secretion

Secretion is a cell deciding not just to make something, but to release it at the right moment — like a fire crew that keeps hoses charged and ready, then opens the valve only when the alarm sounds. Making a hormone is one job; letting it out in a controlled, timed way is a separate, carefully managed step.

Secretion is the regulated release of a substance — such as a hormone, enzyme, or fluid — from a cell or gland. For peptide and amine hormones, the molecules are typically pre-packaged in storage vesicles called secretory granules and released by exocytosis when a trigger arrives, often a rise in intracellular calcium. Steroid hormones, by contrast, are not stored but synthesized and released on demand.

How secretion is patterned over time matters enormously: it can be steady (tonic or basal), bursty (pulsatile), or tied to the day-night cycle (circadian). A caveat: secretion is not the same as synthesis. A gland can hold a large reserve of pre-made hormone and release it rapidly, so a sudden rise in blood hormone may reflect release of stores rather than fresh manufacture.