# Pathophysiology

Pathophysiology

Classic teaching points to a reflex inhibition of  intestinal motility caused by deranged ANS inputs. This teaching, which fits nicely with basic ‘fight and flight’ concepts of  increased sympathetic signalling and parasympathetic withdrawal during trauma (including surgery), has been superseded by the concept of  a two-phase response. First, an immediate stress response, mediated by spinal reflexes and activation of the hypothalamic–pituitary–adrenal axis (HPA) axis, leads to a decrease or abolition of  motility . This is then followed very rapidly by evolution of  a more prolonged inflammatory response in the bowel wall itself, mediated first by mast cell activation and thence recruitment and activation of  macro - phages and neutrophils ( Figure 73.3 ). These lead to inhibition of  enteric neuronal and smooth muscle function as well as further e ff ects on spinal reflexes. 

Nomenclature
Ileus (including postoperative ileus)
Acute colonic pseudo-obstruction
Intestinal pseudo-obstruction
Megacolon
Constipation and irritable bowel syndrome

Pathophysiology

This is poorly understood. It can however be appreciated that, like ileus, risk factors reflect both ‘imbalanced’ extrinsic autonomic innervation and an ‘inflammatory’ state. Evidence to support the former is provided by the response to anticho - linesterase pharmacological therapy .