I thought vitae was a unit of potency not volume although I cannot remember if this is anywhere in RAW. It certainly implies it. 

Vitae seems to be a measure of potency which in an ordinary human corresponds to one unit per pint(ish) of blood -- or ten per human. Some older vampires can store more vitae in their blood (as determined by their generation) but that does not seem to affect the quantity of blood present in the vampire. So, a 7th generation does not contain twice the amount of blood of a 13th. Instead, a pint of their 7th gen blood is worth two vitae.

As for how much blood there is in a vampire, the question is never really answered by RAW as far as I can tell. Vampires are described as paler if hungry. Vampire hit by bullets or slashing damage are shown to splatter blood but never bleed. Neither do they lose "blood points" by blood lose.

I always ruled that when a blood point (aka vitae) is lost, a proportionally equivalent amount of blood was lost -- so half a pint in the case of the 7th gen. This meant that the lower the vitae, the more the vampire looks like a corpse. At 0, they are a shrivelled husk. Thus, the more hungry the vampire the less human they appeared. This is a house rule born of not finding anything in RAW.