Epithelial tissues

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