Cartilage & Bone Flashcards
Is cartilage avascular or vascular?
Avascular
Does cartilage contain nerves? Why or why not?
No - needs to withstand forces exerted on it in joints without pain or vascular damage
What type of collagen is abundant in cartilage?
Collagen type II - weaker than type I but imparts tensile strength
Cartilage is rich in a proteoglycan monomer called _____.
Aggrecan
What is aggrecan?
- Proteoglycan monomer
- Links to HA forming massive aggregates that avidly bind water
- Results in ECM that is 60-80% water
- Permits cartilage to withstand huge compressive forces and maintain overall volume even under pressure
What is the role of adhesive glycoproteins?
- Bind cells and components of the ECM together and to cell surfaces
- Have binding sites for collagen, GAGs, and integrins
What are chondrocytes?
- Cartilage cells
- Sparse and isolated in cartilage, surrounded by the ECM that they produce
- Produce and maintain fibres and organic components of the GS
- Metabolize glucose via anaerobic glycolysis since they are avascular
- Nourished via nutrient/gas diffusion through GS
- Mature cells tend to be found in isogenous groups
What are isogenous groups?
Daughter cells from a common precursor cell
Cartilage repairs _____.
Slowly
What is perichondrium?
Layer of CT that often surrounds cartilage and contains blood vessels, nerves, lymphatics, and aids in cartilage attachment and growth
What two layers does perichondrium consist of?
1) Fibrous layer with dense irregular CT consisting of fibroblasts and collagen type I; functions to provide attachment of cartilage to adjacent tissues
2) Inner cellular layer containing chondroblasts; functions to create organic components of cartilage ECM and contributes to cartilage growth
Describe the interstitial growth of cartilage.
- Growth from within
- Mesenchymal cells differentiate into chondroblasts, which secret organic components of ECM
- Chondroblasts surround themselves with matrix, move apart, and become isolated in their lacunae
- They may divide, forming isogenous cell groups, which secrete matrix and add to the thickness of developing cartilage
- Ultimately, isolated chondroblasts become dormant and maintain the matrix as chondrocytes
Describe the appositional growth of cartilage.
- Growth at the surface of newly-forming cartilage, rather than from its core
- Mesenchymal cells at the surface differentiate into fibroblasts, which secret collagen type I and form the fibrous layer of perichondrium
- Mesenchymal cells deep to the fibrous layer differentiate into chondroblasts, forming the cellular layer of the perichondrium
- Thickness of cartilage increases
What are the three subtypes of cartilage?
1) Hyaline cartilage
2) Elastic cartilage
3) Fibrocartilage
What is hyaline cartilage?
- Most common, weakest type of cartilage
- Forms tracheal rings, laryngeal, nasal, costal, articulate cartilages
- Also forms fetal and immature skeleton, and epiphyseal growth plates
- Functions to resist compression and reduce friction between bony surfaces
All hyaline cartilage is surrounded by perichondrium except…
Articular cartilage - vessels and nerves of perichondrium would be damaged by friction
What is elastic cartilage?
- Higher proportion of elastic fibres compared to hyaline cartilage
- Cartilage has greater flexibility and resiliency (ability to snap back after deformation)
- Forms pinna of external ear, epiglottis, and pharyngotympanic tube
What is fibrocartilage?
- Has a lot of collagen type I fibres with little GS
- Resistive to compressive forces and tensile forces
- No perichondrium
- Forms the annulus fibrosis, pubic symphysis, intra-articular disks, and entheses
How can we tell the difference between fibrocartilage and dense regular CT?
- Fibrocartilage has rows of round chondrocytes embedded between collagen fibres
- Dense regular CT has fibroctyes that are flattened and scattered throughout tissue
What is the composition of bone matrix?
- 1/3 organic matter, called osteoid, which is mostly collagen type I with some GS, which imparts tensile strength and flexibility to bone
- 2/3 inorganic matter, including hydroxyapatite and other minerals that mineralize osteoid and impart compressional strength on bone tissue
What is the only type of bone cell not derived from osteoprogenitor cells?
Osteoclasts - derived from the macrophage-monocyte linage
Osteoprogenitor cells are _____ found on the _____ of bone.
Squamous cells; surfaces
Osteoblasts are _____ located on the ______ of existing bone matrix.
Cuboid to columnar cells; surface
What are three fates of osteoblasts?
1) Become quiescent as bone-lining cells
2) Die by apoptosis
3) Become surrounded by the matrix they produce and differentiate into osteocytes
What are canaliculi?
Microscopic channels in bone matrix containing the mineralized cell processes of osteocytes and a very small but important volume of tissue fluid
What are osteocytes?
- Mature bone cells
- Found in lacunae
- Stellate and extend their processes through canaliculi to communicate via gap junctions
- Function to maintain bone tissue, sense mechanical stresses, and organize bone remodelling
What is a characteristic feature of osteoclasts?
