question_answer 8)

Describe various types of epithelial tissues with the help of labelled diagrams?

Answer:

Epithelial tissues Epithelial tissues provide covering to the inner and outer lining of various organs. There are two types of epithelial tissues: (a) Simple epithelium Simple epithelium is composed of a single layer of cells. If functions as a lining for body cavities, ducts and tubes.  (b) Compound epithelium The compound epithelium consists of two or more cell layers. It has protective function as it does in our skin. It covers the dry surface of the skin, the moist surface of buccal cavity, pharynx, inner lining of ducts of salivary glands and of pancreatic ducts.  On the basis of structural modifications of the cells, simple epithelium is further divided into three types. These are:  (a) 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 a functions like forming a diffusion boundary.  (b) Cuboidal epithelium The cuboidal epithelium is composed of a single layer of cube-like cells. This is commonly found in the ducts of glands and tubular parts of nephrons in kidneys. Its main functions are secretion and absorption.  (c) Columnar epithelium The columnar epithelium is composed of a single layer of tall and slender cells. They are found in the lining of stomach and intestine and help in absorption and secretion.  (i) When 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 organs like bronchioles and fallopian tubules.  (ii) Some of the columnar or cuboidal cells get specialized for secretion are caled glandular eptheilium. They are unicellular and multicellular.