5.3 - Lecture - Cartilage + Bone

Question 1

Cartilage is responsible for and confers

Answer 1

• structure with flexibility
• specialized to respond to repeatable stressors
• confers structural integrity in the context of intermittent forces (joints, respiratory system)
• functions as shock absorbers
• is fast growing

Question 2

Bone is responsible for and characterized by

Answer 2

• withstanding compressive forces
• being very light but not brittle
  FXNs:
  A) levers for movement
  B) protect organs
  c) support body
  D) store Calcium

Question 3

Hyaline cartilage

Answer 3

• matrix is smooth and flexible
• haylos = greek for glassy
• comprised of cells in specialized matrix

Question 4

Describe the morphology of cartilage

Answer 4

• mostly water ~ 70%
• Organic materials include 40-60% Type I collagen
• remainder is ground substance - adhesive glycoproteins (e.g. fibronectin) and proteoglycans
• has no dedicated blood supply (explains why so many artefacts in LM)

Question 5

Describe Aggrecan

Answer 5

• a proteoglycan with 2 types of GAGs
  1) chondroitin sulfate
  2) keratan sulfate
• has around ~160 GAGs total?
• aggregates of aggrecan are specific in that they bind a tremendous amount of water and some ind collagen type II fibrils to the proteoglycan aggregates

Question 6

Describe how Proteogylcans and Collagen give rise to the anti-compressibilty function of Cartilage

Answer 6

• Proteoglycan aggregates bind to collagens to form a dense meshwork
• collagen type II has a small positive charge but the proteoglycans attached to it make it possess a large net negative charge attracting a lot of water to the proteoglycan aggregates –> which fxn to transport nutrients to chondrocytes via compressive forces
• this underlies the turgor pressure that gives cartilage its anti-compressiblity FXN

Question 7

What are the 2 regions of the cartilage matrix

Answer 7

• Cells are organized into isogenous groups that forms two regions within the matrix
  1) Territorial Region
  2) Interterritorial Region

Question 8

Describe the territorial region of cartilage matrix in terms of LM appearance

Answer 8

• interior part of the matrix (closer to chondrocytes)
• more basophilic than interterritorial region
  (typical of increased binding of hematoxylin dye - because increased number of negative charge due to proteoglycen presence and large amount of water in the area)

Question 9

Describe the interterritorial region of cartilage matrix in terms of LM appearance

Answer 9

• the outer-region, farther away from chondrocytes

- less basophilic than the territorial region

Question 10

What is the function of the two regions of the cartilage matrix

Answer 10

• creates a local water current allowing water to bring things in/out of the spaces near chondrocytes (which are trapped in the matrix)

Question 11

Describe places where Hyaline Cartilage, FibroCartilage, and Elastic Cartilage are found

Answer 11

1) Hyaline cartilage - most places not occupied by other two?
2) Fibrocartilage - in between vertebrae, pubic symphysis, minucus (pad-like cartilage in knee joint)
3) Elastic cartilage - in external ear, and epiglottis, Eustachian tube

Question 12

Describe elastic cartilage

Answer 12

• composed of type II collagen + elastic fibers
• required when increased flexibility is required to return the structure to normal position after being acted on by external/internal forces
• found in: Eustachian tube, epiglottis, external ear

Question 13

Describe Fibrocartilage

Answer 13

= type I collagen introduced into matrix of hyaline cartilage
- in the spinal cord around nucleus propulsis (also pubci symphysis and miniscus) - in this area it holds together the fluid core of the spinal cord

Question 14

Describe the appearance in LM of fibrocartilage

Answer 14

• round cell clusters (chondrocytes) surrounded by basophilic substance (matrix near chondrocytes)
• has proteoglycans around them (consistent with cartilage - makes the basophilic stain)
• also has invasion of eosinophilic type I collagen fibers coming from CT

Question 15

Synovial Joint is made up of

Answer 15

• articular cartilage
• joint (articular) cavity
• joint capsule
• synovial membrane

Question 16

Articular cartilage is

Answer 16

• Type collagen + chondrocytes

- is hyaline cartilage with addition “gothic arch” style collagen from added support

Question 17

Describe the synovial Membrane

Answer 17

• Has two layers
  1) Intimal layer = 1-4 layers of cells largely composed of the two types of synoviocytes ( A and B)
  2) Fibrovascular layer (subintimal) = between the intima and the joint capsule
• contains the internal synovial fluid- a mixture of transulate from capillary plexus and ground substance (plasma + HA)

Question 18

Describe Type A synoviocytes

Answer 18

• derived from monocytes (like macrophages and osteoclasts)

