Eli5: how does your belly know what’s food and what’s water… break it apart and disperse the nutrients throughout your body?
In: Biology
It isn’t able to tell anything apart. The acid and enzymes in your stomach try to work on everything but each enzyme is only really able to break down a specific molecule so they can’t do much to the ones they are not supposed to work on.
As for water there isn’t much your stomach can do to it, water is already a simple and stable molecule that can be readily absorbed by your body.
Your belly doesn’t really do much with water, water just passes through you guts directly into your bloodstream without needing to be processed or broken down. For everything else, your stomach and your intestines have many many different proteins and chemicals in them to break down all kinds of food and get as much nutrients from it as it can. Then once these nutrients are broken down into their basic blocks, they also just pass through the intestines into the blood stream just like water.
And it is your blood that naturally spreads through your whole body, pumped onward by your heart, that properly disperses the water and nutrients.
It has a bunch of chemicals called enzymes that react with certain food molecules to turn both food and water into a mix of a few different energy chemicals and water. Your intestine then absorbs all this by having different little intakes for sugar and water.
Your stomach doesn’t absorb much, since it’s lined with mucus and filled with acid. Your stomach’s job is to make your food into sludge, with help from your tongue, teeth, and saliva above.
Saliva has enzymes that break down starch into smaller sugars.
Strong acid in your stomach breaks down proteins and carbohydrates into smaller molecules. Some stuff is absorbed here but not much.
Once sufficiently goopified and simplified, it goes to the small intestine. There, it gets further mashed and broken down as a slew of enzymes and bile from the liver go to town to break down what’s left, including fats and even lactose in some people. Good bacteria feast and throw off vitamins and neurotransmitters. Tiny absorbing projections put your red blood cells in contact with these simplified nutrients and the red blood cells rush them off to where they can be accepted, processed, and used – to the liver, marrow, cells, and tissue everywhere. The good stuff basically travels through your blood bound to red blood cells and such until something goes “gimmie, I can use that”.
Next, the liquidy and bile rich goop goes to the large intestine. A lot of what’s left is inorganics (minerals, vitamins, ions) and starches that you can’t process directly. Some of these starches are broken down by good bacteria who feast and throw off more beneficial stuff and organic compounds, some starches just remain and help keep hold of water and sweep through. Water, vitamins, and minerals – all inorganic – are absorbed here. Bile also has waste transported from the liver, so this moves through as waste.
What’s left over is bacteria-processed and fermented starches as organics, inorganics, toxic waste from your liver, fats that didn’t get processed, sugars that didn’t get processed like lactose if you’re intolerant, some water, bacteria, and fiber.
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