50. Glandular epithelium - exocrine type. Classification of glands.

Glandular Epithelium

Epithelial cells that specialize in the production and secretion of macromolecules, primarily proteins, glycoproteins, and other complex molecules.

Classification of Glands

• Exocrine Glands:

  • Definition: Glands that secrete substances onto an epithelial surface through ducts. They retain their connection to the surface epithelium from which they originated.

  • Structure: Composed of tubular ducts and secretory portions that transport and deliver the secreted material to the surface.

  • Classification:

    • Based on Duct Structure:

      • Simple: Unbranched ducts.

      • Compound: Branched ducts.

    • Based on the Shape of Secretory Units:

      • Tubular: Tube-like secretory portions.

      • Acinar (or Alveolar): Rounded, sac-like secretory portions.

      • Tubuloacinar: Combination of tubular and acinar structures.

• Endocrine Glands:

  • Glands that lose their connection to the surface epithelium and are ductless. They secrete hormones directly into the bloodstream or surrounding tissue.

• Paracrine Glands:

  • Glands that secrete substances locally to adjacent cells, affecting cells in the immediate vicinity.

Mechanisms of Secretion in Exocrine Glands

Exocrine glands employ three basic mechanisms for secretion:

1. Merocrine Secretion:

   • The most common method of secretion.

   • Involves the release of products, such as proteins or glycoproteins, by exocytosis from secretory vesicles.

   • Examples: Salivary glands, pancreas.

2. Holocrine Secretion:

   • Involves the release of entire cells. The secretory cells accumulate their products and then rupture, releasing both the cellular debris and the secretory product.

   • This process destroys the cells in the process of secretion.

   • Example: Sebaceous glands (associated with hair follicles).

3. Apocrine Secretion:

   • Involves the release of the secretory product along with a portion of the cytoplasm and cell membrane.

   • The apical portion of the cell pinches off and releases the secretory product.

   • Example: Mammary glands.

Types of Cells in Exocrine Glands

• Serous Cells: Produce watery, enzyme-rich secretions. Example: Digestive enzymes secreted by the pancreas.

• Mucous Cells: Produce viscous, glycoprotein-rich mucus. Example: Goblet cells in the respiratory and intestinal tracts.

• Mixed (Seromucous) Cells: Glands that contain both serous and mucous cells and produce a combination of watery and mucous secretions. Example: Submandibular glands (salivary glands).