Exocrine Glands (EG)
Exocrine Glands (EG)
Exocrine glands (EG) are specialized glands that produce and secrete substances through ducts onto epithelial surfaces, either external (skin) or internal (lining of the digestive tract). Unlike endocrine glands, which release hormones directly into the bloodstream, exocrine glands deliver their secretions to specific target sites via ducts.
Functions
Exocrine glands secrete a variety of substances essential for bodily functions, including:
- Sweat (for thermoregulation)
- Saliva (aids digestion and oral health)
- Tears (lubricate and protect eyes)
- Milk (nourishes infants)
- Digestive enzymes and bile (facilitate digestion)
- Sebum (lubricates and protects skin)
Structure
Exocrine glands consist of two main parts:
- Glandular portion: Produces the secretory product; composed of specialized cells (serous cells for protein-rich secretions, mucous cells for mucus).
- Ductal portion: Tubular channels lined by epithelial cells that transport secretions to the surface; ducts may be simple or branched.
Types of Exocrine Secretion
- Merocrine (Eccrine): Secretion via exocytosis without loss of cellular material (e.g., sweat glands).
- Apocrine: Part of the cell’s cytoplasm is pinched off with the secretion (e.g., mammary glands).
- Holocrine: Entire cell disintegrates to release its contents (e.g., sebaceous glands).
Examples of Exocrine Glands
| Gland | Location/Function | Secretion Type |
|---|---|---|
| Sweat glands | Skin, regulate body temperature | Merocrine (eccrine) |
| Sebaceous glands | Skin, secrete sebum to lubricate skin and hair | Holocrine |
| Salivary glands | Oral cavity, produce saliva for digestion | Merocrine |
| Mammary glands | Breasts, produce milk for infant nutrition | Apocrine |
| Pancreas (exocrine part) | Abdomen, secretes digestive enzymes into small intestine | Merocrine |
| Liver (biliary system) | Abdomen, secretes bile into digestive tract | Merocrine |
| Lacrimal glands | Eyes, produce tears to lubricate and protect | Merocrine |
Key Points
- Exocrine glands secrete substances onto surfaces via ducts.
- They play vital roles in digestion, thermoregulation, lubrication, and protection.
- Some organs, like the pancreas and liver, have both exocrine and endocrine functions.
- Disorders of exocrine glands include cystic fibrosis (affecting mucus secretion), acne (sebaceous gland dysfunction), and Sjögren’s syndrome (affecting salivary and lacrimal glands).
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References
- StatPearls: Physiology, Exocrine Gland
https://www.ncbi.nlm.nih.gov/books/NBK542322/ - A comprehensive review of exocrine gland structure, secretion mechanisms (merocrine, apocrine, holocrine), and their physiological roles is provided in “Exocrine gland structure-function relationships” (DOI: 10.1242/dev.197657).
- Development Journal: Exocrine Gland Structure-Function Relationships
https://journals.biologists.com/dev/article/149/1/dev197657/273906/Exocrine-gland-structure-function-relationships
Exocrine glands are essential for maintaining homeostasis by producing and delivering secretions that facilitate digestion, protect and lubricate tissues, regulate temperature, and support reproduction and immunity.
