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Epithelial tissues

Where are epithelial tissues present?

  • Skin, lining of the mouth, lining of blood vessels, lung alveoli, kidney tubules are a few of the places epithelium is present in.

Just like the epidermis in plants, epithelium is the protective covering tissue of most organs and cavities of animals.

It acts as a barrier or wall between different systems of the body

  • The cells are tightly packed and thus continuous
  • There is a small amount of cementing material between the cells and almost no intercellular spaces
  • Since it is the covering tissue, different substances entering and leaving have to cross the epithelium and thus the permeability plays an important role in exchange of substances.
  • The epithelium is separated from the tissue under it by an extracellular fibrous basement membrane .

 

Functions of Epithelial tissues:

  • Protects the cells beneath from injury, drying, infections etc.
  • Protects the organs by forming an outerlining
  • Helps in absorption of water and nutrients
  • They help in elimination of waste
  • Sometimes they secrete substances like sweat, mucus, saliva, enzymes etc.

Thus based on the purpose there are different types of epithelial tissues.

 

Simple Squamous Epithelium

These tissues form a delicate lining and allow transport of substances through a selectively permeable surface ; they allow only certain substances to pass through.

  • They are simple, thin and flat .
  • They are present in 
    • Cells lining blood vessels 
    • Cells lining lung alveoli 
    • Oesophagus 
    • Lining of the mouth

 

Stratified Squamous Epithelium

  • The skin forms the outermost layer of the body
  • So naturally the skin is also lined by squamous epithelium
  • But unlike the simple squamous epithelium, skin epithelial cells are arranged in many layers 
  • This is to prevent wear and tear
  • So layered squamous epithelium is called stratified squamous epithelium  

 

Columnar Epithelium

Columnar means pillar-like →  Columnar epithelium - Tall epithelial cells

It is present in the inner lining of the intestine

 

Do you know what the role of cilia is in our body?

  • Cilia are hair-like projections that increases the surface area
  • So in regions where absorption and secretion occur cilia is present.
  • In the respiratory tract , the columnar epithelial tissue also has cilia
  • The cilia moves and pushes the mucus forward to clear the respiratory tract.
  • This variation is called Ciliated Columnar Epithelium

 

Cuboidal Epithelium

  • Cuboidal cells are box or cube shaped .
  • They provide mechanical support
  • It is present in the lining of kidney tubules and ducts of salivary glands

 

  • Sometimes epithelial cells are capable of secreting substances
  • This specialisation makes them gland cells
  • Sometimes a portion of the epithelial tissue folds inward , and a multicellular gland is formed
  • This is glandular epithelium

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CA Maninder Singh is a Chartered Accountant for the past 12 years and a teacher from the past 16 years. He teaches Science, Economics, Accounting and English at Teachoo