Medical Device Loading Systems, Devices, and Methods

A cartridge insertion system, comprising:

• a chassis supporting a fluid circuit, the chassis having a forward end with key pins projecting from said forward end and a rear end;
• a medical treatment device having a slot opening closed by doors having a major dimension, the doors having key openings spaced apart a same distance as said key pins such that when said chassis is pushed toward said slot opening, said key pins enter said key openings before said forward end meets said doors;
• latches on said medical treatment device immediately behind said key openings, each of the latches configured to pivot on a latch axis;
• the doors pivoting on door axes parallel to the major dimension;
• and
• the latches and the doors being configured to interfere such that when the latches are closed in a home position, prior to contact with said key pins, the doors are prevented from opening and such that when said key pins push against said latches, the latches move to one side, releasing the doors.