Steroid

This article is about the chemical family of steroids in general. For discussion of performance-enhancing steroids and their effects, please see Anabolic steroid.

A steroid is a lipid characterized by a carbon skeleton with four fused rings. All steroids are derived from the acetyl CoA biosynthetic pathway. Different steroids vary in the functional groups attached to these rings. Hundreds of distinct steroids have been identified in plants, animals, and fungi. Their most important role in most living systems is as hormones. Steroid hormones produce their physiological effects by binding to steroid hormone receptor proteins. The binding of steroid hormones to their receptors causes changes in gene transcription and cell function.

Steroid skeleton. Carbons 18 and above can be absent.

In human physiology and medicine, the most important steroids are cholesterol, the steroid hormones, and their precursors and metabolites. In the bloodstream steroids are bound to carrier proteins.

Cholesterol is an important steroid alcohol, being a common component of animal cell membranes. However, a high level of it can cause various conditions and diseases, such as atherosclerosis. Most other steroids are synthesized from cholesterol. Also, various hormones, including vertebrate sex hormones, are steroids created from cholesterol.

Some of the common categories of steroids include:

• 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. These are the "steroids" used by athletes to increase performance.
• Corticosteroids include glucocorticoid and mineralocorticoids:
  • Glucocorticoids regulate many aspects of metabolism and immune function, and often prescribed by doctors to reduce inflammatory conditions like asthma and arthritis.
  • Mineralocorticoids are corticosteroids that help maintain blood volume and control renal excretion of electrolytes.
• Sex steroids are a subset of sex hormones that produce sex differences or support reproduction. They include androgens, estrogens, and progestagens.
• Phytosterols - steroids naturally occurring in plants.

The term steroid is often used more restrictively in specific contexts. For instance, steroid in common medical usage by non-endocrinologists usually refers to corticosteroids, nearly always glucocorticoids. In an athletic or body-building context, steroid commonly refers to anabolic steroids.

Sex steroids include estrogen (U.S spelling) or oestrogen (UK spelling), progesterone and androgen. Oestrogen and progesterone are made primarily in the ovary and in the placenta during pregnancy and testosterone in the testis.

External links

• Michael W. King's Medical Biochemistry. Steroids and retinoids are both terpenes which are hydrophobic, pass through cell membranes and bind to intracellular receptors. However, retinoic acid is not a steroid because is 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. [http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=Books&cmd=Search&term=steroid+AND+stryer%5Bbook%5D&doptcmdl=TOCView steroid topics in this