ion moves back from the outlet of system towards its beginning, it is called feedback/back action. As a result the negative feedback (NF) occurs. A "Y" receptor and reciprocate path comprise NF and together with the analyzer-informant and efferent cannels (Stimulator) form a NF loop. Depending on the need and based on the NF information the control block would engage or disengage the functions of controllable SFU as necessary. The difference of this system from the composite SFU lies only in the presence of a "Y" receptor which measures the result of action and reciprocal paths through which the information is transferred from this receptor to the analyzer. The number of active SFU is determined by NF. The NF is realized by means of NF loop which includes the "Y" receptor, reciprocal path, through which information from "Y" receptor is transferred to the analyzer-informant, analyzer proper and efferent channels through which the control block decisions are transferred to the effectors (controllable SFU). Thus, the system, unlike SFU, contains both DPC and NF. Direct positive (Controllable) communication activates the system, while negative feedback determines the number of activated SFU. For example, if larger number of alveolar capillaries in lungs will be opened compared to the number of the alveoli with appropriate gas composition, arterialization of venous blood will be incomplete, and there will be a need to close a part of alveolar capillaries which "wash" by bloodstream the alveoli with gas composition not suitable for gas exchange. If the number of such opened capillaries will be smaller, overloading of pulmonary blood circulation would occur and the pressure in pulmonary artery will increase and there will be a need to open part of alveolar capillaries. In any case the informant of pulmonary blood circulation would snap into action and the control block would decide what part of capillaries needs to be opened or closed. Hence, the diffusion part of vascular channel of pulmonary bloodstream is the system containing simple control block. The goal of the system is that the result of action of "Y" should be equal to the command "M" (Y = M). Actions of system aimed at the achievement of goal are implemented by executive elements. Control block would watch the accuracy of implementation of actions. The control block containing DPC and NF loop is simple. The algorithm of simple control blocks operation is not complex. The NF loop would trace continually the result of performance of executive elements (SFU). If the result of action turns out to be of a larger scale than the preset result, it needs to be reduced, and if the result is of a smaller scale than the preset one it needs to be increased. Control parameters (the "database") are set through the command; for example, what should be the correlation between external influence and the result of action, or what level of the result of action will need to be retained, etc. At th...