Cartilage and Bone Flashcards
1
Q
Cartilage
A
- Specialized connective tissue
- Has a semi-rigid extracellular matrix that is highly hydrated and has viscoelastic properties
- Predominantly avascular
- Has a capacity for continued interstitial and appositional growth
2
Q
Functions of Cartilage
A
- Found in areas that require soft tissue support along with flexibility
- Trachea
- Larynx
- Eustachian tube
- External ear
- Nose
- Found in areas where needed as a developmental precursor for much of the skeleton
- Bones that undergo endochondrial ossification
- Found on joint surfaces, particularly in synovial joints ⇒ articular cartilage
- Enhances movement
- Cushions surfaces transmitting mechanical stress
- Acts as a shock absorber
3
Q
Types of Cartilage
A
- Hyaline Cartilage
- Most common
- Type II collagen
- Elastic Cartilage
- Type II collagen and elastic fibers
- Fibrocartilage
- Type I collagen
4
Q
Perichondrium
A
- Dense fibrous CT that surrounds hyaline and elastic cartilage structures except within joint capsules
- Fibrocartilage has no perichondrium
- Functions in the growth and maintenance of cartilage
- Rich in Type I collagen fibers
- Houses the vascular supply to cartilage tissue
- In actively growing cartilage the perichondrium appears as a two layered structure
- Outer layer
- Fibrous
- Poor in cells
- Comprised primarily of fibroblasts and Type I collagen
- Inner layer
- Cellular
- Composed of chondroblasts and chondrogenic cells
- Outer layer
- Chondroblasts associated with the perichondrium capable of producing new cartilage matrix through appositional growth
5
Q
Chondrogenic Cells
A
- Derived from mesenchymal cells
- Can differentiate into chondroblasts
- Found within the inner cellular layer of the perichondrium
6
Q
Chondroblasts
A
- Found within the inner layer of perichondrium
- Responsible for secreting cartilage matrix at the surface of the cartilage
- When they become completely surrounded by matrix they are known as chondrocytes
7
Q
Chondrocytes
A
- Cells occupy spaces called lacunae
- With mitotic division tend to occur in groups of up to 8 cells called isogenous groups
- Active chondrocytes by LM basophillic with perinuclear clear staining area representing the golgi zone
- Mature active chondrocytes have the typical characteristics of a secretory cell
- As cell ages become heterochromatic, lipid vacuoles accumulate, increased glycogen stores.
8
Q
Cartilage Extracellular Matrix
A
- Includes fibers, proteoglycans with sulfated GAGs, and adhesive glycoproteins
- Forms a semi-firm gel
- Basophillic and PAS + due to sulfated GAGs
- Territorial marix
- Directly surrounds chondrocytes
- Higher concentration of sulfated GAGs and less water
- More basophillic
- Interterritorial matrix
- Lighter staining
- GAGs more dispersed
- Fibers
- Varys depending on cartilage type
- Collagen forms ~ 50% dry weight of cartilage
- Ground substance
- Consists of sulfated GAGs for proteoglycans
- Proteoglycans bound to hyaluronan core via link proteins to form aggrecan aggregates
- Matrix is 60-80% water by weight because negatively charged GAGs attract water
- Gives cartilage its resilience and compressive resistance
9
Q
Cartilage Histogenesis
A
- Most cartilage derived from the mesoderm
- Except cartilage of the branchial arches which is dervied from neural crest ectoderm
- Cartilage cells differentiate from mesenchyme into chondroblasts
- Mesenchyme surround the developing cartilage becomes the perichondrium
10
Q
Cartilage Nutrition
A
- Most cartilage is avascular
- Except very rapidly growing cartilage which may contain cartilage canals
- House branches of the perichondrial vessels
- Except very rapidly growing cartilage which may contain cartilage canals
- Nutrients diffuse through intervening matrix
- Limits the thickness of cartilage to a few mm
11
Q
Cartilage Growth
A
-
Appositional growth
- Growth that takes place on inner surface of perichondrium along a free surface
- Produces increase in size by adding material to the periphery
- Mesenchymal cells → chondrogenic cells → chondroblasts → chondrocytes once enclosed by matrix
-
Interstitial growth
- Growth due to mitosis of chondrocytes within the matrix
- Forms isogenous groups
- Chondrocytes within an isogenous group grow and secrete matrix thus moving apart from one another
- Results from expansion from within
- Great advantage for growth
- Adaptive reason for the retention of cartilage by the growing skeleton
- Important during periods of rapid growth as part of endochondrial ossification or at articular surfaces where perichondrium absent
- Growth due to mitosis of chondrocytes within the matrix
12
Q
Cartilage Degeneration
A
- Occurs in deep areas of thick cartilage because cells cannot get nutrients from diffusion
- Chondrocytes begin to atrophy and shrink
- Cartilage may calcify
- Process important as part of normal process of endochondrial bone formation
- Also occurs as cartilage ages ⇒ osteoarthritis
