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 Depending on how their products are secreted, exocrine glands are categorized as
merocrine,
apocrine, or
holocrine. •
Merocrine – the cells of the gland excrete their substances by
exocytosis into a duct; for example, pancreatic acinar cells,
eccrine sweat glands,
salivary glands,
goblet cells,
intestinal glands,
tear glands, etc. •
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. File:405 Modes of Secretion by Glands Merocine.png|Merocrine secretion File:405 Modes of Secretion by Glands Apocrine.png|Apocrine secretion File:405 Modes of Secretion by Glands Holocrine.png|Holocrine secretion
Product secreted •
Serous cells secrete
proteins, often
enzymes. Examples include
gastric chief cells and
Paneth cells •
Mucous cells secrete
mucus. Examples include
Brunner's glands,
esophageal glands, and
pyloric glands • 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. •
Sebaceous glands secrete
sebum, a lipid product. These glands are also known as oil glands, e.g.
Fordyce spots and
Meibomian glands. ==Additional images==