Bone Ossification and Repair Flashcards
What is the functional unit of bone?
haversian system/ osteon
Where does the blood supply for the osteocytes come?
osteon canals
How does blood supply get from the center of the osteon to the periphery?
Haversian canals
What lines the outer margin of osteons?
cement line
Is bone an active tissue?
yes, it is always going through remodeling
What are the three phases of the remodeling cycle of bone?
-resorption
-reversal
-formation
What happens during the resorption phase of bone remodeling?
osteoclasts digest old bone
What happens during the reversal phase of bone remodeling?
mononuclear cells appear on the bone surface
What happens during the formation phase of bone remodeling?
osteoblasts lay down new bone until the resorbed bone is completely replaced
What are bone lining cells?
inactive osteoprogenitor cells that are lining the bone when they are not being replaced
What are the two major hormones that work to maintain the calcium homeostasis?
parathryoid hormone and calcitonin
What hormones help in signalling bone remodeling?
growth hormones, glucocorticoids, thyroid hormones, and sex hormones
What is Wolfe’s law?
is you apply a force to a bone, that is how it will remodel
What is endochondral ossification?
Start with a cartilage model
-lay down bone (usually woven bone)
-woven bone is either changed to lamellar bone, or lamellar bone is added to the periphery of the woven bone
Where does endochondral ossification occur?
long bones, vertebrae, pelvis, and base of skull
What is intramembranous ossification?
direct placement of mesenchyme by bone
-no cartilage precursor
Where does intermembranous ossification occur?
vault of skull
What type of cartilage makes up the model for endochondrol ossification?
hyaline
Where is bone placed first during endochondral ossification?
in the mid-diaphysis
-produce a bone collar
What does the bone collar do to the cartilage cells?
kills them by blocking blood supply
-bring in blood supply and then osteoprogenitor cells and osteoblasts come in to lay more bone
What is the epiphyseal plate?
cartilage that remains at the metaphysis that allows for bone to get longer
When does the ephiphyseal plate of the femur close?
18-20 years
What is the zone of reserve cartilage?
hyaline cartilage with clusters of chondrocytes
-no cell proliferation
What is the zone of proliferation?
successive mitotic divisions of chondrocytes
-columns of chondrocytes
What is the zone of maturation?
division increases, chondrocytes increase in size
What is the zone of hypertrophy?
chondrocytes enlarge greatly, contain large amounts of glycogen, become vacuolated and calcify
What is the zone of degenation?
capillaries of marrow cavity grow from diaphysis into growth plate
What is the zone of ossification?
blood vessels from marrow cavity grow into cartilage mass
Five basic steps of endochondral ossification:
- mesenchymal cells form cartilage model of bone
- chondrocytes near center undergo hypertrophy and secrete contents of matrix causing mineralization
- chondrocytes undergo apoptosis due to decreased nutrients- blood vessels invade and bring osteogenic cells
- primary ossification centers form in diaphyseal region
- secondary ossification centers develop in epiphyseal region
Are there primary and secondary ossification sites in intermembranous ossification?
no, but there are many ossification sites
What are spicules?
random islands of bone that form during intermembranous ossification
-eventually fuse together
What forms where is a lot of oxygen present?
bone
five steps of intramembranous ossification:
- mesenchymal cells differentiate into osteoblasts and group into ossification centers
- osteoblasts become entrapped by the osteoids they secrete, becoming osteocytes
- trabecular bone and periosteum
- cortical bone forms superficially to the trabecular bone
- blood vessels form the red marrow
What is a simple or closed fracture?
no break in skin
What is a compound of open fracture?
damage to skin exposing bone
What is a comminuted fracture?
bone broken into little bits and pieces
What are the steps of bone repair?
- blood fills fracture site- hemotoma
- neutrophils arrive, infiltrate hemotoma, macrophages come
- fibroblasts and capillaries proliferate
- granulation tissue forms and becomes more fibrous
- mesenchymal cells differentiate into chondroblasts and lay down hyaline cartilage (callous)
- osteoprogenitor cells and osteoblasts come to make woven bone
- transforms to boney callous and help stabilize fracture
- bone callous is removed and becomes lamellar bone
What are synovial joints?
characterized by extensive movement
-diarthroses
What lines synovial joints ?
synovium that secretes synovial fluid
Is there a basement membrane of synovial joint?
no
-4 layers of synovial cells
What are type A synovialcytes?
resemeble macrophages
-nonfixed cells that can phagocytose cell debris and wastes
-antigen presenting ability
What are type B synovialcytes?
resemble fibroblasts
-make specialized matrix including hyaluronan, collagens, and fibronectin
What is lubricin?
surface active mucinous glycoprotein secreted into synovial cavity that is important in cartilage integrity
