Merocrine, apocrine and holocrine, by how much cell is lost
Expansion
Three modes, distinguished by how much of the cell is lost
- Merocrine (eccrine) - exocytosis only, the cell is unchanged. Most glands: eccrine sweat glands, salivary glands, pancreas
- Apocrine - the apical cytoplasm is pinched off with the product. Apocrine sweat glands of the axilla and groin, and the breast during lactation
- Holocrine - the entire cell disintegrates and becomes the secretion. Sebaceous glands only
“Mero keeps the cell, apo loses its top, holo dies.”
Sebaceous glands must continually replace their cells because each secretion event destroys one, which is why they are so proliferative and why they are the site of acne.
Classification by shape and duct: simple or compound (whether the duct branches), and tubular, acinar or tubuloacinar (the shape of the secretory unit). So the pancreas is compound acinar and eccrine sweat glands are simple coiled tubular.
Classification by product: serous (watery, protein rich, with a round central nucleus and basophilic cytoplasm, as in the parotid), mucous (viscous, with a flattened basal nucleus and pale cytoplasm, as in sublingual), or mixed with serous demilunes, as in the submandibular gland.