The epithelium makes the basic animal tissue. The epithelial cells form a thin protective layer in most organisms. They mostly cover the outer surface of blood vessels and organs and also the inner surface of body cavities. For example, the human skin is made up of stratified squamous epithelial cells.
Keratinized Epithelium
The stratum corneum is the outermost layer that is composed of keratinized squamous cells. This keratin forms the outer layer of the skin of reptiles, birds and mammals. These keratinized cells are actually dead cells that shred periodically. They form an effective barrier against abrasions.
Here, the protoplasm of the cell is replaced by a protein called keratin. This protein layer is usually dry and is impermeable to water. Thus, it acts as a better protective layer. Keratinized epithelium is found in the epidermis of the skin, sole of the foot and palm of the hand.
Nonkeratinized Epithelium
The stratified squamous epithelial cells that lack the keratin protein are called the nonkeratinized epithelium. It is found in the buccal cavity, lips, the underside of the tongue, upper oesophagus, conjunctiva of eyes, rectum, vagina, etc. This nonkeratinized epithelium is mostly moist and acts as a less effective barrier.
Depending on age and damage, certain nonkeratinized surfaces also show a minor layer of superficial keratin.
Difference between Keratinized and Nonkeratinized Epithelium
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Keratinized Epithelium |
Nonkeratinized Epithelium |
|---|---|
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It is a stratified squamous epithelium that has keratin protein. |
It is a stratified squamous epithelium that lacks keratin protein. |
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Its cell layer is made of dead cells. |
Its cell layer has living cells. |
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It is a dry layer and is impermeable to water. |
It is moist and is permeable to water. |
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It forms an effective barrier. |
It forms a less effective barrier. |
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It is found in the epidermis of the skin, sole of the foot and palm of the hand. |
It is found in the buccal cavity, lips, the underside of the tongue, upper oesophagus, conjunctiva of eyes, rectum, vagina, etc. |
Explore: Structure and Function of Skin
Frequently Asked Questions
What are the different types of epithelial cells?
Usually, epithelial cells are found in three different shapes, namely – columnar, squamous and cuboidal. If they are arranged in a single layer, then it is termed simple epithelium. Example – simple squamous epithelium. If there are two or more layers, then it is termed stratified.
What is the stratum corneum?
The stratum corneum is a layer of dead cells that protect against mechanical abrasions, water flux, cellular invasions, etc. It is composed of layers of flattened cells that have no nuclei or organelles. Their cytoplasm has filamentous keratin.
What is keratin?
Keratin is a fibrous protein that makes the outermost skin in most vertebrates. They are the key structural elements of hairs, nails, scales, horns, feathers, hooves and claws. They protect the epithelial cells from stress or damage.
Also Read: Epithelial Tissue and Connective Tissue
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