Epithelium and Connective Tissue Flashcards
Epithelial Tissue
Aggregated Polyhedral Cells, small amount of extracellular matrix (ECM).
Functions: Protective Lining ( can be specialized), Glandular Secretions and Transport
Connective Tissue
All sorts of different cell types. Some fixed, some forever voyaging. Generally quite a bit of ECM
Functions: Support and protect body structures, i.e. tends to attach epithelial tissues etc.
Muscle Tissue
Contractile tissue. NB: A muscle contains connective tissue, but muscle tissue is distinct (moderate amount of ECM)
Nervous Tissue
Conducts nerve impulses. Very little ECM
Epithelium has 3 primary functions:
- Covering, lining and protecting surfaces (Skin/epidermis)
- Absorption (intestinal lining)
- Secretion (e.g. Parenchymal cells of the gut)
Basement Membrane
ECM sheet attaching epithelium to connective tissue.
Cells anchored to basement membrane via HEMIDESMOSOMES.
50-100nm thick.
3 zones: lamina lucida, lamina densa, lamina fibroreticularis (epithelial tissue)
Epithelial Tissues are classified based on 2 factors:
- Layering (how many cells contact the basement membrane)
2. Shape of cells at the surface
Epithelial Types
- Squamous (simple & stratified)
- Cuboidal (simple & stratified)
- Columnar (simple & stratified)
- Urothelium
- Pseudostratified columnar
Cytoskeletal Components (3)
- Microfilaments
- Intermediate Filaments
- Microtubules
Microfilaments
Composed of Actin.
6-8nm in diameter.
Structural function, microvilli, filopodia, gives shape to the cells
Forms tracks for myosin, giving contractility
Intermediate Filaments
Different in various tissues; vimentin (mesenchymal origin), cytokeratin
Around 10 nm in diameter
Anchors, structural
Non-contractile
Microtubules
Tubulin
Around 25 nm in diameter (bigger than other two)
Monorail system (kinesins); Cilia and Flagella (dynein)
How do cells attach?
- Tight junctions (Zonula Occludens)
- Cell to cell adhesive junctions (Zonula adherens)
- Focal Adhesion Junctions
- Desmosomes
- Hemidesmosomes
- Gap Junctions
Tight Junctions (Zonula Occludens)
Homotypical interactions between transmembrane proteins.
Very narrow gaps between cells, controls movement of ‘stuff’ between cells
Maintains cell polarization
Bind to actin microfilaments
Roles in various cell signaling pathways
Cell to Cell Adhesive Juctions (Zonula Adherens)
Holds cells together (important)
Contact inhibition - cells knows what cells are around it and when they’re not they just keep growing and cancer forms.
Cadherins (outside) + Catinins (inside) complexes
Cadherins are Ca+ dependent
Vinculin and actinin attachments to actin filaments
Gap of 20nm
Focal Adhesion Junctions
Hold cells to extracellular matrix (bind cells to surfaces)
Similar to Cell-cell adhesions
Integrins replace cadherins as transmembrane component
Integrins interact with many ECM proteins eg collagen, fibronectin
Integrin receptors: role in cell signaling
Vinculin, actinin and talin attachments to actin filaments
Desmosomes
More Cell-Cell Adhesion Attach to intermediate filaments Heterotypical interaction Gaps of 25 nm Help resist shearing forces
Hemidesmosomes
More Cell-Matrix adhesion
Similar in appearance to desmosome (intracellular plaque visible)
Attach to intermediate filaments
Tightly attach to basal lamina by integrin-laminin and collagen XVII
Resist shear
Gap Junctions
Cell-Cell Aqueous Pores 6X connexins = 1X Connexon Forms a 2nm pore, 2-3 nms between cells Ions and small water soluable molecules may pass nucleic acids, sugars and proteins too large Propagation of electrical signals
Progenitor Cells (pluripotent)
Turn into epithelial cells
Epithelial Function: Protection
Provides a physical barrier due to junctions
Augmented by various secretions: mucus + cilia to trap and move things along, defensins in some cases
Provides a zone for antigen detection
Ex. ‘barrier epithelia’ skin, upper respiratory tract, oral mucosa, gut, urinary system
Epithelial Function: Transport
Selective way
Active or Passive transport
Can secrete things (mucus/fluid) and can absorp things (GI tract)
Blood gases passively diffuse across an epithelial barrier
Most interactions with the outside world occur across an epithelial barrier
Basic Characteristics of Connective Tissue
Cells are generally separated by ECM, generally not linked together. It is generally holding some other tissue in place, and not at a free (i.e. ‘outside’) surface.
Consists of cells, ECM fibers, and ECM ground substance
Cells derived from mesoderm, contains multipotent mesenchymal progenitor cellls
Connective Tissue Function
- Mechanical/protective support of other tissues
- Stores interstitial fluid, water, electrolytes
- Involved in early repair of damaged organs, if repairs not complete, can lead to permanent scar formation/fibrosis
- Contains immune system cells and presents a physical barrier so provides defense and protection
Fibroblasts
-Main go-to cell of connective tissue
-Highly motile, involved in ECM production and tissue repair
-Rarely have cell-cell connections (exception: periodontal ligament)
-Often have cytoskeletal (actin) connections from integrins to fibronectin the ECM (fibronexus)
-Many subtypes in many different tissues (pulp, PDL, oral mucosa)
-Fibroblasts age- slower healing with age
incredible diversity of secretory products
Collagen
Triple Helical Structure Most abundant protein in the body Dentin: mostly type I, some type III Pulp: Mixture of collagen type I and III Cartilage: type II Basement membrane: Collagen IV
Elastin
Fibroblast product
assembled into sheets or fibers
Connective Tissue Ground Substance
Everything in between the cells (mainly proteoglycans and glycoproteins)
Gel-like
Gives compressive strength to tissues (cartilage)
