4.1 - Lecture - CT Flashcards
Mesenchymal Stem Cell (MSC)
Gives rise to the cells that are responsible for generating connective tissue
Unilocular Adipocytes
- also known as white fat cells
- large cells that store lipids
- often occur together in large masses as adipose tissue
Multilocular Adipocytes
- lipid storing cells specialized for heat production
- occur primarily in neonates
Fibroblasts
- responsible for production, remodeling , degradation of the extracellular matrix fibers and ground substance
Myofibroblasts
- Myosin-producing subtype of fibroblasts
- specialized to generate force
Type I Collagen
- the dominant fiber of connective tissue
- synthesized as triple-helix procollagen molecules within fibroblast
- synthesized inside of fibroblasts
- extracellular are aligned + cross-linked into fibrils
Type III Collagen
- known as reticular fibers
- much smaller than collagen type I
- do not have a space-filling function
Elastic Fibers
- Composed of elastins and fibrillins
- found where stretchiness is required
Types IV and VII Collagen
- Found within basement membranes
- type IV is incorporated into/makes up a large portion of the lamina densa
- Type VII forms rings in the lamina reticularis to connect with other cytoskeletal elements
Type II Collagen
Crucial to the structure of cartilage
Type X Collagen
Found in the growth plate of bones
Ground Substance
= the space between connective tissue cells and fibers
- consists of highly hydrated complexes of glycosaminoglycans, proteoglycans, glycoproteins
- has extracellular long-chain proteins that keep ECM hydrated by binding water in lg. quantities
Glycosaminoglycans
- part of the highly hydrated complexes making up the ground substance
Proteoglycans
- have large sugar chains
- repeating units of the sugar chains
Glycoproteins
- have seen before as secretions (mucins) or intergral membrane proteins (contributing to a glycocalyx)
- also form component of ground substrates distinct from proteoglycansand fibers
- sugar chains are much smaller than those found in proteoglycans
Hyaluronic Acid
= a typical glycosaminoglycan “backbone molecule”
- organizes into numerous proteoglycan “core” molecules
- each subunit consists of numerosu glycosaminoglycan chains which attract water
Dermatan Sulfate
- a typical glycosaminoglycans
Heparan Sulfate
- a typical glycosaminoglycan
Keratan Sulfate
- a typical glycosaminoglycan
Chondroitin Sulfate
- a typical glycosaminoglycan
3 components of connective tissue proper
1) loose (aveolar)
2) Dense irregular
3) Dense regular
4 specialized connective tissue types
1) adipose tissue
2) blood
3) bone
4) cartilage
Loose (aveolar) CT (irregular) contains:
- Lots of ground substance (white space in lm)
- lots of cells
- very little fibers
Dense irregular CT contains:
- lots of fibers (dominated by them in volume and function), the 3D organization of fibers to be ready for forces from all side
- little ground substance space
- little space for cells
Dense Regular CT
- tight packed fibers (organized in 1 direction)
- FXN : single force vector
A tendon connects:
Muscle to bone
A ligament connects:
bone to bone
a aponeuroses connects:
muscle to muscle
FXN of resident cells of CT
responsible for creating, elaborating, maintaining, degrading ECMatrix of CT
Resident Cells of Loose, Dense Irregular, and Dense regular CT (and any technical nomenclature):
= Fibroblasts
- called tendenocytes in dense regular tissue (because of their extreme specialization that causes them to be squished)
Resident cells of adipose tissue
Adipocytes
Resident cells of bone
osteocytes
Resident cells of cartilage
chondrocytes
3 exceptions to the function of resident cells of CT
1) Epithelial Tissue - epithelial cells make the Ct of the basement membrane
2) Muscle tissue - smooth muscle cells in walls of blood vessel make the ECMatrix elements
3) Nervous Tissue - Schwann cells make CT element
Describe the LM appearance of fibroblasts
- fusiform + flattended nucleus
- long cytoplasmic processes
3 main components of the ECM Fibers
- collagen
- reticular fibers
- elastic fibers
3 main components of ground substance
- glycosaminoglycans
- proteoglycans
- adhesive glycoproteins
