Dude, yeah, I asked a urologist a few years ago, when I was afraid of a little bump on my nut. I told him about my dick bleeding once from jelquing, and he didn't know what that was, and I told him what it was, and he was like "oh, so its like pumping?".
Needless to say, he only knew about pumping.
Most urologists don't know shit.
Doctors won't know anything signifigant. All of the hours spent researching about the nature of ligaments, hormones, etc is the best information, and much of it is posted on this forum.
Dr Lin, actionlove.com, while scoffed at by many, probably knows the most about how the penis works. I learned a lot from him, but I do not agree with many of his ways, such as no stretching, or very little protein or exercise.
There is good information about hormones and dht receptors, though. And that holding a hard erection for 30 minutes can increase the dht in the receptors, thus leading to more possible growth.