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.
Bile and stomach acid can reflux into the esophagus when another muscular valve, the lower esophageal sphincter, malfunctions. The lower esophageal sphincter separates the esophagus and stomach. The valve normally opens just long enough to allow food to pass into the stomach.