Skip to main content Accessibility help
  • Print publication year: 2015
  • Online publication date: June 2015

7 - Regulation of hormone synthesis, storage, release, transport and deactivation


The endocrine system is driven by hormones released into the bloodstream in order to regulate other, distant organs (see Figure 1.3). These hormones are chemical messages that are decoded by specific recognition sites, or receptors, located in the target cells. Hormones are synthesized and stored in endocrine cells and, when required, they are released into the circulatory system. A number of hormones are transported in the bloodstream by carrier proteins. For example, sex hormone binding globulin is specifically responsible for transport of estradiol and testosterone. Other proteins such as albumin are less specific and serve to transport a variety of hormones. Hormone synthesis, storage, release, transport and deactivation occur through a variety of different mechanisms, depending on the chemical structure of the hormone. For example, peptides such as oxytocin are different in almost every respect from steroid hormones like estradiol. For this reason, the first section of this chapter will examine the chemical structure of hormones.

The chemical structure of hormones

In terms of chemical structure, hormones can be divided into three major groups: (1) steroid hormones; (2) amines; and (3) peptide hormones (Table 7.1). Steroid hormones, like estradiol, are different from the other two groups because of their very low solubility in blood. This is because they are essentially hydrocarbons and therefore need a binding protein to carry them in the bloodstream. A further distinction is the mechanism of their synthesis; steroids and amines are produced from precursors (such as cholesterol and tyrosine, respectively) via specific enzymes, whereas peptides are encoded by specific genes (DNA) that transcribe messenger RNA (mRNA) that is then translated into precursor peptides.

7.1.1 Steroid hormones

The steroid hormones are biosynthesized from cholesterol in the adrenal cortex and gonads. Adrenal steroids include cortisol and aldosterone and the gonadal steroids are progesterone, testosterone and estradiol (see Table 7.1). Note that some steroids are also made in the brain, fat tissue and placenta.

Banerjee, I. and Clayton, P. E. (2006). “Clinical utility of insulin-like growth factor-I (IGF-I) and IGF binding protein-3 measurements in paediatric practice,” Pediatr Endocrinol Rev 3, 393–402.
Besser, G. M. and Thorner, M. O. (2002). Comprehensive Clinical Endocrinology, rd edn. (St. Louis, MO: Mosby).
Bicknell, A. B. (2008). “The tissue-specific processing of pro-opiomelanocortin,” J Neuroendocrinol 20, 692–699.
Fisker, S. (2006). “Physiology and pathophysiology of growth hormone-binding protein: methodological and clinical aspects,” Growth Horm IGF Res 16, 1–28.
Keenan, D. M., Roelfsema, F. and Veldhuis, J. D. (2004). “Endogenous ACTH concentration-dependent drive of pulsatile cortisol secretion in the human,” Am J Physiol Endocrinol Metab 287, E652–661.
Legros, J. J. and Geenen, V. (1996). “Neurophysins in central diabetes insipidus,” Horm Res 45, 182–186.
Mullis, K. (1990). “The unusual origin of the polymerase chain reaction,” Sci Amer 262, 56–61.
Nillni, E. A. (2007). “Regulation of prohormone convertases in hypothalamic neurons: implications for prothyrotropin-releasing hormone and proopiomelanocortin,” Endocr 148, 4191–4200.
Nussey, S. S. and Whitehead, S. A. (2001). Endocrinology: An Integrated Approach (Oxford: Bios Scientific Publishers),
Rholam, M. and Fahy, C. (2009). “Processing of peptide and hormone precursors at the dibasic cleavage sites,” Cell Mol Life Sci 66, 2075–2091.
Sanger, G. J. (2008). “5-hydroxytryptamine and the gastrointestinal tract: where next?”Trends Pharmacol Sci 29, 465–471.
Wells, S. and Murphy, D. (2003). “Transgenic studies on the regulation of the anterior pituitary gland function by the hypothalamus,” Front Neuroendocr 24, 11–26.
Widmaier, E. P., Raff, H. and Strang, K. T. (2010). Vander's Human Physiology: The Mechanisms of Body Function, th edn. (New York: McGraw-Hill).