Why would a sandwich progress through your digestive tract even if you ate it standing on your head?

Answer 1

Technically, you would probably find it very difficult to swallow the mouthfuls of sandwich if you were to eat it upside down. (It's not something I've personally tried, but I think gravity helps to get chewed food to progress from your mouth to your oesophagus. Hence it's probably necessary to be the right way up for swallowing).

I would say it might be best to try this when there's no one watching, but there is a choking risk associated with "attempting to swallow whilst upside down", so if you do try it make sure there's someone nearby.

However, let's assume you'd finished eating the sandwich then decided to stand on your head. So, all your meal is chewed and in your stomach. Then you flip upside down:

-To begin with, there is a valve at the top of your stomach, which prevents your food from immediately sloshing back out again. Useful, really.

- Your stomach acid will break down the sandwich into very thin liquidy substance called chyme. This will take around 2-3 hours for a sandwich.

-At the same time, your stomach will make small contractions in order to persuade the chyme to flow downwards to your small intestine. (Likewise, nausea and vomiting is created when there contractions "reverse", coaxing things to go upwards again. ) These contractions would still occur when standing on your head, and hopefully will maintain the normal direction of towards your small intestine.

- The small intestine transports your food via small contractions, but also contains tiny "villi", which sort of "waft" your food along the digestive tract. As far as I'm aware, the direction of "wafting" is not reversible, hence it will still occur if you're upside down, and will head in the normal direction.

- Your sandwich would then reach your large intestine, as normal.

To answer your question more fully, digestion (apart from swallowing) actually relies very little on gravity. Hence why astronauts can eat in space.