Hormone secretion is the process by which specialized endocrine cells, located in glands like the thyroid, adrenals, or gonads, synthesize and release hormones directly into the bloodstream or surrounding interstitial fluid. This is the initial and critical step in hormonal signaling, determining the circulating concentration of the chemical messenger that will ultimately act upon distant target tissues. The rate and pattern of secretion are tightly controlled by neurological and hormonal stimuli.
Origin
The term is derived from the Greek word secretio, meaning “to separate or release,” and is a foundational concept in classical physiology and endocrinology. The historical distinction between endocrine (internal secretion into blood) and exocrine (external secretion into ducts) glands cemented the meaning of hormone secretion as the primary mode of chemical communication for the endocrine system. Understanding the secretory patterns is essential for interpreting hormone profiles.
Mechanism
The mechanism of hormone secretion varies depending on the chemical nature of the hormone. Peptide hormones, like insulin, are synthesized as pre-prohormones, stored in secretory vesicles, and released via exocytosis in response to a specific stimulus, often involving calcium influx. Steroid hormones, like testosterone, are synthesized from cholesterol on demand and typically diffuse across the cell membrane immediately upon synthesis, with their rate of secretion governed by the activity of the rate-limiting enzymes in their biosynthetic pathway.
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