[1] HISTO LEC

Epithelial Tissue

Parenchyma

Composed of cells responsible for organ’s specialized functions

Stroma

Cells which have a supporting role in the organ

Lamina Propria

Connective tissue that underlies the epithelia lining the organs (eg, digestive, respiratory, and urinary systems)

Papillae

Increases area of contact between connective and epithelial tissues

Papillae

Most frequent in areas subject to friction (eg, covering of the skin or tongue)

Basal Pole

Region of cell contacting ECM and connective tissue

Apical Pole

Opposite end of basal pole (usually facing a space)

Lateral Surfaces

Regions of cuboidal or columnar cells that adjoin neighboring cells

Basement Membrane

Rests on thin extracellular, felt-like sheet of macromolecules

Basement Membrane

Semipermeable filter for substances reaching epithelial cells from below

Basement Membrane

Provide structural support for epithelial cells

Basement Membrane

Attach epithelia to underlying connective tissue

Basement Membrane

Its components organize integrins and other proteins in the plasma membrane which maintains cell polarity and helps localize endocytosis, signal transduction, etc.

Basement Membrane

Its proteins mediate cell-to-cell interactions involving epithelia and mark routes

Basement Membrane

Serves as scaffold that allows rapid epithelia

Basal Lamina

20-100 nm thick

Basal Lamina

Consists of network of fine fibrils

Basal Lamina

Denotes fine extracellular layer

Basal Lamina

Macromolecules are secreted from its which form sheet-like array

Type IV Collagen

Monomers self-assemble into two- dimensional network of evenly spaced subunits

Laminin

Large glycoproteins attach to integrins at cells’ basal surface and project through network of type IV collagen

Nidogen and Perlecan

Short, rod-like protein and proteoglycan, these cross-link laminin to collagen network and determine porosity of basal lamina and size of molecules able to filter through it

Reticular Larmina

Bound basal lamina by anchoring fibrils of Type VII collagen

Reticular Larmina

Contains Type III collagen which are its more diffuse meshwork

Reticular Larmina

Both collagen types are produced by cells of connective tissue

Tight or Occluding Junctions

Form seal between adjacent cells

Tight or Occluding Junctions

Also called zonulae occludens

Tight or Occluding Junctions

Most apical

Tight or Occluding Junctions

Adjacent membranes appear fused or tightly apposed

Claudin and Occludin

Interacts tightly to create seal between two cell membranes

Claudin and Occludin

Ensures molecules crossing epithelium do so by going through the cells (a transcellular path) rather than between them (the paracellular pathway)

Tight or Occluding Junctions

Restricts movements of membrane lipids and proteins at the apical cell surface into lateral and basal surfaces

Tight or Occluding Junctions

Maintains apical and basolateral, which allows its sides of epithelium to display different receptors and to function differently

Apical Cell

Part of luminal compartment of a tissue or organ

Basolateral Domains

Part of basal compartment that encompasses underlying connective tissue

Adherens Junction

Sites of strong cell adhesion

Adherens Junction

Also called zonula adherens

Adherens Junction

Encircles cell, immediately below tight junction

Cadherins

Mediates cell adhesion Bind each other in presence of Ca2+

Catenins

Link to actin filaments with actin- binding proteins

Terminal Web

Partly from linked actin filaments

Terminal Web

Cytoskeletal feature at the apical pole

Desmosome

Also called macula adherens

Desmosome

Resembles single “spot-weld” and does not form belt around cell

Desmosome

Disc-shaped structures at surface of cell that matches with identical structures at adjacent cell surface

Desmosome

Contain larger members of cadherin family called desmogleins and desmocollins

Desmoplakins

Catenin-like proteins formed as cytoplasmic ends of desmogleins and desmocollins and bind intermediate filament proteins rather than actins

Electron-Dense Plaque

Larger proteins which link to desmoplakins

Hemidesmosomes

How cells attach to basal lamina

Hemidesmosomes

Resemble half-desmosome ultrastructurally

Hemidesmosomes

Clustered transmembrane proteins that indirectly link to cytokeratin intermediate filaments are integrins rather than cadherins

