Stratified squamous epithelium definition

The stratified squamous epithelium is composed of numerous layers of cells, including squamous cells constituting the apical layer as well as numerous layers underneath it, with cuboidal to columnar cells constituting the deeper layers. These activities fluctuate in the same manner as the structure itself, despite the fact that the only difference between the simple epithelium and the stratified epithelium is the number of cells in each layer. The cells in the superficial layers are driven towards the surface, where they are shed due to the ongoing cell division in the lower (basal) layers.

Structure of the stratified squamous epithelium

The stratified squamous epithelium has at least two cellular layers. Squamous cells compose the apical layer and several layers underneath it, although cells in lower levels might be cuboidal or columnar.
Just a single layer of the stratified squamous epithelium is completely attached to the basal membrane; all other layers remain linked to each other to maintain the structure’s integrity.
As basement cells split, daughter cells created during fission drive older cells toward the apical surface.
The epithelium’s cells are closely packed together and have relatively few intracellular gaps.
On the apical surface of the stratified epithelium, just the uppermost layer of tissue is displayed towards the lumen, in contrast to the simple epithelium. By means of cell junctions and adhesions, all other sides of the cells are connected to other cells.
These cells flatten as they migrate towards the surface, contain many desmosomes and other adhesins, and have an uneven form.
As they move closer to the surface and farther from the blood circulation in the underneath connective tissue, they dry out and become less metabolically active.
As cytoplasm decreases and cells transform into solid, hard structures that finally die, tough proteins prevail.
At the apical layer, damaged cells that have broken their cell connections are shed, while fresh basal cells continually replace them.
The stratified squamous epithelium has a discrete nerve supply rather than a direct blood supply, like all other epithelial tissue.

The stratified squamous epithelium may be classified into two groups depending on the manner in which the cells collect keratin as they approach the surface:

1. Keratinized stratified squamous epithelium

A kind of stratified squamous epithelium known as keratinized stratified squamous epithelium has cells that contain multiple layers of thick keratin in the apical portion of the cells.
Skin and underlying tissues may benefit from the stiff, fibrous intracellular protein keratin’s ability to protect them from heat, bacteria, and chemicals.
In the keratinization process, the cells build up keratin as they ascend, transforming into thin keratin squames devoid of nuclei that are biologically dormant.
Cellular detachment occurs as cells separate themselves from the nutrient-rich blood supply and also the organelles ultimately die. The relative quantity of keratin in the cells rises.
The cells in the uppermost stratum no longer serve any purpose after keratinization; they now solely serve to defend against mechanical stress and dehydration.

2, Non-keratinized stratified squamous epithelium

Non-keratinized stratified squamous epithelium is an epithelium with hydrated cells by salivary or mucus gland mucus rather than a significant amount of keratin deposits.
The bulk of the surface layer’s cells retain their nuclei and continue to conduct their metabolic functions.
It is common to see non-keratinized stratified squamous epithelium in areas that need moisture management or are susceptible to dryness because it has fewer keratin deposits.
The amount of keratin in this epithelium differs with the maturity of the tissue layer and also with the level of mechanical stress it has received.
A few of the cells in this epithelium also produce minute amounts of mucus as well as various lubricants to keep the surface from drying up.

Functions of the stratified squamous epithelium

The main and most crucial role of the stratified squamous epithelium is protection.

1,Protection

The stratified squamous epithelium shields the body against radiation, chemical abrasions, and mechanical stress.
The skin’s keratinized epithelium shields the body from dangerous radiation and keeps interior organs and tissues from being exposed to it.
In a similar manner, it also stops internal organ damage from any physical discomfort and heat-related water loss.
This epithelium replaces the outer layer when it is injured, boosting stress and invasion resistance.
Given that the surface is kept continuously moist, the non-keratinized stratified squamous epithelium resists the entrance of foreign intruders.
As the first layer of protection against any physical harm or microbial invasion, both forms of stratified squamous epithelium, play a crucial role.
2. Secretion

The non-keratinized stratified squamous epithelium is composed of cells that release some mucus to keep the surface wet, as was already stated.
The mucus contributes to preserving the pH balance of the environment, just as the vaginal epithelium does.
Additionally, it functions as a lubricant in the buccal cavity, an area that is regularly prone to friction.

Location and Examples of Stratified squamous epithelium

The area that is continually stressed and exposed to the outside environment, much like the top layer of skin, is lined with keratinized epithelium.
Additionally, it creates the epidermis of the foot and hand soles.
Interior surfaces as well as spaces that are subject to physical wear and tear from friction are lined by non-keratinized epithelium.
The tongue’s surface, the mouth’s hard upper palate, the oesophagus, and the anus are all lined by stratified squamous epithelium in the digestive system.
The vagina, cervix, and labia majora are examples of female reproductive organs where it may also be present.
Additionally, the upper respiratory tract, which might also come into contact with foodstuffs, is lined with stratified epithelium.
The stratified epithelium protects the cornea, which safeguards the delicate structures found within the eye.
In the urinary system, the urethra’s epidermis is likewise composed of stratified squamous epithelium.

References and Sources

Mescher AL (2016). Basic Histology. Fourteenth Edition. McGraw-Hill Education.
Tortora GJ and Derrickson B (2017). Principles of Physiology and Anatomy. Fifteenth Edition. John Wiley & Sons, Inc.
Waugh A and Grant A. (2004) Anatomy and Physiology. Ninth Edition. Churchill Livingstone.
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