Preface

This book explains the basic science of steroids and is targeted towards professionals engaged in health services.

It should be noted that medical science evolves rapidly and some information like the understanding of steroids and their therapeutic use may change with new concepts quickly.

Steroids are either naturally occurring or synthetic fat-soluble organic compounds. They are found in plants, animals, and fungi. They mediate a very diverse set of biological responses. The most widespread steroid in the body is cholesterol, an essential component of cell membranes, and the starting point for the synthesis of other steroids.

Since the science of steroids has an enormous scope, we decided to put the clinical aspects of steroids in a different book titled "Steroids: Clinical Aspects". The two books complete each other.

We hope that the reader will gain valuable information from both books and enrich their knowledge about this fascinating topic.

> **Hassan Abduljabbar**  Professor of Obstetrics and Gynecology, King Abdulaziz University, Kingdom of Saudi Arabia

**Part 1** 

**Physiology of Steroid Hormones** 

**Part 1** 

**Physiology of Steroid Hormones** 

**1** 

*México* 

**Hormonal and Neural Mechanisms** 

*1Facultad de Estudios Superiores Zaragoza, 2Facultad de Estudios Superiores Iztacala Universidad Nacional Autónoma de México* 

 **Regulating Hormone Steroids Secretion** 

Roberto Domínguez1, Angélica Flores1 and Sara E. Cruz-Morales2

Hormonal and neural signals participate in regulating the synthesis and release of steroid hormones from the adrenals, ovaries and testicles. Hormonal signals arise from the hypothalamus, pituitary, thyroid, thymus, adipose tissue, as well as from the adrenals, ovaries and testicles. Neural signals originating in the hypothalamus and other regions of the central and peripheral nervous system modulate the responses to the hormonal signals

In female, the involvement of the adrenal and ovarian innervations in regulating the synthesis and release of steroid hormones have shown that right and left organs have different abilities to carry out these functions (Gerendai et al., 2000; Domínguez et al., 2003). The asymmetric capacity to release steroid hormones is related to differences in the origin and type of innervations received by right and left organs (Tóth et al., 2007; Gerendai et al., 2009). In addition, the way neuroendocrine signals participate in regulating steroid hormones secretion is different for each hormone, and the release of ovarian hormones is

Scientific reviews on the biochemical steps that take place during the capture and processing of cholesterol and synthesis of steroid hormones, as well as in the regulation of the enzymes activities have been published in the last decade (Auchus & Miller, 2000; Straus & Hsue, 2000; Stocco, 2008; Boon et al., 2010; Chung et al., 2011). In such regard, the present chapter presents only a summary of those aspects we think are relevant to analyze the

Steroid hormones are classified according to the number of carbon (C) atoms in the molecule deriving from the pregnane (C-21), androstane (C-19) or estrane (C-18) nucleus. C-21 hormones include progesterone, cortisol, corticosterone and aldosterone; C-19 testosterone, androstenedione (A4) and dihydrotestosterone; and C-18 estradiol, estrone and estriol. Based on its functional actions, steroid hormones are classified into five principal classes: estrogens (estradiol, estrone, estriol), progestins (progesterone), androgens (testosterone, A4,

**1. Introduction** 

**2. Steroid hormones** 

sent to the adrenals, ovaries and testicles.

regulated according to the day of the estrus cycle.

neuroendocrine regulation of steroid hormones secretion.
