Overview of Absorption Disorders
Absorption disorders, also sometimes called malabsorption syndromes, are characterized by problems digesting or absorbing substances (called nutrients) in the diet. Nutrients include vitamins, minerals, carbohydrates (e.g., sugars, starches), fats, and proteins. The term, "absorption disorder," does not refer to a specific diseasein most cases, the disorders are related to another medical condition.
Digestion, which occurs in the gastrointestinal (GI) tract or digestive system, is the process of breaking down food into a form that can be absorbed into the bloodstream and used by the body.
The digestive tract consists of the following organs:
- Esophagus (muscular tube that carries food to the stomach)
- Small intestine (small bowel)
- Large intestine (large bowel or colon)
- Biliary system (i.e., liver, pancreas, gallbladder, bile ducts)
During digestion, most nutrients in food are absorbed in the small intestine. The lining of the small intestine (called the mucosa) contains folds, creases, and finger-like projections (called villi and microvilli) that increase the surface area of the intestinal lining, providing a larger surface with which to absorb nutrients. The mucosa also contains special cells that increase the absorption of nutrients.
Types of Absorption Disorders
There are a number of different types of absorption disorders, most of which result in a decreased ability to absorb nutrients (i.e., malabsorption). Disorders that increase the absorption of certain nutrients include hemochromatosis (increased iron absorption; also called iron overload disease) and Wilson's disease (increased copper absorption).
Common absorption disorders include celiac disease (caused by intolerance to gluten, a protein in wheat, barley, and rye) and lactose intolerance. Lactose intolerance is an inability to break down a sugar in dairy products (lactose). It is caused by a lack of a certain enzyme (called lactase) that helps convert lactose into a form that can be used by the body (i.e., dextrose and galactose).
Lactose intolerance also is called primary or secondary lactase deficiency. Primary lactase deficiency is a common condition that develops over time as the body produces less lactase. This process begins around 2 years of age, but symptoms usually develop much later in life.
Secondary lactase deficiency occurs when damage to the small intestine reduces the production of lactase. Conditions that can cause secondary lactase deficiency include celiac disease and inflammatory bowel disease (e.g., Crohn's disease, ulcerative colitis).
Other types of absorption disorders include tropical sprue and Whipple's disease. Tropical sprue is more common in tropical and subtropical areas of the world, including the Caribbean and Southeast Asia. The exact cause for the condition is unknown, but it may be related to an infection that damages the lining of the small intestine. Symptoms include anemia, diarrhea, weight loss, and malnutrition. Tropical sprue is treated with antibiotics.
Whipple's disease is caused by bacteria (Tropheryma whippelii) that usually infect the small intestine and cause malabsorption. Whipple's disease also can affect other areas of the body (e.g., the joints, eyes, heart, lungs, brain) and cause serious complications.
Patients who have Whipple's disease often experience joint pain and stiffness years before developing intestinal symptoms (e.g., severe diarrhea, GI bleeding, abdominal pain). Treatment involves antibiotics to destroy the bacteria and also may involve intravenous (IV; through a vein) fluid and electrolyte replacement and dietary supplements. Electrolytes are substances (e.g., salts) in the body that are necessary for proper function of vital organs, such as the brain, heart, and kidneys. If left untreated, Whipple's disease can be fatal.