- Articular surfaces can become undulated
- Loss of protective articular cartilage will affect underlying bone causing chronic inflammation
13
Q
Cartilage Regeneration
A
- Very limited ability to regenerate
- Chondrogenic ability of perichondrium limited to active growth periods before adulthood
- Intra-cartilage division of chondrocytes too slow to repair damage
- Acute injuries during adulthood results in deposition of vascularized CT which eventually loses vascularity and persist as fibrous tissue
- Cartilage suited for transplantation without marked immune response
14
Q
Hyaline Cartilage
A
- Most common type
- Glassy non-fibrous matrix composed primarily of Type II Collagen
- Found in fetal and growing skeletons prior to ossification
- Persists at growth plates of immature long bones until skeletal maturity
- Remains cartilaginous in adults in:
- Articular surfaces of bones
- Reinforces/supports areas of respiratory tract
- Forms costal-sternal border
15
Q
Articular Cartilage
A
- Found on the articular surface of bones especially in synovial joints
- Specialized form of hyaline cartilage
- Has no perichondrium
- Cells and fibers are more regularly arranged
- Vertical rows deep
- Horizontal rows near surface
16
Q
Elastic Cartilage
A
- Most cellular type of cartilage with larger cells
- Matrix more opaque than hyaline
- Contains elastic fibers and Type II Collagen
- Has perichondrium
- Less susceptible to degeneration than hyaline
- Not susceptible to calcification as with hyaline
- Found:
- Eustachian tube
- External auditory canals
- Ear
- Epiglottis
- Cuneiform cartilages of larynx
17
Q
Fibrocartilage
A
- Matrix with numerous bundles of thick collagen fibers
- Mainly Type I collagen
- More fibrous and less cellular than other cartilage
- Always associated with and grading into dense CT
- No perichondrium
- Chondrocytes may be in isogenous clusters or single file in isogenous columns between fiber bundles
- More acidophillic d/t Type I fibers
- Greater tensile strength than hyaline
- Able to withstand repeated tension and friction
- Found in areas where tissue experiences compressive stresses in one direction and tensile stresses in another direction
- Annulus fibrosus of intervertebral discs
- Pubic symphysis
- Regions where tendons or ligaments attach to bone
- Joint menisci
23
Q
Classification of bones by shape
A
- Classified by bone shape
- Long bones
- Short bones
- Flat bones
- Irregular bones
- Sesamoid bones
24
Q
Parts of long bone
A
- Diaphysis
- The shaft
- Contains the marrow cavity
- Metaphysis
- Flared region between diaphysis and epiphysis
- Epiphysis
- Ends of the long bone
25
Q
Tissue Distribution
in
Bone
A
-
Cancellous bone (aka spongy bone, trabecular bone)
- Plates of bone organized into interconnected vertical and horizontal struts
- Marrow occupies the spaces in spongy bone
- Found primarily in:
- Flat bones of the skull
- Ends of long bones
- Inside other “spongy” bones such as vertebrae
-
Compact bone (aka cortical bone)
- Densely packed bone matrix
- Forms the outer cortex of all bones
- Found in abundance along the shafts of long bones
26
Q
Periosteum
A
- Covers the exterior of a bone except at articular surfaces
- Continuous with CT of tendons and skeletal muscles
- Two layers
- Outer fibrous
- Inner cellular
- Sharpey’s fibers insert into the bone surface and connect the periosteum to the bone tissue
- Provides the vascular supply to the bone
- Serves as a source of osteoprogenitor cells
27
Q
Endosteum
A
- Thin single cell layer of CT which covers the interior surfaces of bone
- Covers most internal surfaces of bone including Haversian canals, Volkmann’s canals, and marrow cavity
- Contains osteoprogenitor cells
28
Q
Sharpey’s Fibers
A
- Bundles of collagen fibers that insert into bone tissue
- Prominent where tendons and ligaments insert on bone
- Also connect the periosteum to the bone tissue
30
Q
Bone
Vascular Supply
A
- Fairly extensive blood supply
- Nutrient arteries
- Long bones usually have a nutrient artery that penetrates the bony collar of the diaphysis and divides in the marrow cavity
- Branches then enter the Haversian canals
- Periosteal arteries enter the Haverisan canals from the outer surface of the bone
- Metaphyseal and epiphyseal arteries
33
Q
Osteoprogenitor Cells
A
- Determined but not differentiated mesenchymal cells
- Derived from pluripotent stromal cells in bone marrow and other CT
- When activated, divide and produce osteoblasts
- Characteristics:
- Flattened cells
- Found in inner layer of periosteum or endosteal lining of bone
- Resembles young fibroblasts
34
Q
Osteoblasts
A
- Cells that synthesize bone
- Secretes collagen and ground substance as unmineralized osteoid
- Secrete matrix vesicles that contribute to the mineralization process
- Vesicles slowly accumulate mineral over time
- Forms a single layer of cells on surfaces of developing or remodeling bone
- Characteristics:
- Cuboidal
- Typical characteristics of protein-secreting cells
