It does, very slowly. That’s essentially what a bruise healing is: the blood breaks down, and the breakdown products are scavenged, partially recycled, and removed by the body.
But the bloodstream is under pressure. Ordinarily we measure blood pressure in millimeters of mercury for historical reasons, but if we measure it in the more familiar kilopascal, we find that normal blood pressure is around 11-16 kPa, that is, about 11-16% of atmospheric pressure (normal air pressure is ~100 kPa). That’s a substantial amount of pressure – it’s about the same amount of pressure you can exert by blowing air out of your mouth as hard as you can – and to get fluid back into such a pressurized environment, you would need a pump. The body does not have one to use. So even if it had a way of collecting the blood quickly, which it also doesn’t, it would have no way to get it back into circulation.
“Internal bleeding” refers to the situation where blood is escaping the circulatory system within the body. It’s caused by the same exact thing as external bleeding, which is broken veins/arteries. Just because the blood is still inside your body doesn’t mean it has a way to get back into your circulatory system where it’s actually needed.
Blood is a connective tissue connecting nutrients, oxygen, etc from the organ of origin to the organ in need. Like roads in a city. Internal bleeding is like a city scraping up all its blacktop and paving the business district. Suddenly it isn’t where it is useful and now nothing is getting where it needs to go
The circulatory system is like your bodies highway system. Red Blood Cells the transport trucks. Imagine damage to your blood vessels like a terrible blizzard during an earthquake. An overpass collapses and transport trucks and cars go careening off onto the streets below. The wreckage immense, doing damage to the other streets, any cars or buildings in the area, and the clean up (or re-absorption as you put it) takes weeks. The city (your body) impaired and forced to redirect traffic the entire time, and most of the wreckage is essentially useless. The goods being transported in the trucks never reached the destination they were meant for, there are less cars and trucks overall to do the tranportation work, and anything reabsorbed is at best recycled.
Blood vessels keep blood in by making it hard for blood to pass through the vessel walls and get out. As a side effect, blood can’t easily get back in either.
The problem with internal bleeding is that if blood leaves the blood vessels, it isn’t going where it needs to go.
ETA: your brain uses a lot of oxygen, which it gets from your blood. If you bleed into your chest cavity, that’s less blood that can go to your brain. It’s the same case with all your organs and a bunch of other stuff your blood carries.
Sure it can, eventually… But in the meantime, it’s not going where it’s supposed to be.
The circulatory system isn’t like an engine where oil collects in the sump and is picked up from a pool at the bottom – it’s a closed system like an AC unit and pipes lose pressure the whole thing stops working
To take some very simplistic examples:
No blood in the muscles? Can’t use those… No blood in the lungs? looks like you’re not getting any oxygen or getting rid of any CO2. No blood in the brain? Doesn’t take long to damage it permanently or fatally.
Eventually it does get reabsorbed, but that happens slowly (it’s how bruises heal).
The bigger problem with internal bleeding is that if blood is going where it shouldn’t be, it means it’s not going where it should be, and it’s leaving the circulatory system, so you get the same problem as bleeding out: there’s less and less blood circulating.
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