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 diaphragm is the muscle wall that separates the stomach from the chest. The diaphragm helps keep acid from coming up into the esophagus. When you have a hiatal hernia, it's easier for the acid to come up. The leaking of acid from the stomach into the esophagus is called gastroesophageal reflux disease (GERD).