Histology Lecture 3: Glandular Epithelium

Glandular Epithelium

• Glandular epithelial cells produce secretions, synthesizing, storing, and secreting proteins, lipids, and complexes of carbohydrates and proteins.

Development of Glands

• Glands form from covering epithelia through cell proliferation, penetration into connective tissue, and further differentiation.
• Glands may maintain contact with the surface, forming exocrine glands, or lose contact, forming endocrine glands.

General Histological Structure of Glands

• A gland is surrounded by a dense layer of connective tissue, forming a capsule, which extends into the gland, dividing it into lobes and lobules.
• The functional part of a gland, formed by its secretory cells, is known as the parenchyma, while the supporting elements, mainly connective tissue, are the stroma.

Classification of Glands

• Exocrine glands release products onto an epithelial surface, either directly or through a duct, e.g., salivary glands, mammary glands.
• Endocrine glands release products into the bloodstream, e.g., thyroid gland, pituitary gland.
• Mixed glands possess both exocrine and endocrine functions, e.g., pancreas, liver cells.

Histological Classification of Exocrine Glands

• According to secretory mechanisms:

  • Merocrine: secretory product is released by exocytosis, without loss of cell substance, e.g., pancreas, salivary glands.
  • Apocrine: apical part of cytoplasm is lost with secretory product, e.g., female mammary gland.
  • Holocrine: entire secretory cell and product are discharged, e.g., sebaceous glands.

• According to duct system:

  • Simple: ducts are not branched.
  • Compound: ducts are branched.

• According to secretory portion:

  • Tubular: shaped like a tube, e.g., glands of intestine, stomach.
  • Acinar or alveolar: flask-shaped with narrow centrally placed lumen, e.g., pancreas, parotid salivary gland.
  • Tubuloacinar: combination of tube ends with sac-like dilatation, e.g., submandibular and sublingual salivary glands.

Histological Classification According to Nature of Secretions

• Mucous glands: produce viscid, slimy, carbohydrate-rich secretion, e.g., Pyloric glands of stomach.
• Serous glands: produce thin, watery, protein-rich secretions, often high in enzymatic activity, e.g., Exocrine pancreas, parotid salivary gland.
• Mixed glands: produce both mucous and serous secretions, e.g., sublingual and submandibular salivary glands.