Bone and Cartilage Flashcards
What does cartilage consist of?
Chondrocytes and extracellular matrix
What is cartilage?
Avascular and aneural tissue
Where are chondrocytes located?
Within the ECM lacunae
True/False: Chondrocytes can divide and generate matrix.
True
What are chondrocytes replenished by?
surrounding perichondrium
What is perichondrium?
Connective tissue layer
What does the inner layer of perichondrium differentiate into?
Chondroblasts (i.e. growing cartilage (GC) cells)
When does a chondroblast become a chondrocyte?
When they stop dividing
ECM is richly hydrated. What leads to this?
- High Gylcosaminoglycans (GAGs) to collagen ratio
- Creates a 60-80% level of hydration
GAG binds ______ tightly to confer resilience
Water
GAG bind some water loosely which permits what?
Diffusion of substances to and from the blood
What are characteristics of hyaline cartilage?
Contains homogeneous and amorphous matrix
Resilience makes hyaline cartilage useful for which type of surfaces?
Articular
What type of cartilage is the earliest form of cartilage in embryogenesis?
Hyaline
What does the hyaline cartilage become as a person grows?
Growth plates of growing bones
What are 3 functions of hyaline cartilage?
- Supports
- Reinforces
- Resists compressive stress
Hyaline cartilage has been used as a model for what?
Endochondral ossification of bone
Hyaline cartilage covers the articular surfaces of moveable bone and forms what structures?
Costal cartilages
What is the difference between elastic cartilage and hyaline cartilage?
Elastic cartilage has more elastic fibers and contains a perichondrium
Where is elastic cartilage found?
- Epiglottis
- External ear
- Auditory (Eustachian) tube
What is the function of elastic cartilage?
Maintains the shape of a structure while allowing great flexibility
What makes up fibrocartilage?
Combination of hyaline cartilage and dense regular CT
NO perichondrium
What two cell types are present in fibrocartilage? What do they generate?
Chondrocytes and fibroblasts; ECM
The CT component of fibrocartilage resists compression and shearing in which areas?
- Intervertebral disc
- Pubic symphysis
- Articular discs in TMJ
- Menisci in the knee
Where is cartilage originally formed from?
Mesenchyme
True/False: Mesenchymal cells are differentiated into chondroblasts
True
Cartilage growth occurs up to the end of adolescence in which two phases?
- Appositional growth
- Interstitial growth
Both phases of cartilage growth are common, but which one becomes more predominate with age?
Appositional growth
At what period of growth does growth cease? Why?
Late teens; chondrocytes stop dividing
What is interstitial growth and were does it take place?
Division of the chondrocytes; within the distensible matrix
When does most interstitial growth occur?
Embryogenesis
What is taking place during interstitial growth during embryogenesis?
Mesenchymal cells aggregate and differentiate into chondroblasts
Once mesenchyme cells differentiate into chondroblasts, what do they secrete, form, and become?
ECM; lacunae; chondrocytes
Chondrocytes divide one or more times to form what groups?
Isogenic groups
Each chondrocyte lays down ______ causing it to form its own _______ and spread apart.
matrix; lacunae
As chondroblasts differentiate into chondrocytes, they form clusters that secrete what? Causing what?
secrete matrix; pushing cells apart
Where does appositional growth occur? During which stage of development?
On the surface of cartilage; later stages of development
Which cells of appositional growth differentiate into chondroblasts and what do they initiate?
Perichondrial cells; cartilage matrix formation
Matrix formation increases what type of mass?
Cartilage; making it more rigid
Cells of appositional growth mature into what type of cell and where are they embedded?
Chondrocytes; rigid matrix
The high water content of the matrix permits what action? To and from which structures, in what area?
Diffusion of nutrients and waste products; to and from the blood vessels; in the perichondrium
What are 3 reasons cartilage ceases growing in adulthood?
- Avascularity
- Immobility of chondrocytes
- Limited ability of chondrocytes to proliferate
Repair following injury only occurs under what circumstances, involving which type of cells?
If the defect involves the perichondrium; which can provide new chondrocytes, but mostly dense CT.
In appositional growth, what happens to some damaged cartilage?
It is calcified and vascularized leading to bone substitution.
Why is it that articular cartilage cannot be regenerated?
It has no perichondrium on either the free or bone-facing surfaces
In what types does bone come?
