How your gut works
So here's what I'm doing while you're tucking into a plate of ribs: The upper section of my bean-shaped body, or fundus, serves as a pantry, storing food until it travels through my central region, the corpus, to be processed by my lower half, or antrum. That's where all the actual work of digestion takes place. And it is work. I have to flex my muscles (yes, I do have them! They form the muscularis, the third layer of about five I have) in a rhythmic, agitating motion, like a washing machine, to mix your food with acid and digestive juices that break it down into its basic components: proteins, sugars, and fats.

It's a big job, but I have help from the 35 million acid-secreting glands in my lining. On a normal day, I produce two to three liters of gastric juices. Dropping all that acid (hey, a little stomach humor!) doesn't just help with digestion; it also kills bacteria, protecting you from infection. Normally, a healthy layer of mucus over my lining keeps me safe from the acid's harmful effects, but from time to time, you aggravate that layer--with a bacterial infection, or by popping aspirin like it's Pez--and acid can erode through. Too much of that kind of damage could mean--gulp--an ulcer. Every stomach's worst nightmare.

Anyway, after I've churned the food into a nice, mushy mixture called chyme, I squeeze it every 20 seconds through the pyloric sphincter, a strong ring of smooth muscle at the end of my food-passing canal, into the duodenum, the first part of the small intestine. It typically takes me several hours to work through an entire meal, and if it's really big or fatty, I have to put in overtime.

The only time I ever stop is when your brain releases the stress hormone cortisol. That "fight-or-flight" response either shuts down digestion completely, making me feel full of butterflies, or speeds it up to the point that you feel sick. That's what stress will do to you, though.