Why is it that when you sprain or injure a bone, it tends to throb alot?

I recently sprained my wrist(minor sprain) though it still throbs like crazy whenever i hang it down. I have broken many bones in my past(fingers, wrists, ankles) and they all did the same. Why is this?Why is it that when you sprain or injure a bone, it tends to throb alot?
attracting attention ,

chuckecheese

ameren missouri