Well now you got me wondering about vampire anatomy in a distinctly non-sexy way.
According to Wikipedia, the human stomach can hold up to ~ a liter of food. If these vampires can drink two quarts (a little under two liters) of blood without physical discomfort, and still pass for human...
They definitely can get intoxicated by drinking from an intoxicated human, so they probably need a liver. If they can eat humans' food and not have trouble with it, presumably they have something much like a human's digestive tract. Maybe they can do without a pancreas somehow, and smaller lungs?
















