Now let’s consider two main types of secretory products produced by exocrine glands, serous and mucous secretions.

In these two slides of mixed serous/mucous and purely serous salivary glands (submandibular gland and parotid gland), respectively, note the staining differences that result from the two different types of secretory products made by these glands. These staining differences are important and reflect fundamental differences in cell function.

• Serous acini secrete a protein-rich product containing various digestive enzymes. These secretory products stain well with eosin, giving the apical cytoplasm where these secretory vesicles are stored an intense pink color. Because these cells are producing a great deal of secreted proteins, they will also exhibit basophilia in the cytoplasm due to the presence of abundant rER.
• Mucous acini, like goblet cells, secrete mucus, which is a watery, carbohydrate-rich substance that is low in protein. Mucus-producing cells stain very poorly because they contain little rER and their mucin secretory granules react poorly with most stains, except PAS-Alcian blue, which stains mucus purple.

So, how do the secretory cells actually produce and release their product?