++
The assimilation of ingested nutrients involves a complex integrated
process of digestion and absorption with subsequent transport of
the breakdown products across the intestinal mucosa into the systemic circulation.
Normal digestion and absorption is discussed in Chapter 381. The term malabsorption is
broadly used to characterize abnormalities of both digestion and
absorption. The schema in Table 408-1 lists
the major pathogenic mechanisms of various specific malabsorptive
disorders that are generally due to disorders in luminal digestion,
mucosal function, or lymphatic transport. Malabsorption may involve
multiple nutrients (as occurs with celiac disease or pancreatic
insufficiency) or only a single molecule (as found in isolated glucose-galactose
malabsorption or vitamin B12 malabsorption). Defects may
be congenital, with onset of symptoms shortly after birth, or acquired,
when the age of onset of symptoms is variable.
++
++
The nutritional consequences of malabsorption vary from mild
or none to severe, with malnutrition and even death. Abnormalities
that impair absorption tend to have greater nutritional consequences than
those impairing digestion. In general, growth is affected, manifest
first by poor weight gain or weight loss and subsequently by linear
growth retardation. Additional consequences may involve specific nutrients
causing conditions such as rickets, osteoporosis, or tetany (vitamin
D and calcium deficiency), coagulation disturbances (vitamin K deficiency),
or anemia (iron, folate, or vitamin B12 deficiency).
++
The evaluation of children with chronic diarrhea is discussed
in Chapter 385. The most prominent clinical
manifestation of children with disorders of digestion or absorption
is diarrhea, except in those conditions involving malabsorption
of a single molecule such as vitamin B12. Diarrhea is often
accompanied by symptoms of abdominal distension, excessive flatulence,
and growth failure in the older infant, toddler, or child. In the
newborn or in early infancy, growth failure may not be evident and
diarrhea may lead to dehydration. Very watery stools may soak into
the diaper and be mistaken for urine, especially in infants with
disorders such as congenital chloride-losing diarrhea.1...