Why do people vomit when they have a bowel obstruction?

Blocked pipes. The stomach and small bowel secrete gallons of fluid every day that is reabsorbed, aiding nutrient absorption. If the small intestine is obstructed, this fluid upstream from the blockage accumulates and, left with no place to go, backs up into the stomach. Also, we all swallow air--this furthers the upstream distention. A key sign of successful resolution is gas +/- stool out the bottom.

Related Questions

Why do you vomit with bowel obstruction?

Its gotta go somewhe. If it can't go down because of an obstruction it's going to go back up.
Becuase you are obst. The contents of your bowel has no place else to go.

Why do people vomit with a bowel obstruction?

Blocked pipes. The stomach and small bowel secrete gallons of fluid every day that is reabsorbed, aiding nutrient absorption. If the small intestine is obstructed, this fluid upstream from the blockage accumulates and, left with no place to go, backs up into the stomach. Also, we all swallow air--this furthers the upstream distention. A key sign of successful resolution is gas +/- stool out the bottom.

I'm curious as to why do I vomit with bowel obstruction?

Because. Intestinal contents backs up due to obstruction, like your clogged faucet.

I passed out watery stool and vomited after few hours. And I have been burping a lot. Is this some kind of bowel obstruction?

Gastroenteritis. The symptoms and their acuity argue more towards acute gastroenteritis than a bowel obstruction. This could be food-borne or viral. If you're passing some sort of stool and gas, it would be unlikely that you have a bowel obstruction. Give this a few days, see how it goes. If you become very distended in the abdomen, seek immediate medical attention.

Had gastric bypass in '04, bowel obstruction in '09 & hernia in '12. Surgeries for each. 10/14 I started with upper ab pain, 10/15 vomited bile. Pain's constant 3/4 at times 8/10. What should I do?

See your Doctor NOW. I would see your doctor urgently or consider going to the er-or at least call your surgeon and let them know-now.
See your surgeon. Vomiting bile after a gastric bypass is unusual, but does happen. You could be having intermittent symptoms of another bowel obstruction, internal hernia, or intussusception. May need some tests to help make the diagnosis. Ideally, see the surgeon that performed the gastric bypass.