Merokrina

Merokrina, or merocrine secretion, is a mode of exocrine gland secretion in which secretory products are released from secretory cells by vesicular exocytosis. In this process, secretory granules manufactured in the cell are packed into vesicles, transported to the plasma membrane, and released into a duct or lumen without any loss of the cell’s cytoplasm or structural integrity.

Mechanistically, the secretion occurs through membrane fusion of secretory vesicles with the apical plasma membrane. The secretory cells themselves remain intact and capable of repeated rounds of secretion, making merocrine secretion the most common form of exocrine discharge in many tissues.

Merocrine secretion is distinguished from holocrine secretion, in which the entire cell disintegrates to release its contents, and from apocrine secretion, where a portion of the cell’s apical cytoplasm is shed along with the secretory product. In practice, many glands employ merocrine secretion as the primary mechanism, though secretions from some glands may involve multiple modes depending on tissue and stimuli.

Common examples of merocrine secretion include eccrine sweat glands, many salivary gland secretions, pancreatic exocrine enzymes, goblet cells in the respiratory and gastrointestinal tracts, and various mucous-producing glands. This secretion mode is typically regulated by neural and hormonal signals and is essential for functions such as thermoregulation, digestion, lubrication, and protection of mucosal surfaces.