The models of osmolarity and volemia are proposed in this paper. These two different models, characterized by a different time scale, represent a typical example of embedded physiological feedback control in medicine. Extensive simulation tests have been performed, showing that the models agree with the findings published in the literature of endocrine physiology and with medical practice. As a relevant example of application of the models, the diabetes insipidus pathology was considered. In the case of center insipidus diabetes, it is possible to predict effects of a therapy, giving out synthetic ADH for restoring homeostatic conditions. This model may be a helping tool in the study and development of micro-infusors with sensor and controllers embedded able to release a controlled drug quantity, accorded to the patient and optimized for avoiding hyper or ipoconcentrations of plasma ADH hormone.