Each human has two of these, unless removed or destroyed.
Each kidney accounts for 50% of a person's blood filtration. While it is possible to survive with only one, if the remaining one is destroyed the person will die.
Kidneys can be removed from humans be sold or transplanted into somebody else. Warning! Removing a kidney from a guest or prisoner will decrease faction goodwill by 20 points down to the cap of -100. It always, even if it's from your own colonist, gives the victim -30 mood for ? time and the other colonists -5 mood for ? time. unless the organ was damaged? also is there a damage breaking point, or will just any damage not give mood penalties anymore?