8.11:
Exocrine Glands: Types of Secretions
Exocrine glands can be serous, mucous, or mixed depending on the nature of their secretory products.
Serous glands produce thin aqueous secretions that are rich in glycoproteins and enzymes.
For example, the parotid salivary glands are serous glands positioned in front of the ears. They produce saliva, rich in amylase that helps break down starchy food.
Mucous glands consist of cells whose cytoplasm is filled with mucin-rich secretory vesicles, giving them a frothy appearance.
A good example of mucous glands are sublingual glands that lie below the tongue at the floor of the mouth. These glands secrete mucin that dissolves in water, forming a thick, slimy mucus coat that lubricates the oral cavity and helps make food easier to swallow.
Mixed exocrine glands are composed of serous secretory units intermixed with mucous secretory units and can produce both serous and mucous secretions.
The submandibular salivary glands are mixed glands located towards the back of the mouth that discharge saliva through the submandibular duct.
8.11:
Exocrine Glands: Types of Secretions
Exocrine glands produce and release a variety of glandular products. Exocrine glands can be classified into serous, mucous, or mixed types based on their secretory products.
Serous glands produce watery secretions rich in digestive enzymes and proteins. The constituent cells of the serous gland have centrally located nuclei and eosinophilic secretory granules in the cytoplasm. The parotid gland is an example of a serous gland. It secretes saliva, which contains enzymes, such as lipases and amylases that help digest the food.
Mucous glands release viscous products rich in the glycoprotein mucin. The constituent cells of mucous glands are characterized by flattened nuclei located at the basal surface of the cells and cytoplasm filled with secretory granules. Examples of mucous glands include sublingual salivary glands and the submucosal glands of the small intestine.
Mixed exocrine glands contain both serous and mucous glands and release both types of secretions. Submandibular salivary glands are examples of mixed glands.
This text is partially adapted from Openstax, Anatomy and Physiology 2e, Section 4.2: Epithelial Tissues