Epithelial Tissue Student Version PDF

EPITHELIAL TISSUE Basic Histology Insert Image Here  Learning Objectives 1. Describe the general features of epithelial tissues. 2. List the various types of specialized cell junctions, and briefly describe their morphology and functions. 3. Describe the basement mem...

EPITHELIAL TISSUE Basic Histology Insert Image Here  Learning Objectives 1. Describe the general features of epithelial tissues. 2. List the various types of specialized cell junctions, and briefly describe their morphology and functions. 3. Describe the basement membrane and its various components (basal lamina layers, types of fibers involved). 4. Describe the differences between the structure and functions of microvilli, cilia, and stereocilia. 5. List the various types of epithelia and describe their specialized structural attributes and functions. 6. Identify the histological appearance and classify each type of epithelium. 2 1: Basic Features 2: Apical Surface Modifications 3: Epithelial Cell Modifications 4: Classifications EPITHELIAL TISSUE  Four Basic Tissue Types Muscle: Contractile Nerve Tissue: Tissue Transmits electrical signals Connective Tissue: surrounds and supports Epithelia: lines or other tissues covers surfaces, ducts and glands  General Features of Epithelia Cells align side by side to form layers: Cover external surfaces Linings of internal surfaces, lumen of sac-like or tubular organs Junctions Immune cells ( Ex: lymphocytes ) Epithelial Layers  Selective Barriers Substances can cross an epithelial layer: 1. Through junctions between cells 2. Transported through cells => endocytosis 3. Diffuse freely through cells => small mole  Epithelial Junctions Terminal Web: Woven Zonula occludens matt of MFs and IFs (Tight Junction): Belt-shaped; forms seal Zonula adherens between adjacent (Adherens Junction): epithelial cells. Belt-shaped; binds plasma membrane to a Gap junction (Nexus): ring of contractile Plaque-shaped; microfilaments in transmembrane channels adjacent epithelial cells. allowing direct communication between adjacent cells. Macula adherens (Desmosome): Hemidesmosome: Plaque- Plaque-shaped; links shaped; binds intermediate filaments in intermediate filaments, adjacent cells together; and anchor epithelial cells strong adhesion. to basement membrane.  The Basement Membrane 1. Lamina Lucida (LL) Extracellular domains Basal Lamina of integrin proteins (BL) made by 2. Lamina Densa (LD) epithelial cell Laminin, Fibronectin, Collagen Type IV 3. Reticular Layer (RL) Collagen Type III made by fibroblasts Extracellular matrix sheet separating the epithelium from the connective tissue. Consists of proteins secreted by the epithelial cells and by underlying connective tissue fibroblasts. Functions as supporting and anchoring scaffold for epithelial cells. Provides differentiation signals to epithelial cells. Hemidesmosomes attach to intermediate filaments  Glomerulus, TEM LL BL LD BM RL PAS Epithelial lining Bronchus, H&E  Knowledge Check A 5-year old boy is seen by a dermatologist after experiencing a series of unexplained blisters and scars that often become infected. He is diagnosed with bullous pemphigoid, a genetic skin condition that results from inadequate adhesion of epidermal epithelial cells to their underlying structures. Abnormalities in which of the following structures would most likely be associated with bullous pemphigoid? A. Basal bodies The primary structures involved in this adhesion are hemidesmosomes in the basal junctions. Hemidesmosomes are located at the base of epithelial cells and play a critical role in attaching the B. Apical junctions epidermis to the basement membrane. When these structures are compromised, it leads to the separation of the epidermis from the dermis, resulting in blisters. C. Connective tissue D. Luminal fluids E. Basal Junctions 1: Basic Features 2: Apical Surface Modifications 3: Epithelial Cell Modifications 4: Classifications EPITHELIAL TISSUE  Apical Surface Modifications Cilia Microvilli Stereocilia Core of microtubules Core of microfilaments Core of microfilaments Anchored to basal bodies Anchored to terminal web Anchored to terminal web Bendable Rigid “Long branched microvilli” Function: MOTILITY of Fn: INCREASE SURFACE AREA Fn: INCREASE SURFACE AREA lumen contents for absorption for absorption Ex. Respiratory Epithelium Ex. GI Tract Ex. Epididymis  Review: Microfilaments Thin filaments of F-actin, (7 nm diameter) polymerized from globular proteins: G-actin. Highly dynamic (constant remodeling of length) Function: Forms network along cell membrane which maintains cell shape (found in microvilli), Microfilament tracks for the movement of motor proteins (Actin Filament) Microvilli (myosin), cell motility.  