Bone Flashcards
Describe some general characteristics of bone, including what type of CT it is.
- bone is classified as specialized connective tissue (mineralized and rigid)
- it is living tissue with cells, vessels and nerve fibers
- continuously remodeled
When pressure is applied to bone, what will result?
bone resorption (breakdown)
When tension is applied to bone, what will result?
bone deposition (addition)
How do orthodontists manipulate characteristics of bone to realign and straighten teeth
applying pressure and tension to bone that reshapes the bony tooth sockets
What is the function of bone?
- to support and protect organs of the body
- provide leverage for movement
- storage depot for minerals (99% of calcium is store in bone)
What is bone marrow?
blood cell-forming tissue
What are some structures of long bones
epiphyses epiphyseal (growth) plates metaphysis diaphysis marrow cavity
What are epiphyses?
2 bulbous ends that are covered by hyaline cartilage (articulating surfaces)
What are epiphyseal plates?
aka growth plates
- consist of hyaline cartilage plates that allow bone growth in length. disappear around age 18-20
What is metaphysis?
angulation between the epiphyseal plate and the diaphysis
What is diaphysis?
long cylindrical shaft between 2 epiphyses
Where is the marrow cavity?
aka medullary cavity
- core of the long shaft
What is the outer most layer of bone called and what does it cover?
periosteum
- connective tissue covers the outer surface of bone, except articular surfaces and where tendons attach to bone
What are the two types of periosteum?
active (growing)
inactive (mature)
What is the difference between active and inactive periosteum?
- actively growing bones has 2 distinct layers (outer fibrous and inner cellular)
- mature periosteum has a well-developed outer fibrous layer and the inner layer is not well defined due to the inactive state
What are some features of the outer fibrous layer of periosteum?
- consist of dense collagenous CT
- contains blood vessels, lymphatic vessels and nerves (both blood vessels and nerves perforate and supply the bone)
What are Sharpey’s fibers?
bundles of collagenous fibers that run perpendicular to longitudinal axis of bone and anchor the outer fibrous layer to it to prevent the layer from sliding and peeling off of bone
What are some features of the inner cellular layer of periosteum?
- covers an actively growing bone, containing osteoprogenitor cells
- also covers a bone where bone formation is not in progress, containing periosteal cells
- important in repair of bone fractures
What do osteoprogenitor cells differentiate into?
osteoblasts to deposit bone on bone surface
What do periosteal cells do?
may differentiate into osteoblasts, if necessary, to form bone (during bone repair)
What is the most inner layer of bone called?
endosteum
What does the endosteum consist of?
- thin CT layer with a single row of osteoprogenitor cells that may differentiate into osteoblasts or bone-lining cells
What lines the bone marrow cavity?
endosteum
Haversian and Volkman canals are lined with what and what’s the purpose of these canals?
endosteum
- these canals are interconnected tunnels that allow small vessels and nerve fibers to reach deep into the bone marrow
What are all the things endosteum cover?
- bone marrow cavity
- Haversian and Volkman canals
- bony spicules and trabeculae of spongy bone
What are the components of bone matrix?
inorganic and organic
What does the inorganic component of bone matrix consist of?
inorganic minerals that give bone its hardness
- about 65% of the dry weight of bone
- hydroxyapatite crystals (calcium phosphate)
- bicarbonate, citrate, magnesium, sodium, potassium
What does the organic component of bone matrix consist of?
fibers and ground substance
What type of fibers are found in the organic component of bone matrix?
mainly type I collagen (acidophilic)
- 80-90% of the organic component
What prevents bone from becoming brittle?
type I collagen of the organic component of bone matrix
What are found in the ground substance of the organic component of bone matrix?
- proteoglycans
- glycoproteins
- growth factors
What GAG side chains are found in proteoglycans of ground substance of bone matrix?
hyaluronan
chondroitin sulfate
keratan sulfate
- bind growth factors
What are some glycoproteins found in the ground substance of bone matrix?
