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The below mentioned article provides a quick note on the Discovery of Hormones.
The first hormone was discovered by the English physiologist William M. Bayliss and Ernest H. Starling in 1903. The term hormone was introduced by Starling in 1905.
Properties of Hormones (General Characteristic Features of Hormones):
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(1) They are synthesized and secreted by living endocrine glandular cells within the body or in cultures of endocrine cells in vitro (artificial medium). Hormones are non-nutrient chemicals which act as intercellular messengers and are produced in trace amount.
(2) Hormones are transported by the blood stream from the endocrine cells to serve as ‘chemical messenger’ which act on target cells or organs.
(3) Hormones do not provide energy or building materials but they do have effects on growth differentiation and metabolic activities of their target cells.
(4) They have low molecular weight.
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(5) Hormones belong to different types of chemical structure. They may be amino acid derivatives, peptides, polypeptides (proteins) or steroids.
(6) Hormones are effective in low concentration.
(7) Excess or deficiency leads to disorders.
(8) They may accelerate or inhibit specific physiological process.
(9) Many hormones are produced in inactive form called pro-hormones. For example, insulin is secreted as pro-insulin.
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(10) Hormones are often used up in their regulatory action.
Hypo-and Hyperactivity of Hormones:
When hormones are secreted in deficiency, the role of the hormones decreases which leads to hypo activity of the hormones. Excess secretion of the hormones increases hormone action which is called hyperactivity of the hormones.
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Hypo activity or hyperactivity of the hormones can cause disorders. For example, deficiency of insulin causes diabetes mellitus. Excess of growth hormone from early age causes gigantism.
Types of Hormones Based on their Chemical Nature:
1. Amino Acid Derivative Hormones:
Epinephrine and norepinephrine are derived from the amino acid tyrosine. Melatonin and serotonin are derived from tryptophan.
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2. Peptide Hormones and Protein Hormones:
Examples of peptide hormones are hypothalamic hormones (e.g., antidiuretic hormone (ADH), Oxytocin). Protein hormones include insulin, glucagon, pituitary hormones (e.g., growth hormone, thyroid stimulating hormone), thyrocalcitonin hormone, parathyroid hormone.
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3. Iodothyronines:
Iodothyronines is group of iodinated amino acids with a diphenyl ether ring system in the side chain. Thyroxine is the longest and best known of this group.
4. Steroid Hormones:
Examples: Aldosterone, cortisol, androgens, calcitriol, testosterone, oestrogens and progesterone.
