Epithelial Tissues PDF

Tissues – Characteristics – Basic types Epithelium – Characteristics – Types (Distinguishing features) – Adhesive structures – Surface specializations – Gland types  TISSUES Aggregates or groups of cells Perform similar function Molecules Organelles Cells...

Tissues – Characteristics – Basic types Epithelium – Characteristics – Types (Distinguishing features) – Adhesive structures – Surface specializations – Gland types  TISSUES Aggregates or groups of cells Perform similar function Molecules Organelles Cells Tissues Organs Systems  BASIC TISSUE TYPES Epithelial tissue Connective tissue Muscle tissue Nervous tissue  EPITHELIUM Covers body surfaces Lining of cavities Glands  CONNECTIVE TISSUE Underlies or surrounds other tissues Supportive Includes various types: connective tissue proper, cartilage, bone...  MUSCULAR TISSUE Contractile cells Responsible for movement of body and its parts  NERVOUS TISSUE Receive, process and transmit information Controls activity of body and its parts  EPITHELIUM Places found: – Covering exterior of body (skin and derivatives) – Lining cavities and tubes (G.I. tract, blood vessels) – Secretory and duct portions of glands  EPITHELIUM Characteristics: – Cells in close apposition to one another – Free surface – Opposite surface (adjacent to underlying connective tissue) adheres to basement membrane Free Surface Basement Membrane C.T.  EPITHELIAL FUNCTIONS Barrier (epidermis of skin, lining of urinary bladder) Secretory (glandular epithelium) Absorption (intestinal epithelium) Free Surface C.T.  CLASSIFICATION OF EPITHELIA Based on arrangement and shape of component cells  CLASSIFICATION Simple Stratified EPITHELIAL CLASSIFICATION Squamous Cuboidal Columnar EPITHELIAL CLASSIFICATION Simple Squamous Simple Cuboidal Simple Columnar EPITHELIAL CLASSIFICATION Stratified * Named by shape of cells next to free surface Free Surface Basement Membrane Connective Tissue Free Surface Basement Membrane  SPECIAL EPITHELIAL TYPES Pseudostratified Transitional  PSEUDOSTRATIFIED Appears layered but all cells touch the basement membrane Stratified Pseudostratified B.M.  TRANSITIONAL EPITHELIUM Stratified epithelium that accommodates distension and stretching of organ Lining of urinary bladder and ureters  BASEMENT MEMBRANE Noncellular, protein-proteoglycan-rich layer separating epithelial cells (as well as nerve cells and muscle cells) from surrounding connective tissue Usually relatively indistinct in routine Hematoxylin-Eosin preparations- visible by light microscopy with special stains (PAS reacts with sugars of proteoglycans, for instance)  BASAL LAMINA Discrete layer (50-100nm thick) of electron dense material between epithelium and connective tissue Hemidesmosome Lamina Lucida Basal Lamina Anchoring Fibers (Collagen IX) Reticular Fibers (Collagen III) BASAL LAMINAE- FUNCTIONS Attachment of cells to connective tissue Compartmentalization or separation of epithelium from connective tissue Filtration Establish polarity of epithelium Tissue scaffolding during development and regeneration  BASAL LAMINAE- COMPOSITION Type IV collagen- nonfibrillar collagen, short filaments that provide structure Proteoglycans Laminin Entactin/Fibronectin  CELLULAR ADHESION AND INTERCELLULAR CONTACTS Terminal Bar – Site of specialized attachment for adjoining epithelial cells at apical portions – Helps form barrier to diffusion of substances between cells  JUNCTIONAL COMPLEX Structural components APICAL SURFACE making up adhesive attachments and diffusion barriers zonula occludens Includes: zonula adherens – zonula occludens – zonula adherens macula adherens – macula adherens ZONULA OCCLUDENS (TIGHT JUNCTION) Ring or band of plasma membrane union between adjacent cells At most apical point between adjoining cells Microvilli Zonula Occludens  ZONULA ADHERENS Continuous circumferential adherence of epithelial cell to its neighbors Uniform space between adjacent cells (20-30nm)  MACULA ADHERENS (DESMOSOME) plaque Disc-shaped spot attachments (not a if continuous band- “spot- weld”) Electron dense plaque on cytoplasmic side anchoring intermediate filaments (10nm) Intercellular space occupied by adhesive material  HEMIDESMOSOMES Found at basal surface of stratified squamous epithelia Cytoplasmic portion has attachment plaque with 10nm filaments Nu Hemidesmosomes Basal Portion of Cell  ADHESIVE SITES Zonula occludens- principally restricts passage of substances across epithelium Zonula adherens, macula adherens- guard against physical disruption of epithelium (adhesive)  CELL SURFACE MODIFICATIONS OF EPITHELIUM Microvilli Stereocilia Cilia Lateral and basal infoldings  MICROVILLI Cytoplasmic, finger- like protrusions of apical surface of epithelium Number and shape usually correlate to absorptive capacity (increase free surface area)  MICROVILLI Intestinal epithelium- distinctive border of vertical striations Detectable by light microscopy- CT striated border  MICROVILLI- Microvilli STRUCTURE Core of actin microfilamentsanchore d to tip and sides of Terminal Web microvillus Interact with terminal web of horizontal filaments just below base of microvilli (Cause contractile ZA oscillations that facilitate absorption)  STEREOCILIA Very long, irregular projections from apical portion of epithelial cells of epididymis and sensory cells of ear Long microvilli  CILIA Short, fine structures projecting from apical portion of cell Dark-staining bodies at base of cilia due to basal bodies (modified centrioles)  CILIA Range from 1 to hundreds per cell  CILIA- STRUCTURE 2 central microtubules surrounded by 9 doublets Outer paired microtubules continuous with basal body Plasma Membrane Microtubule Doublet Dynein  CILIA Undergo regular synchronous undulating movements creating a wave across the epithelium Creates flow of mucous and other materials across epithelium  CILIARY MOVEMENT Based on movement of microtubules in relation to one another Dynein arms form bridges between adjacent doublets Addition of ATP produces sliding movement  KARTEGENER’S SYNDROME Absence of dynein arms Respiratory difficulty Males sterile- flagellum of sperm is modified cilium  LATERAL CELL SURFACE INFOLDINGS Prominent in cells that transport fluid rapidly  BASAL INFOLDINGS Also prominent in cells that transport fluid (kidney tubules) Nu Mitochondria (Active Transport)  GLANDS- CLASSIFICATION Exocrine- secrete substances onto a surface (usually through ducts or tubules) Endocrine- secrete products (hormones) into blood stream- ductless  EXOCRINE GLANDS- CLASSIFICATION Unicellular- goblet cells in lining of intestine and respiratory tract Villus of human ileum- Junqueira et al., 1995  EXOCRINE GLANDS- CLASSIFICATION Multicellular- several types characterized by arrangement of glandular cells and organization of ducts – Simplest is “sheet” of secretory cells- lining of stomach “TYPICAL” EXOCRINE GLAND STRUCTURE Surface Epithelium Duct Secretory Portion  MULTICELLULAR GLANDS Duct Structure: – Simple- unbranched duct – Compound- branched duct Shape of Secretory portion: – Tubular – Acinar/Alveolar (Flask-shaped) – Tubuloacinar  GLANDULAR SECRETORY CELLS Mucous producing cells- viscous, slimy secretions; appear empty by routine H/E; nuclei often flattened against base of Sublingual Gland Junqueira et al., 1995 cell  GLANDULAR SECRETORY CELLS Serous producing cells- watery secretions; usually intensely stained with eosin ; nuclei usually rounded or oval Pancreas Junqueira et al., 1995