steroid

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Any of numerous naturally occurring or synthetic fat-soluble organic compounds having as a basis 17 carbon atoms arranged in four rings and including the sterols and bile acids, adrenal and sex hormones, certain natural drugs such as digitalis compounds, and the precursors of certain vitamins.

[STER(OL) + –OID.]

Any of a group of organic compounds belonging to the general class of biochemicals called lipids, which are easily soluble in organic solvents and slightly soluble in water. Additional members of the lipid class include fatty acids, phospholipids, and triacylglycerides. The unique structural characteristic of steroids is a four-fused ring system. Members of the steroid family are ubiquitous, occurring, for example, in plants, yeast, protozoa, and higher forms of life. Steroids exhibit a variety of biological functions, from participation in cell membrane structure to regulation of physiological events. Naturally occurring steroids and their synthetic analogs are used extensively in medical practice.

Each steroid contains three fused cyclohexane (six-carbon) rings plus a fourth cyclopentane ring (see illustration). Naturally occurring steroids have an oxygen-containing group at carbon-3. Shorthand formulas for steroids indicate the presence of double bonds, as well as the structure and position of oxygen-containing or other organic groups.

methyl groups.">
Steroid skeleton. (a) Structure and numbering. (b) Shorthand formulation; the lines attached to the rings represent methyl groups.

The most abundant steroid in mammalian cells is cholesterol. The levels and locations of planar cholesterol molecules, embedded in the phospholipid bilayers that form cell and organelle membranes, are known to influence the structure and function of the membranes. A second major function of cholesterol is to serve as a precursor of steroids acting as physiological regulators (such as the steroid hormones). Enzyme systems present in a hormone-secreting gland convert cholesterol to the hormone specific for that gland. For example, the ovary produces estrogens (such as estradiol and progesterone); the testis produces androgens (such as testosterone); the adrenal cortex produces hormones that regulate metabolism (such as cortisol) and sodium ion transport (such as aldosterone). A third major function of cholesterol is to serve as a precursor of the bile acids. These detergentlike molecules are produced in the liver and stored in the gall bladder until needed to assist in the absorption of dietary fat and fat-soluble vitamins and in the digestion of dietary fat by intestinal enzymes.

Some examples of diseases treated with naturally occurring or synthetic steroids are allergic reactions, arthritis, some malignancies, and diseases resulting from hormone deficiencies or abnormal production. In addition, synthetic steroids that mimic an action of progesterone are widely used oral contraceptive agents. Other synthetic steroids are designed to mimic the stimulation of protein synthesis and muscle-building action of naturally occurring androgens.

Steroids comprise a large group of substances that mediate a very varied set of biological responses. The most widespread in the body is cholesterol, an essential component of cell membranes, and the starting point for the synthesis of other steroids — the sex hormones, adrenal cortical hormones, and the bile salts.

The steroids are grouped together because their chemical structures are all very similar. The steroid chemical nucleus consists of four carbon rings, three 6-sided and one 5-sided, joined together by their edges. The specificity of their different biological actions is due to the various groups attached to a common nucleus. When alcohol groups (OH) are attached, steroids should properly be called sterols (such as cortisol), whereas ketone groups (C=O) make them sterones (such as aldosterone).

Different steroids react with different membrane receptors in cells, and a precise fit between the steroid and the receptor is required. Therefore a single steroid can be expected to have a specific effect.

Steroids have major responsibilities as hormones, controlling metabolism, salt balance, and the development and function of the sexual organs as well as other bodily differences between the sexes. Steroids in the form of bile salts assist in digestive processes, while another steroid is a vitamin that takes part in calcium control.

Steroid hormones

Steroid hormones are made and secreted into the circulating blood by the cortex of the adrenal glands and the gonads (testes or ovaries). Mostly, their secretion is regulated by hormones from the pituitary gland, and those in turn by chemical messages from the hypothalamus.

Two types of steroids are released from the adrenal cortex, the glucocorticoids, mainly cortisol (hydrocortisone) and the mineralocorticoids, mainly aldosterone. Both types of hormone are important in stress situations such as disease or injury.

Glucocorticoids mobilize glucose, which is particularly important in fasting conditions. They do so by promoting glucose formation from non carbohydrate sources in the liver, increasing glycogen levels, and raising the blood glucose concentration. Liberation of glucocorticoids from the adrenal cortex is caused by adrenocorticotrophic hormone (ACTH), released from the pituitary gland. When the glucocorticoid level in the blood is low, ACTH is released, but when it is high the release of ACTH is suppressed. This is a good example, one of many that occur in the body, of a feedback system. Large doses of glucocorticoids are anti-inflammatory and at one time it was thought they would provide suitable treatment for inflammatory conditions such as rheumatoid arthritis. However, the excessive breakdown of proteins, mobilized to form glucose in the liver, leads to muscle weakness and osteoporosis and there is also ‘moon face’ and obesity. This describes exactly the features of Cushing's syndrome, a condition caused by excess secretion of corticosteroids. Furthermore, if therapy with glucocorticoids is withdrawn rapidly the pituitary system is so suppressed that the body's own system takes a while to trip in, leading to an ‘Addisonian crisis’, mimicking Addison's disease in which there is a deficiency in glucocorticoid production. With due precautions, however, corticosteroids remain a useful treatment in some severe allergic and inflammatory conditions.

