Riddonkulous

I twist and I turn like a long, winding road, Processing everything you have swallowed and stowed. I map out the journey from the throat to the end, With acid and enzymes to break and to blend. From the burning of reflux to the depths of the gut, I look inside chambers that are usually shut. A scope is my flashlight, the liver my guide, I fix up the troubles that swallow inside. What medical specialty am I?