Merocrine

Merocrine secretion is a mode of exocrine secretion in which secretory products are released by exocytosis through the plasma membrane, with no loss of the secreting cell. It contrasts with apocrine secretion, where a portion of the cell’s apical cytoplasm is shed, and holocrine secretion, in which the entire cell disintegrates to release its product.

Mechanistically, secretory proteins and enzymes are synthesized in the rough endoplasmic reticulum and processed in the Golgi apparatus, then packaged into secretory vesicles. These vesicles accumulate near the cell membrane and fuse with it, discharging their contents into ducts or onto body surfaces while the secretory cell itself remains intact and functional.

Classic examples of merocrine secretion include eccrine sweat glands, pancreatic acinar cells, serous cells of the salivary glands, and goblet cells that produce mucus in the respiratory and gastrointestinal tracts. In these tissues, secretory products are released via exocytosis without damaging the secretory cells, enabling rapid and repeated secretion.

Compared with other secretory modes, merocrine secretion is characterized by cellular preservation after product release, whereas apocrine secretion involves loss of apical cytoplasm and holocrine secretion results in cell rupture. This mode is the most common mechanism of secretion among many exocrine glands in humans.