Porth's Essentials of Pathophysiology, 4e

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Gastrointestinal and Hepatobiliary Function

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surface of the intestine. They include disorders such as celiac disease and Crohn disease. Disorders of lymphatic transport interfere with the transport of absorbed lipids. The process can be interrupted by congenital defects, neoplasms, trauma, and selected infectious diseases. Malabsorption Syndrome In many malabsorption disorders one or more of the intestinal absorptive processes predominate, but more than one usually contributes to the manifestations of the disorder. As a result, malabsorption syndromes resem- ble each other more than they differ. Weakness, muscle wasting, and weight loss occur despite normal or exces- sive caloric intake. General symptoms include diarrhea (from nutri- ent malabsorption and intestinal secretion), flatu- lence, bloating, abdominal cramps, and weight loss. A hallmark of malabsorption is steatorrhea, characterized

by fatty, bulky, yellow-gray, and foul-smelling stools. Along with loss of fat in the stools, there is failure to absorb the fat-soluble vitamins. This can lead to easy bruising and bleeding because of vitamin K deficiency, as well as bone pain and a predisposition to the devel- opment of fractures and tetany from vitamin D and cal- cium deficiency. In addition, there may be macrocytic anemia and peripheral neuropathy as a result of vitamin B 12 deficiency. Table 29-2 describes the signs and symp- toms of impaired absorption of dietary constituents. Celiac Disease Celiac disease, also known as celiac sprue and gluten- sensitive enteropathy, is an immune-mediated disorder triggered by ingestion of gluten-containing grains (wheat, barley, and rye). 53–56 Until recently, celiac disease was considered to be a rare malabsorption syndrome that manifested during early childhood, but today it is known

TABLE 29-2 Sites of and Requirements for Absorption of Dietary Constituents and Manifestations of Malabsorption Dietary Constituent Site of Absorption Requirements Manifestation

Water and electrolytes

Mainly small bowel

Osmotic gradient

Diarrhea Dehydration Cramps

Fat

Upper jejunum

Pancreatic lipase Bile salts Functioning lymphatic channels Amylase Maltase Isomaltase α -dextrins

Weight loss Steatorrhea Fat-soluble vitamin deficiency

Carbohydrates Starch

Small intestine

Diarrhea Flatulence Abdominal discomfort

Sucrose Lactose Maltose Fructose

Small intestine Small intestine Small intestine Small intestine Small intestine

Sucrase Lactase Maltase

Protein

Pancreatic enzymes (e.g., trypsin, chymotrypsin, elastin)

Loss of muscle mass Weakness Edema

Vitamins A

Upper jejunum

Bile salts

Night blindness Dry eyes Corneal irritation

Folic acid

Duodenum and jejunum Absorptive; may be impaired by some drugs (i.e., anticonvulsants)

Cheilosis Glossitis Megaloblastic anemia Glossitis Neuropathy Megaloblastic anemia

B 12

Ileum

Intrinsic factor

D

Upper jejunum

Bile salts

Bone pain Fractures Tetany Uncertain Bone pain Fractures Tetany

E K

Upper jejunum Upper jejunum

Bile salts Bile salts

Easy bruising and bleeding

Calcium

Duodenum

Vitamin D and parathyroid hormone

Iron

Duodenum and jejunum Normal pH

Iron-deficiency anemia Glossitis

(hydrochloric acid secretion)