Lec 3 Cartilage and Bone Flashcards
What are characteristics of cartilage ECM
How does it function
Highly specialized: abundant, firm, pliable, smooth and resilient
Covers surfaces of bones (articular) so the bones can slide against each other
Cartilage can withstand compressive forces - intervertebral discs
Explain cartilage innervation and flow
Cartilage is avascular, no lymphatics, no nerves
Can withstand force without pain or vascular damage, but heals slowly
Explain cartilage in terms of structure
Gives structure to soft tissues without being rigid
-trachea rings, larynx, pinna
Func in development of long bones
What are components of ECM of cartilage
THE ECM determines characteristics of cartilage
Rich in type 2 collagen fibers, other types less common
Rich in cartilage specific GAGs - chondroitin 4/6 sulfate, keratin sulfate)
- linked to core protein forming proteoglycan - AGGRECAN
Adhesive Glycoproteins - Chondronectin, bind cells and parts of the ECM
Upshot: Withstands tensile and compressive forces (GAG pulls water in)
What is chondrocytes function
produce, maintain fibres and organic products of GS - GAG and adhesive glycoproteins
How does cartilage get nutrients and gas
They are avascular and depends on gas/nutrient diffusion through GS from vessels
Metabolizes glucose by anaerobic glycolysis
Thus slow repair and thick cartilages are limited
How are mature chondrocytes found as
Isogenous groups - groups of daughter cells from a common parent/precursor cell
What kind of CT is cartilage surrounded by
And its func/ characteristic
Perichondrium - dense irregular CT
- forms the interface btwn cartilage and tissues
- for cartilage attachment and support
Has BVs, nerves and lymph nodes
Explain the layered struc of the perichondrium
2 Layers
- Outer fibrous layer: Dense irregular CT (collagen type 1 and fibroblasts) - this layer provides attachment to tissue
- Inner cellular layer: has chondroblasts making organic stuff of ECM - this func for cartilage growth
Explain interstitial growth of cartilage
Cartilage forms from mesenchyme (embryonic CT)
In places where cartilage is to form, mesenchymal cells diff into chondroblasts that will secrete organic components of into matrix (collagen 1 and 2)
Chondroblasts will surround themselves with matrix and separate from each other and are isolated in their lacunae
- this way they cant communicate
Chondroblasts can then divide creating isogenous groups that secrete matrix and grows apart - adding thickness to cartilage
What happens to isolated chondrocytes
They become quiescent (inactive, dormant) and maintain matrix as chondrocytes
Explain APPOSITIONAL growth of cartilage
Is growth at surface
Mesenchymal cells at surface cartilage start diff into fibroblasts, secreting type 1 collagen - forms fibrous layer of perichondrium
Mesenchymal cells deep to the fibrous layer diff into chondroblasts - forming the cellular layer of the perichondrium. SECRETES MATRIX ONTO NEW CARTILAGE SURFACE.
What are the 3 subtypes of cartilage and where are they found
Hyaline cartilage: Ribs (costal), Nose, Articular (shoulder), epiphyseal plates, fetal/immature skeleton
Elastic cartilage: Pinna, larynx, epiglottis
Fibrocartilage: intervertebral discs
How strong is hyaline cartilage
What is its function
Other characteristics
Weakest of the cartilage - Type 2 collagen in ECM along with gel like GS
Functions to resist compression, gives tough and flexible support, reduces friction
How come all hyaline cartilage structures are covered in perichondrium EXCEPT Articular cartilage
Articular cartilage no perichondrium so it cant get nutrients
Its missing perichondrium cause it need to contact another hyaline cartilage for smooth movement
What is Elastic cartilage function
How is it diff from Hyaline
Provides greater flexibility and resiliency (can recover from deformation) (compared to Hyaline)
Similar to Hyaline but with more elastic fibres
Has perichondrium
What is fibrocartilage
What is its characteristics
What function
How strong
Like hyaline but with large amts of type 1 collagen fibres
Little GS, Is densely woven type 1 and 2 collagen fibres
