Initially the valve where locked on bacteria counts similar to the final valve that opens to the heart. But during play testing players got stuck with not enough bacteria to pass the threshold for opening (the idea was that the bacteria could force their way in with number), so we scrapped that. However making some valves clause in a more autonomous way is a good idea, definitely noted.
The white blood cells used to be everywhere, but at moments caused an unplayable drop in frame rate (when a lot of them started to collide), due to time constraints we where unable to optimize them enough, so we placed them in the main chambers and behind some valves where the infectable cells are. A lot of optimization went into the environment to get a good balance in tessellation density for meaty movement closely and proper distortions far away.
Thanks for the feedback, it is very helpful!