when people are in zero gravity environments, like an astronauts going to space, what keeps all of their organs/blood/liquid inside of their body as opposed to flowing out from their mouth?
Your blood is inside your circulatory system, basically an enclosed system of tubes if you will. It doesn’t connect to the outside world or the rest of your body unless it ruptures.
Your digestive tract is more or less a tunnel through your body from the mouth to the anus. Your mouth opening leads into the oesophagus (food tube), which in turn leads into the stomach. The stomach leads into the intestines which connect back to the outside world by means of the anus.
Something that’s inside your digestive tract can exit through the mouth (throwing up) or by the anus (pooping) but your organs aren’t inside your digestive tract.
Your torso is basically a big cavity in which all of your organs are arranged. Your organs are sort of webbed into place though and the entire cavity is contained within a ‘sack’ so to speak. And as we already pointed out, none of your organs are inside your digestive tract.
Aside from that, zero gravity simple means you’re weightless. There’s no gravity pulling you down but that doesn’t mean there’s a force violently trying to pull your organs out of your mouth. It’s kinda like floating under water. You feel less gravity tugging you downward, well there isn’t any down without gravity when it comes to that.
Gravity isn’t what holds you together. You are held together by connective tissue, which includes tendons, ligaments, and a bunch of stretchy, tough proteins that hold all your cells together.
If this wasn’t the case, people would explode in the manner you envisioned every time they were upside down.