Which mode describes secretion via exocytosis without loss of cytoplasm?

• A. Merocrine
• B. Holocrine
• C. Apocrine
• D. Endocrine

Answer: (A)

Merocrine secretion is the mode where secretory products are released by exocytosis in secretory vesicles, while the cell itself remains intact and no cytoplasm is lost. The vesicles fuse with the plasma membrane and release their contents to the exterior, preserving the cell’s cytoplasm and architecture for continued secretion. This is different from holocrine secretion, where the whole cell disintegrates to release its contents, and from apocrine secretion, where a portion of the cell’s cytoplasm and membrane buds off along with the secretory product. Endocrine refers to secretion into the bloodstream rather than the mechanism by which the product exits the cell, so it does not describe the exocytosis-without-cytoplasm-loss process.