Physiology—the Discipline

PHYSIOLOGY—THE DISCIPLINE RICHARD CHARLES MARSH* In the years I have studied physiology, I have frequently been asked what the field includes. The answer for the layman or novice is that physiology is the study of function in living systems. I shall define anew the discipline ofphysiology by offering a classifying schema. To study a living system, one has to choose a system of function on which to focus. This schema enumerates ten systems offunction which are all familiar to physiologists: skeletal, muscular, nervous, circulatory, respiratory, renal, digestive, excretory, endocrine, and reproductive. Levels ofcomplexity identify places in the anatomical hierarchy ofthe system offunction studied. The system offunction is seldom researched at all levels at the same time. Six levels are suggested here: (i) subcell: those functions specific to atoms, molecules, macromolecules, organelle, etc., on up to but excluding whole cells; (2) cell: those functions carried out by the whole cell but not solely by its parts (a cell can function beyond the limits of the summated subcellular functions); (3) tissue: those functions specific to cell aggregates, cell circuits, and other such cell groupings; (4) organ: those functions specific to ordered tissue formed into bodies which can carry out new functions by virtue ofthat order; (5) organ system : those functions relying on more than one organ for their manifestation ; and (6) organism: those functions specific to the body as a whole. Physiological phenomena occur at different levels of complexity. Mitochondrial oxidative phosphorylation is a subcellular (membrane-enzyme) function. Tissue perfusion is an organ system function. A further dimension ofany study is the viewpoint, that is, the format ofthe intellectual perspective. I interject the word "format" to emphasize * Department of Physiology, University of California, Los Angeles, California 90024. 369 that the topic is independent of the viewpoint. Four viewpoints can be distinguished: (i) biochemical: treats the elements and atomic relations of matter and the various compounds ofthe elements in living systems; (2) biophysical: treats the laws and phenomena of living systems, but especially ofthe forces and general properties ofmatter; (3) biomathematical : treats quantities, magnitudes, and forms, and their relationships, attributes , etc., by the use ofnumbers and symbols in living systems; and (4) bioengineering: the maneuvering or managing of biological information into plans or constructions. Biochemical, biophysical, and biomathematical viewpoints tend to focus on mechanism. The bioengineering perspective tends to focus on input-output. In terms of the "black box" concept , the input-output analysis renders formulations and constructions regarding the box. For the purposes of this discussion, it is emphasized that these are viewpoints ofphysiology, not disciplines in themselves. The system of function, level of complexity, and viewpoint can be designated as three dimensions (aspects) ofphysiology. A matrix ofthree dimensions can be represented. This matrix is 10 X 6 X 4 because there are ten systems of functions (SF's), six levels of complexity (LC's), and four viewpoints (VP's). The three dimensions relate only to the number ofSF's, LC's, and VP's. For instance, in a study which questions the relationships of the renal, respiratory, and circulatory systems, SF = 3. In a study dealing with skeletal, muscular, and nervous systems, SF = 3 as well. In a study specifically on the cellular level, LC = 1. To be counted as an LC, all SF's have to be studied at that LC. In another effort with a singular LC of organ system, again LC = 1. Viewpoints are computed in the same manner. To be counted as a VP, all SF's in the study and all LC's in the study have to be perceived from that viewpoint. The following equation represents the matrix. It has three dimensions with a 10 X 6 X 4 display. There are 240 divisions ofstudy. The matrix is: [SFf1LC,-,VP4], where i,j, and k are integers and i = 1 to 10,y = 1 to 6, and k = ? to 4. Some interesting facts arise from such a matrix. It is apparent that any study possible in physiology can be located in the matrix, classified therein, and then designated by a three-digit code. All data, facts, conclusions, theories, papers, books, etc., can be classified and coded likewise. The matrix is easily transformed into a...