Page 32 - To keep a balance in disease specific intestinal insufficiency. Diagnostics and practical nutritional aspects - Nicolette Wierdsma

Chapter 3
Introduction in intestinal failure
Intestinal failure (IF) is nowadays defined as the reduction of gut function below the minimum necessary for the absorption of macronutrients or water and electrolytes, such that intravenous supplementation is required to maintain health or growth. Reduction of gut absorptive function that doesn’t require intravenous supplementation to maintain health and/or growth, can be considered as ‘intestinal insufficiency’. On the basis of onset, metabolic and expected outcome criteria, intestinal failure is classified into three types. Besides it can be classified into five major pathophysiological conditions, which may originate from various gastrointestinal or systemic diseases i.e. short bowel, intestinal fistula, intestinal dismotility, mechanical obstruction and extensive small bowel mucosal disease (1). As a consequence major nutritional problems as malnutrition may occur. Malnutrition is, in turn, related to infectious complications, in-hospital duration and morbidity. It has been stated that adequate nutrition and drug supply, is essential for recovery (2). For the diagnosis and (nutritional) treatment of IF or intestinal insufficiency, knowledge on (patho)physiology of the gastrointestinal (GI) tract, as well as its assessment, is necessary.
In this chapter, an introduction in GI (patho)physiology will be provided and availability, precision, accuracy, clinical applicability and (dis)advantages of various tests on intestinal function, including digestion, absorption, motility, assimilation or intestinal barrier will be summarized.
(Patho)physiology of the GI tract
Physiology
The gut is the largest surface directly interacting between internal and external milieus. It has two major functions: first digestion and absorption of nutrients, and secondly, immune response against a wide variety of antigenic challenges (i.e. forming a selective, semi-permeable intestinal barrier for food components and -other- immunological challenges).
Regulatory mechanisms of the intestinal tract encompasses production of hormones like gastrin, secretin, cholecystokinin (CCK), ghrelin, peptide YY, and somatostatin. They stimulate digestive enzyme production, secretion of
30