Exocrine glands are
glands that secrete substances onto an
epithelial surface by way of a
duct.[1] Examples of exocrine glands include
sweat,
salivary,
mammary,
ceruminous,
lacrimal,
sebaceous,
prostate and
mucous. 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. The
liver and
pancreas are both exocrine and endocrine glands; they are exocrine glands because they secrete products—
bile and
pancreatic juice—into the
gastrointestinal tract through a series of ducts, and endocrine because they secrete other substances directly into the bloodstream. Exocrine sweat glands are part of the integumentary system; they have eccrine and apocrine types.
Classification
Structure
Exocrine glands contain a glandular portion and a duct portion, the structures of which can be used to classify the gland.[1]
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
Depending on how their products are secreted, exocrine glands are categorized as
merocrine,
apocrine, or
holocrine.[1]
Apocrine – the apical portion of the
cytoplasm in the
cell membrane, which contains the excretion,
buds off. Examples are sweat glands of arm pits, pubic region, skin around anus, lips and nipples;
mammary glands, etc.
Holocrine – the entire cell disintegrates to excrete its substance; for example, sebaceous glands of the
skin and nose,
meibomian gland,
zeis gland, etc.
Seromucous glands (mixed) secrete both protein and mucus. Examples include the
salivary glands: although the
parotid gland (saliva secretion 25%) is predominantly serous, the
sublingual gland (saliva secretion 5%) mainly mucous gland, and the
submandibular gland (saliva secretion 70%) is a mixed, mainly serous gland.