Extracellular Matrix Of CT Flashcards
Fibers (in general)
In general provide tissue integrity, stretchiness, or resistance to stretch
-include: collagen containing fibers (collagen fibers, reticular fibers)
-Elastic fibers
Reticular fibers (function and composition)
FXN:
-support for delicate tissues: ex. Lymph nodes, liver, lung (gives cells a place to rest)
-support during development and wound healing
Composition: delicate network (reticulum) of thin fibers, consisting of slender fibrils, consists mainly of collagen type III, covered by glycoproteins that react with silver stains to black stain
Collagen fibers (function and composition)
FXN:
-provide support with some flexibility
-tensile strength Ex. Resistance to stretching
-maintain tissue integrity (in bones, skin, tendons, ligaments)
Composition:
-thick bundles of fibers, each consisting of clusters of relatively thick fibrils
-consist mainly of collagen type I
-parallel fibers (give strength)
Composition of collagen
-class of proteins that constitute ~30% of the total body protein
-typically exist as a triple helix with 3 polypeptide chains (alpha chains) - different types of collagen are dependent on alpha chain combination
Biosynthesis of collage: intracellular events
(Synthesis of procollagen)
- In the RER, synthesis of alpha chain with registration peptides at each end (registration peptides are thought to help alpha chain line up)
- Chemical modification of alpha chains: hydroxylation and glycosylation
- Formation of the procollagen molecule = triple helix confirmation
- Packaging of procollagen into secretory vesicles (in the golgi)
- Exocytosis of procollagen (into extracellular environment)
Biosynthesis of collagen: extracellular events - synthesis of tropocollagen
- Cleavage of registration peptides, to form tropocollagen molecules
- Polymerization of the tropocollagen molecules to form collagen fibrils (for most types of collagen)
Structure of collagen
-Amino acids form alpha chains
-alpha chains entwine to form the triple helix of a tropocollagen molecule
-tropocollagen molecules line up in a parallel but staggered arrangement (hole zones) to form a fibril
Collagen degradation
-an enzyme called college are breaks down the triple helix, exposing the individual peptide chains to peptidases, which degrade them
- under normal conditions, collagen synthesis degradation are constant, ongoing processes regulated by fibroblasts. The rates of the process are usually equal in order to maintain the connective tissue in a steady state
Scurvy
-deficiency of vitamin C, which is needed for hydroxylation of the alpha chains
-reduced stability of procollagen triple helix and decreased tissue integrity
Problems: soreness and stiffness of joints and lower extremities, poor wound healing, skin lesions, bleeding gums and loosened teeth
Ehlers-Danilo’s syndrome
-genetic variations that cause defect in collagen synthesis
Problems: overly flexible joints, loose skin, frequent bruising, chronic pain
Keloid scars
-excess production of collagen
-may occur in response to injury or to minor irritations such as bug bites or acne
*problem with large scars: scar tissue does not stretch and may interfere with movement (due to the high tensile strength of collagen)
Elastic fibers: composition
-microfibrils consisting of glycoproteins (especially fibrillin)
-elastin (in between microfibrils): gobular, amorphous protein, permits stretching and recoiling
Elastic fibers: function
-elasticity: ability to stretch
-resilience for organs that transiently expand Ex. Lungs, urinary bladder, aorta
Disease associated with loss of elastin: Emphysema
-compounds in smoke destroy elastin
-lung loses elasticity and recoil causing shortness of breath and chronic hypoxia
-Also causes muscle wasting
Disease associated with defect in fibrillin gene: Marfan’s syndrome
-predisposition to rupture of the aortic wall
-other anomalies: very long limbs, spinal deformities, ocular changes
*abraham Lincoln is thought to have had this
