Exocrine gland

Exocrine glands are a type of ductal glands that secrete their products (including hormones and other chemical messengers) into ducts that lead directly into the external environment. They are the counterparts to endocrine glands, which secrete their products (hormones) directly into the bloodstream (ductless glands) or release hormones (paracrines) that affect only target cells nearby the release site.

Examples
Typical exocrine glands include sweat glands, salivary glands, mammary glands, stomach, liver, pancreas. (An example of an endocrine gland is the adrenal gland, which is found on top of the kidneys and secretes the hormone adrenaline, among others).

Types
There are many ways of classifying exocrine glands:

Structure
Exocrine glands contain a glandular portion and a duct portion, the structures of which can be used to classify the gland.
 * The duct portion may be branched (called compound) or unbranched (called simple).
 * The glandular portion may be tubular or acinar, or may be a mix of the two (called tubuloacinar). If the glandular portion branches, then the gland is called a branched gland.

Method of secretion
Exocrine glands are named apocrine gland, holocrine gland, or merocrine gland based on how their product is secreted.


 * Apocrine glands - a portion of the plasma membrane buds off the cell, containing the secretion.
 * Holocrine glands - the entire cell disintegrates to secrete its substance, an example is sebaceous glands for skin and nose.
 * Merocrine glands - cells secrete their substances by exocytosis an example is pancreatic acinar cells.

Product secreted

 * Serous cells secrete proteins, often enzymes. Examples include chief cells and Paneth cells
 * Mucous cells secrete mucus. Examples include Brunner's glands, esophageal glands, and pyloric glands
 * Mixed glands secrete both protein and mucus. Examples include the salivary glands, although the parotid gland is predominantly serous, the sublingual gland is predominantly mucous, and the submandibular gland is both serous and mucous.

List of exocrine glands
Glands typically may be referred to by two or more means, though some terms are rarely seen. The names of the anatomists who first described them are often employed, as: