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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 numbering. Steroid reductases. 5α-Reductase (1, 2, 3) – androgen and neurosteroid synthesis, progestogen metabolism; 5β-Reductase – androgen and progestogen metabolism, neurosteroid synthesis; Conjugation (and deconjugation) Glucuronosyltransferase – steroid metabolism [6] Glucuronidase (β-glucuronidase) – steroid synthesis [7]
Sterols and related compounds play essential roles in the physiology of eukaryotic organisms, and are essential for normal physiology of plants, animals, and fungi. [4] For example, cholesterol forms part of the cellular membrane in animals, where it affects the cell membrane's fluidity and serves as secondary messenger in developmental signaling.
Anabolic steroid § Comparison of AAS; Template:Relative affinities of estrogens for steroid hormone receptors and blood proteins; Template:Affinities of estrogen receptor ligands for the ERα and ERβ; Template:Pharmacodynamics of progestogens
The right side shows protein hormones (1) binding with receptors which (2) begins a transduction pathway. The transduction pathway ends (3) with transcription factors being activated in the nucleus, and protein synthesis beginning. In both diagrams, a is the hormone, b is the cell membrane, c is the cytoplasm, and d is the nucleus.
As such, the distinction between the terms anabolic steroid and androgen is questionable, and this is the basis for the revised and more recent term anabolic–androgenic steroid (AAS). [70] [75] [218] David Handelsman has criticized terminology and understanding surrounding AAS in many publications.
A variety of synthetic steroids and sterols have also been contrived. Most are steroids, but some nonsteroidal molecules can interact with the steroid receptors because of a similarity of shape. Some synthetic steroids are weaker or stronger than the natural steroids whose receptors they activate. [8] Some examples of synthetic steroid hormones:
The metabolic clearance rate of a steroid is defined as the volume of blood that has been completely cleared of the hormone per unit time. The production rate of a steroid hormone refers to entry into the blood of the compound from all possible sources, including secretion from glands and conversion of prohormones into the steroid of interest ...