Long, short, flat, irregular
All bone is formed by an outer layer of what type of bone, surrounding what type of interior layer?
compact (dense) bone; spongy (cancellous, trabecular) bone
Long bones illustrate which 5 structures within bone?
- Diaphysis
- Epiphysis
- Metaphysis
- Marrow (medullary) cavity
- Outer bone surface
What is the diaphysis of a long bone?
The shaft
What is the epiphysis of a long bone?
Expanded end
What is the metaphysis of long bone?
It extends from diaphysis to the epiphyseal line
What does the marrow (medullary) cavity of the long bone form? What lines the the inner cavity?
The inner space (most bones are hollow); endosteum
What covers the outer bone surface of long bone?
Periosteum or articular cartilage
What is the periosteum?
Outer bone surface
Which area of bone is innervated, thus sensing pain?
Periosteum
What two layers make up the periosteum?
Fibrous layer and cellular layer
The outer fibrous layer of the periosteum is made up of what type of tissue and is the site for what structure?
Dense irregular CT; tendon attachment
The inner (deep) cellular osteogenic layer on the compact bone contains what type of cells?
Osteoprogenitor
The endosteum (inner/trabecular surface) is made up of an epithelial layer that produces what type of bone cells and is lacking which type of layer?
Progenitor cells; no fibrous layer
From where do osteoprogenitor cells originally differentiate?
Embryonic mesenchymal stem cells
Where, in mature bone, are osteoprogenitor cells located?
On the internal and external bone surfaces
In mature bone, what two areas do the osteoprogenitor cells form?
- Endosteum
- Inner layer of the periosteum
From where do the osteoblast differentiate?
Osteoprogenitor cells
What function does the osteoblast retain after differentiation from osteoprogenitor cells?
Ability to divide
Due to their ability to divide, what are the two directions an osteoblast can take?
- Generate new bone cells
- Remain dormant in periosteum or endosteum
What does the osteoblast secrete?
- Bone matrix proteins (osteoid)
- alkaline phosphatase
What is the purpose of osteoblast secretion of bone matrix proteins (osteoid) and alkaline phosphatases?
Promote matrix mineralization
With what does alkaline phosphatase combine to form crystalization?
Calcium
When enclosed in mineralized matrix, osteoblasts become which type of cell?
Osteocytes
From which type of cells are osteocytes derived? Where are they contained?
Osteoblasts; lacunae
What is lacunae?
Enclosed matrix spaces
Osteocytes send cytoplasmic extensions through what structures leading to adjacent lacunae?
Canaliculi
What is the purpose of the osteocyte sending out cytoplasmic extensions through the canaliculi to adjacent lacunae?
Permits contact with osteoblasts via gap junctions
Osteocytes are able to respond to what type of forces applied to the bone?
mechanical
What are two roles that osteocytes play with regard to structure of bone matrix?
- Synthesizes
- Break down
What causes osteocytes to synthesize new matrix or break it down?
Blood-calcium homeostasis (not so much with bone remodeling)
From which type of cells are bone-lining cells derived?
Osteoblasts
Where are bone-lining cells found?
- Where bone is quiescent (not building or resorbing)
- Periosteum
- Endosteum
What is the function of bone-lining cells?
Maintenance and nutritional support for osteocytes
What is a regulatory action of bone-lining cells?
Regulate movement of calcium and phosphate in and out of the bone.
What area of bone is the major source of blood?
Bone marrow
Where do blood vessels enter bone?
Through epiphyseal and diaphyseal nutrient foramen
Blood that nourishes bone tissue moves from what location, through bone tissue, and out via which veins?
Marrow space; periosteal veins
Which marrow consists of blood cells in different stages of development?
Red marrow
Red marrow is enmeshed in a network of which type of cells and material?
Reticular cells and fibers
When does red marrow form blood cells and what happens over time?
Early years; diminishes with time and is replaced with yellow marrow.
In adults, where is red marrow restricted? What are these reserves used for?
-Sternum
-Iliac crest
Available for bone marrow transplant
What is the main consistency of yellow marrow?
Mostly fat cells
In extreme cases of blood loss, what can happen to yellow marrow?
It can revert to red marrow
What are other names for compact (dense) bone and what type of matrix does it contain?
Cortical bone or lamellar bone; high density matrix
What are cylindrical layerings of concentric lamellae enclosing a central canal?
Osteons
What feature of lamellae increases resistance to twisting forces?
Alternating direction of collagen fibers
What is at the center of an osteon?
