Connective Tissue Flashcards
What is the function of the Extracellular Matrix?
Surrounds cells of a tissue
-provides strength to resist tensile and compressive forces
-directs cells to their proper positions within a tissue and holds cells in place
-regulates development, mitotic activity and survival of cells in a tissue
Amount of ECM in epithelium vs connective
Epithelium - little ECM
Connective - mostly ECM
What is ECM composed of?
-Ground substance - can resist forces of compression
-Proteins fibres - can withstand tensile forces
What is ground substance and what is it composed of?
-Ground substance is colourless and viscous gel-like
-Fills the psace between cells/fibres and delays the spread of infection
-Makes up majority of ECM
-Consists of water, nutrients, ions, 3 fams of macromolecules
-hydrated gel w fibres embedded
What 3 macromolecules is ground substance made of?
-Glycosaminoglycans (GAGs)
-Proteoglycans
-Cell-adhesive glycoproteins (CAGs)
What are Glycosaminoglycans (GAGs)?
-Polysaccharides, made of sugars including glycosamine
-Neg charged, long, inflexible, unbranched polysaccharides-composed of chains of repeating disaccharide units
-Neg charge repel one another when close so slippy texture e.g synovial fluid
-Neg so attract cations like sodium - extra sodium in ground substance attracts extra cellular fluid - resist compression
-e.g chondroitin sulfate, hyaluronic acid, heparin sulfate
What is the only non sulphated GAG?
Hyaluronic acid - doesnt form covalent links with proteins but proteins join to it via link proteins
What are proteoglycans?
-Proteoglycans bind to a long GAG forming proteoglycan aggregate
-Make ECM firmer, more solid and resistant to compression
-Chemical properties mean they bind water, giving gelatinous property to the matrix
-Selective - can form filters with basal lamina
-Can look like a botle brush - protein core is stem w sulfate GAGs projecting in 3D space
What are cell-adhesive glycoproteins (CAGs)
-Made of diff types of glycoproteins
-Holds everything in place - adhere cell to cell and cells to surroundings
-Bind to cell surface proteins as well as protein fibres and proteoglycans - maintain normal tissue architecture
How do CAGs fasten various components of tissues to each other?
-Large and have many domains so one binds to cell surface proteins (INTEGRINS), one to collagen fibres and one to proteoglycans
What is collagen?
-Fibrous component of ECM
-Most abundant protein 20-25% in human body
-Secreted into ECM by connective tissue cells e.g tropocollagen monomer which makes collagen fibrils
-Long straight unbranched fibres
How does tropocollagen monomer contribute to the formation of collagen?
Tropocollagen monomer consists of 3 polypeptide chains each called the alpha chain but not necessarily identical - bond together to form a helical protein structure
-These tropocollagen molecules polymerase longitudinally and side to side to form collagen fibrils - cross linked by enzyme litho oxidase.
What are the categories of collagen?
-fibre forming
-mesh/network forming
-cell-membrane associated proteins
Examples of each type of collagen
-Type I collagen - fibrous supporting tissue, skin, tendons, ligaments, bone
-Type II collagen - hyaline cartilage - consists of fibrils in the cartilage ground substance
-Type III collagen - liver, bone marrow, lymphoid organs- delicate, branched, reticular supporting meshwork - non banded form
-Type IV collagen - constituent of basement membranes - network mesh forming collagen
-Type VII collagen - anchoring fibrils like ECM to basement membrane
When looking at collagen under EM why is there crossbanding?
-From polymerisation of tropocollagen molecules
What is elastin?
-Protein arranged in fibres in ECM
-Properties of stretching and elastic recoil
-Fibroblasts synthesise precursor monomer tropoelastin
-Tropoelastin polymerised by lysyl oxidase
-Requires presence of template for assembly - glycoprotein fibrillin and associated glycoproteins
-Slender, long branching fibres in loose connective tissue
-Found in lung, skin, urinary bladder, blood vessels
Under H and E stain:
-Elastin stains black and collagen stains red
