9.8.20 Lesson #3 Digestion/Stomach

Today we’ll cover a few details about what happens in the stomach for the digestion process. Let’s pick up where we left off in the north to south process with our food going down the esophagus and entering the stomach via the little hatch called the cardiac sphincter.

The pH of our stomachs should be between 1.5 - 3 (NTA slides 2019). That is about as acidic as battery acid and can dissolve metal! To keep the acid where it needs to be and not break down the rest of our innards, we have 3 main layers that make up the stomach organ like a three layered balloon. The center of these layers is made of three layers of muscles. The inner layer is a thick mucosal barrier that secretes important elements for digestion as well as protects us from the acid. This inner layer is thick with folds like bunching up a piece of cloth.

In these folds are gastric glands that produce pepsinogen, hydrochloric acid, intrinsic factor, and gastrin, together called gastric juice (yum!). Pepsinogen is an inactive enzyme that must have hydrochloric acid (HCl) to activate it. Then call pepsin, it works to break down protein. The acidity of HCl also helps break down food particles as the muscles of the stomach work to slosh everything back and forth in what is called propulsion and retropulsion. Intrinsic factor is important for B12 absorption, which is needed for red blood cell production. Gastrin is a hormone that is released into the bloodstream to stimulate more production of gastric juice!

All this is sloshed around in our stomach until the particles are small enough to pass through the pyloric sphincter at the lower end of the stomach (Tortora and Derrickson 2015). Carbs digest the quickest with fats digesting the slowest. (This is why protein and fats can make us feel full for longer.) At this point the acidic smoothie of our meal is called chyme. Only small portions can be let through the pyloric sphincter at a time. The goal is to empty our stomachs in 2-4 hours, but the digestion process still has about 15 feet to go before it is all said and done!