Central canal
What structures run through the central osteonal (Haversion) canal?
- Artery with capillaries
- Vein
- Nerve fiber
Periosteal blood vessels cary blood to the osteocytes via which canals?
Perforating (Volkmann’s) canals
Spongy (cancellous) bone is organized into _________ separated by _____ _______, but otherwise has many similarities to compact bone.
trabeculae; marrow spaces
True/False: Spongy bone contains osteon (Haversion systems)
FALSE!!! Spongy bone does NOT have osteon - Haversion systems are ONLY found in compact bone!!
Spongy bone lays down in which structure?
Lamellae
Trabeculae are surrounded by ___________ which also contains which two types of cells?
endosteum; osteoblasts and osteoclasts
True/False: Osteocytes are found within lacunae of spongy bone, interconnected by canaliculi.
True
True/False: Spongy bone is the precursor to compact bone during bone development.
True
Spongy bone trabeculae are organized along force lines in order to…?
Maximally resist tension or compression forces
Homeobox genes signal what structures to form somites?
Paraxial mesoderm segments
Somites establish early spinal levels (cervical, thoracic, etc.) of what three structures?
- Bones
- Muscle
- Dermis
In somite differentiation, sclerotome surround neural tube to form what two structures?
Vertebrae and ribs
In somite differentiation, dermatome becomes…
dermis of the skin
In somite differentiation, myotome becomes…
muscles of the body below the neck
Fusion of dense and loose tissue of adjacent somites forms what?
the intersegmental vertebra
The notochord of somites eventually becomes what structure within vertebral bodies?
Nucleus pulposus
Due to resegmentation of somites myotomes span…
adjacent vertebrae (touching the one above and one below, i.e. bottom half of T5 and top half of T6)
Due to resegmentation of somites, spinal nerves get interposed….
Between vertebrae (which is why we have a C8 nerve root, but no C8 vertebrae)
How is it that we have 8 cervical nerves but only 7 cervical vertebrae? (Hint: what makes up the “8th” cervical vertebrae)
A proatlas anlage that separates into portions of the basioccipital bone and the dens of the axis bone
Limb development comes from?
Local limb bud tissue
What is the first major tissue of limb to differentiate from mesenchyme?
Bone
True/False: In limb development, CT (tendons and fascia) are laid out along bone segments.
True
True/False: Cells of each somite region begin forming specific tissues prior to arriving at their destination.
FALSE!!! Cells of each somite region migrate separately to target destinations before forming specific tissue
Sclerotome cells migrate ________ to form what?
medially; bones (vertebrae and ribs)
Dermatome cells migrate in which direction in relation to ectoderm to form what?
under; connective tissue of skin (dermis)
Myotome cells migrate to form what structures, within which areas?
skeletal muscle; within body and limbs
Which part of mesoderm expands to form limb buds?
Lateral plate mesoderm
Myotomal cells differentiate into muscle and follow what structures during migration?
tendons
From what tissue does the epidermis derive?
ectoderm
In bone pattern formation, what does the AER (apical ectodermal ridge) determine, where, and using which factor?
growth of bones; along proximal-distal axis; using fibroblast growth factor (FGF)
In bone pattern formation, what does the ZPA (zone of polarizing activity) determine and using which factor?
Pattern of bones (which bones: radius, ulna, etc.) using sonic hedgehog (Shh)
True/False: Shh and FGF mutually enhance each other through feedback control
True
What determines the differentiation of digits?
Concentration gradient of Shh factor
Where is the highest concentration of Shh?
On the side of the 5th digit (digiti minimi)
Where is the lowest concentration of Shh?
Technically, the 2nd digit, because there is no Shh present at the pollus.
What process induced by Shh produces fingers?
Interdigital apoptosis
Disruption of interdigital apoptosis by Shh results in what condition? Which areas are most affected?
Syndactyly; most often affecting digist 3, 4, and/or 5
True/False: Hox genes are turned on all at once creating bones along the limb
FALSE!!! Sets of Hox genes are turned on SEQUENTIALLY, each set producing specific bones along the longitudinal axis of the limb.
What is the condition, phocomelia?
Absence of proximal segments, but normal distal segements (hands coming from the shoulder - no humerus, radius, or ulna)
What drug was associated with increased phocomelia, and what seemed to be causing the problem?
Thalidomide; blocks angiogenesis leading to reduction of FGF release.