- Connected to each other by processes that end in gap junctions
- Once they become surrounded in matrix that they produce cells are considered osteocytes
- Quiescent osteoblasts that line the surfaces of a bone formation region after osteoid production is complete are called bone lining cells
- Has receptors for parathyroid hormone (PTH), Vit D3
- Important in regulation of osteoclast activity and calcium levels
- Has estrogen receptors
- Cell membranes rich in alkaline phosphatase ⇒ used as a marker enzyme
35
Q
Osteocytes
A
- Mature, differentiated cells, derived from osteoblasts that have become buried in mineralized bone matrix
- Reside in lacunae
- Communicate with one another through cell processes joined by gap junctions
- Processes run through small fluid filled canals called canaliculi
- Functions:
- Involved in mineral homeostasis
- Can likely remove mineral from a limited region surrounding the lacuna via osteogenic osteolysis
- Have mechano-sensory role in the stimulation of remodeling
36
Q
Osteoclasts
A
- Cells responsible for the resorption of bone
- Large, multinucleated cells
- Structural syncitium
- Derived from a common bone marrow precursor as monocytes
- Differentiate first into uninucleate osteoclast precursors
- Activated precursors fuse to produce mature multinucleated osteoclasts
- Create resorption bays called Howship’s Lacunae along the surface of bone being removed
- Ruffled border formed by folds of the plasma membrane that increase cell surface area and represents the zone of contact with bone
- Actin microfilaments in the clear zone surrounding the ruffled border healp seal the cell to the bone surface
- Release of acid (H+) by the osteoclasts into the Howship’s lacunae to dissolve the mineral crystals
- Organic matrix degraded by lysosomal enzymes ⇒ collagenases
- Activity indirectly stimulated by PTH through osteoblasts
- Activity directly inhibited by calcitonin
38
Q
Macroscopic Divisions of
Bone: The tissue
A
Cancellous vs compact bone
Differentiated based on the amount of space (porosity) of the bone.
39
Q
Woven Bone
A
Applies to both cancellous and compact bone.
AKA immature bone
- A form of immature non-lamellar bone tissue
- First bone to appear during bone formation
- Eventually replaced by lamellar bone during the growth and remodeling process
- Found in areas of injury repair
- Characteristics:
- Deposited quickly during growth and fracture repair
- Randomly oriented collagen fibers and cells
- Highly cellular
- More porous & less dense than lamellar bone
- Not as strong as lamellar bone
40
Q
Lamellar Bone
A
- Bone organized into layers of aligned collagen called lamellae
- Layers usually seperated from one another by a single layer of osteocytes
- Slow deposition due to highly organized structure
- Stronger material better able to resist biomechanical loads than woven bone
- Found in both cancellous and compact bone tissue types
- In cancellous bone
- lamellae will not form Haversian systems
- Instead form layers on the surface of the trabeculae that make up cancellous bone
- In compact bone
- Lamellae will either be circumferential or in Haverisan systems
- In cancellous bone
Circumferential Lamellar Bone
- Organized into linear sheets that encircle the bone
- In adults primarily found as the outer circumferential lamellae and inner circumferential lamellae
- Encircles the bone just deep to the periosteum and just superficial to the endosteum respectively
Haversian System
(Secondary Osteons)
- Represents bone that has formed by the secondary remodeling process
- Forms much of the bone matrix in adult human compact bone
- As we age, more lamellar bone will remodel to form Haversian systems
41
Q
Haversian System Structure
A
- Layers of lamellae arranged concentrically around a central Haversian canal
-
Haversian canal
- Long tubular branching structures that run predominantly longitudinally through the bone
- Act as vascular channels which run longitudinally through the center of the osteon
- Contains blood vessels and nerves which supply the bone tissue
-
Volkmann’s Canals
- Obliquely oriented vascular canals linking the Haversian canals of neighboring osteons
- Allows blood to pass through a large network throughout the bone
- Some also connect with vessels in the marrow cavity or periosteum
- Cells within an osteon communicate with one another via cellular processes/gap juctions that run along the canaliculi
- Communication between osteons limited due to cement lines
-
Cement lines
- Marks the outer edge of each Haversian system
- Represent reveral lines where osteoclasts stopped resorbing bone and osteoblasts started refilling the space
- Functionally seperates neighboring osteons since canaliculi generally do not cross cement lines
-
Interstitial lamellae
- Remnants of old Haversian systems or circumferential lamellae
- Found between exsiting HAversian systems
- Formed as a result of the remodeling process
