Info Collector

There are two groups of epithelial tissues according to their structure and function.

1- Covering epithelia, which cells are organized in membranous layers that cover the external surface or the line cavities of the body.

2- Glandular epithelia, which cells are specialized to produce a fluid secretion.

1- Covering epithelia:

Covering epithelia are classified according to the number of cell layers and morphology of the cells in the surface layer:

1- Simple epithelia, consists of only one layer of cells. They are almost found on absorptive or secretor surfaces.

2- Stratified epithelia, consists of tow or more layers of cells they are more suited to protection than absorption or secretion because of their thickness.

There are four types of simple epithelia:

a- Simple squamous epithelium, composed of flattened and irregularly-shaped cells, it is often found in lungs and walls of blood capillaries.

b- Simple cuboidal epithelium, it is cuboidal cells; it is often found in ducts of kidney, salivary glands and pancreas.

c- Simple columnar epithelium, it is appear taller in sections than cuboidal cells, it is often found in small intestine and secretory surfaces of the stomach.

d- Pseudostratified epithelium, it is a true simple epithelium, because all cells lie on the basement membrane, it is often found in trachea of mammals.

There are four types of stratified epithelia:

a- Stratified squamous epithelium, it is well adapted to resist moderate abrasion but not desiccation. It is often found in oral cavity, pharynx, oesophagus and vagina.

b- Stratified squamous keratinizing epithelium, it is adapted to resist constant abrasion and desiccation, it is found in the epidermis of the skin.

c- Stratified cuboidal epithelium, it consists of two or three layers of cuboidal or columnar cells, it is found in the lining of salivary gland and pancreas.

d- Transitional epithelium, it is highly specialized to give a degree of stretch, so it is found only in the urinary tract in mammals.