Humoral Regulation

the coordination of physiological and biochemical processes effected through the body’s fluids (blood, lymph, interstitial fluid) by means of biologically active substances (metabolites, hormones, parahor-mones, ions) released by cells, organs, and tissues in the course of their vital activities.

In highly developed animals and man, humoral regulation is subject to nervous regulation and together with it forms a single system of neurohumoral regulation. Metabolic products act not only directly on effector organs but also on the endings of sensory nerves (chemoreceptors) and nerve centers, causing various reactions humorally or reflexively. For example, if intensification of physical exertion elevates the CO₂ level in the blood, this elevated level itself excites the respiratory center, which leads to an intensification of respiration and elimination of the excess CO₂ from the body. Humoral transmission of nerve impulses by chemical substances (so-called mediators) occurs in the central and peripheral nervous systems. The products of intermediate metabolism, along with hormones, play an important role in humoral regulation. The biological activity of body fluids is a function of the ratio of the catecholamine content (epinephrine, norepinephrine, their precursors, and catabolites), acetylcholine, histamine, serotonin, other biogenic amines, and some polypeptides and amino acids, as well as a function of the state of the enzymatic systems, the presence of activators and inhibitors, the ion and trace-element content, and so forth. The theory of humoral regulation was formulated by a number of Soviet scientists (V. Ia. Danilevskii, A. F. Samoilov, K. M. Bykov, L. S. Shtern) and foreign scientists (the Austrian O. Loewi, the American W. Cannon).