I've been drafting a fantasy world with dragons, obviously becuase it's a fantasy world. I was thinking about the science behind flying animals and how reptiles and birds are sort of related, yadda yadda. But I was thinking about how a dragon might be fore resistant and/or can breath fire. Surely its insides would burn up. Not to mention, if they're reptiles they're exothermic, so being high in the mountains would make them cold. But then I thought, maybe if they had fire/heat inside them as a defense mechanism and as means to have internal body temperature, that could sort of explain that. But fire is... hot? So that would kill it, unless maybe it had some sort of fire resistant cells/tissue. I thought maybe a metallic plating could make sense for their internals/scales?
But I'm no biologist, so I'm not sure any of that makes any sense or is plausible.