Short-loop negative feedback

Ang II inhibits renin secretion. The inhibition, which results from a direct action of the peptide on the juxtaglomerular cells, forms the basis of a short-loop negative feedback mechanism controlling renin secretion. Interruption of this feedback with inhibitors of the renin-angiotensin system (see below) results in stimulation of renin secretion. 

Set point control Most process control is done with feedback set point control. This means that the controlled variable is measured as an output of the process and the signal is sent back to be compared with a set point (desired value). The generated error is the difference between the set point and the measured value. The error signal is acted on by the controller to make a corrective action which is sent as a command signal to a final control element. In this kind of control loop, the error is corrected only after it has occurred. The closed-loop negative feedback control works best if the distance velocity lag or dead time (DT) is very short. Fig. 17.4 illustrates atypical closed-loop, negative feedback, control loop. 

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