Types of epithelial tissues
Epithelial tissues are tissues that line the outer and inner surface of organs and blood vessels.
All over our body, we can find many types of epithelial tissues.
Epithelial tissues are usually classified based on the number of cell layers and the shape of the cell.
On the basis of number of layers, there are 2 different types of epithelial tissues.
Simple epithelial tissues are made of single layer of cells.
The cells in simple epithelial tissue are in direct contact with the basement membrane.
Simple Epithelial Tissues are further classified into 5 different types -
Squamous, cuboidal, columnar, ciliated, pseudostratified.
Let us know about squamous epithelium.
Squamous epithelial tissues are made of thin, large and flat cells.
The cells in squamous epithelial tissue are closely packed and have prominent nuclei. Nuclei are mostly located at centre.
Simple squamous epithelial tissue is found in the alveoli of the lungs, blood vessels, Bowman’s capsule of nephron. Its functions are protection, excretion, gaseous exchange.
Let us know about Cuboidal Epithelium
Cuboidal epithelial tissues are cuboidal in shape. The nuclei are rounded and lie in the centre of the cells.
Simple cuboidal epithelial tissues line the lumen of collecting ducts in the kidney.
They are also found in the glandular ducts of the salivary glands and pancreas. Their functions are protection, secretion, absorption, excretion.
Let us learn about the Columnar Epithelium
Simple columnar epithelial tissues contain cells that are cylindrical in shape and placed side by side like columns.
Nuclei are slightly elongated and lie near the base of the cells.
Simple columnar epithelial tissues are found in the stomach, intestine, gall bladder.
The glandular epithelium is a special type of columnar epithelium.
Certain cells of columnar epithelium (like Goblet cells) contain secretory substances. Such an epithelium is called Glandular epithelium.
These glandular epithelium cells can be found in the lining of the stomach and the small intestine.
The glandular epithelium folds inwards to form tubular glands such as sweat glands.
Let us learn about Ciliated Epithelium.
The cells in ciliated epithelium have thread-like projections called cilia.
These cilia lash constantly and aid in the movement of materials.
Ciliated epithelium are of two types -
Ciliated Columnar Epithelium
Ciliated Cuboidal Epithelium
The ciliated columnar epithelium cells have cilia on the free surface.
The ciliated columnar epithelial cells can be found in the trachea or the windpipe, Fallopian tubes, Eustachian tube.
Cube-like or cuboidal cells having cilia on the free surface form ciliated cuboidal epithelial tissue. It is present in renal tubule of nephrons.
Let us learn about Compound Epithelium
Compound epithelium is made up of layers of cells.
Compound Epithelium is of two types -
Let us learn about Stratified Epithelium
The stratified epithelial tissue is composed of several layers of epithelial cells of same shape or different shape.
Only one layer of stratified epithelial tissue is in direct contact with the basement. The remaining layers support the upper layer.
Stratified squamous epithelial tissue is found in the skin.
Stratified cuboidal epithelial tissue is found in the salivary glands.
Stratified columnar epithelial tissue is rarely found. Conjunctiva of the eye is one such organ.
Lets us learn about Transitional Epithelium
Cell are present in multilayers in Transitional Epithelium. Cells of different layers vary in shape and size.
Cells of basal layer are columnar or cuboidal in shape, middle layers are polyhedral and upper layer are globular in shape.
Transitional epithelial cells allow distension. They line the organs of urinary system. Hence, they cells of urinary bladder can be stretched without damaging.
Let us learn about Pseudostratified Epithelium
This is a special type of simple tissue which appears to be compound.
Columnar cells of unequal size forms the pseudostratified epithelium. Long cells have oval nuclei whereas short cells have rounded nuclei.
It appears multilayered as nuclei are present at different levels. Hence, it is called pseudo-stratified epithelium.
It is found in the linings of the trachea, salivary glands. Its function is protection, secretion.
Let's revise epithelial tissues.
Epithelial tissue is a thin and continuous sheet of cells, which protects the body organs.
These tissues are found on the uppermost part of the skin and line the internal organs.
There are 2 different types of epithelial tissues depending on the layers of cells: simple and compound
Simple epithelial tissue is of 5 types - Squamous, cuboidal, columnar, ciliated, pseudostratified.
Compound epithelial tissue is of two types - Stratified and transitional.
The major functions of the epithelial tissues are to protect, secrete and absorb.