Murphy E A, Renie W A
Am J Med Genet. 1984 May;18(1):99-113. doi: 10.1002/ajmg.1320180114.
A zero-order homeostatic process is one in which the corrective force a has sign opposite to that of what the displacement from the homing value was one lag (L) time earlier, but is unrelated to magnitude of displacement. The properties of a zero-order process are considered in some detail. Its stable state is an oscillation with a period of 4L and a maximum amplitude of aL. It is suggested that this property is exploited in evolution for intrinsically rhythmical processes, and several examples (respiration, menstruation, and heart beat) are discussed. The parameters may be modulated by an ancillary cybernetic (retreat) circuit and hence the properties of the oscillation controlled as need be. Zero-order oscillation has means of conserving information through phase shifts. Also, when it is combined with a linear cybernetic process (with restoration constant b), it prevents information in the latter from dying out, even if Lb is less than pi/2 (which in a pure linear process would ensure extinction of all signs of perturbation). A further elaboration is the Dilman process of zero order in which there is a threshold of displacement below which homeostatic responses are not evoked. The merits of the value of the threshold are discussed. The properties of the zero-order process with a first-order retreat function furnish a tentative explanation for why hormonal homeostasis does not operate directly through the pituitary but involves the hypothalamus and intermediate hormone-releasing factors.
校正力a的符号与归巢值的位移在一个延迟（L）时间之前的符号相反，但与位移的大小无关。我们将较为详细地考虑零阶过程的特性。其稳定状态是一种周期为4L、最大振幅为aL的振荡。有人认为，在进化过程中，这种特性被用于内在节律性过程，文中讨论了几个例子（呼吸、月经和心跳）。这些参数可以由一个辅助控制论（反馈）回路进行调节，从而根据需要控制振荡的特性。零阶振荡具有通过相移来保存信息的方式。此外，当它与一个线性控制论过程（恢复常数为b）相结合时，即使Lb小于π/2（在纯线性过程中，这将确保所有扰动迹象的消失），它也能防止后者中的信息消失。进一步阐述的是零阶的迪尔曼过程，其中存在一个位移阈值，低于该阈值不会引发稳态反应。文中讨论了该阈值取值的优点。具有一阶反馈函数的零阶过程的特性，为激素稳态为何不直接通过垂体起作用，而是涉及下丘脑和中间激素释放因子提供了一个初步解释。
