Classification of Glands

Classification of Glands

• Glands are classified based on their mechanism of secretion.

Types of Glands

• Types include serous glands, mixed glands, mucous glands, endocrine glands, exocrine glands, merocrine (eccrine) glands, apocrine glands, and holocrine glands.

Serous Glands

• Produce non-viscous, watery fluids.
• Functions include carrying wastes to the skin surface, providing milk for nursing, and delivering digestive enzymes from the pancreas to the small intestine.
• Example: parotid salivary gland; also produces sweat, tears, and digestive juices.

Mucous Glands

• Secrete mucin that forms mucus when mixed with water.
• Located in the digestive system and sublingual salivary glands.
• Found on the surface of the tongue and roof of the mouth.

Mixed Glands

• Contain both mucus and serous cells; produce a mixture of secretions.
• Example: submandibular salivary glands.

Endocrine Glands

• Ductless glands that release secretions directly into the bloodstream.
• Examples include the pancreas, pituitary gland, and thyroid.

Exocrine Glands

• Typically have ducts and are formed from epithelial tissues.
• Secrete materials onto free epithelial surfaces.
• Examples include glands in the digestive tract, eyes, mammary glands, and sweat glands.

Types of Exocrine Glands

• Categorized into unicellular and multicellular types.
• Multicellular exocrine glands include merocrine, apocrine, and holocrine glands.

Unicellular Exocrine Glands

• Composed of a single cell; principal function is to secrete mucin.
• Lack ducts.
• Example: Goblet cells located in respiratory and digestive systems.

Merocrine Glands

• Also known as eccrine glands; located in the dermal layer.
• Secretion leaves the cell intact, comprising mucin or watery perspiration.
• Purpose: regulates body temperature, eliminates excess water and electrolytes, and prevents microbial growth.
• Examples include lacrimal glands, salivary glands, exocrine glands of the pancreas, and gastric glands.

Apocrine Glands

• Found in the dermal layer and are also sudoriferous glands.
• Secretion involves pinching off the top part of the cell, resulting in a viscous, milky substance rich in proteins and lipids.
• Activated during puberty and take part in secretion into hair follicles.
• Examples: mammary glands and sweat glands in axillary and pubic regions.

Holocrine Glands

• Also known as sebaceous or oil glands; secrete by rupturing, whereby cells die and become the secretion.
• Purpose: secretes sebum, which keeps hair healthy and prevents brittleness.
• Activity increases during puberty.
• Example: glands located in skin hair follicles.