Epithelial Tissue Overview

Introduction

• Epithelial tissue is one of the four types of tissue in the human body.
• Found throughout the body, from the heart to skin.
• Focus on histology of epithelial cells and how it relates to visible anatomy.

Role and Importance

• Epithelial tissue is not a major mass in the body but is essential for several functions.
• Main Functions:
  • Forms layers covering internal and external surfaces (e.g., blood vessels, skin).
  • Secretes substances within or outside the body.
  • Forms functional bulk of certain organs (parenchyma).
• Example: Liver is 80% hepatocytes (epithelial cells).

Characteristics

• Epithelial cells are polar, with distinct basal and apical poles.
  • Basal pole: adjacent to basement membrane.
  • Apical pole: faces lumen (inside of tubes like blood vessels).
• Structures:
  • Apical surfaces can have structures like cilia.
  • Lateral faces allow cell communication (gap junctions, tight junctions, desmosomes).
  • Avascular tissue, relies on diffusion from capillaries for nutrients.

Tissue Organization

• Layers:
  • Basement membrane
  • Lamina propria (connective tissue with blood vessels)
  • Epithelium
• Classification System:
  • Based on cell shape (squamous, cuboidal, columnar) and layer arrangement (simple, pseudostratified, stratified).
  • Simple Epithelium: One cell layer thick (e.g., simple squamous in blood vessels).
  • Pseudostratified Epithelium: Appears layered due to varied cell heights.
  • Stratified Epithelium: Multiple layers; includes special types like keratinized epithelium (skin).
  • Transitional Epithelium: Found in organs needing stretch, like the bladder.

Functional Aspects

• Glandular Epithelium:
  • Epithelial cells in glands, essential for secretion.
  • Exocrine Glands: Release substances outside the body or into cavities (e.g., salivary glands, goblet cells).
  • Endocrine Glands: Release hormones into the bloodstream (e.g., pineal gland, Leydig cells in testes).
• Examples:
  • Pineal gland: Contains pinealocytes that secrete melatonin.
  • Testes: Leydig cells secrete testosterone.

Conclusion and Further Learning

• Recognizing epithelial tissue involves identifying the basement membrane and apical surface.
• For more detailed exploration, refer to additional resources such as videos on digestive histology or playlists on histology.
• Encouragement to support via Patreon or sharing with fellow students.