Describe the structure and function of different types of epithelial tissues. Draw diagram of each type of epithelial tissue.
Epithelial tissues are the covering or protective tissues in the animal
body. Epithelium covers most organs and cavities within the body and keep
different body systems separate.
The skin, the lining of the mouth, the lining of blood vessels, lung alveoli and
kidney tubules are all made of epithelial tissue.
Epithelial tissue cells are tightly packed and form a continuous sheet.
They have only a small amount of cementing material between them and almost no
intercellular spaces.
The permeability of the cells of various epithelia play an important role in
regulating the exchange of materials between the body and the external
environment and also between different parts of the body.
Regardless of the type, all epithelia are usually separated from the underlying
tissue by an extracellular fibrous basement membrane.
Epithelial tissues are of following types�
(1) Simple squamous epithelium
(2) Stratified squamous epithelium
(3) Columnar epithelium, and
(4) Cubodial epithelium.
(1)Simple squamous epithelial cells
Simple squamous epithelial cells are extremely thin and flat and form a delicate
lining. The skin, oesophagus and the lining of the mouth are also covered with
squamous epithelium.
These tissues differ in structure that correlate with their unique functions.
For example, in cells lining blood vessels or lung alveoli, where transportation
of substances occurs through a selectively permeable surface, there is a simple
flat kind of epithelium. This is called the simple squamous epithelium.
(2) Stratified squamous epithelium
Skin epithelial cells are arranged in many layers to prevent wear and tear.
Since, they are arranged in a pattern of layers,
(3) Columnar epithelial tissue
Where absorption and secretion occur, as in the inner lining of the intestine,
tall epithelial cells are present. This columnar epithelium facilitates movement
across the epithelial barrier. In the respiratory tract, the columnar epithelial
tissue also has cilia, which are hairlike projections on the outer surfaces of
epithelial cells. These cilia can move, and their
movement pushes the mucus forward to clear it. This type of epithelium is thus
ciliated columnar epithelium.
(4)
Cuboidal epithelium forms the lining of kidney tubules and ducts of salivary
glands, where it provides mechanical support. Epithelial cells often acquire
additional specialisation as gland cells, which can secrete substances at the
epithelial surface. Sometimes a portion of the epithelial tissue folds inward,
and a multicellular gland is formed. This is glandular
epithelium
