Epithelial Tissue Lecture PDF

Epithelial tissue Dr. Abeer Abdel Mohsen Professor of Histology Faculty of Medicine, ASU ILOs of epithelial tissue are: 1. Mention the general characters of epithelial tissue. 2. List types of epithelium. 3. Describe structure & site of each type of epithelium. 4. Describe structure...

Epithelial tissue Dr. Abeer Abdel Mohsen Professor of Histology Faculty of Medicine, ASU ILOs of epithelial tissue are: 1. Mention the general characters of epithelial tissue. 2. List types of epithelium. 3. Describe structure & site of each type of epithelium. 4. Describe structure of glandular epithelium. 5. Classify glandular epithelium. 6. Describe structure & correlated function of neuroepithelium & myoepithelium. 7. Mention the specialization of epithelial cell The human body is composed of four basic Epithelial types tissue of tissues Nervous 4 Basic Connective tissue Tissues tissue Muscular tissue General characters of epithelial tissue 1. Composed mainly of cells + little intercellular substances. 2. Is non-vascular: no penetration of blood vessels or lymphatics but nerves do. 3. Cells lie on basement membrane separating them from connective tissue (C.T.). 4. Nutrition comes from blood vessels of  Classificatio n of Epithelial I. tissue Surface IV. epitheliu Myoepitheli m II. um Glandul ar epitheli um III. Neuroepitheliu m  I- Surface (covering or lining) epithelium A.Simple B.Stratified epithelium epithelium Classification of epithelial membranes According to number of cell layers: Simple: one layer. Stratified: more than one layer. According to shape of apical surface cells : Squamous Cuboidal Columnar  A. Simple epithelium 1- Simple squamous epithelium One layer of flat cells Thin cytoplasm Flat oval nucleus  Examples of simple squamous epithelium: 1. Lining blood vessels: endothelium (for active transport). 2. Lining lung alveoli (for exchange of gases).  2- Simple cuboidal epithelium One layer of cubical cells Single round central nucleus Sites: as lining thyroid follicles & small ducts  3- Simple columnar epithelium One layer of columnar cells Single basal oval nucleus Examples: A. In stomach (secretory) B. In small intestine (absorptive)  4- Pseudostratified columnar epithelium One layer of overcrowded cells resting on basement membrane. Some cells are shorter than others. Nuclei are at different levels. False impression of being stratified. Sites & types: A.Non-ciliated: e.g. large ducts. B.Ciliated: usually with goblet cells in respiratory tract→ e.g. trachea, & is called  B. Stratified epithelium 1.Stratified squamous epithelium Two or more layers of cells and basal layer is resting on basement membrane. Types: A- Stratified B- Stratified squamous non- squamous keratinized keratinized epithelium epithelium  A- Stratified squamous non- keratinized epithelium Basal layer: columnar cells Intermediate cells: polygonal in shape then gradually flatten & become squamous cells at surface Sites: All cavities opening to skin surface as: oral cavity, tongue, cornea, vagina, …….  Function: protection of  B- Stratified squamous keratinized epithelium Basal layer: columnar cells Intermediate cells: polygonal in shape, then gradually flatten & become squamous cells Top cells at surface are changed to cells containing keratin without organelles or nucleus. Site: epidermis of skin Function: is tough, resists  2. Stratified cuboidal epithelium Site: as lining the duct of sweat gland 3. Stratified columnar epithelium Upper most cells are columnar Site: as lining large ducts of salivary gland  4.Transitional epithelium Specialized type to withstand distension Empty or relaxed state: 6-8 layers of cells stretched state: 3-4 layers of cells Site: in urinary system e.g. urinary bladder II. Glandular epithelium Endocrine glands: Loose their connection to the surface, no ducts, their secretions (hormones) are transported by blood. Exocrine glands: have ducts carrying their secretions to the surface e.g. Salivary glands & Sweat glands.  Unicellular→ Goblet cell Exocrine Number Classification: glands Multicellular , e.g. salivary glands Goblet cells Are unicellular (one cell) exocrine in function. Scattered between epithelial cells lining parts of digestive tract & respiratory tract. Function: is mucous secretion for protection.  Mucous →viscous mucous secretion Exocrine glands 1- Type of Multicellular: Serous→ watery rich in enzymes Mixed (seromucous) secretion can be classified by:  Simple Tubularbranched ducts Exocrine glands 2-Branching 3-Shape of of ductspart secretory Compound branched ducts Alveolar (acinar) Tubulo-alveolar Multicellular: can be classified by: Tubulo- alveolar  Merocrine: by exocytosis Exocrine glands 4-Mode of secretion Mode of Apocrine: top of cell is lost with secretion secretion Holocrine: released by rupture of the cell Multicellular: can be classified by: Merocrine Apocrine Holocrine  III. Neuroepithelium Modified epithelial cells to receive stimuli For special sensations Then, convert them into electrical impulses→ brain For example: Taste buds  IV. Myoepithelium Modified epithelial cells for contraction. Have long branching processes containing actin & myosin & are called basket cells. Present surrounding the secretory cells e.g. as in salivary glands. Myoepithelial cells  Polarity of epithelial cells (Structural & functional asymmetry) The three surfaces of epithelial cells show different structures to adapt their functions. Specialization of apical surface of epithelial cells A- Cilia & flagella Are hair-like motile structures Extending from free surfaces of some epithelial cells e.g. cilia on some cells of respiratory tract & flagella of sperms  Specialization of apical surface of epithelial cells B- Microvilli Finger-like projections Extending from apical free surface Core contains bundles of longitudinally- arranged Actin filaments for support Function: to increase surface area of  Specialization of lateral surface of epithelial cells Cell junctions 1. Occludens (tight) junctions: Cell membranes of 2 adjacent cells fuse together & prevent flow of material between the cells. 2. Adherens (anchoring) junctions: adjacent cell membranes are connected by strong adhesion to prevent separation. e.g.: Desmosomes: are spot junctions as in epidermis of skin. 3. Gap (communicating) junctions: small channels for communication between epithelial cells & present also  Specialization of basal surface of epithelial cells Example: Basal lamina Epithelial cells are separated from C.T. by extracellular material called basal lamina (is a part of the basement