THE ENDOCRINE SYSTEM
1. INTRODUCTION
1.1 General Endocrinology can be defined as the study of
communication between cells by a chemical messenger (Hormone)
synthesized by endocrine cells in vivo and directed at specific
target cells.
1.2 Most endocrine cells that synthesise the hormones have a
limited capacity to store the hormone. Thus these glands need to
turnover several times just to keep pace with daily requirements
for the hormones. The normal thyroid gland contains two weeks
stored supply in the form of thyroglobulin. Nerve endings may have
several days supply of norepinophrine.
1.3 The rate of different hormone release is periodic in the form
of a set rhythm, the cycles varies from minutes to hours or daily
(Circadian) loss of this rythm in clinical cases may be an early
evidence of a disordered state.
2. A HORMONE
A hormone, being the chemical substance synthesized by a
group of endocrine cells (in ductless glands) and secreted
directly into the blood stream (since there are no ducts) for
quick transport to target organs so as to influence their internal
metabolism.
2.1 The important body functions responsive to hormone actions
are:
2.1.1 The Milieu Interior (fluid, Electrolytes). The internal
environment
2.1.2 Emergency stress response i.e.metabolic response to injury
2.1.3 Reproduction i.e. ova and sperm production, fertilisation
and implantation
2.1.4 Growth and development of both
i) Normal tissue and
ii) Neoplastic tissue
2.2 The hormones we know are either
* Peptides (made of sequence of amino acids)
* Steroids (The hormones has a six sided steroid ring and the
precursor is cholesterol) or
* amines (are also derived from amino acids)
Hormone action starts with the step of binding with a cell
membrane or intracellular specific receptor for the hormone.
2.3 There is evidence available that the Endocrine System is
integrated in its activity to achieve biologic goals. The ed by
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