Bloodstream signaling, or endocrine signaling, describes the physiological process where chemical messengers, predominantly hormones, are secreted directly into the circulatory system by specialized endocrine glands. These messengers travel via the bloodstream to reach distant target cells, tissues, and organs throughout the body. This systemic mode of communication ensures coordinated regulation of complex physiological functions, including metabolism, growth, reproduction, and stress response. The concentration of hormones in the blood provides a critical measure of endocrine status in clinical assessment.
Origin
The concept of chemical messengers traveling through the blood was formally established with the discovery of the first hormone, secretin, in 1902 by William Bayliss and Ernest Starling, who coined the term “hormone” from the Greek word hormao, meaning “I excite” or “I arouse.” This discovery shifted the understanding of physiological control from purely nervous to integrated neuroendocrine regulation. Understanding this signaling route is fundamental to modern endocrinology and hormonal therapy.
Mechanism
The mechanism involves the endocrine cell synthesizing and releasing a hormone into the capillaries, where it binds to transport proteins or travels freely in the plasma. Upon reaching a target tissue, the hormone binds to highly specific receptors, which can be located on the cell surface (for peptide hormones) or intracellularly (for steroid hormones). Receptor binding initiates a cascade of intracellular events, altering gene expression or enzyme activity to produce the final biological response. This circulatory route ensures systemic, long-distance communication essential for maintaining whole-body homeostasis.
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