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
- 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 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 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