Epithelial Tissue

Histology 2016-2017
Department of Anatomy &Histology: Dr.Rajaa Ali
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EPITHELIAL TISSUE
Epithelium is a sheet of cells that covers the external surface of any solid structure and the internal surface of any hollow tubular (e.g. lumen/cavities) structure. Thus it serves as a barrier membrane separating the underlying tissue from various external and internal environments.

CLASSIFICATION OF EPITHELIAL TISSUE
On the basis of the function(s) performed, epithelial tissue can be broadly classifi ed into four types(fig. 1).

SURFACE (OR) LINING EPITHELIUM
GENERAL FEATURES
Epithelium, _ the ‘cellular sheet’, is made of either single layer or many layers of cells.
_ Epithelial cells are adherent to each other by means of junctional complexes (vide infra).
_ Very little intercellular material is found between the cells.
_ The deep surface (basal) of the epithelium rests on a basement membrane, which separates it from the vascular connective tissue.
_ Basement membrane (Fig. 2.1) is made up of (a) basal lamina (amorphous substance) – product of epithelium (b) reticular lamina (reticular fi bres) – product of connective tissue.
_ The superfi cial surface (apical) of the epithelium is free and exposed to air or fl uid and often shows modifi cations (i.e. presence of microvilli or cilia) depending upon the function it is destined to perform.