Histology (2) Epithelial Tissue 3 PDF

HISTOLOGY 1.02 EPITHELIAL TISSUE DR. RICO P. LASACA 14, 19 SEPTEMBER 2023 B. BASIC TYPES OF TISSUE OUTLINE I. Introduction A. Level of Organization...

HISTOLOGY 1.02 EPITHELIAL TISSUE DR. RICO P. LASACA 14, 19 SEPTEMBER 2023 B. BASIC TYPES OF TISSUE OUTLINE I. Introduction A. Level of Organization B. Basic Types of Tissue II. Epithelial Tissue A. Subdivision of Epithelial Tissue B. Important Attributes of Epithelium C. Approach in Classifying and Naming Surface Epithelia III. Types of Surface Epithelia A. Number of Cell Layers B. Cell Shape IV. Simple Epithelium A. Simple Squamous Epithelium B. Simple Cuboidal Epithelium C. Simple Columnar Epithelium V. Stratified Epithelium A. Stratified Squamous Epithelium B. Stratified Cuboidal Epithelium II. EPITHELIAL TISSUE C. Stratified Columnar Epithelium D. Other Types Greek words: epi, on/upon + thele, nipple VI. Glandular Epithelia A. Exocrine Glands Epithelium = lining/covering a. Subclassification Composed of closely aggregated polyhedral B. Endocrine Glands cells adhering strongly to one another. C. Paracrine Glands Forming cellular sheets that line the cavities of VII. Epithelial Specializations or Modifications A. Apical or Free Surface Modification organs, cover the body surface, and also body B. Lateral Surface Specializations tubes that communicates with the exterior (eg. C. Basal Surface Specializations alimentary, respiratory, genitourinary tract) VIII. Special Epithelium A. Myoepithelium B. Neuroepithelium A. SUBDIVISION OF EPITHELIAL TISSUE C. Germinal Epithelium IX. References 1. Surface Epithelia ○ Function: Cover or Protection, Barrier or Absorption Must Know Book Prev Trans Lecturer ○ Location: a. Exterior surface of the body I. INTRODUCTION b. Closed cavities (cardiac [pericardial tissue]), thoracic, abdominal [peritoneal A. LEVEL OF ORGANIZATION tissues]); hollow structures. c. Tubes which communicate with the exterior such as: The alimentary tract (covering from mouth to anus) The respiratory tract The genitourinary tract 2. Glandular Epithelia ○ All are glands ○ Function: Secretions ○ Location: a. Exocrine Glands b. Endocrine Glands Cell → tissue → organ → organ system → organism 3. Specialized Epithelia ○ Function: Contraction (Myoepithelium of breast), Specialized Communications (ex. from the Tongue to the brain to sense the taste; nose/eyes to the brain) ○ Location: a. MYOepithelium [HISTOLOGY] Epithelial Tissue – Dr. Rico P. Lasaca Page 1 of 11  ○ e.g., breasts (lining of the ducts for contraction to expel the milk); blood vessels. b. NEUROepithelium - ○ found in the coverings of the retina and tongue. c. GERMINAL epithelium ○ covering of the seminiferous tubules; more on the reproductive part. SURFACE and GLANDULAR epithelia are non-specialized epithelia. B. SUBDIVISION OF EPITHELIAL TISSUE 1. Limited Intercellular Space ○ Inter – between cells ○ They are closely apposed and adhere to one another by means of specific cell-to-cell adhesion molecules that form specialized cell junctions. ○ Cells have good communication because of limited space. 2. Layer of Cells ○ Squamous (Single Layer) for easy passage of molecules/ nutrients (e.g. blood vessels) ○ Stratified (Multiple Layers) thicker for protection (e.g. skin) ○ BASEMENT MEMBRANE ○ most epithelia form linings or coverings Part of the epithelium 3. Polarity Specialized layer for attachment of ○ All epithelia possess a free apical surface at underlying connective tissue some time. Felt-like sheet of extracellular material Hard to identify in an ordinary CELL SURFACES microscope Composed of two layers that can only Apical Surface - faces the exterior surface or the be seen with Transmission Electron lumen of an enclosed cavity or Microscope (TEM): Basal lamina and tube. Lamina reticularis Lateral Surface - sideward/end of a specific type of epithelium; communicates with BASAL LAMINA LAMINA RETICULARIS adjacent cells and is characterized by specialized attachment areas. Nearest to the associated with reticular epithelial cells fibers of the underlying Basal Surface - rests on the basement membrane Consist of fine fibrils. connective tissue. Thin meshwork of more diffuse and fibrous ○ Cell Surfaces can be positive or negative type IV collagen and depending on how tissues are cut in the laminin produced by