Merocrinos

Merocrinos, or merocrine secretion, is a common modality of exocrine secretion in glandular tissue. In merocrine secretion, secretory products are discharged from the secretory cell by exocytosis in membrane-bound vesicles, while the cell itself remains intact and capable of continued synthesis and release.

Mechanism: Secretory proteins are synthesized in the endoplasmic reticulum, processed in the Golgi apparatus, and stored in secretory granules near the cell apex. Upon stimulation, the granules fuse with the plasma membrane and release their contents into the lumen or exterior, with no loss of cytoplasm. The secretory membrane is replenished and the cell can repeat the cycle.

Examples: Pancreatic acinar cells secrete digestive enzymes by merocrine exocytosis. The serous component of many salivary glands and the eccrine sweat glands are typically described as merocrine. Some tissues also shed components via vesicles but without cytoplasmic loss. In certain glands, secretions exhibit a mixed or context-dependent mechanism.

Relation to other modes: Holocrine secretion involves rupture and disappearance of the secretory cell (as in sebaceous glands). Apocrine secretion, historically described as apical cytoplasm shedding, is variably defined; many authorities classify its secretions as merocrine with occasional cytoplasmic blebs. Merocrine secretion is favored for rapid, continuous secretion and genetic control, whereas holocrine and apocrine strategies may be advantageous for storing or exporting lipid-rich products or protecting cells during stress.

Significance: Understanding merocrinos clarifies differentiation of gland types and how secretory products are released. It has implications for physiology, histology education, and pathology when secretion dynamics are altered by disease or toxins.