Lecture Notes: Structure and Classification of Glands

Overview

• Glands are multicellular organs or individual cells that secrete substances for use in the body.
• Made primarily of epithelial tissue.
• Secretions include mucin, hormones, electrolytes, enzymes, and waste products.

Types of Glands

• Endocrine Glands

  • Secrete hormones directly into the bloodstream or interstitial fluid.
  • Examples: adrenal, thyroid, and pituitary glands.

• Exocrine Glands

  • Secrete products into a duct or onto a surface (not into the bloodstream).
  • Can be unicellular or multicellular.
  • Unicellular Exocrine Glands
    • Do not contain ducts.
    • Example: Goblet cells - secrete mucin to form a mucus layer (e.g., in the trachea).
  • Multicellular Exocrine Glands
    • Contain a duct system.

Classification of Multicellular Exocrine Glands

By Form

• Simple Glands

  • Single duct.
  • Types:
    • Simple straight tubular
    • Coiled tubular
    • Simple branched tubular
    • Simple acinar
    • Simple branched acinar

• Compound Glands

  • Branching ducts.
  • Types:
    • Compound tubular
    • Compound acinar
    • Compound tubuloacinar (both tubular and acinar regions)

By Secretion Method

• Merocrine Glands

  • Release secretions via exocytosis without damaging the cell.
  • Example: Salivary glands.

• Apocrine Glands

  • Pinch off a portion of the cell to release secretory products.
  • Cell repairs itself and continues secretion.
  • Examples: Mammary glands, some sweat glands.

• Holocrine Glands

  • Cells accumulate products and rupture to release them.
  • Ruptured cells are replaced by new cells through division.
  • Examples: Certain skin and eyelid glands.

Conclusion

• This lecture covered the basics of gland structure and classification.
• Future lectures will explore the structure and functions of individual glands.