Difference Between Pseudostratified and Transitional Epithelium

The key difference between pseudostratified and transitional epithelium is that pseudostratified epithelium has only one cell layer attached to the basement membrane while transitional epithelium has multiple layers of differently shaped cells.

Epithelial tissue is one of the four types of tissues which provides the first line of protection to our body. It is a sheet of cells that cover the surface of the body and line the outside of organs and body cavities. Epithelial tissue is avascular and absorbs nutrients via diffusion through the basement membrane. Epithelial tissue is classified into several categories based on the shape of the cells and the number of cell layers. Pseudostratified epithelium and transitional epithelium are two such categories. Pseudostratified epithelium has a single cell layer in which the cells are irregularly shaped, giving the appearance of more than one layer. Transitional epithelium is a specialized stratified epithelium in which the shape of the cells can vary.

CONTENTS

1. Overview and Key Difference
2. What is Pseudostratified Epithelium
3. What is Transitional Epithelium
4. Similarities Between Pseudostratified and Transitional Epithelium
5. Side by Side Comparison – Pseudostratified vs Transitional Epithelium in Tabular Form
6. Summary

What is Pseudostratified Epithelium?

Pseudostratified epithelium appears as a stratified epithelium, but it has a single cell layer in which all cells contact the basement membrane. Nuclei of the cell are located in different layers in the pseudostratified epithelium. Moreover, the cells vary in height.

Under the microscope, pseudostratified epithelium appears as a stratified epithelium composed of several cell layers as the cells are of different heights. Only the tallest cells reach the surface. However, every cell rests on the basement membrane.  Due to this illusion, the epithelial tissue is named as pseudostratified. Most cells have cilia, and they can be seen along the trachea, bronchi and other respiratory structures. The main function of the pseudostratified epithelium is to trap dust and infectious particles. It also provides protection to those tissues.

What is Transitional Epithelium?

Transitional epithelium is a specialized stratified epithelium composed of multiple cell layers (about six layers). The shapes of the cells vary. Transitional epithelium is found only in the urinary system, especially in the bladder, urethra and uterus. Cells in the transitional epithelium can expand and contract. Moreover, they can undergo a change in their shape and structure.

When the bladder is empty, the epithelium is convoluted and has cuboidal apical cells with convex, umbrella shaped, apical surfaces. It appears thicker and more multilayered. When the bladder fills with urine, epithelium loses its convolutions and the apical cells changes from cuboidal to squamous. It appears more stretched out and less stratified. The transitional epithelium in the urinary system is capable of stretching and contracting to accommodate fluctuating volumes of urine.

What are the Similarities Between Pseudostratified and Transitional Epithelium?

• Pseudostratified and transitional epithelia are two types of epithelial tissues.
• Both epithelia are very important to us.

What is the Difference Between Pseudostratified and Transitional Epithelium?

Pseudostratified epithelium is a type of epithelium which has a single layer of cells of various heights. In contrast, transitional epithelium is a type of stratified epithelium composed of multiple layers of cells that are capable of contracting and expanding. So, this is the key difference between pseudostratified and transitional epithelium. Furthermore, pseudostratified epithelium is found in the respiratory tract, while transitional epithelium is found only in the urinary tract.

Moreover, pseudostratified epithelium traps dust and other foreign particles, while transitional epithelium allows urinary tract organs to expand and stretch. Thus, this is the main functional difference between pseudostratified and transitional epithelium. Another difference between pseudostratified and transitional epithelium is that all cells of pseudostratified epithelium touch the basal membrane while only the lowest cell layer of transitional epithelium touches the basal membrane.

Below tabulation summarizes the differences between pseudostratified and transitional epithelium.

Summary – Pseudostratified vs Transitional Epithelium

The key difference between pseudostratified and transitional epithelium is that pseudostratified epithelium has only one cell layer while transitional epithelium has multiple layers. Moreover, cells of the pseudostratified cells are in various heights, and their nuclei are at different levels. Cells of the transitional epithelium are of varying shapes and structure. More importantly, the cells can contract and expand. Furthermore, the pseudostratified epithelium is found in the respiratory tract, while transitional epithelium is found in the urinary tract.

Reference:

1. “Transitional Epithelium”. Biology Dictionary, 2020, Available here.

Image Courtesy:

1. “Pseudostratified columnar epithelium” By Kamil Danak – Own work (CC BY-SA 3.0) via Commons Wikimedia
2. “Harnblase Urothel” By User:Polarlys – Own work (CC BY 2.5) via Commons Wikimedia