Introduction to Endocrinology

Abstract

Endocrine (hormones) system and central nerve system are two types of communication system between different parts of the body through chemical and electrical signals, to keep the body homeostasis against internal and external stresses. Endocrine system controls important functions such as metabolism, reproduction and homeostasis by regulating secretion of molecular messengers known as hormones from glands located throughout the body. This chapter defines the location and function of endocrine glands and explains how coordination between endocrine and nerve cells regulates secretion of hormones, neurotransmitters, cytokines and electrical signals. Hormone has been defined primarily as a stimulant, inhibitor, or chemical messenger that after releasing in the systemic circulation imparts specific change in cellular activity of targeted cells. Present classification of hormones delivery describes autocrine signal where the sender cell is the origin/identical to the receptor cell. Matching to this state, paracrine signalling defines signalling from a hormone-producing cell to a near target cell. Juxtacrine signalling explains the delivery of signals from adjacent cells by direct contacting cell contact, whereas endocrine signalling (classic model) defines the signalling between endocrine cell and the receptor cells (distant cells/organs) via the blood circulation. The classic model of endocrine functions is greatly improved with the field of intracrinology which is becoming extensively recognized. Intracrine principal concepts have been accepted as intracrinology to study physiological functions and to develop strategy for advanced drug treatments. Signalling protrusions is an emerging function of contact-mediated cell message that can deliver signals in both ways, from sender (endocrine cell) to target cell and vice versa in directly contact through extended distances. These mechanisms are effective in normal functions, tissue development and diseases. This emerging concept of the various signaling could be applied on the sites that synthesize hormones and target cells responding to hormones. Generally, hormone is an organic molecule synthesized biochemically and secreted by cells of endocrine glands in intracrine, juxtacrine, paracrine, or autocrine signals. Hormones can be classified into peptides and proteins, steroid hormones and amino acid derivatives according to their chemical nature, secretion pattern and mechanism of action. Terpenes are also type of hormones that varied greatly and contain retinoids, carotenoids, dolichols, steroid hormones, aromatic metabolites. Aberrant or mis-regulation of hormone signalling pathways has been related with inflammatory disorders including cancer, diabetes, neurological and cardiovascular diseases. Recent data evidenced the role of long non-coding RNAs (lncRNAs) in tumour initiated in organs that play endocrine functions.