process begins in the mouth
with saliva, receives a major boost from gastric peptic digestion, and
continues in the small intestine, assisted by the detergent action of
bile salts.


  2. Terminal digestion, which involves the hydrolysis of carbohydrates
and peptides by disaccharidases and peptidases in the brush border of the
small intestinal mucosa.      3. Transepithelial transport, in which
nutrients, fluid and electrolytes are transported across the epithelium
of the small intestine for delivery to the intestinal vasculature.
Absorbed fatty acids are converted to triglycerides and with cholesterol,
are assembled into chylomicrons for delivery to the intestinal lymphatic
system.      This classification is most helpful for disease in which
there is a single, clear cut abnormality. In many malabsorptive
disorders, adefect in one pathophysiologic process predominates, but
others may contribute. Although many causes of malabsorption can be
established clinically, diagnosis may require small intestinal mucosal
biopsy to exclude celiac sprue satisfactorily.       Clinically the
malabsorption syndromes resemble each other more than they differ. The
consequences of malabsorption affect many organ systems, as follows:
Alimentary tract: Diarrhea (both from nutrient malabsorption and from
excessive intestinal secretions) flatus, abdominal pain, weight loss, and
mucositis resulting from vitamin deficiences.      Hematopoietic system:
Anemia from iron, pyridoxine, folate, or vitamin B12 deficiency and
bleeding from vitamin K deficiency.      Musculoskeletal system:
Osteoopenia and tetany from calcium, magnesium, vitamin, and protein
malabsorption.      Endocrine system: Amenorrhea, impotence, and
infertility from generalized malnutrition and hyperparathyroidism from
protracted calcium and vitamin D deficiency.      Epidermis: Purpura and
petechiae from vitamin K deficiency; edema from protein deficiency; and
determines and hyperkeratosis from deficiencies of vitamin A, zinc
essential fatty acids, and niacin      Nervous system: Peripheral
neuropathy from vitamin A vitamin B122 deficiencies.       The passage of
abnormally bulky, forthy, greasy, yellow or gray stools (steatorrhea) is
a prominent feature of malabsorption, accompanied by weight loss, Medical
anorexia, abdominal distention, borborygmi, and muscle wasting. The
malabsorptive disorders most commonly encountered in the United States
are celiac sprue, pancreatic insufficiency, and Crohn disease
Pancreatic insufficiency, primarily from chronic pancreatitis or cystic
fibrosis is a major cause of defective intraluminal digestion. Excessive
growth of normal bacteria within the proximal small intestine (bacterial
overgrowth) also impairs intraluminal digestion and can damage mucosal
epithelial cells. Immunologic deficiencies, inadequate gastric acidity,
and intestinal stasis as from surgical alteration of small intestinal
anotomy, predispose to bacterial overgrowth. Typical features of
defective intraluminal digeswtion are an osmotic diarrhea from undigested
nutrients and steatorrhea, which is excess output of undigested fat in
stool. The intestinal mucosa in bacterial overgrowth either is normal or
is minimally damaged.


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posted:11/24/2011
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