It is made up of a numerous types of cells that make it thick. There are 3 types:
a.Stratified squamous epithelium
It is made up of numerous cells of lif shapes that are located inner layer of the body, these from the germinative layer of the skin whose cells is either columnar or cuboidal and divides actively to form new once. At the free surface the cells are flatten tough and impervious to form the epidermis of the skin. The cells are coated with keratin making them tough and hard.
Location: in the lining of the esophagus, buccal cavity, anus, vagina, the surfaces of these tissues are constantly moisten and active
Function: they protect the under lying tissue from mechanical injury
b.Transitional epithelium
It consist of 3 or 4 layer of cells with very simple sized and shapes. At the free surface the cells are flatten and modify themselves for protection and distension
Location: in the urether and urethra
Function: the prevent urine from escaping into surrounding tissues.
- Glandular epithelium
It is made up of many layers of cuboidal cells which are specialized for secretory of substances into ducts and into the blood stream. There are two types of glandular cells:
- Exocrine cells: they release their secretion through special ducts to the target organs
- Endocrine cells or ductless cell: they release their secretion directly into the blood stream to target cells
NB: an exocrine gland may consist of a single epithelium called unicellular gland or numerous cells called multi cellular glands. There are also two types of glands: simple and compound glands
- Simple gland: they consist of unbranched ducts which communicates with the surfaces of glands, they are classified as follows:
- menocine gland: they release their secretion by exocytosis though the cell membrane e.g. salivary, sweat glands and pancreas
- Apocrine glands: they release their secretion by a loss of some portion of their free ends of granduler cells e.g. mammary gland
- Holocrine glands: they release their secretions together with the cells that produce them.
