Gastroduodenal motor activity

Gastroduodenal motor activity

The motility of the gastrointestinal tract is modulated by its intrinsic nervous system. Critical in this process is the migrat - - ing motor complex (MMC). In the fasting state, and after food has cleared, there is a period of quiescence in the small bowel lasting in the region of 40 minutes (phase I). There follows a series of waves of electrical and motor activity , also lasting about 40 min utes, propagated from the fundus of the stomach in a caudal direction at a rate of about three per minute (phase II). These pass as far the pylorus, but not beyond. Duodenal slow waves are generated in the duodenum at a rate of about 10 per minute, which potentiate into the small bowel. The - amplitude of these contractions increases to a maximum in - phase III, which lasts for about 10 minutes. This 90-minute cycle of activity is then repeated. From the duodenum, the MMC moves distally at 5–10 /uni00A0 cm/min, reaching the terminal ileum after 1.5 hours. Following a meal, the stomach exhibits receptive relax - ation, which allows the proximal stomach to act as a reservoir. Most of the peristaltic activity is found in the distal stomach (the antral mill) and the proximal stomach demonstrates only tonic activity . The pylorus, which is most commonly open, con - - tracts with the peristaltic wav e and allows only a few millilitres of chyme to pass into the duodenum at a time. The antral con - traction against the closed pylorus is important in the milling activity of the stomach. Although the duodenum is capable of generating 10 waves per minute, after a meal it only con - tacts after an antral wave reaches the pylorus. Coordination of the motility of the antrum, pylorus and duodenum means that only small quantities of food reach the small bowel at a - time. This control of gastric emptying can be abolished after g astric surgery , leading to significant symptoms (discussed in Sequelae of peptic ulcer surgery ). -