The mineralocorticoid aldosterone is released at an increased rate from the adrenal glands if the body is salt depleted; this is stimulated by a complex detecting system in the kidneys, resulting in an increase in circulating angiotensin, which acts in turn on the adrenal glands. Aldosterone promotes sodium reabsorption by the kidneys, so that there is less salt in the urine, thus correcting the deficiency. It acts on sweat glands similarly, diminishing salt loss in sweat.

Male steroid sex hormones, androgens, are produced in the testes. Testosterone is the most important of the androgens and is responsible for controlling the production and maturation of sperm, as well as male characteristics, such as the distribution of body hair. Anabolic steroids are derivatives of testosterone and act on androgenic receptors. They build up muscle mass and cause virilization — features of masculinity. They are useful in the treatment of debilitated patients to help restore their physique. Unfortunately these substances have been taken illicitly by athletes for body-building. Their use carries considerable risk, as sudden withdrawal will leave the body's natural processes suppressed, by interference with the feedback system as described above. Detection of the use of anabolic steroids has become difficult as it appears that one that is commonly used, namely nandrolone, can be synthesized by the body itself in small quantities, especially when under physical stress. Female steroid sex hormones are of two types, oestrogens and progestins, both from the ovaries. Again under pituitary hormone regulation, their relative secretion varies within the menstrual cycle. Oestrogens promote the growth of the lining of the uterus in preparation for implantation of a fertilized egg. Once the egg has been shed from the ovary, the corpus luteum (yellow body), which develops in the cavity left behind, secretes progesterone; this promotes further development of the uterine lining and, if implantation of an embryo occurs, maintains changes here and elsewhere for the duration of pregnancy.

The understanding of these processes is the basis of the contraceptive pill. Synthetic steroids were devised for this purpose, as natural steroids are metabolized by the liver if taken by mouth. As with the other steroid hormones, there are feedback systems involving the pituitary gland. Taking oestrogens inhibits the release from the pituitary of the follicular stimulating hormone that would normally cause maturation of eggs in the ovary: so, no ovulation, no conception. Contraceptive pills usually contain both oestrogens and progestins, which are taken concurrently or sequentially during the 4 week course, menstruation following when the course ceases. A large dose of both an oestrogen and progestin promotes uterine bleeding within a few hours and is the basis of the ‘morning after’ pill.

Steroids and bile

Cholesterol, taken up from the blood into the liver or synthesized there, can be oxidized in the liver to cholic acid. Conjugation of this with taurine or glycine gives the bile salts, taurocholate and glycocholate. These bile salts pass into the small intestine and have important actions in aiding the digestion and absorption of fats. Cholesterol itself is excreted in the bile.

The steroid vitamin

Exposure to ultraviolet light converts a steroid, dehydrocholesterol, in the skin to vitamin D. This is what happens when you sunbathe, but in climes where exposure to the sun is limited it is necessary to supplement the diet with the vitamin. Fish oils are rich in vitamin D and the Eskimo diet ensures that they get a sufficient supply. The vitamin primarily promotes calcium absorption from the gut. Calcium is essential for bone growth and maintenance, muscle contraction, and many signalling processes in the body.

While steroids have many different actions on the body, their mechanism of action is similar in all instances. The receptors for steroids are inside cells (unlike those for many other substances, which are on the cell membrane). The complex formed by combination of the steroid with its specific receptor enters the nucleus and switches on or off the appropriate genes, which then gives rise to the characteristic effect. Their actions are not therefore immediate as with, for example, neurotransmitters, nor are they as rapid as those of the peptide hormones; several hours elapse before the effect appears. To give one example, the receptors for aldosterone are located in the end part of the kidney tubules. Here genes are switched on which lead to the synthesis of the molecules that actually handle the reabsorption of sodium ions from the urine back into the blood. The process becomes more efficient because there are a larger number of molecular entities dedicated to the task.

— Alan W. Cuthbert

See also bile; body building; hormones; menstrual cycle; sex hormones.

Chemically, compounds that contain the cyclopenteno-phenanthrene ring system. All the biologically important steroids are derived metabolically from cholesterol; they include the sex hormones (androgens, oestrogens, and progesterone) and the hormones of the adrenal cortex. See also phytosterols; sitosterol.

