Question 50: Describe the structure and function of different types of epithelial tissues. Draw diagram of each type of epithelial tissue.
Answer:
Types of Epithelial Tissue: Depending upon the shape and function of the constituent cells, epithelial tissues are of following types:
- Squamous (cells flattened)
- Columnar (cells tall, columnar or pillar¬like)
- Cuboidal (cells cube-like)
- Ciliated (cells with cilia)
- Glandular (cells secretory in nature)
- Stratified (cells many layered)
Squamous epithelium: The squamous epithelium is made of a single thin layer of flattened cells with irregular boundaries. They are found in the walls of blood vessels and air sacs of lungs and are involved in functions like forming a diffusion boundary.
Columnar epithelium: The columnar epithelium is composed of a single layer of tall and slender cells. Their nuclei are located at the base. Free surfaces may have microvilli. They are found in the lining of the stomach and intestine and help in secretion and absorption.
Cuboidal epithelium: Cuboidal epithelium is composed of a single layer of cube like cells. This is commonly found in duvets of glands and tubular part of nephrons in kidneys and its main functions are secretions and absorption. The epithelium of proximal convoluted tubules (PCT) of nephrons in the kidney has microvilli.
Ciliated epithelium: If the columnar or cuboidal cells bear cilia on their free surface they are called Ciliated epithelium. Their function is to move particles or mucus in a specific direction over the epithelium. They are mainly present in the inner surface of hollow organs like bronchioles and fallopian tubes.
Glandular epithelium: Some of the columnar or cuboidal cells that specialized for secretion and are called glandular epithelium.
Stratified epithelium: This is a compound epithelium in which cells are arranged in many layers one above the other. It is found in places where there is much wear and tear, such as the epidermis of skin, lining of the mouth cavity.
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