How do apocrine, exocrine, merocrine, and holocrine glands differ?
Exocrine glands secrete their products in duct system as happens in case of enzymes, milk, sebum or sweat. This is different from the mode of secretion seen in ductless endocrine glands, which release their products (mainly hormones) directly in blood stream.
Merocrine glands secrete product through exocytosis of secretory vacuoles. No part of cell is lost in the process.
Apical regions (=away from basement membrane side) of cells in apocrine glands get pinched off as secretion, thus cells partially lose cytoplasm during secretion.
Cells of holocrine glands dislodge from basement membrane to give rise to secretory material, thus whole of cells are lost to give rise to secretory material.