Fundamentals of Biochemistry - Filippovich, Yu. B. 1999

Hormones and Their Role in Metabolism
Nomenclature and Classification of Hormones

Currently, several dozen HORMONES are known. Although the Chemical Nature of the vast majority of them has been elucidated and, consequently, each can be assigned a precise chemical name, trivial names are generally preferred. This is due to two main reasons. First, the chemical nomenclature of many hormones is extraordinarily cumbersome and complex, and in some cases (Peptide and Protein hormones) practically unusable. Second, a trivial name typically reflects either the function or the Water/144.html">Origin of the hormone.

Class="center">Table 27 Classification of Signaling Substances (Chemical Messengers) (after P. Karlson)

¹ The substances listed here function primarily as Neurotransmitters and neuromodulators.

² The substances named in this Column are frequently referred to as mediators.

A similar dichotomy exists regarding the Classification of hormones. On the one hand, a classification based on hormone origin has long been in use. According to this approach, hormones are grouped together, with each group taking its name from the endocrine gland where it is synthesized. Meanwhile, numerous hormones, especially those discovered more recently, are not biosynthesized exclusively in Endocrine glands. Since the chemical structures of both types are thoroughly understood, a chemical classification of hormones is much more practical, distinguishing at least three main groups:

1. Steroid Hormones. This group comprises hormones that are derivatives of sterols. They are synthesized in the Adrenal Glands, Testes, Ovaries, and certain other Organs and Tissues (such as The Liver and Placenta).

2. Peptide Hormones. This category includes all hormones whose chemical Structure is represented by Polypeptides of varying molecular weight. Their sites of Biosynthesis include the neurosecretory Cells of the Brain, Hypothalamus, Pituitary Gland, thyroid and Parathyroid glands, Pancreas, liver, and gastrointestinal mucosa.

3. Other Hormones. These encompass all remaining hormones that are neither steroids nor polypeptides. Examples of this hormone type in humans and animals include thyroxine, adrenaline, prostaglandins, and others synthesized in The Thyroid Gland, adrenal glands, reproductive organs, and various tissues. This category also includes Plant Hormones (Auxins, heteroauxin, Gibberellins, Cytokinins, etc.) produced in the cells of higher and lower plants, as well as arthropod juvenile hormones.

At the same time, a promising attempt has recently been made to classify hormones based not only on their chemical nature, but also taking into account their origin and physiological function, primarily as signaling molecules (Table 27). This classification more adequately reflects the purpose of hormones within the Organism.

Let us examine the structure, Functions, MECHANISM OF ACTION, and biosynthetic pathways of individual groups of hormones in accordance with their chemical classification.