Mechanics and Regulation of Gastric Emptying

Publisher Website
Google Scholar
Abstract
Gastric emptying of a meal begins as soon as any considerable part at the gastric contents become fluid enough to pass the pylorus. Once started it proceeds rhythmically, a small amount being evacuated once in about 20 seconds in man. Regulation of emptying begins as soon as the evacuated material has accumulated in the intestine to the point where any one of numerous stimuli associated with the chyme reaches threshold value. These stimuli are comprised in the volume and chemical composition of the chyme. The chemical stimuli listed in the order of inhibitory potency when in the concentrations usually encountered are: fats, fatty acids, proteoses, peptones, amino acids, sugars and other products of starch digestion and hydrogen ions between pH 3.5 and 6.0; also effective are osmotically active substances and nonspecific irritants. These stimuli decrease the tone and peristaltic activity of the stomach, thus reducing the pressure gradient which develops with each gastric cycle and which is responsible for the passage of fluid through the pylorus. With the more powerful inhibitors, for example fat, the gradient may be reversed and duodenal contents will then regurgitate into the stomach. The inhibitory effect of the regulatory stimuli is exerted through a reflex involving the vagus nerves (the enterogastric reflex) or through a hormone (enterogastrone) released into the blood from the intestinal mucous membrane, or both. Products of protein digestion, acid and nonspecific irritants act mainly through the reflex mechanism, fats and carbohydrates through the hormone, enterogastrone; however, there may be a reflex element in the effect of the latter group and there is probably a hormonal component in the effect of HC1. The pyloric sphincter plays a part by preventing regurgitation of duodenal contents into the stomach. It also contracts rhythmically to limit the volume evacuated at each cycle; but there is as yet no evidence that this function is utilized in regulating the overall rate of emptying.