Bone Flashcards
names for spongy bone
cancellous, trabecular, spongy
names for compact bone
cortical, lamellar, compact
where is spongy bone found
within epiphyses (but is covered with a layer of compact bone) of long bones, between the thick plates of the skull’s flat bones (diploe)
where is compact bone found?
the diaphysis of long bones (but has a thin layer of spongy lining the bone marrow cavity), thin covering surrounding epiphyses, tables/plates of flat bones - always lamellar bone
composition of outer layer of periosteum
fibrous layer of dense irregular connective tissue with collagen fibers, fibroblasts, blood vessels, nerves
composition layer of inner layer of periosteum (cellular layer)
periosteal (osteoprogenitor cells)
what are sharpey’s fibers
collagen fibers that extend into bone and are continuous with collagen fibers of the extracellular matrix - they are the sticky fibers that help connect periosteum to bone
what is the endosteum
thin layer of simple epithelium that lines internal marrow cavities and contains osteoblasts and osteoprogenitor cells
what is the periosteum
fibrous, vascular, nerve-containing outer layer of collagen bundles and fibroblasts and inner layer of osteoprogenitor cells
circular components of compact boneq
osteon, with central or Haversian canal in center
what is within Haversian canals?
vasculature, lymph, nerves (neurovascular bundle)
osteon made of
concentric lamellae with lacuna that houses the osteocytes
what is canaliculi
dendritic processes coming off of the lacuna (where the osteocyte is) that contain gap junctions that allow osteocytes to communicate
what role does the osteocyte play?
controls metabolic and remodeling rate of bone
what is a haversian canal
central canal in osteon containing neurovasculature, and runs parallel to bone length
waht is a volkman’s canal or perforating canal
vascular canal running perpendicular to bone length
what is lacuna
an embedded, hollowed out area between lamella that house osteocytes, are filled with canaliculi for cell communication
what is lamaella
concentric rings of compact bone that make up osteon rings
how do lamellae maintain strength while keeping a light weight?
regular bone remodeling/maintenance provides differing fiber orientations
what are the bony parts between spaces in spongy bone?
trabeculae/spicules
where is red bone marrow located and what is the function
epiphyses, site of hematopoiesis (synthesizes RBC, WBC, platelets)
where is yellow bone marrow located
diaphysis
osteoblasts
synthesis of bone matrix, rounded cells forming a simple row along outer edge of bone
osteoclasts
bone degeneration/resorption, large and motile and multinucleated cells derived from monocytes
MACROPHAGES THAT SECRETE ACID AND PROTEASES and COLLAGENASE TO BREAK DOWN BONE MATRIX
osteocytes
maintain matrix components, flattened and found within lacunae of bone matrix
REGULATE CA AND PO4 (PHOSPHATE)
they also sense mechanical stress and if bones are not used or there is stress, will signal to osteoblasts/clasts
where are osteoblasts derived from
osteoprogenitor stem cells (which are themselves derived from mesenchyme)
what is derived from osteoblasts
osteocytes and bone lining cells
what is osteoclast derived from
hemopoietic stem cells (CFU-GM)
components of bone matrix
65% inorganic components
35% organic components
what inorganic components are in bone
hydroxyapatite, bicarbonate, citrate, Mg, K, Na, CaPO4, H2O
what organic components in bone
type 1 collagen (type one = bONE)
ground substance rich in osteonectin and osteocalcin (for calcium binding, dependent on vitamin k)
why is the composition in bone minerals and type I collagen?
rigidity and flexibility
steps of mineralization in bone matrix
- osteoblasts release components as vesicles
- the released vesicles interact with collagen, Ca and PO4 in the osteoid layer (soup)
- Ca and PO4 start to mineralize around vesicles
- matrix becomes confluent between vesicles/mineralizes
what is osteosarcoma and where is it common
malignant tumor of osteoblasts, common in children around the knee joint
what is rickets/osteomalacia
vitamin D/calcium deficiency of absorption problem that impedes structural stability (decreases strength) of bone (ossification), so there is excess of non-mineralized osteoid
how do osteoclasts produce acid
proton pump to create acidic environment that dissolves hydroxyapatite
what is howship’s lacuna
a clear resorption zone within small depressions in the bone matrix adjacent to osteoclasts (ruffled border)
what is the ruffled border
the surface against the resorbed bone matrix that is folded/irregular to increase surface area for assistance in breaking down border
what is marble bone disease?
osteopetrosis, a defect in bone resorption causing overgrowth and thickening of bones that is prone to fracture, obliteration of bone marrow cavities and reduction in blood cell production
pathology osteopetrosis
genetic defect in osteoclast fct with loss of ruffled borders and resorption bays/howships lacunae, usually caused by mutation in ATPase proton pump or chloride channels)
what is intramembranous ossification
- where osteoblasts differentiate from mesenchyme directly and secrete osteoiid
- ossification occurs between membranes of embryonic mesenchymal tissue
- osteoblasts lay down woven bone which gets remodeled into lamellar bone
what is endochondral ossification
where the hyaline cartilage precursor is replaced by osteoblasts producing osteoid, usually in long bones
what is the 1st type of bone to appear during osteogenesis pathways ?
woven/primary bone - less mineralized, darker on xray, higher osteocyte to matrix ratio
describe general woven bone
forms during embryonic development or after fx
randomly arranged bundle of calcified type I collagen
describe general lamellar bone
parallel collagen fibers in concentric rings (lamellae)
what type of ossification occurs mainly in flat bones?
