On changing position from lying down to standing position there is a drop in 10 mm of Hg. Immediately he recovered by 8 mm Hg leaving behind 2 mm Hg. The gain for baroreceptor system for the control of BP is

Ans. (b) 4(Ref: Guyton, 13th ed/p.7)The formula for calculating gain is,Gain=ErrorCorrection So here, Gain =8/2=4The degree of effectiveness with which a control system maintains constant conditions is determined by the GAIN of the negative feedbackAny system which leaves error is not 100 percent effective in preventing changeImagine what would happen if the denominator becomes zero???.The ratio becomes infinity.Such a principle is called INFINITE FEEDBACK GAIN PRINCIPLE. It is the KIDNEY which displays infinite feedback gain principle in regulation of BP which means it won't leave any error during correction of BP.It exactly brings BP back to the previous value