What is Epithelial tissues? What are its different types? Explain the structure and
with the help of diagram
Answers
All layers and organs in the body are lined by a group of tissues called epithelial tissues which are commonly referred to as epithelium. They cover the surface of all internal as well as external organs. Epithelial tissue is highly permeable. Thus, it plays a significant role in the exchange of substances across the cells and helps in maintaining the osmoregulation. Depending on the number of layers of cells it is composed of, the epithelium has been divided into the simple epithelium and compound epithelium. The main functions of epithelial tissue are protection, secretion, absorption, and sensation.
=>Simple Epithelial Tissue
This type of epithelium is composed of a single layer of cells which mainly make up the linings of ducts, tubes and other cavities in the body. Based on the structure of the cell, the simple epithelial tissue is classified into three types viz.:
=>Squamous epithelium:
It is a simple single-layered epithelium.
Structurally, the squamous epithelium is made up of flat cells with irregular boundaries.
It forms linings of blood vessels and alveoli.
=>Cuboidal epithelium:
The tissue is made of cube-shaped cells.
It forms the lining of kidney tubules and ducts of salivary glands.
=>Columnar epithelium:
It is composed of tall and slender, column-shaped
It forms the lining of the stomach and intestine.
In some organs, cuboidal and columnar epithelial have cilia present on the outer surface which is called the ciliated epithelium. It helps in the directional movement of materials along with the hollow organs like the respiratory tract. The cuboidal or columnar epithelia which are specialized in secretions are called glandular epithelium which includes the exocrine and endocrine glands.
=>Compound Epithelial Tissue
The compound epithelium is a multilayered (two or more layers of cells) tissue. The key function of compound epithelium is protection and has a limited role in secretion. Skin is a compound epithelium which functions as a barrier against chemical and mechanical stresses.
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