HORMONES AND THEIR MEDICAL RELEVANCE

Hormones are chemical substances produced in the body or in a plant that encourages growth or influences how the cells and tissues function. Hormones act through specific high-affinity cellular receptors. Studies have shown that the locus of the interaction between hormone and receptor may be extracellular, cytosolic or nuclear depending on the hormone type. There is usually a change in membrane potential as a result of the opening or closing of a hormone-gated ion channel.



The mode of classification of hormones is as follows; endocrine hormones, paracrine hormones, and autocrine hormones. Endocrine hormones are released into the blood and carried to target tissues and cells throughout the body. Paracrine hormones are released into the extracellular space and diffuse into neighbouring target cells. Autocrine hormones are released by and affect the same cell, binding to receptors on the cell surface. Hormones can be grouped as follows; peptide hormones,catecholamine hormones and steroid hormones.



Peptide hormones are water-soluble and act extracellularly by binding to cell surface receptors that span the plasma membrane. They require the use of a second intracellular messenger such as cyclic AMP (cAMP).Examples include the pancreatic hormones insulin, glucagon and somastostatin,the parathyroid hormone and all the hormones of the hypothalamus and pitutiary. These hormones are concerned with carbohydrate metabolism and so on.



Catecholamines are produced in the brain and other neural tissues. They are water-soluble compounds and have tyrosine as their precursor. They function as neurotransmitters (e.g dopamine).The adrenal glands synthesize epinephrine and norepinephrine. They are released by exocytosis from their secretory vessicles. They also mediate a wide variety of physiological responses.



Steroid hormones are lipid-soluble. Their precursor is cholesterol. They travel to their target cells through the blood stream bound to carrier proteins. They are classified as glucocorticoids, mineralocorticoids, androgens and estrogen. Glucocorticoids (e.g cortisol) primarily affect carbohydrate metabolism, mineralocorticoids such as aldosterone regulate electrolyte concentrations in the blood. Androgens and estrogens are synthesized in the testes and ovaries. Testosterone and progesterone are sex hormones and affect sexual development and a variety or reproductive functions. Recent research indicates that they have more rapid effects, mediated by receptors localized in the plasma membrane.



Hormone replacement therapy is an invaluable tool used in the treatment of diseases. Insulin Dependent Diabetes Mellitus (IDDM) can be treated by beta cell replacement therapy, infertility can also be treated by carrying out a hormonal assay/profile on sex hormones found in humans to know their levels.



Hormones are invaluable chemical messengers whose roles are very vital in living organisms as they mediate metabolic and physiological processes.