Hemidesmosomes

Integrins of hemidesmosomes bind primarily to laminin molecules in basal lamina

Focal Adhesion

Also called focal contact

Focal Adhesion

Basal anchoring junction found in cells that are moving during epithelial repair

Focal Adhesion

Resembles hemidesmosomes but smaller and more numerous

Focal Adhesion

Consist of integrins linked indirectly to bundled actin filaments

Gap Junctions

Channels for communication between adjacent cells

Gap Junctions

Mediate intercellular communication

Gap Junctions

Functionally important in nearly all mammalian tissue

Gap Junctions

Consist of aggregated transmembrane protein complexes that form circular patches in plasma membrane

Connexins and Connexons

Has central hydrophilic pore about 1.5 nm in diameter o When two cells attach, connexins in adjacent cell membranes move laterally and align to produce connexons between two cells, with each junction having dozens or hundreds of aligned connexon pairs

Cyclic Nucleotides and Ion

Move rapidly through gap junctions, allowing cells in many tissues to act in a coordinated manner rather than as independent units

Microvilli

Projected in epithelial surface

Microvilli

Specialized for absorption

Microvilli

Usually uniform in length

Microvilli

Certain cells (eg, lining of small intestine) with densely packed microvilli appear striated projecting into lumen

Glycocalyx

Thick covering of the intestinal brush border with membrane-bound proteins and enzymes for digestion of certain macromolecules.

Microfilament Arrays

Dynamic and undergo various myosin- based movements, which maintain optimal conditions for absorption via channels, receptors, and other proteins in the plasmalemma

Terminal Web

From cortical microfilaments at base of the microvilli and site where actin filaments insert

Stereocilia

Less common type of apical process

Stereocilia

Best seen on absorptive epithelial cells lining male reproductive system

Stereocilia

Increase surface area which facilitates absorption

Stereocilia

Resemble microvilli in containing microfilaments and actin-binding proteins, with similar diameters and connections to terminal web

Stereocilia

Much longer and less motile than microvilli

Stereocilia

May show branching distally

Cilia

Long, highly motile apical structures

Cilia

Larger than microvilli

Cilia

Contains internal arrays of microtubules

Primary Cilia

Not motile but is enriched with receptors and signal transduction complexes for detection of light, odors, motion, and flow of liquid past

Motile Cilia

Abundant on cuboidal or columnar cells of many epithelia

Axoneme

9 + 2 assembly of microtubules and main extracellular part of cilia and flagella in eukaryotes

Kinesin and Cytoplasmic Dynein Motors

Move along peripheral microtubules for transport of molecular components into and out

Basal Bodies

Apical cytoplasmic structures below cell membrane

Basal Bodies

Structure similar to centrioles (triplets of microtubules and dynamic tubulin protofilaments anchoring entire structure to cytoskeleton)

Ciliary Motion

Occurs through successive changes in conformation of axoneme (accessory proteins make each cilium relatively stiff, but elastic)

Stratified Squamous Keratinized Epithelium

Found mainly in epidermis of skin (helps prevent dehydration from tissue)

Stratified Squamous Keratinized Epithelium

Have many desmosomes and become more irregular in shape

Stratified Squamous Keratinized Epithelium

Flatten as keratin accumulates in process of keratinization

Stratified Squamous Keratinized Epithelium

Moved progressively toward skin surface, becomes thin, metabolically inactive packets (squames) of keratin lacking nuclei

Stratified Squamous Nonkeratinized Epithelium

Lines moist internal cavities (eg, mouth, esophagus, and vagina) where water loss is not a problem

Stratified Squamous Nonkeratinized Epithelium

Flattened cells of surface layer retain nuclei and most metabolic functions

Stratified Cuboidal Epithelium

Relatively rare epithelia that occurs in excretory ducts of salivary and sweat glands

Stratified Columnar Epithelium

Relatively rare seen in conjunctiva lining eyelids (protective and mucus secretin)

Transitional Epithelium or Urothelium

Lines urinary tract, extending from kidneys to proximal part of the urethra

Umbrella Cells

Superficial layer of large, dome-like cells sometimes that characterizes the urothelium

Transitional Epithelium or Urothelium

Cells are specialized to protect underlying tissues from hypertonic and potentially cytotoxic effects of urine

Transitional Epithelium or Urothelium

Unique morphological features allow distension as urinary bladder fills

Pseudostratified Columnar Epithelium

Tall, irregular cells are attached to basement membrane • Nuclei are at different levels

Pseudostratified Columnar Epithelium

Does not extend to free surface, giving stratified appearance (eg, lining of upper respiratory tract, heavily ciliated)

Glands

Develop from covering epithelia in fetus by cell proliferation followed by further differentiation