Only intelligent brains can solve this :-
There is a pair of bear - shaped organs ‘P’ in human body towards the back, just above the waist. A waste product ‘Q’ formed by the decomposition of unused proteins in the liver is brought into organ ‘P’ through blood. The numerous tiny filters ‘R’ present inside the organ ‘P’ cleans the dirty blood by removing the waste product ‘Q’. If due to some reason, the organs P of a person stop functioning completely. The persons blood can be cleaned periodically by a process ‘S’ so as to save his life. What are P,Q,R and S?