TEM Plasma Membrane: Hydrophobic layer stains light, hydrophilic layers stain dark H&E Cell Borders: Visible due to membrane proteins TEM that pick up eosin stain  Microvilli = inside microvilli we have many Actin microfilaments holding these microvilli upright Characteristics : 1. Tightly Packed 2. Same length GOAL is to have more plasma More plasma membrane => membrane, which increases the larger surface area : for surface area = which allows absorption cells to endocytose more molecules Terminal Web Terminal Web (anchors microfilaments): In light microsc.. slide => “ Brush Border “ Woven matt of microfilaments & intermediate filaments on apical surface beneath microvilli  Review: Microtubules Hollow tube (25 nm diameter) polymerized from tubulin subunits Cilia Highly dynamic (constant remodeling of length) Function: Tracks for movement of motor proteins (Kinesins and Dynein), maintain cell shape, found in cilia, flagellum, centrosomes & in mitotic spindles  Cilia CC : In Cardiogennic syndrome, the motor protein Dynein is affected = no longer bending of cilia = No flow Microtubules Microtubules => similar to individual Cilia are visible microfilaments, form tracks for motor proteins ( called Dynein ). As Dynein walks on microtublues on opposite directions, it causes bending. + Center pair Basal Body : holding down Doublet of Microtubules = cilia / anchoring down cilia 9 total ( 9 +2 MTs) Characteristics : Triplets of MTs x 9 BUT NO CENTER 1. Long 2. Different length Microvilli was anchored down by spider web, Cilia needs to be anchored 3. Not tightly packed down by basal bodies Basal Bodies Kartagener (anchor microtubules) Syndrome  Cilia and Microvilli Cilia: Longer, unequal lengths, less densely packed, core of MTs anchored to basal bodies: MTs (dark thick line), motile. Microvilli: Shorter, equal lengths, densely packed, core of MFs anchored to terminal web: MFs and IFs (dark thin line), absorptive. Terminal Web SEM Basal Bodies Cilia Microvilli SEM  Stereocilia Actin Microfilaments “pain brush “ SEM “Long branched microvilli” found only in the epididymis (absorption) and epithelium of the inner ear (mechanoreceptors). Core of actin MFs anchored to terminal web like microvilli, but unequal lengths and less densely packed. Inner Ear Stereocilia  Knowledge Check A 53-year old man with a history of breathing abnormalities is being evaluated for Kartagener syndrome. This condition can result from a mutated structures within cilia. Which of the following functional deficits is most likely causing this patient’s symptoms? A. Abnormal absorption of nutrients B. Increased mucus secretion C. Decreased flow of luminal fluids D. Inadequate permeability E. Changes in electric transmission  Knowledge Check Identify the structure within the green circle Cilia Microvilli 1: Basic Features 2: Apical Surface Modifications 3: Epithelial Cell Modifications 4: Classifications EPITHELIAL TISSUE  Secretory Glands Glands are groups of modified epithelial cells secreting one or several products either onto a surface, or into blood vessels. Form from invagination (downgrowth) and specialization of surface epithelia into the underlying connective tissue.  Review: Cytoplasmic Inclusions Mucus Carbohydrate-rich substance, acts as a lubricant along cell surface. Specialized cells store mucus in membrane-bound vesicles until signal is received to secrete substance.  Goblet Cells Modified epithelial cells form unicellular secretory glands. Found intercalated between epithelial lining cells. Secrete mucus for lubrication and protection of lining.  Keratin Epithelial cells differentiate and migrate to form a layer of dead cells: Anuclear flat cells, cytoplasm primarily filled with densely packed keratin filaments. Provides protection from mechanical stress at apical surface. 