In complex malabsorption syndromes isn’t just the absorption of one nutrient impaired but rather multiple. It occurs in:
- Chronic pancreatitis
- Coeliac syndrome
- Cystic fibrosis
- Short bowel syndrome
- Bacterial overgrowth
Prolonged hyposecretion of pancreatic juice is most commonly seen in chronic pancreatitis but also in lasting starvation, cachexia, protein deficiency and sclerosis of the pancreatic artery. In severe hyposecretion is one third of ingested protein lost and 40-70% of fats. Carbohydrates are least affected.
Coeliac syndrome, also called gluten-sensitive enteropathy, is a condition where ingestion of gluten causes inflammation of the small intestinal mucosa. In severe cases does it result in villous atrophy, which impairs the mucosas ability to absorb properly. The absorption of nutrients, vitamins, minerals and bile acid is very low. Frequent diarrhoea-like stool often occurs.
It’s a genetic condition and therefore present at birth. The first symptom is often growth retardation around age 2. It’s associated with the HLA-DQ2 and HLA-DQ8 alleles. The pathogenesis involves the conversion of the gluten protein to a protein called gliadin by an enzyme called transglutaminase. Gliadin then evokes an immune reaction.
Treatment is by a life-long gluten-free diet.
Cystic fibrosis is a genetic disorder that affects chloride ion transport through the ion channel CFTR. It may affect all organs as chloride transport is present in almost every tissue. Mucoviscidosis is a term often used to describe the dysfunction of the pancreas due to cystic fibrosis.
Most of the damage associated with cystic fibrosis is due to how secretions are become much thicker, which blocks passages like ducts. This also occurs in the pancreas, where the pancreatic duct is obstructed, leading to chronic pancreatitis.
The name cystic fibrosis comes from the fact that cysts develop in tissues that have underwent fibrosis, especially the pancreas.
Short bowel syndrome
Short bowel syndrome is a malabsorption disorder that follows the removal of parts of the small intestine, often due to Crohn’s disease or volvulus. It usually presents when there is less than 2 meters of healthy small intestine left, down from the average 6 meters.
The loss of small intestine leads to a reduction in absorptive area. Consequences include:
- Diarrhoea and steatorrhea– less bile acid is reabsorbed and therefore reaches the distal intestines. Secretory diarrhoea follows.
- Weight loss
- B12 deficiency – if the terminal ileum is lost
- Osteoporosis or osteomalacia – due to malabsorption of calcium and vitamin D
- Protein/energy malnutrition
The small bowel normally contains <105/mL aerobic bacteria and no anaerobic bacteria. The colon normally contains 108/mL aerobic bacteria and 1010/mL anaerobic bacteria. Multiple factors contribute to prevent overgrowth of bacteria in the small intestine:
- Ileocoecal valve
- Gastric acid, bile and mucin
- Normal bacteria flora
- Secreted IgA
Hypomotility, hypochlorhydria, antibiotic treatment or formation of diverticula may allow for bacterial overgrowth. These bacteria produce ammonia and deconjugate bile acids, which reduces their reabsorption. This causes secretory diarrhoea. Bacteria also digest nutrients, leading to complex malabsorption and gas formation.
Inflammation of the small intestine (enteritis) or of both intestines (enterocolitis) due to an infective agent leads to complex malabsorption by the same mechanisms as above.
7. Specific malabsorption syndromes (level or substrate of disorder)
9. Diarrhoea. Causes, pathophysiological forms, consequences