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A steroid is an organic compound with four fused rings (designated A, B, C, and D) arranged in a specific molecular configuration. Steroids have two principal biological functions: as important components of cell membranes that alter membrane fluidity; and as signaling molecules.
Steroid hormones help control metabolism, inflammation, immune functions, salt and water balance, development of sexual characteristics, and the ability to withstand injury and illness. The term steroid describes both hormones produced by the body and artificially produced medications that duplicate the action for the naturally occurring steroids.
[2] [3] The most familiar type of animal sterol is cholesterol, which is vital to the structure of the cell membrane, and functions as a precursor to fat-soluble vitamins and steroid hormones. While technically alcohols, sterols are classified by biochemists as lipids (fats in the broader sense of the term).
The left diagram shows a steroid (lipid) hormone (1) entering a cell and (2) binding to a receptor protein in the nucleus, causing (3) mRNA synthesis which is the first step of protein synthesis. The right side shows protein hormones (1) binding with receptors which (2) begins a transduction pathway.
Cortisol is a steroid hormone in the glucocorticoid class of hormones and a stress hormone. When used as medication, it is known as hydrocortisone. It is produced in many animals, mainly by the zona fasciculata of the adrenal cortex in an adrenal gland. [1] In other tissues, it is produced in lower quantities. [2]
The name mineralocorticoid derives from early observations that these hormones were involved in the retention of sodium, a mineral.The primary endogenous mineralocorticoid is aldosterone, although a number of other endogenous hormones (including progesterone [1] and deoxycorticosterone) have mineralocorticoid function.
Corticosterone, also known as 17-deoxycortisol and 11β,21-dihydroxyprogesterone, [1] is a 21-carbon steroid hormone of the corticosteroid type produced in the cortex of the adrenal glands. In the very rare case of congenital adrenal hyperplasia due to 17α-hydroxylase deficiency cortisol production is blocked. [2]
Transport of cholesterol from the outer to the inner membrane is facilitated by steroidogenic acute regulatory protein and is the rate-limiting step of steroid synthesis. [29] The layers of the adrenal gland differ by function, with each layer having distinct enzymes that produce different hormones from a common precursor. [4]