What is the Origin of Circulating Hormone Levels?

This is a foundational concept in classical endocrinology, stemming from the development of radioimmunoassay (RIA) and other techniques capable of quantifying hormones in peripheral blood samples. The term "circulating" simply refers to the hormones being transported via the vascular system from their site of secretion to distant target tissues. Understanding these levels is the first step in clinical hormonal assessment.

What is the Mechanism of Circulating Hormone Levels?

Hormones are secreted by endocrine glands into the circulation in response to specific regulatory signals, such as trophic hormones from the pituitary or direct feedback from metabolite concentrations. Once in the blood, they bind to transport proteins, like sex hormone-binding globulin (SHBG) or albumin, which modulate their half-life and distribution. Only the unbound fraction can diffuse across capillary walls and engage intracellular or membrane receptors to exert its biological effect.

Circulating Hormone Levels

Meaning

Circulating Hormone Levels represent the measurable concentration of specific endocrine signaling molecules present in the bloodstream at any given time. These levels include both protein-bound and unbound (free) fractions, with the free fraction being the biologically active component available to interact with target cell receptors. Accurate assessment of these concentrations is fundamental for diagnosing endocrine imbalances and guiding replacement therapy.