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The term “malabsorption” denotes disorders in which there is a disruption of digestion and nutrient absorption. The clinical and laboratory manifestations of malabsorption are summarized in Table 15–11.

Table 15–11.Clinical manifestations and laboratory findings in malabsorption of various nutrients.

Pathogenesis

Normal digestion and absorption may be divided into three phases: intraluminal, mucosal, and absorptive.

A. Intraluminal Phase

Dietary fats, proteins, and carbohydrates are hydrolyzed and solubilized by pancreatic and biliary secretions. Fats are broken down by pancreatic lipase to monoglycerides and fatty acids that form micelles with bile salts. Micelles are important for the solubilization and absorption of fat-soluble vitamins (A, D, E, K). Proteins are hydrolyzed by pancreatic proteases to di- and tripeptides and amino acids. Impaired intraluminal digestion may be caused by insufficient intraluminal concentrations of pancreatic enzymes or bile salts. These conditions will not be covered in detail here (see Chapter 16-01).

Pancreatic insufficiency may be caused by chronic pancreatitis, cystic fibrosis, or pancreatic cancer. Pancreatic enzymes may also be inactivated within the intestinal lumen by acid hypersecretion (Zollinger-Ellison syndrome). Significant pancreatic enzyme insufficiency generally results in significant steatorrhea (due to malabsorption of triglycerides)—often more than 20–40 g/24 h—resulting in weight loss, gaseous distention and flatulence, and large, greasy, foul-smelling stools. The digestion of proteins and carbohydrates is affected to a far lesser degree and is generally not clinically significant. Because micellar function and intestinal absorption are normal, signs of other nutrient or vitamin deficiencies are rare.

Decreased bile salt concentrations may be due to biliary obstruction or cholestatic liver diseases. Because bile salts are resorbed in the terminal ileum, resection or disease of this area (eg, Crohn disease) can lead to insufficient intraluminal bile salts. Finally, destruction or loss of bile salts may be caused ...

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