A fat-soluble organic chemical, formed in the body from cholesterol and fats. Steroids include the male sex hormone, testosterone; the female sex hormone, oestrogen; and the stress hormones secreted by the outer part of the adrenal gland (see corticosteroids). See also anabolic steroids.

A group name for compounds that resemble cholesterol chemically and also contain a hydrogenated cyclopentanoperhydrophenanthrene ring system. Included are cholesterol, ergosterol, bile acids, vitamin D, sex hormones, adrenocor-tical hormones, and cardiac glyco-sides.

For more information on steroid, visit Britannica.com.

Lipid-soluble hormones that can pass through cell membranes. Once inside the cell, a steroid hormone hinds to specific receptors that can enter the nucleus and activate certain genes. Steroids include testosterone and oestrogen. They may occur naturally or he synthesized. See also anabolic androgenic steroid.

A group of molecules that includes cholesterol. The sex hormones estrogen and testosterone are built from steroids, as are many modern anti-inflammatory drugs.

Emanating from or pertaining to steroid.

• s. saponins — see lithogenic saponins.
• s. (Solanum spp.) alkaloid — toxins including solanidine, soladulcidine, solasidine, tomatidine found in solanaceous plants.

This article is about the chemical family of lipids. For the performance-enhancing substance, see Anabolic steroid.

IUPAC recommended ring lettering (left) and atom numbering (right) of the steroid skeleton.[1][2]

Steroid skeleton of lanosterol. The total number of carbons (30) reflects its triterpenoid origin.

Simplified version of the steroid synthesis pathway with the intermediates isopentenyl pyrophosphate(IPP),dimethylallyl pyrophosphate (DMAPP), geranyl pyrophosphate (GPP) and squalene shown. Some intermediates are omitted.

A steroid is a terpenoid lipid characterized by a carbon skeleton with four fused rings, generally arranged in a 6-6-6-5 fashion. Steroids vary by the functional groups attached to these rings and the oxidation state of the rings. Hundreds of distinct steroids are found in plants, animals, and fungi. All steroids are made in cells either from the sterol lanosterol (animals and fungi) or from the sterol cycloartenol (plants). Both sterols are derived from the cyclization of the triterpene squalene.^[3]

Contents 1 Origin 2 Classification 2.1 Taxonomical/Functional 2.2 Structural 3 See also 4 References 5 Further Reading 6 External links

Origin

Steroids include estrogen, cortisol, progesterone, and testosterone. Estrogen and progesterone are made primarily in the ovary and in the placenta during pregnancy, and testosterone in the testes. Testosterone is also converted into estrogen to regulate the supply of each, in the bodies of both females and males. Certain neurons and glia in the central nervous system (CNS) express the enzymes that are required for the local synthesis of pregnane neurosteroids, either de novo or from peripherally-derived sources. The rate-limiting step of steroid synthesis is the conversion of cholesterol to pregnenolone, which occurs inside the mitochondrion.^[4]

Classification

Taxonomical/Functional

Some of the common categories of steroids:

• Animal steroids
  • Insect steroids
    • Ecdysteroids such as ecdysterone
  • Vertebrate steroids
    • Steroid hormones
      • Sex steroids are a subset of sex hormones that produce sex differences or support reproduction. They include androgens, estrogens, and progestagens.
      • Corticosteroids include glucocorticoids and mineralocorticoids. Glucocorticoids regulate many aspects of metabolism and immune function, whereas mineralocorticoids help maintain blood volume and control renal excretion of electrolytes. Most medical 'steroid' drugs are corticosteroids.
      • Anabolic steroids are a class of steroids that interact with androgen receptors to increase muscle and bone synthesis. There are natural and synthetic anabolic steroids. In popular language, the word "steroids" usually refers to anabolic steroids.
    • Cholesterol, which modulates the fluidity of cell membranes and is the principal constituent of the plaques implicated in atherosclerosis.
• Plant steroids
  • Phytosterols
  • Brassinosteroids
• Fungus steroids
  • Ergosterols

Structural

It is also possible to classify steroids based upon their chemical composition. One example of how MeSH performs this classification is available at the Wikipedia MeSH catalog. Examples from this classification include:

Class	Examples	Number of carbon atoms
Cholstanes	cholesterol	27
Cholanes	cholic acid	24
Pregnanes	progesterone	21
Androstanes	testosterone	19
Estranes	estradiol	18

See also

• Batrachotoxin
• List of steroid abbreviations
• Steroid biosynthesis

References

1. ^ "IUPAC-IUB Joint Commission on Biochemical Nomenclature (JCBN). The nomenclature of steroids. Recommendations 1989". Eur. J. Biochem. 186 (3): 429–58. December 1989. doi:10.1111/j.1432-1033.1989.tb15228.x. PMID 2606099. http://www.chem.qmul.ac.uk/iupac/steroid/. 
2. ^ G. P. Moss (1989). "Nomenclature of Steroids (Recommendations 1989)". Pure & Appl. Chem. 61 (10): 1783–1822. doi:10.1351/pac198961101783. 
3. ^ Lanosterol biosynthesis
4. ^ Rossier MF (2006). "T channels and steroid biosynthesis: in search of a link with mitochondria". Cell Calcium. 40 (2): 155–64. doi:10.1016/j.ceca.2006.04.020. PMID 16759697. 