1: Basic Features 2: Apical Surface Modifications 3: Epithelial Cell Modifications 4: Classifications EPITHELIAL TISSUE  Classification and Naming 1. Layering 2. Shape 3. Unique Features How many layers of cells does the What is the shape of cells at the Ciliated, keratinized or with epithelium have? most apical (uppermost) layer? Goblet cells? All cells contact Only most basal the basement layer contacts membrane (BM) BM 1 layer but All cells contact BM, only appears as if some reach the surface 2+ layers Staggered location of nuclei causes stratified appearance  Simple Epithelium Longitudinal Section Cross Section Squamous Simple Cuboidal Columnar  Simple Squamous Epithelium Cross Section Longitudinal Section Thin cytoplasm allows passive diffusion of gases and small molecules: nutrient and waste exchange Function: Barrier, nutrient exchange (diffusion) Location: Blood vessels, body cavities, respiratory spaces, etc. Simple Squamous Epithelium Specialized Types of Simple Squamous Epithelium Endothelium Lines blood vessels, heart chambers and lymphatic vessels Thin cytoplasm allows passive diffusion of gases and small molecules: nutrient and waste exchange Ex. O2 and CO2 exchange between air and blood Simple Squamous Epithelium Specialized Types of Simple Squamous Epithelium Mesothelium Lines body cavities (pleural, pericardial, peritoneal)  Simple Cuboidal Epithelium Cells actively transport substances across their cytoplasm: require more cytoplasmic organelles Cross Section Longitudinal Section Function: Barrier, conduit, absorption, secretion. Location: Excretory ducts, kidney tubules, thyroid follicles.  Simple Columnar Epithelium Cells actively transport substances across their cytoplasm: require more cytoplasmic organelles. Often have abundant microvilli for absorption. Longitudinal Section Cross Section Function: Barrier, high rates of absorption and secretion. Location: Gastrointestinal tract, gallbladder.  Stratified Epithelium Squamous Stratified Cuboidal Columnar (rare) Squamous (rare) Pseudostratified Cuboidal (rare) Columnar  Stratified Squamous Epithelium Function: Barrier, protection from wear and tear. Location: Epidermis, esophagus, oral cavity, vagina. Squamous shaped cells in most apical layer of cells Stem cells in basal layer, proliferate to regenerate cells lost at surface  Stratified Cuboidal Epithelium Function: Barrier and conduit. Location: Large excretory ducts. Cuboidal shaped cells in apical layer Longitudinal Section Cross Section Pseudostratified Columnar Epithelium Function: Conduit, secretion and absorption Location: Tracheobronchial tree Secretory cells: Columnar cells: 1 layer (simple) but appears as if 2+ layers (stratified) due to staggered location of nuclei Columnar cells reach the apical surface All cells contact the basement membrane Specialized Types of Pseudostratified Epithelium Relaxed (empty bladder) Transitional Epithelium Function: Adapts to distention and contraction by changing from a taller to thinner epithelium Location: Urinary tract and bladder (known as Urothelium) Stretched (full bladder)  Knowledge Check A prominent brush border of microvilli, specialized for the active transport of small molecules across the cell membrane, is typically found in which type of epithelium? A. Pseudostratified columnar epithelium. B. Simple columnar epithelium. C. Simple squamous epithelium. D. Stratified squamous epithelium. E. Transitional epithelium.  Relevant Slides INDEPENDENT STUDY Histology Guide Virtual Slide Box: http://www.histologyguide.com/ Cellular Junctions and Basal Lamina http://www.histologyguide.com/EM-view/EM-298-intercellular-junctions/02-photo-1.html?x=0&y=0&z=- 1&page=1 http://www.histologyguide.com/EM-view/EM-072-mesothelium/02-photo-1.html?x=0&y=0&z=-1&page=1 Epithelia http://slides.uwo.ca/Original%20scans/Epithelium/56%20-%20Muscle%20(heart%20-%20cat)-sm.html http://slides.uwo.ca/Original%20scans/Epithelium/2%20-%20Kidney%20(cat)-sm.html http://slides.uwo.ca/Original%20scans/Epithelium/118%20-%20Intestine%20(jejunum)%20-%20118-sm.html http://slides.uwo.ca/Original%20scans/Epithelium/100%20-%20Respiratory%20System%20(trachea)-sm.html http://slides.uwo.ca/Original%20scans/Epithelium/70%20-%20Urinary%20System%20(ureter)-sm.html http://slides.uwo.ca/Original%20scans/Epithelium/9%20-%20Tongue-sm.html http://134.84.138.9/slideview/MH-109-esophagus/02-slide-2.html?x=36790&y=24195&z=100.0&page=1 http://www.histologyguide.com/slideview/MHS-222-trachea/17-slide-1.html?x=6437&y=1260&z=100.0&page=1