Overview
An exocrine gland is a tissue that produces and delivers substances to an external surface or to a body cavity via a duct. Unlike an endocrine gland, which releases hormones directly into the bloodstream, an exocrine gland's products act locally or are transported to the outside environment. Secretions include enzymes, mucus, sweat, oil and milk.
Structure and modes of secretion
Exocrine glands vary in microscopic structure: they can be simple (single, unbranched duct) or compound (branched ducts), and their secretory portions may be tubular, alveolar (saccular), or tubuloalveolar. Cells use different mechanisms to release material:
- Merocrine: secretion by exocytosis without loss of cell material (common in salivary and sweat glands).
- Apocrine: a portion of the cell’s apical cytoplasm is shed with the secretion (seen in some mammary and sweat glands).
- Holocrine: whole cells disintegrate to become the secretion (typical of sebaceous glands).
Common examples and roles
Major exocrine organs include:
- Salivary glands — begin digestion and lubricate food.
- Pancreas (exocrine part) — secretes digestive enzymes into the small intestine.
- Sweat glands — contribute to thermoregulation and skin hydration.
- Sebaceous glands — produce sebum to protect skin and hair.
- Mammary glands — produce milk in mammals.
Development, regulation and distinction
During embryonic development exocrine structures form as epithelial downgrowths that maintain duct connections. Their activity is regulated locally and by neural or hormonal signals depending on the gland; for example, parasympathetic innervation stimulates salivation while hormones influence mammary secretion. The key distinction from endocrine tissue is the presence of a duct and a targeted local delivery rather than systemic hormone release.
Clinical significance and testing
Dysfunction of exocrine glands underlies common conditions: obstructed ducts can cause inflammation (e.g., pancreatitis), abnormal secretions contribute to acne, and genetic disorders such as cystic fibrosis impair exocrine secretions and mucus clearance. Diagnostic tests include imaging, sampling of ductal fluid and functional assays such as the sweat chloride test. Treatments range from ductal drainage and antibiotics to enzyme replacement and topical therapies.