- osteonectin
- sialoproteins (I&II)
- osteopontin
- osteocalcin
What’s the function of osteonectin?
serves as “glue” between collagen and hydroxyapatite crystals
What growth factors are found in ground substance of bone matrix?
bone morphogenic proteins (BMPs)
- induce mesenchymal cells to differentiate into osteoblast (to lay down bone)
What’s the function of osteocalcin?
traps calcium from the blood stream and stimulates osteoclasts to remodel bone
What’s the function of sialoproteins?
bind cells to the bone matrix
What are osteoprogenitor cells and what are they derived from?
early stage immature bone cells that arise from mesenchymal stem cells
Where are osteoprogenitor cells found?
- inner layer of mature periosteum (known as perisoteal cells here)
- endosteum (known as endosteal cells here)
What can osteoprogenitor cells differentiate into?
osteoblasts (mostly) but can also differentiate into chondrogenic cells (in low O2 tension)
When are osteoprogenitor cells acitve?
during bone growth
Are osteoblasts acidophilic or basophilic?
basophilic during matrix protein synthesis, due to the rER
What do osteoblasts make?
synthesize and secrete organic component of the bone matrix (osteoid)
What is osteoid?
newly-formed non-mineralized bone, aka “pre-bone”
- consists of collagen type I and bone matrix proteins
What is the importance of alkaline phosphatase?
cell membrane of osteoblasts have high levels of alkaline phosphatase, when bone is being synthesized, the level of alkaline phosphatase increase in blood
What types of cells are in charge of mineralization of bone matrix?
osteoblasts
What are osteocytes?
“grown up” osteoblasts that have been enclosed within the matrix, called lacuna
What type of cells cover trabeculae and spicules?
bone lining cells
Why are bone lining cells important?
- protect bones from resorption by osteoclasts
- nutritional support of osteocytes
- uptake and release of calcium and phosphate by bone tissue
What do osteocytes occupy?
lacuna “bubble”
What are canaliculi?
cell processes of each lacuna extends
- this is where exchange of nutrients occur
- they point toward Harversian canals because that’s where the nutrients are
- waste products go in reverse direction back to the Harversian canals
What is the space between the osteocyte cell membrane and the lacuna and canaliculi called?
periosteocytic space
Each osteocyte is surround by a halo, what is it?
osteoid (non-mineralized bone matrix)
Does the Haversian canals contain lymphatic vessels?
No, only periosteum contain lymphatic vessels
What are osteoclasts derived from?
mononuclear hemopoietic progenitor cells in the bone marrow
**not mesenchymal stem cells
What are osteoclasts and what are their functions?
osteoclasts are multi-nucleated, motile, acidophilic (lysosomes), enormous cells
- resorb, remodel, “chisel” bone
What are the 3 distinct histological features of an osteoclast that is in the process of breaking down bone?
1) ruffled border
2) clear zone
3) basolateral region
What are the features of the ruffled border of osteoclasts that is in the process of breaking down bone?
- cell membrane is thickened with infoldings “ruffles” that increase cells surface area, resorption occurs here
- site of exocytosis of hydrolytic enzymes and secretion of protons to dissolve the inorganic part of matrix
- site of endocytosis of broken down bone and other metabolic products
What are the features of the clear zone of osteoclasts that is in the process of breaking down bone?
- lack organelles
- contain actin microfilaments, actin ring
- sealing zone that isolates acidic, corrosive resorption compartment from the surrounding region
What are the features of the basolateral region of osteoclasts that is in the process of breaking down bone?
- contains organelles of osteoclasts, multiple nuclei, Golgi, some rER and mitochondria
- functions in exocytosis of broken-down matrix, vesicles unite with cell membrane and contents are released at cell surface
How are inorganic components of bone handled during resorption?
- the acidic environment created by osteoclasts break down the inorganic component
- the minerals released pass into the cytoplasm of osteoclasts and are then transported to capillaries
How are organic components of bone handled during resorption?
organic components of de-mineralized matrix are broken down by lysosomal hydrolases and metalloproteinases (collagenase and gelatinase)
- they are released by osteoclasts into subosteoclastic compartment.
- the broken down material is then pass into the osteoclasts where they are degraded into amino acids, monosaccharides, and dissacharides, that then pass into capillaries
What happens to osteoclasts after they are done with the resorption process?
apoptosis
How do drugs (ie biphosphonates and estrogens) work to slow down bone breakdown in osteoporosis?
stimulate osteoclast apoptosis
What are the two gross structures of bone?
compact and spongy (cancellous)
- every bone in the body contains both, the ratio vary
What are the features of compact bone?
