Epithelial tissue Dept. Histology & Embryology, Faculty of Medicine MU pvanhara@med.muni.cz Petr Vaňhara, PhD ‒ Very early event and very novel innovation in Metazoa evolution ‒ From simple colonies of cells to highly specialized tissue structures ‒ Boundaries and interfaces ‒ Dividing of the body into separated compartments → separating individual milieu ‒ Lining of cavities or interfaces of open space ‒ Attachment and adhesion ‒ Basal membrane  General characteristics of epithelial tissue - lessons from Sponges ‒ Typical morphology and cell connections  General characteristics of epithelial tissue ‒ Avascular (without blood supply) – nutrition by diffusion from a highly vascular and innervated area of loose connective tissue (lamina propria) just below the basement membrane ‒ Highly cellular – cohesive sheet or groups of cells with no or little extracellular matrix  Covering (sheet) epithelium  Trabecular epithelium  Reticular epithelium  Classification of epithelial tissues  Morphology  Function  Covering  Glandular  Resorptive  Sensory  Respiratory  Alveolar  Germinal  ...  Classification of epithelial tissues Vessels Kidney Intestine Respiratory passages Skin Oesophagus Ducts Urinary tract 1. Covering (sheet) epithelia Endothelium. heart, blood, and lymphatic vessels. Mesothelium. serous membranes - body cavities  Simple squamous epithelium ‒ Capillaries ‒ Lung alveolus ‒ Glomerulus in renal corpuscle Selective permeabilty ‒ Single layer of flat cells with central flat nuclei  Simple cuboidal epithelia ‒ Single layer of cubic cells with large, spherical central nuclei Examples: ‒ Ovarian surface epithelium ‒ Renal tubules ‒ Thyroid ‒ Secretion acini ‒ Secretion or resorption Ovarian surface epithelium Thyroid follicles  Simple columnar epithelium ‒ GIT - stomach - small intestine - large intestine Resorption / Secretion ‒ Single layer of columnar cells with large, oval, basally located nucleus  Simple columnar epithelium with kinocilia ‒ Uterine tube ‒ flow of the oocyte towards the uterus © http://www.unifr.ch www.siumed.edu  Simple columnar epithelium with kinocilia (also pseudostratified) ‒ Upper respiratory passages ‒ Removes mucus produced by epithelial glands Other locations: ‒ Spinal cord ependyma ‒ Epididymis ‒ Vas deferens  Stratified squamous epithelium Keratinized vs. non-keratinized  Constant abrasion  Mechanical resilience  Protection from drying  Rapid renewal Examples: ‒ Cornea ‒ Oral cavity and lips ‒ Esophagus ‒ Anal canal ‒ Vagina  Multiple layers of cubic cells with central nuclei, flattening towards the surface  First layer in contact with BM, last layer – flat  Stratified squamous epithelium Keratinized Skin (epidermis) Nail Keratins Fibrous proteins, ~ 40 types Very stable, multimeric Disorders of keratin expression – variety of clinical symptoms e.g. Epidermolysis bullosa simplex  Stratified cuboidal epithelium Large ducts of : ‒ sweat glands ‒ mammary glands ‒ salivary glands ‒ Fluctuation of volume ‒ - organization of epithelial layers ‒ - membrane reserve ‒ Protection against urine ‒ Urinary bladder, kidneys, ureters  Transitional epithelium (urothelium) Empty: rather cuboidal with a domed apex relaxed: flat,stretched Basal cells Intermediate layer Surface cells  Transitional epithelium (urothelium) glycosaminoglycan layer (GAG) on the surface ‒ osmotic barrier ‒ antimicrobial properties Barrier architecture: ‒ GAG-layer ‒ surface cells (tight junctions), uroplakin proteins in the apical cell membrane ‒ capillary plexus in the submucosa ©http://www.cytochemistry.net/microanatomy/epithelia/salivary7.jpg  Stratified columnar epithelia ‒ several layers of columnar cells ‒ secretion / protection ‒ ocular conjunctiva ‒ pharynx, anus – transitions ‒ uterus, male urethra, vas deferens ‒ intralobular ducts of salivary glands 2. Trabecular epithelium Liver – trabecules (cords) of hepatocytes  Classification of epithelial tissues Islets of Langerhans Cords of endocrine active cells  Endocrine glands Adrenal cortex Cortex of adrenal gland – epithelial cells in cords secreting corticoid  Endocrine glands Adenohypophysis – anterior pituitary  Endocrine glands 3. Reticular epithelium Thymus  Classification of epithelial tissues  Hallmarks of epithelial cell © www.webanatomy.net Basement membrane ‒ Attachment of epithelium to underlying tissues ‒ Selective filter barrier between epithelial and connective tissue ‒ Communication, differentiation PASHE Basement membrane • Two basic layers – lamina basalis • lamina densa, • lamina rara ext. et int. – lamina fibroreticularis Basement membrane • Glycosaminoglycans – heparansulphate • Laminin, collagen III, IV, VI Basement membrane Tissue specific distribution - Descemet’s membrane (under endothelial layer of cornea) - Glomerular basement membrane (Bowman capsule) - part of Bruch’s membrane in retina - …. Pathology example- Membranous glomerulonephritis - circulating antibodies bind to glomerular basement membrane - complement (C5b-C9) complex forms and attacks glomerular epithelial cells - filtration barrier is compromised - proteinuria, edema, hematouria, renal failure Modifications of cell membrane – cell junctions Zonula occludens – a tight junction Modifications of cell membrane – cell junctions Zonula adherens (Farquhar, M.G., and Palade, G.E. Junctional Complexes in Various Epithelia, J. Cell Biol.17, 375-412, 1963) Cell adhesion is a regulated event © http://www.hubrecht.eu/research/derooij/research.html Modifications of cell membrane – cell junctions Desmosome - a spot junction (Farquhar, M.G., and Palade, G.E. Junctional Complexes in Various Epithelia, J. Cell Biol.17, 375-412, 1963) Modifications of cell membrane – cell junctions Hemi-desmosome - a spot junction doi:10.1186/1465-9921-7-28. Modifications of cell membrane – cell junctions Nexus – gap junctions Modifications of cell membrane – cell junctions Nexus – gap junctions Modifications of cell membrane – cell junctions Summary Modifications of cell membrane – basal cell surface Basal labyrinth Modifications of cell membrane – apical cell surface Microvilli Modifications of cell membrane – apical cell surface Brush border Modifications of cell membrane – apical cell surface Stereocilia - e.g. inner ear - not actively moving - like microvilli, with parallel actin microfilaments - sensory apparatus Modifications of cell membrane – apical cell surface Kinocilia Modifications of cell membrane – apical cell surface Kinocilia Modifications of cell membrane – apical cell surface Summary Microvilli Brush border Stereocilia Kinocilia BREAK 10 min  Glandular epithelium • Secret ↔ excret • Process of secretion:  Epithelium may posses a function  Glandular epithelium  Single cell glands – Goblet – Enteroendocrine  Goblet cells - Mainly respiratory and intestinal tract - Produce mucus = viscous fluid composed of electrolytes and highly glycosylated glycoproteins (mucins) - Protection against mechanic shear or chemical damage - Trapping and elimination of particular matter - Secretion by secretory granules constitutive or stimulated - After secretion mucus expands extremely – more than 500-fold in 20ms - Dramatic changes in hydration and ionic charge - Chronic bronchitis or cystic fibrosis – hyperplasia or metaplasia of goblet cells  Multicellular glands • Shape of secretion part – Alveolar (acinar) – Tubular – Tubuloalveolar (tubuloacinar) • Branching – Simple – Branched – Compound • Secretion – Mucous – Serous – Compound • Multicellular glands – Endocrine vs. endocrine  Mucous glands  Mucous glands  Serous glands  Compound glands - both serous and mucous  Respiratory epithelium Respiratory passages – Moisten, protect against injury and pathogen – Remove particles by „mucociliary escalator“ – Pseudostratified columanr epithelim with cilia – Basal cells- epithelium renewal Alveolar epitheithelium – Gas exchange – Respiratory bronchiols, alveolar passages and alveoli – Type I and II pneumocytes  Sensory epithelium – Supportive and sensory cells Primary sensory cells – directly convert stimulus to membrane potential Receptory region, body, axonal process Nasal epithelium (regio olfactoria nasi), rods and cones Secondary sensory cells Receptory region and body Signal is trasnimtted by adjacent neurons ending on secondary sensory cell Taste buds, vestibulocochlear appartus  Myoepithelium – Star-like or spindle cells – Connected by nexus and desmosomes – Actin microfilaments, myosin and tropomysoin – Contraction – Sweat and salivary glands – enhance secretion  Regeneration of epithelial tissue Different regenerative potential (epidermis  sensory epithelium of inner ear) Multi- a oligopotent stem cells Microenvironment – stem cell niche Example: Regeneration of intestine epithelium Example: Regeneration of intestine epithelium Metaplasia Squamous metaplasia of cervix uteri Respiratory passages Simple columnar epithelium Stratified squamous epithelium  Plasticity of epithelial tissues Simple columnar epithelium Metaplasia Development of precanerous lesions  Plasticity of epithelial tissues Wikipedia.org; http://radiology.uchc.edu Hyperplasia Normal prostate Hyperplasia of prostate glandular epithelium Prostate adenocarcinoma  Plasticity of epithelial tissues Epithelial to mesenchymal transition (EMT) J Clin Invest. 2009;119(6):1420–1428. doi:10.1172/JCI39104.  Plasticity of epithelial tissues  EMT in embryonic development … has also a reverse side Plasticity and regeneration of the epithelial tissue…  EMT and tumor dissemination J Clin Invest. 2009;119(6):1438–1449. doi:10.1172/JCI38019.  Cancer development and regeneration share common mechanisms Clinical correlations – Epithelial to mesenchymal transition Cancer Thank you for attention pvanhara@med.muni.cz http://www.med.muni.cz/histol/histolc.html