Lecture Notes: Epithelial Tissue

Introduction

• Epithelial tissue plays a crucial role in organizing and maintaining order in biological systems, similar to organizing children in a lunchroom.
• Without epithelial tissue, the body would lack organization and structure.

Types of Epithelial Tissue

1. Proper Epithelium
   • Covers and lines outer and inner body.
2. Glandular Epithelium
   • Forms glands and secretes hormones and other substances.

Functions

• Protects the body inside and out.
• Separates and organizes body parts.
• Covers body surfaces and lines body cavities.
• Protects deeper layers from injury/infection.
• Avascular (no blood supply), relies on surrounding tissues.

Cell Shapes and Functions

1. Squamous Cells
   • Flat, scale-like.
   • Enable easy passage of substances (e.g., oxygen).
   • Found in air sacs of lungs, blood vessels.
2. Cuboidal Cells
   • Cube-shaped, as tall as wide.
   • Absorb nutrients, produce secretions.
   • Found in glands, ducts.
3. Columnar Cells
   • Tall, column-shaped.
   • Cushion underlying tissues, involved in secretion.
   • Found in digestive tract lining.

Layering

• Simple Epithelium: Single layer of cells.
• Stratified Epithelium: Multiple layers.
• Pseudostratified Epithelium: Appears layered due to varied cell shapes.

Cell Classification

• Combination of shape and layering describes tissue type (e.g., simple squamous epithelium).

Tissue Polarity

• Cells have apical (upper) and basal (lower) sides.
• Basal side attached to basement membrane.
• Selectively permeable, allowing absorption, filtration, excretion.

Glands and Secretions

1. Endocrine Glands
   • Secrete hormones directly into bloodstream.
2. Exocrine Glands
   • Secrete substances into ducts or onto surfaces (e.g., sweat, saliva).

Conclusion

• Epithelial tissue is essential for creating boundaries and facilitating interactions with the environment.
• Plays a key role in forming glands and controlling secretions.

Acknowledgments

• Written by Kathleen Yale, edited by Blake deBestino.
• Consultant: Dr. Brandon Jackson.
• Directed and edited by Nicholas Jenkins.
• Sound designer: Michael Aranda.
• Graphics: Thought Cafe.