Gastroenterology MCQ Answer 27

Answer: b, c

When a loop of bowel is obstructed, intestinal gas and fluid accumulate. Approximately 80% of the gas seen on plane abdominal radiographs is attributable to swallowed air. In the setting of acute pain and anxiety, patients with intestinal obstruction may swallow excessive amounts of air. Fluid accumulates intraluminally with open-or closed-loop small intestinal obstruction due to a number of factors. Experimental studies and clinical investigations demonstrate that elevation of luminal pressures above 20 cm H2O inhibits absorption and stimulates secretion of salt and water into the lumen proximal to an obstruction. In closed-loop obstruction, luminal pressures may exceed 50 cm H2O and may account for a substantial proportion of a luminal fluid accumulation. In simple, open-loop obstruction, distention of the lumen by gas rarely leads to a luminal pressure higher than 8–12 cm H2O. Thus, in open-loop obstruction, the contributions of high luminal pressures to hypersecretion may not be important. In response to heightened luminal pressure, total blood flow to the bowel may initially increase. Subsequently, however, blood flow to the bowel is compromised as luminal pressures increase, bacteria invade, and inflammation leads to edema within the bowel wall. Accumulation of gas and fluid in the obstructed lumen also leads to changes in myoelectrical function in the gut, proximal and distal to the obstructed segment. In response to distension, the obstructed segment itself may dilate, a process known as “receptive relaxation.” At sites proximal and distal to the obstruction, changes in myoelectrical activity are time-dependent. Initially, there may be intense periods of activity and peristalsis. Subsequently, myoelectrical activity is diminished and interdigestive migrating myoelectrical complex (MMC) is replaced by ineffectual and seemingly disorganized clusters of contractions.

Category: Gastroenterology MCQs