Difference Between Simple and Stratified Epithelium

Main Difference – Simple vs Stratified Epithelium

Simple, pseudostratified, and stratified epithelium are three arrangements of the cells in the epithelial tissue. Epithelial tissue is one of the four basic types of tissue in animals. Epithelial tissue lines the cavity and the surfaces of organs and blood vessels throughout the animal body. Three principle shapes of epithelial cells can be identified: squamous, columnar, and cuboidal. The pseudostratified epithelium is composed of a single layer of epithelial cells of which the nuclei are arranged in different levels. The main difference between simple and stratified epithelium is that simple epithelium is composed of a single layer of cells while stratified epithelium is composed of multiple layers of cells.

This article looks at,

1. What is Simple Epithelium
– Definition, Structure, Classification, Characteristics
2. What is Stratified Epithelium
– Definition, Structure, Classification, Characteristics
3. What is the difference between Simple and Stratified Epithelium

What is a Simple Epithelium

Simple epithelium is the epithelium that is composed of a single layer of epithelial cells. This is found in regions where absorption, filtration, and secretion occur. All cells in the simple epithelium are bound to the basement membrane. The simple epithelial tissue is classified based on the shape of the epithelial cells. Four types of the simple epithelium are simple squamous, simple cuboidal, simple columnar, and pseudostratified epithelium.

Simple Squamous Epithelium

The simple squamous epithelium is a single-layered, flat and thin epithelium. Since this epithelium is flat, thin and single-layered, substances can move across the epithelium by passive diffusion. Simple squamous epithelium is found in capillaries, linings of the pericardium, and linings of the alveoli of the lungs.

Simple Cuboidal Epithelium

The simple cuboidal epithelium consists of single-layered cells that are tall and wide. This epithelium is important for secretion and absorption. It is found in small collecting ducts of the kidney, pancreas and salivary glands.

Simple Columnar Epithelium

The simple cuboidal epithelium is a single-layered epithelium. These epithelial cells are closely-packed and aligned in rows. They occur in areas with high secretory functions such as the wall of the stomach and absorptive areas such as the small intestine. The simple columnar epithelial cells possess cellular extensions such as microvilli and cilia.

Pseudostratified Epithelium

The pseudostratified epithelium is also a single-layered epithelium. But its nuclei appear in different heights, giving a misleading impression that it is a stratified epithelium. This epithelium possesses fine hair-like cilia. This ciliated epithelium is found in airways such as nose and bronchi. It also lines the uterus and fallopian tubes.

What is Stratified Epithelium

The stratified epithelium is composed of multiple layers of epithelial cells. Only the basal cell layer is attached to the basement membrane. The basal cells reproduce and grow towards the apex. Since multiple cell layers are present, the stratified epithelium is capable of withstanding chemical or mechanical abrasions. Due to this durability, this epithelium provides protection to the tissues below it. Stratified epithelium can be identified in squamous, cuboidal and columnar shapes. The stratified squamous epithelium lines esophagus, mouth, and uterus. It protects the subordinate tissues from abrasions. The stratified cuboidal epithelium is found in sweat glands, salivary glands, and the mammary glands. The stratified columnar epithelium is found in the lining of the male urethra.

However, stratified epithelium consists of other two specializations: keratinized epithelium and transitional epithelium.

Keratinized Epithelium

The stratified epithelium in apical layers of the body is composed of dead cells. These cells have lost their nuclei and cytoplasm. But, they consist of tough, resistant proteins called keratin. The keratinization of the cells in the epithelium makes it waterproof. The keratinized epithelium is abundant in mammalian skin.

Transitional Epithelium

Thetransitional epithelium is found in tissues that are capable of stretching. When the tissue is in its original stage, its epithelium exists as stratified cuboidal. The epithelium becomes stratified squamous when it is stretched. The transitional epithelium is exclusively found in the bladder, uterus, and urethra.

Figure 01: Summary of Epithelial Tissue

Definition

Simple Epithelium: Simple epithelium is the epithelium that is composed of a single layer of cells.

Stratified Epithelium: Stratified epithelium is the epithelium that is composed of multiple layers of cells, stacking on top of each other.

Basement Membrane

Simple Epithelium: All the cells in the simple epithelium are bound to the basement membrane.

Stratified Epithelium: Only the basal cell layers are bound to the basement membrane of the stratified epithelium.

Occurrence

Simple Epithelium: Simple epithelium is found in places where absorption, secretion, and filtration occur.

Stratified Epithelium: Stratified epithelium is found in high abrasion areas where protection is needed.

Protective Role

Simple Epithelium: Simple epithelium is not involved in protection since it can be easily damaged by chemical or mechanical abrasions.

Stratified Epithelium: Since the stratified epithelium is multi-layered, it helps in the protection of tissues below them.

Types

Simple Epithelium: Simple epithelium can be either squamous, columnar or cuboidal.

Stratified Epithelium: Stratified epithelium can be either squamous, columnar, cuboidal, keratinized, or transitional.

Conclusion

Simple and stratified epithelium are two arrangements of the epithelial tissue in animals. The simple epithelium consists of a single epithelial cell layer that is attached to the basement membrane. In contrast, stratified epithelium consists of multiple cell layers which are attached to the basement membrane only through the basal cell layer. Cells in both simple and stratified epithelium can be either squamous, cuboidal or columnar. In addition, the cells in the stratified epithelium can either be keratinized or become transitional. Both types of epithelium line body cavities, organs, and tissues. The major function of simple epithelium is to absorb, secrete and excrete substances. The stratified epithelium provides protection against dehydration, chemical, and mechanical abrasions. However, the main difference between simple and stratified epithelium is the number and formation of layers.

Reference:
1. “Types of Epithelial Tissue – Boundless Open Textbook.” Boundless. Boundless, 16 Dec. 2016. Web. 24 May 2017. .

Image Courtesy:
1. “403 Epithelial Tissue” By OpenStax College – Anatomy & Physiology, Connexions Web site. http://cnx.org/content/col11496/1.6/, Jun 19, 2013. (CC BY 3.0) via Commons Wikimedia