Chapter 4 Epithelial Tissue

Chapter 4: Epithelial Tissue

Overview

• Epithelial tissue is a fundamental tissue type that covers body surfaces, lines cavities and organs, and forms glands.

• Its key functions include:

  • Protection: Acts as a barrier to protect underlying tissues from mechanical injury, pathogens, and dehydration.

  • Secretion: Produces and releases various substances such as hormones, enzymes, and mucus.

  • Absorption: Responsible for the uptake of molecules and nutrients in specific areas of the body, such as the intestines.

Learning Objectives

1. Understand the structure and function of surface epithelial tissues.

2. Identify and differentiate types of simple and stratified epithelia, specifically ( \text{squamous} ), ( \text{cuboidal} ), and ( \text{columnar} ) types.

3. Describe the different types of glands: endocrine and exocrine, along with their secretions.

Classification of Epithelial Tissue

• Types:

  • Surface Epithelium: Covers external and internal surfaces of the body such as skin, lining of the mouth, and blood vessels.

  • Glandular Epithelium: Comprises glands that secrete substances either into the bloodstream (endocrine) or onto surfaces (exocrine).

Structural Features

• Cell Shapes:

  • Squamous: Flat and thin cells, ideal for diffusion and filtration.

  • Cuboidal: Box-like cells that are as wide as tall, involved in secretion and absorption.

  • Columnar: Rectangular cells that are taller than they are wide; they can be specialized for absorption and secretion.

• Cell Layers:

  • Simple Epithelium: A single layer of cells that facilitates diffusion, filtration, or secretion.

    • Types of Simple Epithelium:

      • Simple Squamous Epithelium: Found in areas where rapid exchange is necessary (e.g., alveoli in lungs); allows for diffusion and filtration.

      • Simple Cuboidal Epithelium: Primarily functions in secretion and absorption; seen in kidney tubules and glandular tissues.

      • Simple Columnar Epithelium: Often contains goblet cells that secrete mucus; found in the digestive tract.

      • Pseudostratified Epithelium: Appears multilayered due to differing cell heights but is a single layer; often ciliated and found in the respiratory tract, aiding in mucus movement.

  • Stratified Epithelium: Composed of multiple layers of cells; serves a protective role against abrasion and injury.

    • Types of Stratified Epithelium:

      • Stratified Squamous Epithelium: Most common stratified epithelium;

        • Keratinized: Contains keratin for added protection; found in the skin.

        • Non-Keratinized: Lacks keratin, keeps moist; located in areas such as the esophagus and vagina.

Glandular Epithelium

• Types of Glands:

  • Endocrine Glands: Ductless glands that secrete hormones directly into the bloodstream; examples include thyroid and adrenal glands.

  • Exocrine Glands: Secrete substances through ducts to an epithelial surface; examples include sweat glands and salivary glands.

• Examples of Exocrine Secretion: Saliva, mucus, digestive enzymes, sweat, and other substances.

Key Terms:

• Goblet Cell: A specialized cell within certain epithelial tissues that secretes mucus, contributing to lubrication and protection of the epithelium.

• Basement Membrane: A non-cellular layer that anchors the epithelium to the underlying connective tissue and separates the two tissue types.

• Cilia: Tiny hair-like structures that extend from the surface of some epithelial cells, playing a crucial role in the movement of materials across the cell surface, often found in respiratory epithelial tissues.