Epithelial Tissue PDF

Epithelial Tissue Dr. Lanka Ranaweera Senior Lecturer Department of Anatomy  Objectives ▪ Define the term epithelium. ▪ State the general functions of the epithelial tissue. ▪ Outline the classification of epithelial tissue. ▪ State the location & specific...

Epithelial Tissue Dr. Lanka Ranaweera Senior Lecturer Department of Anatomy  Objectives ▪ Define the term epithelium. ▪ State the general functions of the epithelial tissue. ▪ Outline the classification of epithelial tissue. ▪ State the location & specific function of each type of epithelial tissue. ▪ Explain the term endothelium and mesothelium. ❖ Epithelial tissue ❖ Connective tissue ❖ Nervous tissue ❖ Muscular tissue  Tissue ◼ Collections of specialized cells and cell products that perform a specific function. Epithelial Tissue ◼ Covers exposed surfaces, lines passageways & body cavities, and forms glands.  Epithelial Tissue ◼ 2 main groups ◼ Covering and lining membranes ◼ Glands (derived from epithelial membranes) Why study of epithelial tissue is important ? Smoking and lung cancer  Gastroesophagial reflux disease Gastritis  Common features of Epithelia ◼ Origin: all 3 germ layers ◼ Formed entirely of adherent cells ◼ Very little intercellular substance ◼ Fitted closely by cell junctions ◼ Avascular: nourished by diffusion ◼ Nerve supply – free nerve endings  Some Characteristics …. Microvilli cilia apical surfaces surface lateral surface basal surface interdigitation basement membrane Basal infoldings (underlying connective tissue)  Functional polarity … Mechanical integrity ….. Common features of Epithelia  Epithelia vary in ◼ Cell shape ◼ Number of layers ◼ Type of adherence ◼ Mitotic activity ◼ Secretory or absorptive potential ◼ Adaptation to sensory perception Squamous Cuboidal Columnar Classification based on cell shape Simple Apical surface Basal surface Stratified Apical surface Basal surface Classification based on number of cell layers Epithelial Tissue Classification based on Cell layers + Cell shapes + Specializations on apical surface  Epithelial Tissue Classification Epithelial membranes Glandular tissue Simple Pseudostratified Stratified squamous cuboidal columnar ciliated transitional Special properties  Simple squamous (pavement) epithelium single, thin flat scale like cells little cytoplasm nucleus bulge in the lumen  Apical View of Simple Squamous A B C A – cell membrane , B – nucleus , C - cytoplasm Simple squamous epithelium Cross-Sectional View of Blood Vessel  Simple squamous epithelium - Locations ◼ surfaces involved in passive diffusion alveoli of lung blood capillaries endothelium ◼ lining body cavities mesothelium ◼ subarachnoid and subdural spaces ◼ chambers of the eye  Simple squamous epithelium - Functions ◼ Facilitates the movement of the viscera (mesothelium) ◼ Facilitating diffusion – exchange of gases & nutrients (alveoli & endothelium) ◼ Facilitating exchange and transport of fluids & solutes (actively internalize/ pinocytosis) ◼ Enabling filtration (Bowman's capsule – special structure)  Simple cuboidal epithelium ◼ Functions: secretion/ Absorption/ protection ◼ Locations: ◼ Kidney tubules ◼ Small ducts ◼ secretory portions of small glands Simple columnar epithelium  Simple columnar epithelium ◼ Functions:. Absorption / secretion /Protection ◼ Locations: Lining of intestine, gallbladder, bronchioles, stomach  Simple columnar ciliated epithelium ▪ ciliated - cilia beat to move mucus along the surface. ▪ cilia are found on the luminal surface of most of the lining cells ▪ facilitates transport of the ova in Uterine tube Simple columnar ciliated epithelium Nucleus Cilia Lumen Pseudostratified columnar epithelium ◼ Functions: Protection; cilia- mediated transport of particles rapped in mucus ◼ Locations: ◼ Lining of trachea ◼ Bronchi ◼ nasal cavity.  Pseudostratified columnar ciliated epithelium Lining of the large airways A - Epithelium. B - Cilia C - Nuclei  Epithelial Tissue Classification Epithelial membranes Glandular tissue Simple Pseudostratified Stratified squamous cuboidal columnar ciliated Special properties transitional Stratified squamous epithelium Stratified Squamous Non keratinized (wet) epithelium ◼ Functions: Protection, secretion; prevents water loss ◼ Locations: ◼ Mouth ◼ Oesophagus ◼ Larynx ◼ Vagina ◼ Anal canal Stratified Squamous Non keratinized (wet) epithelium ◼ A - epithelium ◼ B – surface nuclei Stratified Squamous Keratinized (Dry) epithelium ◼ found in parts of the body exposed to the atmosphere. ◼ covered with waterproof coating - keratin. ◼ palms and soles thick keratin protects from abrasion and desiccation.  Stratified cuboidal epithelium ◼ 2-3 layers thick ◼ large ducts of exocrine glands salivary glands sweat glands ◼ more protection than that given by a simple epithelium is needed ◼ no significant absorptive or secretory function.  Stratified columnar epithelium ◼ 2-3 layers thick ◼ Very rare ◼ More protection ◼ Lactiferous duct, male reproductive system & conjunctiva  Transitional epithelium ◼ found in the urinary tract: ◼ specialized to stretch (distensibility) withstand the toxicity of urine. (Protection) ◼ made up of 5-6 layers of cells. ◼ In a relaxed state superficial cells large rounded pale stained ◼ luminal surface scalloped outline ◼ thick plates separated by narrow bands of thin membrane Transitional epithelium  Transitional epithelium ◼ Tight junctions between the surface epithelial cells prevent intercellular diffusion ◼ In the deeper layers desmosomes are fewer ◼ Numerous interdigitations and infoldings ◼ Bladder, ureters, renal calyces SUMMARY SUMMARY SUMMARY SUMMARY  REFERENCES ◼ Junqueira, L.C., Carneiro (1998). Basic histology. 9 th ed., stamford: Appleton & lange ◼ Burkit, H.G, young, B. (1993). Wheaters functional histology. 4 th ed., london:Churchill livingstone  yo u n k h a T