Sense of course of a working life first attested 1803. v. 1590s, to charge at a tournament, from career (n.). The meaning move rapidly, run at full speed (1640s) is from the image of a horse passing a career on the jousting field, etc. Related: Careered; careering.
Contractions of the stomach muscle, called peristaltic waves, grind, crush and mix the food producing a liquefied substance called chyme.. The pyloric sphincter separates the stomach from the duodenum. This valve keeps food and gastric juices in the stomach until liquefied enough to proceed into the duodenum.
When the stomach fills with food, the elastic muscle and rugal folds stretch allowing the stomach to expand. Food enters the stomach from the esophagus. The esophageal sphincter, or valve, separates the stomach from the esophagus. This valve keeps food and gastric juices from returning back into the esophagus.