The chondrocytes arranged in rows between bundles of collagen fibres
NO PERICHONDRIUM - the type 1 collagen fibres will provide attachment - also gets nutrients from adjacent bone like hyaline
FUNCS TO RESIST both compressive and tensile forces
Bone characteristics
Like other CTs, Derived from embryonic mesenchyme, and composed mostly of matrix
UNLIKE CTs bone matrix is solid, but porous for nutrient and gas diffusion
Turns over, is dynamic
Similar to cartilage, bone surfaces are lined by CT layers: Periosteum on external surfaces and endosteum on internal surfaces
Bone functions
Support: Bone supports our body weight and gives structure to soft tissue
Leverage: alters direction and power exerted by muscle
Protection: Vital organs are enclosed within bony overing
Mineral store: Storage depot for Ca and PO4, and deposition/mobilization of minerals - maintain electrolytes
Lipid store: Yellow bone marrow
Hematopoiesis: blood cells and platelets are produced in red bone marrow
What is bone matrix organic matter
What funcs
1/3 organic matter: OSTEOID
- 90% of osteoid is collagen fibres (mostly type 1)
- other parts are GS: noncollagenous proteins - adhesive
glycoproteins and proteoglycans
- organic stuff imparts tensile str and flexibility
- Osteoid is mineralized in the process of matrix formation
What is bone matrix inorganic matter
Osteoid is mineralized largely by calcium phosphate in the form of hydroxyapatite crystals
Also contains: Bicarbonate, citrate, Mg, K, Na
- electrolytes stored in bone and is deposited and
exchanged rapidly to maintain homeostasis
- surface crystals are hydrated, promotes exchange
of electrolytes btwn bone matrix and tissue fluid - blood
Mineralization of osteoid gives compressional strength
What does mesenchymal cells give rise to
Least mature osteoprogenitor cells - cells commited to the bone forming cells
Osteoblasts: Secrete osteoid and then mineralize it to form bone matrix
Bone lining cells: periosteal cells on external surface and endosteal on internal surfaces
Osteocytes: fully differentiated, maintains bone matrix
Can go from squamous bone lining osteoprog to osteoblasts to bone lining squamous again but as endo/periosteal
What are osteoclasts
A fifth type of bone cell that is derived from monocytes
Breaks down bone
Explain Osteoblasts:
Shape, Function, What can it become later
What does it do for tissue fluid
Cuboidal/Columnar cells on bone surface, secretes osteoid
Then they also mineralize the osteoid they secrete
Can become quiescent as endo/periosteal bone lining cell
or die by apoptosis
OR become surrounded by the matrix and diff into
osteocytes
Osteoblasts can also extend fine cell processes into the osteoid and when the osteoid mineralizes around these processes, they become CANALICULI
What are Canaliculi
Microscopic channels in the bone matrix with the osteoblast cell processes and impt volume of tissue fluid
For diffusion of gas and nutrients
What is Lacunae
The spaces in bone matrix that are occupied by osteocytes - small amt of unmineralized matrix surrounding the osteocyte in its lacuna
What shape of cells are Osteocytes
What is its function
Stellate cells - their processes extend thru canaliculi to communicate with osteocytes in adjacent lacunae, with osteoblasts and with bone lining cells by gap junctions
Osteocytes maintain surrounding tissue, senses mech stress and organizes bone remodelling to optimize structure to withstand forces
Osteoclasts function/ characteristics
Where is it found
Motile, Multinuclear, from monocyte cell lineage
Resorb bone during bone growth, remodelling and repair
- can release Ca, PO4 and other electrolytes from bone
matrix
- also releases organic products from collagen digestion
Found on surface in a resorption lacunae (howship’s)
Explain osteolysis
Ocl forms a microenv - a sealing/ clear zone
Its cell membrane on bone matrix side has a ruffled border to increase SA for H+ pumping etc
H+ secreted to decalcify the bone - releasing Ca, PO4 and other electrolytes
Lysosomal enzymes released to digest organic components like collagen type 1. Then even further digested and released into blood for reuse.
