BIOREGULATORS. — The individual functions of the organism do not occur in isolation, but are coordinated with one another so that, under physiological conditions, they begin, cease, are strengthened, and are inhibited exclusively in the interest of the entire organism. The result of this coordination is the continuous modulation of individual functions according to the needs of the organism, which vary from moment to moment with changes in internal and environmental conditions (adaptation).
The relationships that must necessarily exist among the various organs so that their functions may be coordinated to maintain the organism in normal conditions are effected by means of the so-called bioregulators. There are different types of these. The first bioregulator to be discovered was the nervous system, which, through its central and peripheral nerves, connects with all other organs and in this way becomes aware of their functional state and can transmit to them excitatory or inhibitory impulses according to the needs of the organism. Until a few decades ago, the nervous system was considered the only bioregulator in existence. Another type of bioregulator is represented by the ensemble of hormones, that is, those substances which, produced by certain organs (endocrine glands), pass into the bloodstream and act on distant organs. The discovery of hormonal bioregulators is relatively recent. The discovery of the first hormone (secretin) dates to 1902, and since then the number of discovered hormones has multiplied, and the study of their action today constitutes one of the most interesting chapters of biochemistry and is among those most fruitful in applications for the benefit of practical medicine.
Alongside these two fundamental types of bioregulators just mentioned, the nervous and the hormonal, there exist others, discovered only in recent years and still under study. These include bioregulators that act within organs or even within the cells that produced them (tissue hormones, isohormones), those that regulate fertilization (gamones), and those that regulate the development of the embryo (organizers). In plants, too, the presence of bioregulators has recently been demonstrated, the best known of which are the auxins, which regulate plant growth.
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