Epithelium 1 Lecture 1.pdf

Dr Amany Shalaby Assistant professor of Histology and Cell Biology General characters It is formed of continuous sheet of cells arranged in one or more layers with very little amount of intercellular substance. All the cells are resting on a basement membrane. Blood vessels do not penetrate the epit...

Dr Amany Shalaby Assistant professor of Histology and Cell Biology General characters It is formed of continuous sheet of cells arranged in one or more layers with very little amount of intercellular substance. All the cells are resting on a basement membrane. Blood vessels do not penetrate the epithelial tissue, however its nutrition depends on the diffusion of metabolites from the capillaries in the underlying connective tissue. Most epithelial tissues receive nerve ending that form rich nervous network. General characters The shape of nuclei corresponds to the shape of cells. Classification of Epithelium I- Covering and lining epithelium. II- Glandular epithelium. III- Special epithelium I- Covering and Lining Epithelium 1) Simple Epithelium (formed of one layer of cells) 2) Startified epithelium (formed of more than one layer) A- Simple Epithelium Types of simple epithelium: 1- Simple Squamous Epithelium. 2- Simple Cubical Epithelium. 3- Simple Columnar Epithelium. 4- Pseudostratified Columnar Epithelium. 1-Simple Squamous Epithelium Single layer of flat cells with flat nuclei. Sites: It lines the wall of: 1)blood vessels. 2) Alveoli of the lung. 2-Simple Cubical Epithelium Single layer of cubical cells with central rounded nuclei. Sites: 1) Thyroid follicles. 2) Lines the convoluted tubules of the kidney. 3-Simple Columnar Epithelium single layer of tall columnar cells with basal oval nuclei. A) Simple columnar nonciliated e.g. stomach, intestine and gall bladder C) Simple columnar ciliated epithelium: uterus, fallopian tube (oviducts). 4-Pseudostratified Columnar Epithelium Single layer of cells. Some cells are tall while others are short not reaching the surface. However all the cells are resting on the basement membrane. Sites: I) The ciliated type: in the respiratory passage as trachea and is usually associated with goblet cells. II) The non ciliated type is found in the large ducts of the glands. B- Stratified Epithelium Formed of many layers of cells in which the basal layer is columnar in shape and the intermediate layers are polyhedral cells. Classification: according to the shape of the most superficial cells into: 1- Stratified squamous epithelium. 2- Transitional epithelium. 3- Stratified columnar epithelium. 4- Stratified cubical epithelium. B- Stratified Epithelium Classified according to shape of superficial cells. 1- Stratified squamous epithelium 2- Stratified cuboidal epithelium 3- Stratified columnar epithelium 4. Transitional epithelium 13 1-Stratified Squamous Epithelium I) Keratinized (dry type): Covered with non living layer of keratin: skin. II) Non Keratinized (wet) type: oral cavity and oesophagus. 2-Stratified cubical epithelium Cuboidal cells arranged in 2-3 layers. Sites: ducts of sweat glands. 3-Stratified columnar epithelium Most superficial cells are columnar in shape. Sites: 1) Ducts of the glands (nonciliated). 2)Foetal oesphagus: (ciliated). 4- Transitional epithelium The most superficial cells are cuboidal or dome shape with one or two nuclei. Called transitional because the number of layers changed depending on whether the organ is empty or distended. when the urinary bladder is empty: transitional epithelium has several layers (6-8 layers). When the bladder is full the epithelium has two or three layers of squamous cells. Sites: it is present in the urinary tract Empty bladder Full bladder Transitional epithelium II-Glandular Epithelium A special type of epithelium which is specialized in secretory function. Classified according to the presence or absence of duct system into: a) Exocrine glands which have ducts to carry their secretion outside as salivary glands. b) Endocrine glands which have no ducts. They secret hormones directly in the blood as thyroid gland. c) Mixed glands which have exocrine and endocrine functions as pancreas. II-Glandular Epithelium 2-Exocrine glands are classified according to the number of cells into: a) Unicellular gland as goblet cell. b) Multicelluar glands as the salivary glands. Thank you……