Epithelium 2.pdf

Epithelium 2 Classification of epithelial tissues Classification of epithelial tissues: A)Covering and lining (simple and stratified ). B)Glandular epithelium. C)Sensory or neuroepithelium. D)Myoepithelium. simple squamous; It is formed of flattened cells which bulge at the area of the nucleus. The...

Epithelium 2 Classification of epithelial tissues Classification of epithelial tissues: A)Covering and lining (simple and stratified ). B)Glandular epithelium. C)Sensory or neuroepithelium. D)Myoepithelium. simple squamous; It is formed of flattened cells which bulge at the area of the nucleus. The nucleus is also flattened. It lines all the body cavities, e.g. pleural, pericardial and peritoneal cavities , where it gives smooth surface and prevents friction. It lines blood vessels. simple cuboidal: In a cross section the cells of this epithelium appear as squares, containing spherical relatively large nuclei It is found in thyroid follicles, where it provides secretory function and renal tubule where microvilli on the cell serve for reabsorption. Copyright © McGraw-Hill Companies simple columnar Elongated cells with basal oval nucleus. secretory, absorptive, or excretory; Simple columnar epithelium can be ciliated or non-ciliated Non-ciliated columnar epithelium. Columnar epithelia that secrete mucus are found in stomach, colon absorptive epithelium e.g. the lining cells of the small intestine Ciliated columnar is found in the uterine tubes and uterus. pseudostratified columnar epithelium; In this type some cells are tall and reach the surface of the epithelial membrane and others are too short to reach the surface. The tall cells may be secretory goblet cells or ciliated cells. The short basal cells are progenitor cells which differentiate to form cells replacing the tall ones. Sites: Non- ciliated pseudostratified columnar epithelium is found in vas deferens. Ciliated pseudostratified columnar epithelium lines respiratory tract. Copyright © McGraw-Hill Companies Stratified epithelium It is formed of more than one layer. According to the most superficial layer there are many types: 1. Stratified squamous epithelium (non – keratinized and keratinized). 2. Stratified columnar epithelium. 3. Transitional epithelium a) Stratified squamous epithelium (non – keratinized): Stratified epithelia serve as protective membranes. Stratified squamous non- keratinizing membranes are found on wet surfaces which are subjected to mechanical tearing. The innermost cells are columnar, followed by polyhedral cells and become gradually squamous at the surface. Site: Lining of buccal cavity, oesophagus, b) Stratified squamous epithelium (keratinized): It covers dry surfaces, e.g. skin. The outermost squamous cells undergo certain changes which lead to a layer of keratin, covering the epithelium. The keratinizing epithelium protects the body from dryness and harmful agents. Copyright © McGraw-Hill Companies 2) Stratified columnar epithelium It is usually formed of basal columnar cell layer, followed by a layer of polyhedral cells. The most superficial layer is columnar. This type of epithelium is mainly protective. The non ciliated type lines large ducts of glands. 3- Transitional epithelium lines much of the urinary tract. The superficial cells are rounded or domeshaped, and have specialized membrane features enabling them to withstand the hypertonic effects of urine and protect underlying cells from this toxic solution. It lines organs which expand greatly like the urinary. In contracted (empty) state: the superficial layer of cells becomes rounded instead of squamous. - In full (expanded) state: the cell becomes squamous