Places where reticular fibers are commonly found
- lymph node
- spleen
- liver
2 Selective stains of elastic fibers
- Verhoff’s Stain
- resourcin fuschin
The key to Differentiating between reticular and elastic fibers:
Reticular fibers - hold cells together (lots of cellls present)
Elastic fibers - holding structure/tissue together
Difference between EM/LM of collagens
Collagen Fiber = viewable in LM or EM
Collagen Fibril = viewable only in EM
Type I Collagen
- 90% of all collagens
- fibrils assemble into fibers
- high tensile strength + resistance to stretch
Type II Collagen
- only seen in cartilage
- does not assemble into fibers
= 50% type II collagen 50% ground substance (proteoglycans) - are not laid down in organized manner - do not see fibers in LM
Type IV Collagen
- Not fibrillar - propeptides not cleaved
- does not display a typical periodicity
- forms meshwork of dimers to form external/basal lamina
= a very strong web of autopolymerized type IV collagen
Type III Collagen
= main component of reticular fibers
- very high # of glycosylated residues with adjacent hydroxylated groups
- found in stroma of highly cellular tissues
(adipose, hematopoietic, lymphoid)
- enables large changes in volume normally seen in those organs
Type VII collagen
- anchoring fibers: forms sm. + lg. loops that the reticular fibers pass through
- loops are formed with help of anchoring bodies/plaques to connect different strands of Type VII into circles
- secure the fibers of CT to the basal lamina
Describe the interplay of CT and the Basement Membrane
- Laminin = connects lamina lucida with the lamina densa
- lamina densa is largely composed of type IV collagen
- Loops of type VII collagen extend down from lamina dense to form lamina reticular is + connect basement membrane to rest of CT (through the reticular fibers)
Briefly Describe the clinical significance of collagen (collagenopathies) as they relate to Scurvy and Ehlers-Danlos Syndrome
Scurvy: lack of vitamin C - which is necessary for proline + lysine hydroxylations - causes ulcers + disruptions of epithelial surface due to lack of alpha chain binding (esp. in areas of high collagen turnover)
Ehlers-Danlos Syndrome: connection disorder resulting from to improper formation/ assembly of collagen
Elastic Fibers are comprised of
fibrillin glycoprotein microfibrils surrounding an amorphous elastin core
Elastin is
- hydrophobic with very strong tendency to curl up due to hydrophobic forces (that can be overcome by force of stretch)
- cross linking proteins in elastin = desmosine (regulates elasticity and provides structure)
Marfan syndrome
- genetic defect in Fibrillin (FBN1) gene
- affects scaffolding of elastin fibers
- affects: eyes, heart, blood vessels
characteristic of patients = tall with long slender fingers and limbs
Primary + most critical function of GAGs + Proteoglycans is:
hydration of the ECMatrix
Hyaluronic Acid
- Unique GAG
- nonsulfated
- can have up to 25,000 repeating units (others have <300)
- is spun from cell membrane (others are synthesized w/n the cell)
GAGs (glycosaminoglycans)
- long, unbranched linear chains (<300 repeating disaccharide units)
- each repeat has at least 2 (-) charges in the chain
- 1 is an amino sugar - sulfated + carboxylated
- contain massive amounts of electronegativity
Proteoglycans
- proteins with 1+ covalently attached GAG chains (more GAGs = larger hydration shell)
- slippery + resist compressive forces
Glycoproteins
- glue together fibers, ground material, cells
- branched, non-repeating units of sugars
- multiple type of sugars
- often v. short
Fibronectin
= an adhesive glycoprotein
- attached integrins of cell membranes to matrix elements (fibers of GAGs)
- enables cells to tunnel through matrix
Explain how presence + quantity of EC components (FIbers vs. ground substance) confers characteristic to tissues:
Fibers –> Strength, elasticity, flexibilty
Ground substance –> barrier FXN, hydration, anti-compressibilty
Relate the changes of obesity to the changes in adipocytes
1st 15%-25% change in BMI is due to increase in size of adipocytes (hypertrophies)
Next changes (larger changes) in BMI are due to increases in # of adipocytes