intramembranous ossification, 2 layers of compact bone arise with a central spongy inner layer
steps of intramembranous ossification
- ossification centers arise from WITHIN thickened regions of mesenchme - osteoblasts differentiate, secrete osteoid
- osteoid undergoes calcification
- woven bone and surrounding periosteum form - around vasculature - periosteum does not undergo minteralization
- lamellar bone replaces woven bone, compact and spongy bone form
basic steps of endochondral ossification
- hyaline cartilage model forms through condensation and differentiation of mesenchyme (chondrogenesis)
- periosteal bone collar forms through intramembranous ossification
- proliferation of chondrocytes - primary ossification center forms in diaphysis
- hypertrophy of chondrocytes - secondary ossification center form in epiphyses
- calcification of matrix with apoptosis of chondrocytes
- primary cavity formation with remnant condrocyte lacunae - developing bone uses lacunae
- periosteal bud of blood vessels infiltrate primary marrow cavity
- ossification (osteoid deposited, mineralization via osteoblasts
what does calcified cartilage look like
basophillic - purple, the calcified spicules during growth at the growth plate look purple
what does osteoid formation look like
eosinophilic - pink/red, ossified bone looks pink
how does bone grow around the ossification centers/epiphyseal growth plate? (esp in secondary center)
both directions grow toward the growth plate aka toward each other
where does cartilage remain in the long bone
- articular cartilage (caps articulating ends to form joints)
- epiphyseal plate (connects epiphysis to diaphysis)
5 zones of epiphyseal growth plates
- resting phase - hyaline cartilage with typical chondrocytes
- proliferation phase - cartilage proliferates and form columns
- hypertrophic cartilage - chondrocytes swell with glycogen
- zone of calcified cartilage - chondrocytes undergo apoptosis and matrix begins calcification
- zone of ossification - influx of bone cells, further matrix production within lacunae of apoptosed chondrocytes
what is the process of bone fracture repair
- during week 1: hematoma forms around break and granulation tissue forms (fibroblasts, ECM, small blood vessels infiltrate)
- during weeks 2-3: a fibrocartilaginous callus forms from the fibroblasts (fibroblasts form chondroblasts which forms hyaline cartilage, fibroblasts form osteoblasts to form woven bone)
- during weeks 4-16: a hard callus forms - hyaline cartilage and woven bone are replaced by trabecular bone
- week 17+: bone is remodeled - trabecular bone is replaced by compact bone (using osteoclasts and osteoblasts)
what process does bone fracture repair utilize?
both intramembranous ossification and endochondral ossification
what is meant metabolic role of bone?
means that bone remodeling and bone calcium/blood calcium is regulated by hormones
what controlls bone turnover equilibrium?
osteoblasts (tell osteoclasts what to do)
fact about hydroxyapatite
bone stores 99% of the body’s total calcium in the crystals of hydroxyapatite
what occurs in the event of low blood calcium?
- parathyroid hormone is released from the parathyroid gland
- binds to receptors on osteoblasts
- cessation of matrix production and release of osteoclast stimulating factor
- increased bone resorption and decreased bone production
what happens in the event of high blood calcium?
- calcitonin is secreted from parafollicular cells in thyroid gland
- promotion of calcium incorporation into bone tissue via inhibition of osteoclast activity (blocking bone resorption) and stimulates osteoblast
- lowers blood calcium levels
relation of growth hormone in bone growth and maintenance
- anterior pituitary secretes to stimulate bone growth, especially at the epiphyseal plate
what is the consequence of deficient GH
dwarfism (children)
what is the consequence of excess GH
gigantism (children), acromegaly (adults)
relation of FGFR3 in bone growth and maintenance
fibroblast growth factor receptor 3, promotes cartilage growth
consequence of FGFR3 mutation
inhibition of cartilage growth, dwarfism, achondroplasia
what is achondroplasia
inhibition of endochondral ossification due to inhibition of precursor cartilage
what do androgens and estrogens do for bone growth/maintenance
stimulates bone formation and impact timing of ossification center formation and epiphyseal closure
why is androgenous steroid use harmful in developing children
since it impacts timing of ossification center formation and growth plate closure, growth could be stunted
consequence of calcium and vitamin D deficiency
incomplete bone matrix calcification, increased bone resorption
(rickets = children)
(osteomalacia = adults)
consequence of vitamin C and protein deficiency
reduced collagen synthesis, inhibiting bone growth and maintenance, slowing fracture repair
(scurvy)
consequence of vitamin A deficiency
slow bone growth
consequence of Vitamin A excess
slow cartilage growth and accelerated ossification causing skeletal deformities and short stature
consequence of rickets
deformed and slow growing bones caused by Ca deficiency in childhood
consequence of osteomalacia
deficient calcification and partial decalcification of bone caused by calcium deficiency in adults (weakened bone)
consequence of osteoporosis
imbalance in bone turnover so that bone resorption exceeds bone formation (weaker bones)
consequence of osteopetrosis
defective osteoclast function leads to overgrowth, thickening, hardening of bones, obliteration of bone marrow cavities
what are diathroses
joints that permit free bone movement - usually synovial joints
ex. elbow, knee
what are synarthroses
limited or no movement permitted
ex. skull sutures, sternoclavicular joint
type A synoviocytes
macrophage-type cells derived from monocytes
type B synoviocytes
fibroblast-like cells derived from mesenchyme
function of type A synoviocytes
on surface of synovial membranes where they line the joint cavity and clear synovial fluid of waste and cellular debris
function of type B synoviocytes
synthesize hyaluronic acid and other components of ground substance and synovial fluid
components of synovial fluid
plasma like, rich in hyaluronan and lubricin
function of synovial fluid
- reduces friction (lubricant)
- transports nutrients to chondrocytes in the articular cartilage (no perichondrium)
- shock absorption due to viscous consistency
what is articular cartilage
hyaline cartilage that lacks the usual perichondrum covering with the collagen forming arches
