Lecture on Epithelial Tissue Histology

Introduction

• Epithelial tissue is one of four tissue types in the human body.
• Found in various locations from skin to the inside of the heart.
• Focus on histology and microscopic anatomy.

Overview of Epithelial Tissue

• Does not constitute a large portion of body mass compared to muscle and connective tissue.
• Plays crucial roles:
  • Covering Surfaces: Internal and external (e.g., blood vessel linings, skin).
  • Secretion: Substances inside or outside the body.
  • Parenchyma Formation: Major functional part of organs (e.g., liver).
• Often serves as protective layers and secreting cells.

Characteristics of Epithelial Cells

• Polar Nature:
  • Distinct top (apical) and bottom (basal) poles, separated by a basement membrane.
  • Apical side faces lumen (inside of tubes like blood vessels).
  • Basal side touches the basement membrane.
• Special Features:
  • Cilia: Hairlike structures on the apical surface, common in lungs.
  • Lamina Propria: Connective tissue layer beneath the basement membrane.
  • Lateral Faces: Communication between cells through gap junctions, tight junctions, and desmosomes.

Epithelial Tissue Organization

• Avascular Nature:
  • Nutrients and oxygen received via diffusion from capillaries in lamina propria.
  • Quick regeneration (e.g., skin).
• Slide Observations:
  • Respiratory system slide: pink epithelial cells with cilia, thin basement membrane, and thicker lamina propria with blood vessels.

Classification of Epithelial Cells

• Cell Shapes:
  • Squamous: Flat, pancake-like, oval nucleus.
  • Cuboidal: Cube-shaped, large round nucleus, many organelles.
  • Columnar: Tall, often in specialized cells like mucus-secreting cells.
• Layer Organization:
  • Simple Epithelium: Single layer (e.g., simple squamous lines blood vessels).
  • Pseudostratified Epithelium: Appears layered due to varying cell heights, but all cells touch the basement membrane.
  • Stratified Epithelium: Multiple layers, can be squamous, cuboidal, columnar.
  • Keratinized: Stratified cells die and fill with keratin, forming dead outer layers (e.g., skin).
  • Transitional Epithelium: Layers that transition between cell types (e.g., bladder).

Glandular Epithelium

• Function:
  • Form linings and interact with substances in blood.
  • Examples: thyroid gland (endocrine), goblet cells (exocrine).
• Types:
  • Endocrine Glands: Release hormones into bloodstream.
  • Exocrine Glands: Secrete substances outside the body or into cavities.
• Examples:
  • Pineal Gland: Contains pinealocytes that secrete melatonin.
  • Leydig Cells: In testes, secrete testosterone.
  • Goblet Cells: Secrete mucus in the GI tract.
  • Salivary Glands: Secrete enzymes into saliva.
  • Apocrine Glands: Exocrine glands that release odorants.

Conclusion

• Importance of identifying epithelial tissue in histology slides.
• Epithelial cells are crucial for protection and secretion.
• Upcoming content on digestive system histology.
• Support via Patreon or sharing with peers.