section. the epithelial cells. ○ Basement Membrane aids in identifying the Divided into 2 parts: cell surfaces. a. Lamina lucida ○ The lumen could also be a cue in identifying ‒ relatively clear what type of epithelium is present or electron-lucent area ‒ very little staining in EM b. Lamina densa ‒ electron-dense [HISTOLOGY] Epithelial Tissue – Dr. Rico P. Lasaca Page 2 of 11  4. Avascular ○ Tall as they are wide in vertical section ○ All epithelia are avascular except stria 3. Columnar vascularis of the inner ear. ○ Taller than they are wide ○ Epithelia have no blood supply of its own ○ Height of cell appreciably exceeds the width ○ They acquire nutrients from the ○ Nucleus is found on the basal surface subepithelium layer (lamina propria) through diffusion or below the basement IV. SIMPLE EPITHELIUM membrane. 5. Mitotic Capability Contains one/single layer of cells ○ Ability to repair and replace cells attributed to its regenerative capabilities. A. SIMPLE SQUAMOUS EPITHELIUM ○ Common in epithelium that is constantly subjected to wear and tear activities (e.g. Main Function: facilitate diffusion skin) C. APPROACH IN CLASSIFYING AND NAMING SURFACE EPITHELIA ○ They are dependent upon: 1. Number of Cell Layers a. Simple - single cell layer b. Stratified - multiple cell layers 2. Cell Shape Examples: a. Squamous - flat-shaped b. Cuboidal - cube-like shape LINING EPITHELIUM OF THE ALVEOLI IN THE LUNGS c. Columnar - column-like shape 3. Surface Modifications ○ can be present in the a. Surface b. Lateral c. Basal ○ Example: SIMPLE COLUMNAR with CILIA LINING EPITHELIUM OF THE BLOOD VESSEL (CAPILLARIES) III. TYPES OF SURFACE EPITHELIA A. NUMBER OF CELL LAYERS LINING EPITHELIUM OF THE BOWMAN’S CAPSULE IN THE KIDNEYS 1. Simple Epithelium - one/single layer of cells 2. Stratified Epithelium - multiple layers of cells B. CELL SHAPE 1. Squamous ○ Cells are flat ○ Width of the cell is greater than its height ○ Called “squama,” meaning scale-like cells ○ The apical portion is flattened 2. Cuboidal ○ Cells appear approximately square-like [HISTOLOGY] Epithelial Tissue – Dr. Rico P. Lasaca Page 3 of 11  Other distributions: ○ Loop of Henle LINING EPITHELIUM OF THE RENAL TUBULES (KIDNEYS) ○ Inner and Middle Ear ○ Serous Lining of Cavities: Pericardial Cavity Pleural Cavity Parietal Cavity SPECIAL TYPES OF SIMPLE SQUAMOUS EPITHELIUM ENDOTHELIUM MESOTHELIUM Lining of the blood Lining of the vessel. cavities/mesentery/ ○ Other Distribution: serosal surfaces. Covering of the Ovaries Lining of hollow Ducts of Glands organs - organs that have a small/narrow C. SIMPLE COLUMNAR EPITHELIUM cavity or lumen inside them. ○ Main Function: Absorption, Secretion, Protection, and Lubrication IDENTIFYING FEATURE: NUCLEUS NEAR THE BASEMENT MEMBRANE B. SIMPLE SQUAMOUS EPITHELIUM Main Function: Facilitate exchange but are more involved in active mechanisms that require extensive organelles. Needs energy (in the form of ATP) to go in and out of the cell layers. ○ Other Distribution: Oviducts Uterus Small Bronchi Much of Digestive Tract Some Large Ducts ○ TYPES OF SIMPLE COLUMNAR 1. Simple Secretory Columnar For secretion [mostly of mucin] Has mucin glycoproteins Examples: Found in the lining of the stomach and the cervical canal LINING EPITHELIUM OF THYROID FOLLICLE (THYROID GLAND) 2. Simple Striated Columnar Mainly for secretion and absorption. [HISTOLOGY] Epithelial Tissue – Dr. Rico P. Lasaca Page 4 of 11  Has two (2) population of cells: a. Absorptive cells A. STRATIFIED SQUAMOUS EPITHELIUM ○ Has microvilli for an increase surface area for absorption ○ Multiple layers of flat-shaped cells b. Goblet cells (Keratinocytes) ○ Has RER and Golgi Complex ○ Main Function: ○ Filled apically with secretory Protective granules that contain heavily Resistance to Dehydration and Swelling glycosylated proteins called ○ Other Distribution: mucins. Outer Layer of the Skin Oral Layer Throat When mucins are released they Vagina become hydrated and form Anal Canal mucus. ○ Examples: Example: ○ Linings of the intestines ○ Linings of the gall bladder V. STRATIFIED EPITHELIUM Multiple Cell Layers Points to Consider: ○ The shape of the cells at the apical surface. ○ TYPES OF STRATIFIED SQUAMOUS EPITHELIUM 1. STRATIFIED SQUAMOUS KERATINIZING AKA: Orthokeratinizing / Cutaneous Type Contains the greatest amount of cytokeratin (orthokeratin). Distribution: Epidermis of Skin ○ More protective in function Masticatory mucosa of Oral Cavity Attribute to its multiple layers Protective from dehydration and swelling 2. STRATIFIED SQUAMOUS NON-KERATINIZING AKA: Mucus Type / Hypokeratizing ○ Basal Layer Lower amount of cytokeratin Contains stem cells necessary for the Distribution: regeneration of the renewable tissue Oral cavity (replaces damaged tissue layers) Esophagus External Lining of Vagina [HISTOLOGY] Epithelial Tissue – Dr. Rico P. Lasaca Page 5 of 11  Example: A. PSEUDOSTRATIFIED EPITHELIUM ○ “Pseudo” = false ○ Cells of this type appear stratified but in reality they are not. ○ Each cell is in contact with the basement membrane but cells are long and intertwine ○ Commonly found in respiratory-type (those with cilia as they propel foreign bodies) ○ Nuclei at varying levels ○ Main Function: Protection, Secretion, B. STRATIFIED CUBOIDAL EPITHELIUM Cilia-mediated transport of particles trapped in mucus out of the air passages. ○ Generally, 2 or more layers of cube-shaped ○ Distribution: cells. Lining of Trachea ○ Function: Secretion and Protection (but less Bronchi compared to Stratified Squamous) Nasal Cavity ○ Examples: ○ Examples: B. TRANSITIONAL EPITHELIUM ○ Has the ability to transition itself as the structures stretch ○ A special form of epithelium as cells can alter their shape. ○ Only the superficial layer is flattened ○ Relaxed State: appear as CUBOIDAL ○ Stretched: appear as SQUAMOUS ○ Distribution: Bladder, Urethra, Ureters C. STRATIFIED COLUMNAR EPITHELIUM ○ Examples: ○ Main Function: Protection ○ Distribution: Vas deferens Male urethra Parts of the Pharynx ○ Example: VII. GLANDULAR EPITHELIA GLANDS Single or group of cells that function mainly to produce and secrete various macromolecules. A. EXOCRINE GLANDS ○ Secrete their products via ducts onto the apical surface. VI. OTHER TYPES OF SURFACE ○ Highly specialized epithelial cells EPITHELIUM ○ Retain their connection with the surface epithelium. These types of epithelium are considered an ○ Glandular epithelia exception when it comes to the identifying feature used in classifying an epithelium. [HISTOLOGY] Epithelial Tissue – Dr. Rico P. Lasaca Page 6 of 11 SUBCLASSIFICATION: 1. Number of Cells a. Unicellular Glands Single cells interspersed among other epithelial cells of different functions. Mucus secreting goblet cells b. Multicellular Glands Occur as many adjacent secretory cells within the epithelium. Surface mucous cells of stomach Complex glands with ducts. Example: 2. Pattern of Duct System a. Simple Glands Simple, unbranched duct with tubular or acinar shaped secretory pieces Sweat glands, gastric glands, intestinal and uterine glands b. Compound Glands Branched duct system with tubular, acinar, or tubuloacinar shaped secretory units. Salivary Glands, Pancreas. 3. Pattern of Secretory Portion 4. Types of Secretion a. Mucous Glands Secretions: Mucin Structure: mostly tubular with pyramidal to columnar secretory cells. Goblet cells a. Tubular Columnar Elongated Straight or coiled b. Acinar Rounded or Sac-like with small lumen (cavity) c. Alveolar Sac-like with enlarged lumen (cavity) Lumen is bigger than in acinar b. Serous Glands Secretions: Watery Structure: Acinar, nucleus basal and with cytoplasmic basophilia Serous cells synthesize proteins that are mostly non-glycosylated such as digestive enzymes [HISTOLOGY] Epithelial Tissue – Dr. Rico P. Lasaca Page 7 of 11  Not columnar Release entire cells Appears to have contents Complete destruction of secretory cells c. Mixed Glands Contains both mucous and serous units. 5. Mechanism of Secretion B. ENDOCRINE GLANDS a. Merocrine Release products basally → basal lamina → Most common method of protein underlying connective tissue → vascular system. or glycoprotein secretion. Secretions can affect cells located far away from Involves typical exocytosis from the endocrine glands. membrane-bound vesicles or Lack a duct system and secrete directly into the secretory granules. blood or lymph. Expel fluids through vesicles C. PARACRINE GLANDS Similar to endocrine glands but secretions reach target cells by diffusion through the extracellular Intact during secretion space to affect neighboring cells. Deliver to nearby cells VIII. EPITHELIAL SPECIALIZATIONS OR MODIFICATIONS b. Apocrine - Surface modifications Product accumulates at the cells - Morphologic/functional modifications at, on and apical ends, portions of which.or/ within membrane surfaces of epithelial cells. are the extruded to release the product together with small A. APICAL OR FREE SURFACE MODIFICATION amounts of cytoplasm and cell Can be seen under ordinary microscope membrane. 