Simple Location, and Function
Epithelial tissues are characterized by the absence of blood vessels. Instead, it receives the required nutrition through diffusion. They form the outer covering as well as the inner lining of many organs. In epithelial tissues, all cells are densely packed with little intercellular matrix between them. Epithelial tissue is classified into two types – simple epithelium and compound epithelium. Moreover, epithelial tissue can be classified based on its shape as well – cuboidal, squamous, columnar.
Where are the epithelial tissues found in the human body?
The lining of the blood vessels
The lining of the mouth
Structure and functions of the epithelial tissues -
The main function of the epithelial tissues is to act as a barrier and separate different organs and systems from each other.
There is no space between the cells of epithelial tissues
The cells are permeable. This makes it possible for them to exchange materials between different parts of the body and also between the body and the external environment.
The epithelial tissues remain separated from the tissues beneath them because of a thin membrane over them.
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 (squama means scale of skin). Simple squamous epithelial cells are extremely thin and flat and form a delicate lining. The oesophagus and the lining of the mouth are also covered with squamous epithelium.
The skin, which protects the body, is also made of squamous epithelium. Skin epithelial cells are arranged in many layers to prevent wear and tear. Since they are arranged in a pattern of layers, the epithelium is called stratified squamous epithelium.
Ciliated Columnar Epithelium:
Where absorption and secretion occur, as in the inner lining of the intestine, tall epithelial cells are present. This columnar (meaning ‘pillar-like’) epithelium facilitates movement across the epithelial barrier. In the respiratory tract, the columnar epithelial tissue also has cilia, which are hair-like 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.
Cuboidal epithelium (with cube-shaped cells) 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.
Shaalaa.com | Epithelium tissue
Based on the following information, identify the three types of epithelial tissue in the figures given below :
(1) Cuboidal epithelium : It consists of a single layer of cuboidal cells.
(2) Columnar epithelium: It is composed of tall, cylindrical cells with oval nuclei usually placed at the base of the cells.
(3) Ciliated epithelium : It consists of cells being hair-like cilia on their free surface.