Lecture Notes: Epithelial Tissue

Introduction

• Epithelial tissue is essential for creating order in biological systems.
• It maintains separation and organization of cells and tissues.
• Analogous to organizing students in a lunchroom to maintain order.

Functions of Epithelial Tissue

• Lines and covers the body, both externally and internally.
• Organizes body into functional units.
• Protects deeper tissues from injury and infection.
• Avascular: relies on connective tissue for nutrients.

Types of Epithelial Tissue

1. Proper Epithelium

• Covers and lines the outer and inner body.

2. Glandular Epithelium

• Forms glands and secretes hormones and other substances.

Characteristics of Epithelial Tissue

Shapes

• Squamous: Flat, scale-like, allows easy passage of materials.
• Cuboidal: Cube-shaped, absorbs nutrients, and produces secretions.
• Columnar: Tall, column-like, cushions underlying tissues.

Layers

• Simple Epithelium: Single cell layer.
• Stratified Epithelium: Multiple cell layers.
• Pseudostratified Epithelium: Appears layered due to varying cell shapes and nuclei positions.

Classification

• Named by number of layers and cell shape.
  • Example: Simple squamous epithelium (single layer of flat cells).

Polar Nature

• Cells have distinct sides:
  • Apical: Upper side, exposed to outside or internal cavity.
  • Basal: Lower side, attached to basement membrane and connective tissue.

Functionality

• Selectively permeable, allowing absorption, filtration, and excretion.
• Lines intestines for nutrient absorption.
• Involved in secretion via glandular epithelium.

Glandular Epithelium

• Endocrine Glands: Secrete hormones into bloodstream.
• Exocrine Glands: Secrete substances into ducts leading to body surfaces.

Conclusion

• Epithelial tissue is vital for maintaining boundaries and facilitating bodily functions.
• Supports secretions and interactions with the external environment.