Bowel Obstruction
A mechanical block or a paralysed bowel both stop luminal contents moving forward, so gas and fluid accumulate proximally, and the cardinal features (distension, vomiting, absolute constipation) follow directly from where along the gut that stoppage sits.
First principles
Obstruction is either something physically blocking the lumen or the bowel forgetting how to peristalse
Bowel obstruction has two fundamentally different mechanisms that produce a similar picture. Mechanical obstruction is a physical blockage (adhesions from previous surgery, a hernia trapping a loop, a tumour narrowing the lumen, or a volvulus twisting it) against which the bowel initially contracts forcefully, producing colic. Functional obstruction (ileus) is bowel that is anatomically patent but not peristalsing, usually after abdominal surgery, with electrolyte disturbance, or with intra-abdominal inflammation; there is no colic because there is nothing to contract against. Distinguishing the two changes management completely: mechanical obstruction may need surgery, ileus usually resolves with supportive care.
Educational content pending clinical review. Not medical advice.