1. Microvilli Secretions explode from cells Plasma membrane evaginations of the apical surface Increase the surface area for absorption Actin microfilaments Partial destruction of Striated border (intestine) secretory cells c. Holocrine Secretion involves the discharge of whole secretory cells, with subsequent disintegration of the cells to release the secretory product. Occurs principally in sebaceous glands. [HISTOLOGY] Epithelial Tissue – Dr. Rico P. Lasaca Page 8 of 11  Brush border (kidney) 3. Flagella Same microstructure as cilia (also made up of microtubules) Singly Longer in length vs cilia Provides motility for spermatozoa (tail) B. LATERAL SURFACE SPECIALIZATIONS Seen only under electron microscope (except desmosomes but it has another name) Stereocilia (epididymis and ductus deferens) ○ Only microvilli that are long as cilia ○ Nonmotile ○ Ductus epididymis, ductus deferens & hair cells of the inner ear 1. Zonula Occludens Tight Junction Fusion of 2 plasma membrane which acts as a seal Seals neighboring cells Epithelia lining Major link proteins: Occludins, 2. Cilia Claudins, Junctional Adhesion Plasma membrane and cytoplasmic Molecule (JAM) projections Cytoskeleton components: Actin AKA kinocilia = kino “kinetics” filaments Main function: motility (synchronous) Microtubules 2. Zonula Adherens/Adherens Junction Belt desmosome, band desmosome Microfilaments anchor the plaque that occurs under the membrane of each cell Transmembrane proteins Joins actin bundles between cells Seen in heart muscles, layers covering body organs, digestive tract Major link proteins:Cadherin Cytoskeleton components: Actin filaments 3. Desmosomes Macula adherens, spot desmosomes Intermediate filaments anchor the dense Cilia Microvilli plaque that occurs + - under the membrane of each cell Longer Shorter Desmos = bond Thick Thin Found in skin, lining of internal body Microtubule (Centriole) Actin Filament surfaces [HISTOLOGY] Epithelial Tissue – Dr. Rico P. Lasaca Page 9 of 11  Under ordinary microscope it’s called intercellular bridges Disappear when cells are transformed Major link protein: Cadherin Cytoskeleton components: Intermediate filaments Junctional Complexes: 2. Basal lamina Zona occludens Structural attachment site for overlying Zona adherens epithelial cells Desmosomes VIII. SPECIAL EPITHELIUM 4. Gap Junction Nexus, communication junction A. MYOEPITHELIUM Allow direct communication Contractile, branched epithelial cells between cells (open & close) by Between glandular epithelial and basement diffusion, thus permitting the membrane coordinated cellular activity. Contain actin filaments for contraction Close membranes are 2-3 nm Facilitate glandular secretion in: Sweat, salivary, apart lacrimal and mammary tissues Major link protein: Connexin Seen in heart and smooth B. NEUROEPITHELIUM muscles Epithelium which has connection to our nervous system 5. Hemidesmosomes Example: tongue (taste buds), retina Anchors cell intermediate filaments to basal lamina (extracellular matrix) Major link protein: Integrin Cytoskeleton components: Intermediate filaments Can be lateral and basal Tight Junction Seals neighboring cells Adherens Junction Joins actin bundles between cells Desmosome Joins intermediate filaments between cells Gap Junction Cell-cell communication, C. GERMINAL EPITHELIUM passage of small molecules Seminiferous epithelium Hemidesmosome Anchors cell intermediate Help in production of the spermatozoa filaments to basal lamina Stereocilia present to help move the (extracellular matrix) spermatozoa Sperm is stored here C. BASAL SPECIALIZATIONS 1. Hemidesmosomes Facilitate stable adhesion of basal epithelial cells to the underlying basement membrane [HISTOLOGY] Epithelial Tissue – Dr. Rico P. Lasaca Page 10 of 11  Mammary tissues D. REFERENCES Pawlina’s Histology Text and Atlas 7th Edition Dr. Lasaca’s lecture Previous Trans E. FREEDOM WALL [HISTOLOGY] Epithelial Tissue – Dr. Rico P. Lasaca Page 11 of 11