Overview
This lecture covers the characteristics, classification, and functions of epithelial tissues, emphasizing their types, naming system, and roles in the human body.
General Characteristics of Epithelial Tissue
- Epithelial tissues line body surfaces, cavities, and form glands.
- They provide protection, absorption, secretion, and sensation.
- Epithelial tissue has closely packed cells with minimal extracellular material.
- These tissues are avascular (lack blood vessels) and receive nutrients by diffusion.
- Epithelial cells have polarity: an apical (free) surface and a basal (attached) surface.
- They are anchored to underlying connective tissue by a basement membrane.
- Epithelial cells regenerate rapidly through mitosis.
Naming Epithelial Tissues
- Epithelial tissue names reflect cell layers (simple, stratified) and cell shapes (squamous, cuboidal, columnar).
- Simple = single cell layer; stratified = multiple layers.
Simple Epithelial Tissues
- Simple squamous: single layer of flat cells; allows diffusion and filtration.
- Simple cuboidal: single layer of cube-like cells; functions in secretion and absorption.
- Simple columnar: single layer of tall, column-like cells; often contain goblet cells for mucus secretion.
Stratified Epithelial Tissues
- Stratified squamous: multiple layers of flat cells; protects against abrasion (e.g., skin, mouth).
- Stratified cuboidal and stratified columnar: rare; found in some ducts and glands.
Pseudostratified Tissue
- Pseudostratified columnar: appears layered but all cells touch the basement membrane; often ciliated; lines respiratory tract.
Transitional Tissue
- Transitional epithelium lines the urinary bladder and stretches to accommodate fluctuation in volume.
Glandular Tissue
- Glandular epithelium forms glands that produce secretions (endocrine: hormones into blood; exocrine: onto surfaces or into cavities).
Key Terms & Definitions
- Epithelial Tissue — Tissue that covers surfaces, lines cavities, and forms glands.
- Basement Membrane — Thin layer attaching epithelium to connective tissue.
- Avascular — Lacking blood vessels.
- Polarity — Structural difference between the apical and basal surfaces of epithelial cells.
- Goblet Cell — Unicellular gland that secretes mucus.
- Pseudostratified — Appears stratified, but all cells touch the basement membrane.
- Transitional Epithelium — Specialized epithelium that stretches, found in the urinary system.
Action Items / Next Steps
- Review microscope images of each epithelial tissue type.
- Complete reading on epithelial tissue functions and locations in your textbook.
- Prepare to identify epithelial tissue types in lab practicals.