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The word epithelium originates from a Latin word where “epi” means on top and “thele” means nipple. Beneath is the basal layer on which the epithelium rests. Epithelium is a tissue made from epithelial cells, which are tightly packed. It is an animal tissue. It fills up the spaces present in the cavities as well as the surface. Connective tissue, muscle tissue, vascular tissue, nerve tissue and epithelium are the vital animal tissues. Simple, stratified and pseudostratified are the types of epithelium on the basis of the layers present.
Classification can also be done on the basis of shape such as cuboidal, squamous and columnar. Digestive tract and reproductive tract are both lined by epithelial. Its function are absorption, transportation and secretion.
Type of Epithelial Tissue
On the basis of the number of layers, epithelium can be classified into Simple epithelial tissue, which les on the basal membrane and consist of only one layer of epithelial cells.
When there are more layers of epithelial cell present it is called as Stratified epithelium. It provides protection and has other functions.
When there are multiple layers of epithelium it is called as Transitional epithelium which is so called as it changes from squamous to cuboidal.
Epithelial cells consisting of a single layer and are close in proximity to the basal membrane are called as pseudo stratified epithelium.
This has two types and they are mesothelium and endothelium. The tissue, explicitly the epithelial, that lines the organs and the body such as the ventral body and the pericardial cavity, pleural cavity and peritoneal cavity is called mesothelium. The epithelial tissue lining the lymphatic and blood vessel is called as Endothelium. However, these aren’t true epithelium as their characteristic are different from the normal tissue.
Basal membrane distinguishes the connective tissue from the epithelium. The epithelial cells in single layer is called as simple and pseudostratified epithelium. The epithelial cell in multiple layer is called as Stratified epithelium.
The classification is on the basis of shape such as: squamous which are uniform and in thickness are very thin. When their cross-section is viewed, they look polygonal in shape. Rectangular cells which are longer and wider are the columnar epithelial cell. Cube shaped are called the cuboidal epithelial cells. Their length and width is the same.
It is a matrix, which is fibrous, extracellular and thin, it lies beneath the epithelial cell. The connective tissue and the epithelial tissue can be distinguished by the basement membrane. Basal lamina and reticular lamina are the layers of basement membrane. From the secretion of connective tissue fibroblast, reticular lamina is made and from the secretions of epithelial cells, basal lamina is formed.
These are the bridges or the path in between the extracellular matrix and the cell. they are made up of protein complexes. Examples are Desmosomes, Gap junctions, Tight junctions, Hemidesmosomes and adherens junction.
The basic function is to provide protection against radiation, toxins, drying up, physical, chemical stress to the structure present beneath. It inhibits the entry of invaders. For example, whenever we get a cut, the barrier is broken thus allowing pathogens to enter, thus, body starts to treat it through several reactions and get clotting factors to act at the site. Thus, gluing work is done by fibrin. The other functions are absorption, secretion and regulation. Endocrine and Exocrine are the two types of glands. Another function is providing sensation to the skin.
Digestive system, reproductive tract and other organs are lined by epithelial tissue.
There are three germ layers; Ectoderm, Endoderm and Mesoderm. From these three layers, various cells arise. From the mesoderm cell which appear, forms the lining of body cavities. From the ectoderm, forms the epidermis. The digestive tract lining is formed from the endoderm.