Page 164 - Color Atlas Of Pathophysiology (S Silbernagl Et Al, Thieme 2000)

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! Lack of brush-border disaccharidase ! Malabsorption of carbohydrates in the
causes malabsorption of the corresponding small intestine (→ C) means that some of
disaccharide. A lack of lactase, which splits them are metabolized to short-chain fatty
lactose into glucose and galactose, is com- acids and to gases (CO 2 , H 2 ) resulting in dis-
mon. Lactase deficiency, which goes hand in tension and flatulence. If more than 80 g/d
hand with intolerance to milk and lactose- of carbohydrates fail to be absorbed, os-
containing foods, is rarely congenital, but of- mosis-induced watery diarrhea occurs
ten develops after weaning. There are (→ p.150).
marked ethnic differences. ! Malabsorption of fats (→ D) is character-
! Defects of specific mucosal carriers cause ized by fatty stools (steotorrhea) and leads
specific malabsorption. In Hartnup disease, to weight loss from a lack of these high-calo-
for example, there is a specific carrier defect rie components of food. Malabsorption of the
Liver for certain neutral amino acids; in cystinuria fat-soluble vitamins A, D, E, and K occurs
for cationic (basic) amino acids and cystine.
especially if fat malabsorption is caused by a
Stomach, Intestines, peptides is undisturbed, because the mucosa mal formation of micelles (→ D). This is be-
lack of bile salts or by other reasons of abnor-
(The uptake of the affected amino acids as di-
cause these vitamins can only reach the ab-
has its own carrier for dipeptides).
sorbing mucosa in an uninterrupted lipo-
! Global defects of mucosal digestion and
philic milieu for which micelles are essential.
absorption occur in diffuse mucosal diseases,
such as celiac disease, tropical sprue, Crohn’s
If vitamin K deficiency occurs, the glutamyl
clotting factors cannot be γ-carboxylated in
(e.g., with Salmonella), radiation enteritis,
and after resection of large portions of the
the liver, and thus bleeding may occur. Vita-
6 disease, Whipple’s disease, AIDS, infections residues of prothrombin and other blood
small intestine. min D deficiency causes rickets in children
! In addition to alcohol (pancreatic insuffi- and osteomalacia in adults. In vitamin A defi-
ciency, chronic liver disease), a number of ciency hyperkeratosis and night blindness de-
drugs cause malabsorption: colchicine (in- velops.
hibits division of crypt cells and disacchari- ! Malabsorption of the water-soluble vita-
dases), neomycin and similar antibiotics (in- min cobalamine (B 12 ) (for causes, see above)
hibit division of crypt cells and disacchari- and folate (e.g., in global malabsorption or
dases; precipitate bile salts and micellar fat- methotrexate administration) leads to mac-
ty acids), methotrexate (inhibits folate ab- rocytic anemia (→ p. 34), termed pernicious
sorption), cholestyramine (binds bile salts), anemia if there is a cobalamine deficiency,
certain laxatives, biguanides, etc. to glossitis and aphthous ulcers as well as
! Especially in fat absorption, processing neurological defects (nerve degeneration) if
within the mucosal cells (formation of chylo- there is a cobalamine deficiency.
microns) is an important partial step whose ! Iron malabsorption (see also p. 38) leads
disturbance in abetalipoproteinemia (→ to hypochromic anemia.
p. 247) results in fat malabsorption (→ D).
Another cause is lymphatic blockage (lymph-
angiectasia, lymphoma, etc.).
! Finally, malabsorption naturally occurs if
blood flow through the intestine is disturbed
(ischemia, e.g., in vasculitis).
The consequences of malabsorption are
dependent on the kind of malabsorbed sub-
stance:
! Malabsorption of proteins (→ C) can lead
to muscular atrophy and weight loss, while
any resulting hypoproteinemia will result in
154 edema (see also p. 235).
Silbernagl/Lang, Color Atlas of Pathophysiology © 2000 Thieme
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