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 Hallmarks 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 Hallmarks of epithelial cell © www.webanatomy.net Diffusion barriers ‒ Epithelia separate intercellular spaces – compartmentalization • intestine epithelium • kidney epithelium • secretory and duct parts of exocrine glands • endothelium in brain capillaries (blood brain barrier) • plexus choroideus (blood-liquor barrier) microvessel stained for focal adhesion kinase (green), zonula occludens 1 (red) and endothelial nuclei (blue) http://commons.wikimedia.org/wiki/File:Brain_Microvessel.tif Basement membrane (membrana basalis) ‒ Attachment of epithelium to underlying tissues ‒ Selective filter barrier between epithelial and connective tissue ‒ Communication, differentiation, angiogenesis PASHE Basement membrane • 50 – 100 nm • Glycosaminoglycans – heparansulphate • Laminin, collagen III, IV, VI • Nidogen, entactin, perlecan, proteoglycans Dunsmore SE, Chambers RC, Laurent GJ. 2003. Matrix Proteins. Figure 2.1.2. In: Respiratory Medicine, 3rd ed. London. Saunders, p. 83; Dunsmore SE, Laurent GJ. 2007. Lung Connective Tissue. Figure 40.1. In: Chronic Obstructive Pulmonary Disease: A Practical Guide to Management, 1st ed. Oxford. Wiley-Blackwell, p. 467. Basal membrane Kolagen IV Laminin Perlecan, Nidogen/Entactin Basement membrane • Two basic layers – lamina basalis (basal lamina) • lamina densa, • lamina rara ext. et int. – lamina fibroreticularis Architecture of basal membrane Epithelial cell and Basal lamina Lamina fibroreticularis Fibroblasts BM Epithelial layer + lamina propria = MUCOSA Basal membrane in corpusculum renis Basement membrane in corpusculum renis 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 Classification of epithelial tissue -Based on morphology (covering, trabecular, reticular) - Based on function (glandular, resorptive, sensory, respiratory) 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 cuboidal 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, epidydimis, respiratory passages © 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 - cytoreticulum Classification of epithelial tissues Covering Trabecular Reticular Classification of epithelial tissues 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. exocrine Mucous glands - Viscous secretion - Tubular secretion compartments Mucous glands Serous glands - Secretion rich in electrolytes - Acinous secretion compartments Compound glands - both serous and mucous - usually tuboacinous - both compartments individually or in combination (serous demilunes) Resorptive epithelium Resorptive epithelium APICAL BASOLATERAL COTRANSPORTION Channel or transporter WATER RESORPTION WATER SECRETION Respiratory epithelium Respiratory passages – Moisten, protect against injury and pathogen – Remove particles by „mucociliary escalator“ – Pseudostratified columnar epithelium with cilia – Basal cells- epithelium renewal Alveolar epithelium – Gas exchange – Respiratory bronchiols, alveolar passages and alveoli – Type I and II pneumocytes Respiratory epithelium Sensory epithelium – Supportive and sensory cells Primary sensory cells – directly convert stimulus to membrane potential Receptor region, body, axonal process Nasal epithelium (regio olfactoria nasi), retina (rods and cones) Secondary sensory cells Receptor region and body Signal is transmitted by adjacent neurons ending on secondary sensory cell Taste buds, vestibulocochlear apparatus Sensory epithelium Myoepithelium – Derived from epithelium (cytokeratin filaments, desmosomes) – Biochemical properties of smooth muscle cells (α-actin, mysoin, desmin, gap junctions) – Contraction upon nerve or hormonal stimulation – Sweat and salivary glands – enhance secretion Regeneration and plasticity of epithelial tissue Regeneration of epithelial tissue Different epithelia have different capability of regeneration (epidermis × inner ear sensory epithelium) Multi- a oligopotent stem cells Microenvironment – stem cell niche Example: Regeneration of intestinal epithelium Clinical correlations - Metaplasia Squamous metaplasia of the uterine cervix Simple columnar Stratified squamous Clinical correlations – Epithelial to mesenchymal transition Cancer Wikipedia.org; http://radiology.uchc.edu Hyperplasia Normal prostate Hyperplasia of glandular epithelium Plasticity of epithelial tissue Prostate cancer Epithelial – to mesenchymal transition (EMT) J Clin Invest. 2009;119(6):1420–1428. doi:10.1172/JCI39104. Plasticity of epithelial tissue EMT in embryonic development J Clin Invest. 2009;119(6):1438–1449. doi:10.1172/JCI38019. Thank you for attention pvanhara@med.muni.cz http://www.med.muni.cz/histology