5.3 - Lecture - Cartilage + Bone Flashcards
Cartilage is responsible for and confers
- 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
Bone is responsible for and characterized by
- withstanding compressive forces
- being very light but not brittle
FXNs:
A) levers for movement
B) protect organs
c) support body
D) store Calcium
Hyaline cartilage
- matrix is smooth and flexible
- haylos = greek for glassy
- comprised of cells in specialized matrix
Describe the morphology of cartilage
- 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)
Describe Aggrecan
- 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
Describe how Proteogylcans and Collagen give rise to the anti-compressibilty function of Cartilage
- 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
What are the 2 regions of the cartilage matrix
- Cells are organized into isogenous groups that forms two regions within the matrix
1) Territorial Region
2) Interterritorial Region
Describe the territorial region of cartilage matrix in terms of LM appearance
- 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)
Describe the interterritorial region of cartilage matrix in terms of LM appearance
- the outer-region, farther away from chondrocytes
- less basophilic than the territorial region
What is the function of the two regions of the cartilage matrix
- creates a local water current allowing water to bring things in/out of the spaces near chondrocytes (which are trapped in the matrix)
Describe places where Hyaline Cartilage, FibroCartilage, and Elastic Cartilage are found
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
Describe elastic cartilage
- 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
Describe Fibrocartilage
= 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
Describe the appearance in LM of fibrocartilage
- 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
Synovial Joint is made up of
- articular cartilage
- joint (articular) cavity
- joint capsule
- synovial membrane
Articular cartilage is
- Type collagen + chondrocytes
- is hyaline cartilage with addition “gothic arch” style collagen from added support
Describe the synovial Membrane
- 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)
Describe Type A synoviocytes
- derived from monocytes (like macrophages and osteoclasts)
- are the equivalent of macrophages in this area
Describe Type B synoviocytes
- same morphology of fibroblast
- create the HA that makes up fluid of synovial cavity
Describe the cartilage repair ability and efficiency
- 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
The fact that cartilage is avascular and without nerves confers 4 important characteristics to the tissue:
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
What are the 2 mature bone macroscopic classifications (include all common names)
1) Compact Bone = dense bone = cortical bone
2) Trabecular bone = spongy bone = cancellous bone
Describe Compact Bone
- typically outer cortical bone
- will vary in density depending on what part of bone you are observing (e.g. epiphysis vs. diaphysis)
Describe Spongy Bone
- highly organized –> confers strength without increasing weight
= a 3D latticework using rods, arches, plates to counter forces and provide maximum support of weight
What are the 3 main part of adult bone (microscopic - the rel. amounts of each part change with age of bone)
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
Describe the osteons
- 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
Describe Volkmann’s Canals and their relation to the osteons
- carry blood vessels from 1 haversian canal (1 osteon) to another
- run perindicular to osteons (thus run perpindicular to the long axis of bone
Describe the composition of a lamellae of an osteon
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
What are canniculi
= 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)
Compare Osteoprogenitor cells and Bone lining cells (in the broad terms for this course - include morphology)
- Identical in morphology
- distinct in characteristics/FXN
Describe Characteristics of Bone Lining Cells
- derived from osteoblasts
- squamous morphology - reflecting their limits metabolic activity
- connected to each other by gap JXNs
- can become osteoblasts
Describe Characteristics of Osteoprogenitor Cells
- Derived from mesenchymal stem cells
- can transform into osteoblasts
- present in
A) inner cellular periosteum
B) endosteum
C)lining of Haversian canals
Describe osteoclasts
- (clast = claw) –> bone clawing cells
- responsible from resorption of bone
- are large multinucleated cells
- derived from fusion of multiple monocytes
Describe Osteoclast regulation of Calcium homeostasis when there is - low serum calcium
- 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
Describe Osteoclast regulation of Calcium homeostasis when there is - high serum calcium
- 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
What is bone remodeling
Transition from woven (immature) bone to lamellar (mature) bone
Describe the process of remodeling
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
