Exocrine glands are glands of the exocrine system that secrete their essential product by way of a duct to some environment external to itself, either inside the body or on a surface of the body. Exocrine glands are one of two types of glands in the human body, the other being endocrine glands, which secrete their products directly into the bloodstream. Examples of exocrine glands include the sweat glands, salivary glands, mammary glands, and liver.
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.
By method of excretion
Exocrine glands are named apocrine glands, holocrine glands, or merocrine glands based on how their products are excreted.
Merocrine glands or (eccrine glands) - cells excrete their substances by exocytosis; for example, pancreatic acinar cells.
Apocrine glands - a portion of the plasma membrane buds off the cell, containing the excretion.
Holocrine glands - the entire cell disintegrates to excrete its substance; for example, sebaceous glands of the skin and nose.
By product excreted
Serous cells excrete proteins, often enzymes. Examples include chief cells and Paneth cells
Mucous cells excrete mucus. Examples include Brunner's glands, esophageal glands, and pyloric glands
Mixed glands excrete 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.