Lecture Notes: Epithelial Tissue by Dr. Mike

Overview

• Epithelia form boundaries between environments in the body.
• Functions of epithelia:
  • Allow passage of substances.
  • Restrict passage of certain substances.
  • Facilitate movement across surfaces.

Form Equals Function

• The structure of epithelial tissue suggests its function.
• Simple vs. Stratified:
  • Simple: Single layer; facilitates easy passage.
  • Stratified: Multiple layers; provides protection.

Types of Epithelial Tissue

Simple Squamous Epithelium

• Location: Lungs
• Function: Gas exchange (e.g., oxygen and carbon dioxide).
• Structure: Single layer of squished cells allows easy passage.

Stratified Squamous Epithelium

• Structure: Multiple layers of squished cells.
• Function: Protection; cells are often dead and can slough off.
• Locations:
  • Oral cavity: Non-keratinized; allows moisture.
  • Skin: Keratinized; provides waterproof protection.

Pseudostratified Columnar Ciliated Epithelium

• Location: Trachea (windpipe).
• Function:
  • Produces and secretes mucus.
  • Cilia move pollutants and particulates out to be expelled by coughing.
• Structure: Appears multilayered but is a single layer; has cilia and intracellular components.

Columnar Epithelium in the Small Intestines

• Function:
  • Secretes mucus and digestive enzymes.
  • Absorbs nutrients from digested food.
• Structure: Has microvilli and villi to increase surface area for absorption.

Simple Cuboidal Epithelium in Kidneys

• Location: Nephron (convoluted tubules).
• Function:
  • Selective absorption and reabsorption.
  • Decides whether substances are excreted or returned to blood.
• Structure: Single layer of cube-shaped cells.

Transitional Epithelium in the Bladder

• Function: Allows stretching and recoiling.
• Structure: Can change shape (cuboidal, columnar, squamous) to accommodate bladder expansion and contraction.

Summary

• Epithelial tissue varies greatly in form, reflecting the wide array of functions it performs in the body.
• Understanding the structure of each type allows for insights into its specific role and location in the body.
• Epithelial tissue is integral to protection, secretion, absorption, and filtration in various organs and systems.