Lec 3 Cartilage and Bone

Question 1

What are characteristics of cartilage ECM

How does it function

Answer 1

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

Question 2

Explain cartilage innervation and flow

Answer 2

Cartilage is avascular, no lymphatics, no nerves

Can withstand force without pain or vascular damage, but heals slowly

Question 3

Explain cartilage in terms of structure

Answer 3

Gives structure to soft tissues without being rigid
-trachea rings, larynx, pinna
Func in development of long bones

Question 4

What are components of ECM of cartilage

Answer 4

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)

Question 5

What is chondrocytes function

Answer 5

produce, maintain fibres and organic products of GS - GAG and adhesive glycoproteins

Question 6

How does cartilage get nutrients and gas

Answer 6

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

Question 7

How are mature chondrocytes found as

Answer 7

Isogenous groups - groups of daughter cells from a common parent/precursor cell

Question 8

What kind of CT is cartilage surrounded by

And its func/ characteristic

Answer 8

Perichondrium - dense irregular CT
- forms the interface btwn cartilage and tissues
- for cartilage attachment and support
Has BVs, nerves and lymph nodes

Question 9

Explain the layered struc of the perichondrium

Answer 9

2 Layers

1. Outer fibrous layer: Dense irregular CT (collagen type 1 and fibroblasts) - this layer provides attachment to tissue
2. Inner cellular layer: has chondroblasts making organic stuff of ECM - this func for cartilage growth

Question 10

Explain interstitial growth of cartilage

Answer 10

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

Question 11

What happens to isolated chondrocytes

Answer 11

They become quiescent (inactive, dormant) and maintain matrix as chondrocytes

Question 12

Explain APPOSITIONAL growth of cartilage

Answer 12

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.

Question 13

What are the 3 subtypes of cartilage and where are they found

Answer 13

Hyaline cartilage: Ribs (costal), Nose, Articular (shoulder), epiphyseal plates, fetal/immature skeleton
Elastic cartilage: Pinna, larynx, epiglottis
Fibrocartilage: intervertebral discs

Question 14

How strong is hyaline cartilage
What is its function
Other characteristics

Answer 14

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

Question 15

How come all hyaline cartilage structures are covered in perichondrium EXCEPT Articular cartilage

Answer 15

Articular cartilage no perichondrium so it cant get nutrients
Its missing perichondrium cause it need to contact another hyaline cartilage for smooth movement

Question 16

What is Elastic cartilage function

How is it diff from Hyaline

Answer 16

Provides greater flexibility and resiliency (can recover from deformation) (compared to Hyaline)
Similar to Hyaline but with more elastic fibres
Has perichondrium

Question 17

What is fibrocartilage
What is its characteristics
What function
How strong

Answer 17

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

Question 18

Bone characteristics

Answer 18

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

Question 19

Bone functions

Answer 19

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

Question 20

What is bone matrix organic matter

What funcs

Answer 20

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

Question 21

What is bone matrix inorganic matter

Answer 21

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

Question 22

What does mesenchymal cells give rise to

Answer 22

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

Question 23

What are osteoclasts

Answer 23

A fifth type of bone cell that is derived from monocytes

Breaks down bone

Question 24

Explain Osteoblasts:
Shape, Function, What can it become later
What does it do for tissue fluid

Answer 24

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

Question 25

What are Canaliculi

Answer 25

Microscopic channels in the bone matrix with the osteoblast cell processes and impt volume of tissue fluid For diffusion of gas and nutrients

Question 26

What is Lacunae

Answer 26

The spaces in bone matrix that are occupied by osteocytes - small amt of unmineralized matrix surrounding the osteocyte in its lacuna

Question 27

What shape of cells are Osteocytes | What is its function

Answer 27

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

Question 28

Osteoclasts function/ characteristics | Where is it found

Answer 28

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)

Question 29

Explain osteolysis

Answer 29

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.

Question 30

How is bone structured (layers)

Answer 30

Dense cortical layer | Anastomosing spicules/trabeculae in open spaces deeper in bone - SPONGY BONE

Question 31

How are bone classified

Answer 31

Bones are organs | Classified by shape: long, short, flat, irregular

Question 32

What are SESAMOID bones

Answer 32

Is the patellae Develop in tendons due to friction Rubbing of the tendon stimulates the bone formation

Question 33

Explain long bone structure

Answer 33

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

Question 34

How is bone tissue arranged

Answer 34

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

Question 35

Spongy bone characteristics vs compact

Answer 35

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

Question 36

Explain the func of the layers of PERIOSTEUM

Answer 36

1. 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 2. Deep cellular/osteogenic layer - Bone growth and repair - has osteoprog cells, osteoblasts and clasts and bone lining cells

Question 37

What does endosteum do | what layers of the endosteum is there

Answer 37

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

Question 38

What are types of bone development

Answer 38

Intramembranous ossification: bone develop directly from mesenchyme Endochondral ossification: mesenchyme -> hyaline cart -> bone In both ossification types, bone matrix is initially immature WOVEN BONE

Question 39

Explain the process of intramembranous ossification

Answer 39

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

Question 40

Explain the process of endochondral ossification

Answer 40

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

Question 41

Explain parts/layers of the epiphyseal plate

Answer 41

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

Question 42

Explain the how bone diameter is increased

Answer 42

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