Further Reading

• Simons SS (August 2008). "What goes on behind closed doors: physiological versus pharmacological steroid hormone actions". Bioessays 30 (8): 744–56. doi:10.1002/bies.20792. PMID 18623071. 

External links

• Michael W. King's Medical Biochemistry. Steroids and retinoids are both terpenes that are hydrophobic, pass through cell membranes and bind to intracellular receptors. However, retinoic acid is not a steroid because it does not have the defining ring structure. See: Steroids and Related Hydrophobic Molecules.
• "Biochemistry" by Jeremy M. Berg, John L. Tymoczko and Lubert Stryer (2002) W. H. Freeman and Co. steroid topics in this
• Insidermedicine in 60 - Trans Fats, Steroid Rage, Calcium and Needlesticks -- Video: Insidermedicine.com's Dr. Sanjay Sharma on Trans Fats, Steroid Rage, Calcium and Needlesticks.
• Nomenclature of Steroids Home Page at Queen Mary University of London.
• Steroid abbreviations at ISAS (page now defunct, web archive version)

v • d • e Cholesterol and steroid metabolic intermediates Mevalonate pathway to HMG-CoA Acetyl-CoA · Acetoacetyl-CoA · HMG-CoA Ketone bodies Acetone · Acetoacetic acid · beta-Hydroxybutyric acid to DMAPP Mevalonic acid · Phosphomevalonic acid · 5-Diphosphomevalonic acid · Isopentenyl pyrophosphate · Dimethylallyl pyrophosphate Geranyl- Geranyl pyrophosphate · Geranylgeranyl pyrophosphate Carotenoid Prephytoene diphosphate · Phytoene Non-mevalonate pathway DOXP · MEP · CDP-ME · CDP-MEP · MEcPP · HMB-PP · IPP · DMAPP To Cholesterol Farnesyl pyrophosphate · Squalene · 2,3-Oxidosqualene · Lanosterol Lanosterol · Lathosterol · 7-Dehydrocholesterol · Cholesterol Lanosterol · Zymosterol · 7-Dehydrodesmosterol · Desmosterol · Cholesterol Steroid Corticosteroids (C21 pregnane) Mineralocorticoids Pregnenolone · Progesterone · 11-Deoxycorticosterone · Corticosterone · Aldosterone Glucocorticoids Pregnenolone · 17-Hydroxypregnenolone · 17-Hydroxyprogesterone · 11-Deoxycortisol · Cortisol Cortisol · Cortisone Sex steroids Androgens (C19 andrane) DHEA · Androstenedione/5-Androstenediol · Testosterone · Dihydrotestosterone DHEA sulfate · Epitestosterone Estrogens (C18 estrane) Estrone · Estradiol · Estriol Nonhuman Phytosterols Stigmasterol · Brassicasterol Ergosterols Ergosterol · Ergocalciferol see also enzymes, disorders Major families of biochemicals Saccharides/Carbohydrates/Glycosides · Amino acids/Peptides/Proteins/Glycoproteins · Lipids/Terpenes/Steroids/Carotenoids · Alkaloids/Nucleobases/Nucleic acids · Cofactors/Flavonoids/Polyketides/Tetrapyrroles

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Dansk (Danish)
n. - steroide

Nederlands (Dutch)
steroïde, steroïden

Français (French)
n. - stéroïde

Deutsch (German)
n. - Steroid

Ελληνική (Greek)
n. - (βιοχημ.) στεροειδές

Italiano (Italian)
steroide, steroidi

Português (Portuguese)
n. - esteróide (m)

Русский (Russian)
стероид

Español (Spanish)
n. - esteroide, esteroides

Svenska (Swedish)
n. - steroid

中文（简体）(Chinese (Simplified))
类固醇

中文（繁體）(Chinese (Traditional))
n. - 類固醇

한국어 (Korean)
n. - 스테로이드

日本語 (Japanese)
n. - ステロイド
adj. - ステロイドの

idioms:

• anabolic steroid    蛋白同化ステロイド

العربيه (Arabic)
‏(الاسم) مادة كيماويه ينتجها الجسم ( هرمونات و فيتامينات)‏

עברית (Hebrew)
n. - ‮סטרואיד, חומרים כימיים בעלי מבנה דומה (הורמונים, ויטמינים וכד')‬

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