- dense (no bubbles or space), solid bone that forms a shell around the exterior of long bones
- contains a skull cap (calvaria)
- contains Haversian systems
What is in calvaria (skull cap)?
- outer table of compact bone that is covered by a periosteum, called pericranium
- inner table of compact bone that is lined by periosteal layer of cranial dura mater
What are the features of spongy bone?
1) lines the marrow cavity of long bones
2) bony trabeculae and bony spicules protrude from inner surface of compact bone toward the marrow cavity
3) forms diploe between the inner and outer tables of calvaria
4) fills the epiphyses of long bones
5) smaller bone spicules have bone lamellae, but no Haversian systems
6) contains mainly an irregular arrangement of bone lamellae (layers)
When are primary bone developed?
during fetal development and during bone repair
Under microscopic examination of primary bone, what will you see?
- irregular/ interlacing bundles of collagen (non-lamellar)
- less mineral content than mature bone (weaker)
- has more cells than mature bone and are randomly-arranged
- more ground substance than mature bone
What is the significance of primary bone?
it is a temporary tissue and will be resorbed by osteoclasts and then replaced by secondary bone (new bone formed by osteoblasts)
Bone lining alveolar sockets (tooth sockets) are referred as “bundle” bone, what kind of bone is it?
immature (primary)
- this is why orthodontic treatment is possible even in adults
Describe the microscopic features of secondary bone?
aka mature, lamellar
- consists of parallel or concentric bone lamellae
- collagen fibers are parallel within a lamella
- more mineral content than primary bone, so it’s stronger
- may exist as spongy or compact
What can be seen in a cross-section of a long bone?
1) outer circumferential lamellae
2) interstitial lamellae
3) Haversian canal systems “osteons”
4) inner circumferential lamellae
In a cross-section of a long bone, where can the outer circumferential lamellae be seen and what will you find?
- deep to the periosteum
- surround bone like growth rings of a tree
- contain Sharpe’s fibers (anchor periosteum to underlying compact bone)
Interstitial lamellae are..
lamellar fragments, remnants of former “old” osteons
What are Haversian canals?
osteonal canal
- vascular space that encloses a neurovascular bundle (vein, artery, nerve), but NO lymphatic vessels
What are Volkmann canals?
perforating canals
- not part of the Haversian canals, but are obliquely orientend, and connect osteons that are next to each other.
What’s the difference between Haversian and Volkmann canals?
Volkmann canals DO NOT have concentric lamellae of bone characteristics of Haversian systems
During bone formation, how are Haversian canals formed?
the osteons form from outside inward (bone grows toward and around existing blood vessel)
*once bone is mineralized, blood vessel cannot perforate the bone
Inner circumferential lamellae are found…
around the marrow cavity
Explain the etiology of ankylosis
type of arthritis
- condition in which two articulating bone fuse, obliterating the joint so there is no movement
- results from trauma to a joint that has damaged articular (hyaline) cartilage which becomes calcified, die, and replaced by bone
Explain the etiology of Rheumatoid arthritis
autoimmune disease that attacks the synovial joints, damaging the articular cartilages, producing disfigurement of the joints and severe pain
Explain the eitology of Gouty arthritis “Gout”
caused by accumulation of uric acid crystals in the joints, especially in the joints of fingers and toes. The sharp crystals cause excruciating pain
- can be a side effect of thiazide diuretics used to treat high blood pressure
Explain the etiology of Rickets
it’s a disorder that results from calcium deficiency during development, or from inadequate dietary supply of vit. D, which is necessary for calcium absorption from the GI tract
- osteoid does not mineralize
- in adults, it’s called osteomalacia “bone softening”
Explain the etiology of osteoporosis
condition characterized by reduction in bone mass both in organic and inorganic components of matrix
- bone breakdown by osteoclasts exceeds bone formation by osteoblasts, resulting in very porous ones that fracture and break easily and heal slowly
- occurs most often in postmenopausal women (drop in estrogen levels)