- are the equivalent of macrophages in this area

Question 19

Describe Type B synoviocytes

Answer 19

• same morphology of fibroblast

- create the HA that makes up fluid of synovial cavity

Question 20

Describe the cartilage repair ability and efficiency

Answer 20

• cartilage has a highly limited capacity for repair
• cells in perichondrium have ability to differentiate into chondrocytes but it is very very limited
• defects in cartilage are often filled by fibroblasts, which produce a dense CT –> limiting and impairing the recovery of function of cartilage in that area

Question 21

The fact that cartilage is avascular and without nerves confers 4 important characteristics to the tissue:

Answer 21

1) lower change of transplant rejection with cadaver-base tissue
2) Poor recovery of chondrocyte after damage
3) No direct pain from cartilage damage
4) need to have diffusion from surrounding CT to be substrate for metabolic support

Question 22

What are the 2 mature bone macroscopic classifications (include all common names)

Answer 22

1) Compact Bone = dense bone = cortical bone

2) Trabecular bone = spongy bone = cancellous bone

Question 23

Describe Compact Bone

Answer 23

• typically outer cortical bone

- will vary in density depending on what part of bone you are observing (e.g. epiphysis vs. diaphysis)

Question 24

Describe Spongy Bone

Answer 24

• highly organized –> confers strength without increasing weight
  = a 3D latticework using rods, arches, plates to counter forces and provide maximum support of weight

Question 25

What are the 3 main part of adult bone (microscopic - the rel. amounts of each part change with age of bone)

Answer 25

1) Outer circumferential lamellae (ring of dense bond on exterior side)
2) Inner circumferential lamellae (ring of dense bone on interior)
3) Osteons - Haversian systems

Question 26

Describe the osteons

Answer 26

• Circular structures consisting of Haversian Canal (filled with blood vessels + nerves) at the center of multiple layers (lamellae) of bone
• the rings between the lamellae house osteocyte = the resident cells of bone
• each lamellae (ring of collagen fibers) - has alternating direction in way that it was laid down –> confers strength
• typically run parallel to the long axis of bone

Question 27

Describe Volkmann’s Canals and their relation to the osteons

Answer 27

• carry blood vessels from 1 haversian canal (1 osteon) to another
• run perindicular to osteons (thus run perpindicular to the long axis of bone

Question 28

Describe the composition of a lamellae of an osteon

Answer 28

1 - 10% water
2 - 45% organic material
2.1) mostly type I collagen (90-95%)
2.2) ground components (5%):
2.2A) osteonectin - binds mineral to type I collagen
2.2B) osteoportin - binds cells to matrix
3 - 45% mineral - hydroxyappetitie crystals

Question 29

What are canniculi

Answer 29

= holes that connect osteocytes and their processes
- communicate:
A) nutrients
B) signaling molecules
C) forces applied to bone (through filaments connecting the osteocytes to bones)

Question 30

Compare Osteoprogenitor cells and Bone lining cells (in the broad terms for this course - include morphology)

Answer 30

• Identical in morphology

- distinct in characteristics/FXN

Question 31

Describe Characteristics of Bone Lining Cells

Answer 31

• derived from osteoblasts
• squamous morphology - reflecting their limits metabolic activity
• connected to each other by gap JXNs
• can become osteoblasts

Question 32

Describe Characteristics of Osteoprogenitor Cells

Answer 32

• Derived from mesenchymal stem cells
• can transform into osteoblasts
• present in
  A) inner cellular periosteum
  B) endosteum
  C)lining of Haversian canals

Question 33

Describe osteoclasts

Answer 33

• (clast = claw) –> bone clawing cells
• responsible from resorption of bone
• are large multinucleated cells
• derived from fusion of multiple monocytes

Question 34

Describe Osteoclast regulation of Calcium homeostasis when there is - low serum calcium

Answer 34

• thyroid gland secretes hormone - parathormone
• parathormone inhibits osteoblasts
• osteoblast inhibition causes their secretion of stimulating factor RANKL
• RANKL activates osteoclasts
• Osteoclast breakdown bone releasing calcium
• Serum calcium increases

Question 35

Describe Osteoclast regulation of Calcium homeostasis when there is - high serum calcium

Answer 35

• Thyroid gland secretes hormone - Calcitonin
• Calcitonin inhibits osteoclasts
• Osteoclast inhibition increases the metabolic ratio of bone production/resorption - allowing for increased storage of calcium in bone by osteoblasts

Question 36

What is bone remodeling

Answer 36

Transition from woven (immature) bone to lamellar (mature) bone

Question 37

Describe the process of remodeling

Answer 37

1) A group of osteoclasts form cutting cone -drill down long axis of bone (–> forming resorption tunnel)
2) Osteoclasts disappear
3) Blood vessels + osteoprogenitor cells appear
4) Osteoblasts differentiate + line the tunnel and start producing osteoid (alternating directions each layer)
5) Some cells get trapped in wall as osteocytes
6) Layers progressively laid down until only blood vessels + nerves are left at center
7) Osteoblasts convert to bone lining cells