They have a multinucleated appearance
Where in bone are osteoclasts found?
On the surface of existing bone matrix in resorption (Howship’s) lacunae created by their activity
What is the process by which osteoclasts enact osteolysis?
- Osteoclasts form a sealing with the bone surface and displays a ruffled border at the interface, which increases the SA for molecular and ionic transfer
- Osteoclasts pump H+ and secrete lysosomal enzymes across the ruffled border
- H+ decalcifies the bone matrix, releasing Ca, PO4, and other electrolytes, which are taken up by the blood
- Enzymes digest the organic component of bone matrix
All bones have a core of _____ and a cortex of _____.
A core, or medulla, of spongy bone and a cortex of compact bone
Compare the epiphysis, diaphysis, and metaphysis.
Epiphysis - ends of the bone
Metaphysis - transitional zone between the epiphysis and diaphysis, ending at the epiphyseal line
Diaphysis - the shaft of a long bone
Where is yellow marrow found?
Within the medullary cavity of the diaphysis
Where is red marrow found?
Within spongy bone in the epiphysis and lining of the medullary cavity
Label each letter: A, B, C, D, E, F
A - epiphyseal arteries
B - metaphyseal arteries
C - nutrient artery (supplies cortical bone from the inside outward)
D - perforating arteries (run perpendicular to the long axis of the bone)
E - central arteries (run parallel to the long axis of the bone)
F - periosteal arteries (terminal branches of the perforating arteries, which supply periosteum)
There is lymphatic drainage from the _____ but not the _____.
Periosteum but not the bone tissue
_____ organizes the matrix into layers.
Lamellae
Immature bone is also called _____.
Woven bone
Spongy bone forms _____, which create compressional strength in various directions.
Trabeculae
In compact bone, bone tissue is arranged in _____, which run parallel to applied forces.
Osteons
Osteons consist of…
1) Concentric lamellae of bone matrix, arranged around…
2) Central (Haversian) canal, which contains arteries, nerves and veins
Interstitial lamellae fill the spaces between…
Osteons
Circumferential lamellae are layers of bone matrix that…
Encircle the cortical bone
Osteocytes occupy their lacunae between adjacent _____.
Lamellae
Metabolites diffuse to and from osteocytes along the _____.
Canaliculi
Bone matrix is strengthened by the alternating orientation of ________ in adjacent lamellae.
Collagen fibres
How is spongy bone similar to compact bone?
- Matrix also forms lamellae, with osteocytes within lacunae situated between lamellae
- Canaliculi extend through the matrix
- Same chemical composition
How is spongy bone different from compact bone?
- No central canals or osteons
- Canaliculi open at the surface of trabeculae to exchange nutrients via tissue fluid with vessels in the red marrow
- Trabeculae are covered with endosteum vs periosteum
What are the two layers of periosteum?
1) Superficial fibrous layer - made of dense irregular CT; collagen; fibrocytes produce collagen type I which attaches bone to other structures
2) Deep cellular (osteogenic) layer - consists of various bone cells (except osteocytes) and functions in bone growth, repair and remodelling
What are perforating/Sharpey’s fibres?
- Collagen type I fibres that attach periosteum to superficial circumferential osteons
- More robust at points of ligament/tendon attachment
Where is endosteum found?
- Marrow cavity
- Trabeculae of spongy bone
- Central & perforating canals of compact bone
When bone develops directly from mesenchyme, it is called…
Intramembraneous ossification
When bone develops from a cartilaginous precursor, it is called…
Endochondral ossification
Endochondral ossification is primarily responsible for the formation of which bones?
Long and short bones
What are stages of endochondral formation of long bones?
1) Undifferentiated mesenchyme of the perichondrium differentiate into osteoblasts and form the bone collar via intramembranous ossification; cartilage matrix degenerates and calcifies
2) Blood vessels invade the diaphysis in response to VEGF secreted by dying chondrocytes, and osteoblasts deposit bone matrix, forming the primary ossification centre
3) Remodelling creates a marrow cavity and osteogenesis proceeds towards the epiphyses, forming a secondary ossification centre within each epiphysis
4) A cartilaginous epiphyseal plate forms
5) At maturity, the rate of chondrogenesis slows then stops, and the plate is converted to bone; the epiphyseal line remains as evidence
If the rate of chondrogenesis equals the rate of endochondral ossification…
The bone length will increase
How does bone diameter increase?
- On external surfaces, osteoblast activity in the cellular layer of the periosteum deposit bone matrix
- The medullary cavity is enlarged by osteoclast activity in the endosteum
Identify the labels A through E.
A: Zone of resting cartilage
B: Zone of proliferation
C: Zone of hypertrophy and cell maturation
D: Zone of calcifying cartilage
E: Zone of ossification