How is bone structured (layers)
Dense cortical layer
Anastomosing spicules/trabeculae in open spaces deeper in bone - SPONGY BONE
How are bone classified
Bones are organs
Classified by shape: long, short, flat, irregular
What are SESAMOID bones
Is the patellae
Develop in tendons due to friction
Rubbing of the tendon stimulates the bone formation
Explain long bone structure
Yellow marrow in diaphysis
Red marrow (hematopoietic tissue) in epiphysis
Spongy bone in epiphysis and lining marrow cavity
Metaphysis is where epi and dia join
Articular surface at epiphysis ends
A and V ramifies (breaks into arms) thru medullary cavity
Perforating A&V travels thru cortical bone
Central A&V from the perforating A&V, travels up n down
Periosteal A&V
How is bone tissue arranged
Osteons is the structural organization of compact bone
Run parallel to applied forces
Matrix forms concentric lamellae, and osteocytes are in lacuna between adjacent lamellae
Canaliculi communicate with central canal of A and Vs
Bone is str by alternating orientation of collagen fibres in adjacent lamellae
Spongy bone characteristics vs compact
No central canals - no osteons
Forms trabeculae covered by endosteum
Spaces in spongy bone contain high vascular red marrow
Canaliculi is open at trabeculae surface
Resist compression in many directions
Trabeculae orient along stress lines, responding to forces
Explain the func of the layers of PERIOSTEUM
- Fibrous layer: is a dense irregular CT capsule func in attachment - collagen type 1 fibres that are continuous with bone matrix as perforating fibres/sharpeys AND continuous with those of muscles, tendons etc.
- Sharpeys/perforating fibre to bind down to periosteum - Deep cellular/osteogenic layer
- Bone growth and repair - has osteoprog cells,
osteoblasts and clasts and bone lining cells
What does endosteum do
what layers of the endosteum is there
Lines marrow cavity, trabeculae of spongy bone, central and perforating canals of compact bone
Incomplete layer with osteoprog cells, bone lining cells, osteoblasts, osteoclasts. NOT osteocytes cause they not on surface of bone
Func in bone growth, remodelling and repair
What are types of bone development
Intramembranous ossification: bone develop directly from mesenchyme
Endochondral ossification: mesenchyme -> hyaline cart -> bone
In both ossification types, bone matrix is initially immature WOVEN BONE
Explain the process of intramembranous ossification
Diff of osteoblasts in mesenchyme
- mesenchyme tissue become highly vascularized
- then aggregates and enlarges, diff into osteoblasts
- Osteoblasts cluster to form ossification centers
- Osteoblasts secrete osteoid and then mineralized
Ossification centers come together to form spicules
- bone grows outward from oss center, connect to other
oss centers to make spicules
BVs trapped - bone growth and angiogenesis same time
- spicules connecting -> trap BVs - for gas and nutrients
Spongy bone formed
- deposition of bone matrix -> perforated (BVs) bony plate
Direct conversion of mesenchyme into bone tissue
Explain the process of endochondral ossification
Hyaline cartilage model of long bone grow interstitially and appositionally, diaphyseal cart deteriorate then calcifies
Mesenchymal cells of diaphyseal perichondrium diff into osteoblasts forming the bone collar
BVs, CTs invade diaphysis from deteriorating chondrocytes VEGF, bring mesenchymal cells that diff into osteoblasts that deposit B.matrix onto calcified cartilage
- forms the PRIMARY ossification centre
Remodelling creates a medullary/marrow cavity, osteogenesis -> towards both epiphyses
2ndary ossification centre forms in both epiphyses and become filled with spongy bone
- In epi plate: cart converted into bone at same rate that new cart forms thru interstitial growth - lengthening
MAX bone length attained when when epi plate gone
Articular cart remains - smooth slipping of articular surface
Explain parts/layers of the epiphyseal plate
Zone of reserve (ZR): look like regular cart, resting cart
- chondrocytes quiescent, anchors epi plate to the epi
Zone of prolif (ZP): Chondrocytes in rapid cell cycle
- chondrocytes lined in in exogenous groups, prod matrix
Zone of cell maturation/hypertrophy (ZH): Rate of div slows
- cytoplasm vol inc, see larger lacunae
INTERSTITIAL GROWTH occurs at ZP and ZH
Zone of calcifying cartilage (ZC): chondrocytes die, matrix calcifies
Zone of ossification (ZO): endochondral bone form
- BV, osteoclasts from diaphysis penetrate calcified
cartilage
- Osteoblasts put bone on calcified cart
Explain the how bone diameter is increased
Osteoblasts in cell later of periosteum deposit bone matrix on bone surface - is woven bone then become lamellae which then become osteons
At same time, medullary cavity is incr by osteoclast in endosteum
Good thickness maintained
