In the slides of submandibular gland, note the two different types of staining known as serous and mucous. The staining difference is important and reflects fundamental differences in cell function.

• Serous acini secrete a protein-rich product with various digestive enzymes and stain fairly well due to the presence of rER and secretory granules (dense protein-filled vesicles) in the cytoplasm.
• Mucous acini, like goblet cells, secrete mucus, which contains less protein but much watery “mucopolysaccharide.”
  • Mucous cells stain very poorly because they contain little rER and their mucin granules tend to react poorly with most stains. The distinction between serous and mucous types of secretory cells will be important later in the course (more important actually than the morphological distinctions discussed above.)

Sketch one or two serous and mucous cells and show the differences between them.

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