Tissues of the Body: The Epithelium PDF

Tissues of the body The Epithelium Dr. Amal Abd El hafez Assistant Professor of Histopathology 0  Objective learning At the end of this lecture you will be able to: List the 4 main basic types of t...

Tissues of the body The Epithelium Dr. Amal Abd El hafez Assistant Professor of Histopathology 0  Objective learning At the end of this lecture you will be able to: List the 4 main basic types of tissues in the body Know the definition, criteria and functions of epithelium. Discuss the different types of epithelium. Compare between the types of epithelium. Recognize the distribution of different types of epithelium in the human body. 0  Introduction Despite its complexity, the human body is composed of only 4 main basic types of tissue: epithelial, connective, muscular, and nervous. Definition of epithelial tissue The tissue that cover surfaces of the body or line the surface of cavities within the body. The epithelial cells may be modified to secrete (glandular epithlium), contract (myoepithlium) or receive stimuli ( neuroepithlium) 0 0  Maintaining 9. Poorly defined cell polarty boundaries so, the cells can be identified through their nuclei. 0  Classification of the epithelium I. Surface (covering/lining) epithelium II. Modified (specialized) epithelium 1.Glandular epithelium 2.Myoepithelium 3.Neuroepithelium 0  Functions of Epithelium 1-Protection of covering and lining surfaces (e.g, keratin in skin and mucous in intestines). 2-Absorption (e.g. intestines and kidney). 3-Secretion of hormones, digestive enzymes and mucous ( glandular epithelium). 0  Functions of Epithelium 4-Sensation (e.g. neuropeithlium). 5-Contractility (myoepithelium). 6-Transcellular transport: 0  I-Surface [Covering] Epithelium It is classified according to: Number of its cell layers into:- 1. Simple [only one layer of cells] 2. Stratified [more than one layer]. I Shape and height of surface cells:- 3. Squamous 4. Cuboidal 5. Columnar 6. Transitional 0  1- Simple Squamous Epithelium a) Single layer of flattened cells with central flat nucleus and little cytoplasm. b) Sites: 3. The large body cavities (pleural & peritoneal, pericardium) [mesothelium], 4. blood vessels and lymph vessels [endothelium] 5. Lung alveoli (pneumocyte) 6. Bowman’s capsule of kidney. 0 0 Lung alveoli kidney 0  2-Simple cuboidal epithelium 1. Single layer of cuboidal cells with central rounded nuclei. 2. Sites: a. Follicles of the thyroid gland. b. Tubules of the kidney. 0  3-Simple columnar epithelium 1. Single layer of columnar (taller than they are wide) cells with usually basal oval nuclei located at the same level. 2. The cells may be ciliated or not. 0  3-Simple columnar epithelium 3. Sites: a. All GIT except mouth, esophagus and anal canal. c. Gall bladder. 0  3-Simple columnar epithelium D Sites of ciliated columnar epithelium It moves mucus and other substances via cilia and is found in:- a. Respiratory tract. b. The Fallopian tube. 0  4-Pseudostratified columnar epithelium simple columnar epithelium 1. Single layer of columnar cells. 2. All cells arise from the underlying basement membrane Pseudostratified columnar 0 3.The cells are, so crowded that some cell cannot reach the surface, as well, the shape of each cell is distorted resulting in wide and narrow portions →migration of the nuclei to the wider part of the cells → located at different levels → false impression of stratification. 4. It can be ciliated or shows goblet cells. 5. The ciliated pseudostratified columnar epithelium with goblet cells is called respiratory epithelium as it is lining the respiratory tract (trachea, bronchi). 6. The ciliated type without goblet cells is lining the vas & 0 epididymis 0  Pseudo-stratified columnar ciliated epithelium in epididymis Pseudo-stratified columnar ciliated epithelium with Goblet cells in trachea 0  5- Stratified squamous epithelium 1. Vary in thickness depending on the number of cell layers present. 2. The deepest cells, which are in contact with the basement membrane, are cuboidal or columnar in shape. This layer is usually named the basal cell layer, and the cells are called basal cells. Basal cells I are mitotically active and replace the cells of the epithelium. Repair 0  4- Stratified squamous epithelium 3. The intermediat layers of cells are polyhedral [polygonal]in shape. 4. The superficial cells are more flattened. 6. It may be non-keratinized=moist [lining of oral cavity, oro-pharynx, esophagus, larynx, vagina, anal canal] or keratinized [epidermis of the skin, more thick in palms and soles]. 0 0  SLIDEs : Stratified squamous epithelium non-keratinized keratinized 0  6-Stratified cuboidal epithelium 1. Stratified cuboidal epithelium is not common in the human body. 2. A two-layered cuboidal epithelium is, for example, seen in the ducts of the sweat glands. Stratified cuboidal epithelium 0 0  7- Stratified columnar epithelium 1. Stratified columnar epithelium is not common in the human body. 2. Sites: a. the Conjunctiva. b. the main excretory duct of the large salivary glands [parotid, submandibular, sublingual]. 0  Simple No 8-Transitional epithelium 1. Transitional epithelium is found exclusively in the urinary passages (the renal calyces and pelvis, the ureter, the urinary bladder) so, called urinary epithlium (uroepithelium). 2. The shape of the cells in the surface layer and the number of layers of a transitional epithelium varies with the degree of distension of the organs whose lumen is lined by this type of epithelium. 0 3. In the 'relaxed' state the epithelium is formed multiple cell layers up to 6 layers [basal cuboidal or columnar cells, several layers of polyhedral cells, and a superficial layer of dome-shaped sometimes bi- nucleated cells]. Umberila cells In the distended state of the epithelium it is up to 3 layers. One or two layers of cuboidal cells followed by a superficial layer of large, low cuboidal or squamous [flat] cells. 0 0 SLIDE : Transitional epithelium [urinary bladder] 0 0  RECOMMENDED REFERENCES, WEBSITES Junqueira's Basic Histology: Text and Atlas, Thirteenth Edition 2013 ISBN-13: 978-0071780339 ISBN-10: 0071780335 Edition: 13th The histology tutor: http://www2.yvcc.edu/histology zoomer/HistologyTutorials/hi stology_tutorials.htm 0