  A notion of biologic system or just a system implies a functional wholeness
of comprising system components. Positive and negative feedback are the
examples of how the idea to unite anatomical elements in the whole functional
structure was successfully used in practice to explain regulatory mechanisms in
biology and medicine. There are numerous examples of functional and metabolic
pathways which are not regulated by feedback loops and have a structure of
reciprocal relationships. Expressed in the matrix form positive feedback,
negative feedback, and reciprocal links represent three basis elements of a Lie
algebra sl(2,R)of a special linear group SL(2,R). It is proposed that the
mathematical group structure can be realized through the three regulatory
elements playing a role of a functional basis of biologic systems. The
structure of the basis elements endows the space of biological variables with
indefinite metric. Metric structure resembles Minkowski's space-time (+, -, -)
making the carrier spaces of biologic variables and the space of
transformations inhomogeneous. It endows biologic systems with a rich
functional structure, giving the regulatory elements special differentiating
features to form steady autonomous subsystems reducible to one-dimensional
components.
