exocrine gland

Exocrine glands are glands that secrete their products (excluding hormones and other chemical messengers) into ducts (duct glands) which 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. (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, 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.
• Merocrine glands - cells secrete their substances by exocytosis.

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 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:

See also

• Wikipedia:MeSH A10#MeSH A10.336 --- exocrine glands

The prostate gland is an exocrine gland of the male mammalian reproductive system. It secretes a clear and basic fluid that constitutes 1/3 of the volume of semen.

Additional images

Section of the human esophagus. Moderately magnified.

Dissection of a lactating breast.

References

External links

• Diagram at mhhe.com
• gland at eMedicine Dictionary