Leif,
the caption says
"U-2, equipped with ski landing gear and sanitation cassettes by Schcherbakov, each of which could house two wounded. This plane has also an engine cowl which protects cylinders from hypothermia"
Another photo:
http://crimso.msk.ru/Images6/MA/MA00-1/20-1.jpg
"This variant was called P-2. Schcherbakov cassettes were suspended under the lower wings, two seats each. Wounded were sitting back to back, their heads were at the leading edge of wings and legs were placed in a streamlined body of the cassette. Thus, the plane could carry one lying wounded and five sitting"
Nothing on hatches. Probably these were service ones or kind of entry doors