Steroids are complex derivatives of triterpene. Each type of steroid is compossed of four fused rings called as steroids nucleus. In which ring A, B and C are phenanthrene and ring D is cyclopentane attach to each other. A sterol is a class of steroid characterized by a hydroxyl group at carbon-3.
Cholesterol is best known steroids. It is a precursor of large number of equally important steroids such as—bite acid, adrenocortical hormone, sex hormones, D vitamins, cardiac glycosides. Cholesterol is usually stored within cell as a fatty acid ester.
Cholesterol is a significant constituent of many tissue. Cholesterol is widely distributed in all cells of body especially in nervous tissue. It is major constituent of plasma membrane of plasma lipoproteins. The hydroxyl group on position -3 of cholesterol is esterified with a long chain of fatty acid. It is present in animal but not in plant. Ergosterol is a precusor of vitamin D. It is present in plant and yeast.
20.6.2. Steroid Hormones
Five families of hormones such as androgen, estrogens, progestins, glucocorticoid and mineralocorticoids and bile acid derived from cholesterol.
- Androgens such as - testosterone and estrogen mediate the sexual development and sexual characters in animal.
- Progestin such as - progesterone control the menstrual cycle and pregnancy.
- Glucocorticoids control the carbohydrate, protein and lipid metabolism.
- Mineralo corticoids regulate the salt such as Na+, K+ and Cl– balance in tissue.
- Bile acids consist of cholic and deoxy cholic are detergent molecules secreted by the gall blander, which assist the
absorption of lipid in the intestine.
17 b-hydroxysteroid Dehydrogenase-3 the main role of this Estrogen is in the formation of testosterone. Deficiency of this enzyme cause male pseudohermaphroditism.
Steroid hormones carry messages between tissues. Steroids are oxidized derivative of sterols. Steroids hormones move from their site of production to their target tissue through blood stream. They enter in the cells and bind with highly specific protein in the nucleus. After this they trigger changes in the gene expression and metabolism.
Hormones have very high affinity which is sufficient to produce response. Major group of steroid hormones are female and male sex hormones.
Eicosanoids is a family of very potent biological signaling molecules which act as short range messenger. It is known isosanoids because of their origin from 20 carbon molecule known as (polyunsatured fatty acid) Eicosanoic acids.
Eicosanoids are paracrine hormones which act only on nearby cells by the place of their synthesis. It acts locally instead of being transported in the blood to act on cells in other tissue or organs.
20.7.1. Prostaglandines, thromboxans and leukotrienes
Prostaglandins was first isolated from the prostate gland, thus called as prostaglandins. Prostaglands have five carbon ring which is originated from the chain of arachidonic acid. Two group of prostaglandin PGE ether soluble and PGF phosphate buffer soluble. Each group (PGE) have subtype PGE1, 2 and 3.
- Prostaglandins regulate the synthesis of intracellular messenger i.e. cyclic AMP (cAMP). cAMP mediates the action of diverse hormones. Prostaglandin affects the cellular and tissue function.
- Prostaglandin stimulate the contraction of smooth muscles of uterus during menstruation.
- Prostaglandin also affect the blood flow to specific organs.
- Prostaglandin elevate the body temperature and cause inflammation and pain.
Thromboxanes contain six membered ring containing ether. They produces by thrombocytes. (platelets) The main role of thromboxane is formation of blood clot. It reduce the blood flow to site of a clot.
Anti inflammatory drug (NSAIDs) :
Aspirin, ibuprofen and meclofenamate inhibit prostaglandin H2 synthesis. Which catalyses the early step in the path way from arachidonate to prostaglandins and thromboxans.
Leukotrienes are hydroxy fatty acid derivative of arachidonic acid. Leukotrienes do not contain a ring structure. Leukotrienes is 1st found in leukocytes. Leukotrienes are distinguished by containing a conjugated triene double-bond arrangement. They are powerful biological molecules. e.g., Leukotriene D4, derived from leukotriene A4.
It induces the contraction in the muscle lining to the lung. Leukotrienes causes asthmatic attacks because of the over production.
Body contain a variety of lipids stored in its structure which performs a variety of functions. Fatty acids are the storage material which produces a large amount of energy upon oxidation. Fats transported inside the body in the form of lipoproteins which can be very low density lipoproteins (VLDL), low density lipoproteins (LDL) and high density lipoproteins (HDL).