Hormones

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Hormone are chemical messenger produced in cells that function in the homeostatic control of reactions and processes occurring in organisms. Hormones are produced by almost all the organs and tissues in organisms but the best-known hormones are those produced by the endocrine glands. Almost all hormones are secreted into the bloodstream where they are transported to their target cells. Hormones serve many functions in organisms, some of which include inhibition and stimulation of growth and the immune system as well as regulation of metabolism. They also function in the reproductive system of organisms.

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Physiology

Hormones production is usually regulated by homeostatic methods. These include the use of a negative feedback system. This system depends not only on the amounts of the hormone produced but also on the amount of the hormone being metabolized and excreted. Stimulation or inhibition of hormone secretion is controlled also by the presence of other hormones that may be stimulating or inhibiting, by neuron and mental activity, by plasma concentrations and by environmental alterations. A special group of hormones called trophic hormones can stimulate hormone production of other endocrine glands.

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Types

There are four major classes of hormones found in vertebrates. These are:

  • The amine-derived hormones which include thyroxine. These hormones are derivatives of two amino acids, namely, tryptophan and tyrosine.
  • The peptide hormones are a group of hormones that are made of sequences of amino acids. This class is also applied to proteins which are long chains of amino acids.
  • The steroid hormones which are derived from cholesterol.
  • The lipid hormones which are derivatives of lipids like linoleic acid.
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Pharmacology

Hormones are often prescribed as medicines. They are used as a form of contraception, to treat hypothyroidism and for respiratory diseases. They are also administered when the body has deficiencies for example when insulin production ceases and a disease called diabetes develops.

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