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 is the upper part of the small intestine. The wall of the stomach consists of several layers. The mucosa membrane is the inner-most layer. The mucosa produces enzymes and stomach acids used to kill bacteria and break down the food. Surrounding the mucosa is a muscle layer that produces contractions to mix and churn the food. The serosa provides the outer wrapping of the stomach.