[@Keksalot] Don't worry, it's no trouble. They're good questions to ask. That said, I don't know the exact answers to them, but as far as metabolism goes, I'd assume the answer is "magic demon virus handles it" - assuming blood they've drained is stored at all, which from the way drinking blood is described it probably isn't, it'd probably be contained in the vampire's existing blood vessels and converted via magic into energy, both to fuel the vampire's continued ability to do things (by making the cells do stuff they'd normally do, or by just keeping them from decaying whilst the body functions through magically-powered means) and to keep their soul latched to their body. Circulation is a known "no", since they have no heartbeat, but I can't imagine filling the abdominal cavity with blood would help them in any functional capacity, nor would tearing out their "non-vital" organs, even if they're technically vestigial for the undead, and [i]especially[/i] not their bones.

Alternatively, what Jace said. It could be either, neither, or both. As he says, most settings don't go into extreme detail about how vampirism does what it does, and Shadowhunters is no exception.

If it helps for the future, the main question to ask yourself for queries like this is "What reasons exist that other vampires might not do this thing?" For instance, and to give an example with one of your previous questions, "Why might a vampire not tear out their internal organs and fill their abdominal cavity with blood? Because the other internal organs might actually be necessary, there's a risk of bleeding out during that process, and storing lots of blood like that is probably not helpful due to its location and the need to tear open your abdominal cavity again to drink it, especially given the chance that it'll go bad in a place that, whilst not warm, is nonetheless unrefrigerated." If you can't think of any reasons the thing might not be done, then ask the GMs about it to confirm whether there's no particular reason something might not be done by a vampire. Generally speaking, though, vampires generally don't make alterations to their body because they either can't make a given alteration, or because doing so probably isn't going to help them in any way, especially given their tendency to live in clans alongside others of their kind.