1. Merocrine secretion: This is the most common method
of protein secretion and involves typical exocytosis of pro-
teins or glycoproteins from membrane-bound vesicles.
2. Holocrine secretion: In this process cells accumulate
product as they mature and undergo terminal cell differ-
entiation, culminating in complete cell disruption with
release of the product and cell debris into the gland’s
lumen. This is best seen in the sebaceous glands of skin
(Figure 4–22).
3. Apocrine secretion: Here product accumulates at the
cells’ apical ends, portions of which are then extruded
to release the product together with a bit of cytoplasm
and plasma membrane. This is the mechanism by which
droplets of lipid are secreted in the mammary gland