Overview
This lecture explains the role of epithelial tissue in organizing and protecting the body, its classification by cell shape and layering, and its function in forming glands.
The Function of Epithelial Tissue
- Epithelial tissue creates organization and boundaries in the body, separating organs and systems.
- It covers body surfaces, lines cavities, and coats the internal and external walls of organs.
- Epithelial tissue acts as a barrier, protecting deeper tissues from injury or infection.
- All epithelial tissues are avascular (lack their own blood supply) and rely on nearby connective tissue for nutrients.
Types and Classifications of Epithelial Tissue
- Two main types: proper epithelium (covers and lines surfaces) and glandular epithelium (forms glands and secretes substances).
- Cell shapes: squamous (flat, "scale-like"), cuboidal (cube-shaped), and columnar (tall, column-like).
- Cell layering: simple (one layer), stratified (multiple layers), and pseudostratified (appears layered, but isn't truly).
- Tissue is named by combining layering and shape (e.g., simple squamous, stratified cuboidal).
Structure and Function Relationships
- Squamous cells are thin for easy absorption/transport; found in lungs and blood vessels.
- Cuboidal and columnar cells are larger for secretion/absorption; found in glands and stomach lining.
- Stratified squamous epithelium is durable, allowing easy cell loss and replacement (e.g., skin, mouth).
- Epithelial tissue regenerates quickly, making it resilient to damage.
Polarity and Permeability
- Epithelial cells are polar with an apical (upper) side exposed to the environment/cavity and a basal (lower) side attached to the basement membrane.
- Boundaries formed by epithelial tissue are selectively permeable, enabling absorption, filtration, and excretion.
Glandular Epithelium
- Glandular epithelium forms endocrine glands (release hormones into blood) and exocrine glands (release substances into ducts).
- Endocrine glands (e.g., thyroid) secrete hormones like thyroxin directly to blood.
- Exocrine glands secrete products like sweat, saliva, mucus, and stomach acid into ducts.
Key Terms & Definitions
- Epithelial tissue â tissue that lines, covers, and organizes body surfaces and organs.
- Avascular â lacking its own blood vessels.
- Squamous/cuboidal/columnar cells â flat, cube-shaped, and column-shaped epithelial cells, respectively.
- Simple/stratified/pseudostratified â one layer, multiple layers, and seemingly multilayered epithelial cell arrangements.
- Polarity â presence of distinct apical and basal sides in epithelial cells.
- Basement membrane â thin layer anchoring epithelium to connective tissue.
- Endocrine gland â gland that releases hormones into the bloodstream.
- Exocrine gland â gland that releases substances via ducts to surfaces or cavities.
Action Items / Next Steps
- Review examples of each epithelial tissue type and their locations.
- Study diagrams showing epithelial cell shapes and layering.