Epithelial tissue covers the internal organs from outside and inside and the entire body from outside. Based on shape of cells these epithelial tissues are of following types:
Squamous epithelium: contains flat cells with wider length & width. This epithelium is found in blood vessels and serous body cavities.
Cuboidal epithelium: contains cells of cube shape i.e. equal in height and width. They are found in renal tubules, ducts of glands.
Columnar epithelium: contains cells with column like height i.e. elongated in height. They are found in digestive and respiratory tract.
Based on number of cell layers, the epithelium are either:
Simple epithelium which contains single layer of cells e.g. endothelium of blood vessels, mucosa of stomach and intestines.
Stratified epithelium: This contains more than one layer of cells. e.g. skin contains stratified squamous epithelium, transitional epithelium in urinary bladder.
Pseudo stratified epithelium: containing actually single layer of cells, but appears multilayered due to arrangement of nuclei. e.g. nasal epithelium and trachea epithelium is pseudostratifed columnar.
Different organs have epithelium of their specific type suit to their functions. Some important functions of epithelial tissue are listed below:
Epithelial lining provides protection and shape to particular organ e.g. skin provides protection and particular shape to whole body.
Epithelial tissue of digestive system and renal tissue helps in secretion and absorption functions.
Epithelial tissue of glands produces various enzymes and other secretions required for digestive function.
Epithelial lining of peritoneum, pleura etc. produce specific fluid for protection of visceral organs, heart and lungs etc.
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