What is the Origin of Bioactive Steroid Fractions?

This essential concept arose in endocrinology to distinguish between the total amount of hormone present and the fraction that is truly active, unbound by carrier proteins. Carrier proteins, like Sex Hormone-Binding Globulin (SHBG) and albumin, temporarily sequester the majority of circulating steroids. The term highlights the biological relevance of the free component.

What is the Mechanism of Bioactive Steroid Fractions?

Steroid hormones, such as testosterone, progesterone, and estradiol, must dissociate from their binding proteins to freely diffuse across cell membranes. Once inside the cell, they bind to intracellular receptors, which then translocate to the nucleus to regulate gene expression. Only the unbound or weakly bound fraction possesses this capacity to initiate the cascade of genomic and non-genomic cellular responses, making it the determinant of the hormone's biological efficacy.

Bioactive Steroid Fractions ∞ Area

Bioactive Steroid Fractions

Meaning

Bioactive Steroid Fractions refer to the specific, unbound portions of steroid hormones circulating in the bloodstream that are immediately available to engage with target cell receptors and exert their physiological effects. These fractions, often clinically referred to as “free hormones,” represent the actual functional hormonal signal, providing a more accurate assessment of tissue-level hormonal activity than total hormone measurements. The concentration of these fractions dictates the magnitude of the biological response.