Abdominal problems are common in critically ill patients, either as the primary indication for admission or, more commonly, as a reflection of underlying illness. The interaction between abdominal organs and critical illness are complex and can present in a variety of ways. 

In order to manage abdominal problems effectively, a comprehensive initial diagnostic work up, together with an understanding of normal physiology and early assessment of disease severity (aetiological factors and predisposing conditions) is required, followed by continuous monitoring in anticipation of complications. This global approach should form the basis of patient management.  

 This is first of four modules dedicated to abdominal problems in critically ill patients. The key objective of this module is to describe normal physiology of GI tract, and how this is affected by critical illness.