Exocrine gland

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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.

Contents

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, 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,an example is fat droplet secretion by mammary gland.
  • 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

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