Which of the following sets correctly lists the three modes of secretion in epithelial glands?

• A. Merocrine; Apocrine; Holocrine
• B. Merocrine and Holocrine
• C. Apocrine and Endocrine
• D. Holocrine and Paracrine

Answer: (C)

In epithelial glands, the way secretions exit the secretory cells defines three classic modes: merocrine, apocrine, and holocrine. Merocrine secretion releases product by vesicles fusing with the membrane and exocytosis, so the cell remains intact. Apocrine secretion involves release with a portion of the apical cytoplasm pinching off along with the product, with the cell then rebuilding. Holocrine secretion requires the entire cell to disintegrate to release the product, and new cells replace it from below.

Endocrine and paracrine describe signaling effects (hormones into blood or signals to nearby cells), not how glandular cells secrete into ducts or surfaces. So the set that truly lists the three glandular secretion modes is merocrine, apocrine, and holocrine. The option given mixes in endocrine, which isn’t one of the glandular secretion modes.