Types of epithelial tissue | Examples, Characteristics, and Functions

In this article, we will learn about types of Epithelial tissue.

Alongside this, we will also let you know What is an Epithelial Tissue, examples of epithelial tissue, how are epithelial tissue named, characteristics, and functions of epithelial tissues.

WHAT IS AN EPITHELIAL TISSUE?

Tissue is a collection or group of cells that are similar in structure and they function together as a unit.

These cells are connected with the help of an intercellular matrix.  Epithelial tissue is a group of epithelial cells.

Epithelial cells are the cells that are densely packed. These cells reside on a membrane which is known as the basement membrane.

EXAMPLES OF EPITHELIAL TISSUE

Simple squamous epithelium, Simple cuboidal epithelium, stratified squamous epithelium, pseudostratified columnar epithelium, transitional epithelium, and keratinized epithelium are examples of epithelial tissue.

HOW ARE EPITHELIAL TISSUE NAMED

Epithelial tissue is named on the basis of the shape of cells that make it such as squamous for flat cells, cuboidal for cube shape cells, columnar for cells that are in form of the column, and also on the basis of the layer of cells present when one layer is present it is the simple epithelium and when more than one layer is present it is the stratified epithelium.

TYPES OF EPITHELIAL TISSUE

SIMPLE EPITHELIUM

This is a type of epithelium that contains a single layer of cells.

These cells are found in the organs of the body where absorption, secretion, and filtration occur.

This layer is thin which is why it is able to perform these functions.

Simple epithelium is again classified on the basis of the shape of cells that make it.

The different types of simple epithelium are:-

Simple squamous epithelium

The cells of this epithelium are flat in shape and are arranged in a single layer.

This layer is thin and it allows the passive diffusion (It is the movement of components from a region of high concentration to a region of lower concentration without the use of energy) of components.

• Location: It is found in the air sacs of lung; lining of heart is formed by this tissue, blood vessels, and lymphatic vessels.

• Function: Materials pass through this layer by diffusion and filtration.

This layer also secretes the lubricating substances.

Simple cuboidal epithelium

The cells of this epithelium are cuboidal in shape, their tallness and wideness are the same.  They are also arranged in a single layer.

• Location:  It is found in ducts and secretory parts of small glands, it is also found in kidney tubules.

• Function: It plays role in secretion and absorption.

Simple columnar epithelium

This is a single layer of tall cells. These cells are closely packed. These cells possess cellular extensions.

• Location:  These are found in ciliated tissues of bronchi, uterine tubes and uterus. Non- ciliated cells are present in digestive tract.

• Function: It plays role in secretion. It secretes enzymes and mucous.

PSEUDOSTRATIFIED EPITHELIUM

These are types of simple columnar epithelium but there is a difference that nuclei in these cells are situated at different heights which gives a false impression that the tissue is stratified when these cells are viewed in cross-section.

They can also possess cilia which are hair-like projections. If they possess cilia then it is known as the ciliated pseudostratified epithelium.

• Location:  This tissue is present in lining of trachea and upper respiratory tract.

• Function: It secrete mucous. The ciliated tissue is also responsible for moving mucus.

STRATIFIED EPITHELIUM

This tissue is made of many layers of cells. It is durable i.e. it can withstand stress and provide protection to other tissues. These cells contain two or more layers. The basal cells of this tissue divide and push the cells towards the apex and because of this apical cells become flat.

The stratified epithelium is of three types:-

Stratified squamous epithelium- The cells of this tissue are flat in shape and are arranged in multilayer.

• Location: It lines some parts of the gastrointestinal tract such as the esophagus and mouth. It is also found in the vagina.

• Function: It protects the organ against abrasion and damage.

Stratified cuboidal epithelium- Cells of this tissue are cuboidal in shape i.e. they have equal length and breadth.

• Location: Present in sweat glands, mammary glands, and salivary glands.

• Function: It protects the organs in which they are present.

Stratified columnar epithelium- Cells of this tissue are columnar in shape i.e. their length is more than their breadth.

• Location: Present in male urethra and in ducts of some glands.

• Function: It is involved in secretion and protection.

KERATINIZED EPITHELIA

In this epithelium most exterior layers of cells are dead and they have lost their nucleus and cytoplasm.

They also contain a resistant protein which is known as keratin. This layer is waterproof.

• Location: Present in the skin of mammals and in the lining of the esophagus.

• Function: It makes the skin resistant to many factors such as bacteria, fungus, etc.

TRANSITIONAL EPITHELIA

It appears in two forms- it can appear as stratified cuboidal when tissue is not in stretched condition and it can appear as stratified squamous when the organ is stretched.

It is also known as the urothelium (as it is found in the bladder, ureters, and urethra).

• Location: Present in bladder, ureters, and urethra.

• Function:  It allows the organs of the urinary system to expand and structure.

CHARACTERISTICS OF EPITHELIAL LAYERS

Different characteristics of epithelial layers are:-

• Epithelial tissues are present in form of sheets.

• Cells are attached to each other by strong attachments.

• Protein connections are responsible for attaching the cells together.

• The layer of epithelial tissue is avascular (which means there is no circulatory system).

• Nourishment to the cells is provided by the diffusion of substances from blood vessels of the connective tissue which are present under the epithelial tissue.

• There is two sides of epithelial tissue- one side is towards the surface of tissue, body cavity or external environment. The second side is joined to the basement membrane.

• Epithelial tissue is cemented to the underlying structure with the help of the basement membrane which is non-cellular.

FUNCTION OF EPITHELIAL TISSUE

Epithelial tissue performs many functions that are listed below:-

• It acts as boundaries between the environment and body of an individual.

• It allows the passage of almost all substances across it.

• It protects the tissues that are situated deep in our body from radiation, desiccation, physical trauma, and toxins.

• It is modified in the gastrointestinal tract which helps in the absorption of food from the gastrointestinal tract.

• It also regulates the flow of chemicals between underlying tissues and body cavity.

• It is also involved in the excretion of chemicals from the body.

• It also helps in the secretion of hormones into the blood vascular system.

• The glandular epithelium is involved in the secretion of sweat, mucus, enzymes, and many different products that are delivered by ducts.

• It also detects the sensation.

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