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.
The duodenum lies at the beginning of the small intestine. Together with the jejunum, and the ileum it forms the small intestine. It is connected to the stomach above and the jejunum below it. When food enters the duodenum, there are multiple feed-back pathways and nervous reflexes that will affect how fast the stomach empties as well as the secretion of other hormones.