Based on the consistency of the secretion, glands are classified into Serous, Mucous and Mixed glands.
Serous glands produce a whey-like serous secretion. Mucous gland produces a slightly more viscid fluid.
The glands that secrete mucin, glycoprotein which when mixed with water become mucous are termed as mucous glands. Any gland that produces a mixture of serous and mucous secretions is called a mixed gland.
Serous secretory unit
- The nucleus of a serous secretory cell is usually rounded and lies towards the base of the cell.
- At the base of the cytoplasm contains secretory granules called zymogen granules.
- Cytoplasm and Zymogen granules stain with eosin (acidophilic).
Mucous Secretory unit
- The nuclei of the mucous secretory cells are flattened and located at the base of cells that contain them.
- There is less chromoideal substance. Above the level of the nucleus the cytoplasm contains mucin droplets, which impart a vacuolated appearance to the very light staining cytoplasm, since with ordinary staining techniques mucin is dissolved.
- Cytoplasm stains only lightly with haematoxylin.
- Mixed glands posses both mucous and serous secretory units.
