Replying to Calculus explanation (cartesian ----> spherical coordinates)

i was in a calc 4 class last year (i was on the quarter system) and we were learning really quickly about double and triple integrals and some vector and multivariable stuff. one thing that my professor skipped over that i don't understand is why you add p^sin(phi)dpdthetadphi when switching from cartesian to spherical coordinates. can anyone explain this to me? does it have something to do with a thing called jacobian?