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 first part of the small intestine (5-7 m), followed by the jejunum and ileum (in that order); it is also the widest and shortest (25 cm) part of the small intestine. The duodenum is a C-shaped or horseshoe-shaped structure that lies in the upper abdomen near the midline (see the image below).