This is answered but I wanted to point out this is why we tested the safety of space travel on dogs and monkeys and not birds. Birds lack peristalsis and rely on gravity to swallow, so they’d die of hunger and dehydration before achieving useful science.
I guess this response assumes you know that that we historically used birds to test for safety, like in mining operations. Dead bird = get the fuck out of the mine.
Our bodies don’t use gravity to move food. The digestive tract is covered in muscles, and has muscular seals (called sphincters) at certain points where backwards flow is considered particularly bad.
The stomach has two sphincters – one at the top, to let new food in; and one at the bottom, to let old food out into the small intestine.
When you swallow new food, the stomach relaxes and the top sphincter opens to let it in. Meanwhile, the food is pushed in by the muscles of the esophagus.
Now, when the stomach is done digesting that food, it keeps the top sphincter closed, opens the bottom sphincter, and pushes the food into the small intestine.
Once there, the walls of the small intestine contract in waves, moving from its entrance to its exit, to move the food along without relying on gravity.
It’s a process called peristalsis. Basically, your stomach muscles will push food into your small intestines. It’s not like there’s simply a gate at the bottom of your stomach that food drops through because of gravity.
Peristalsis is the same reason that you can eat even when you’re standing on your head.
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