Block IV: Bone formation Flashcards
what initiates bone formation?
condensation of mesenchymal cells during 8th week
into what does messenchymal cells differentiate into?
osteoprogenitor cells and express CBFA1 transcription factor
osteoprogenitor cell differentiates into?
osteoblast, produce matrix and becomes osteocytes
Where does intramembranous ossification occur?
in the development of flat bones in the head, in the periosteum during bone remodeling, and plays a role in fracture repair
identify
In this relatively early stage of
development, the mandible consists
of bone spicules of various sizes
and shapes. The bone spicules
interconnect with each other and
form trabeculae, providing the
general shape of the developing
bone
Explain endochondral ossification starts with a shape of?
- A hyaline cartilage model with the general shape of the bone is formed
when does endochondral ossification start, induced by and first sign?
- Starts in 12th week of gestation. Influenced by fibroblastic growth factor (FGFs) and bone morphogenic proteins (BMPs).
- The first sign of ossification is the appearance of the bony collar around the cartilage model.
What do chondrocytes in midregion synthesize?
- The chondrocytes in the midregion become hypertrophic and synthesize alkaline phosphatase
Cartilage matrix undergoes?
5.The cartilage matrix undergoes calcification. This calcification of the matrix inhibits diffusion of nutrients and the chondrocytes die.
Where do messenchymal cells migrate to?
- Mesenchymal stem cells migrate into the cavity along with blood vessels and osteoprogenitor cells that become osteoblast.
What is the primary ossification center?
This first site when bone begins to form in the dyaphysis of a long bone
Whne does second ossification center occur?
Shortly after birth in the proximal epiphysis
What is the epiphyseal plate?
the Hyaline cartilage that persists between the two epiphyses and continues interstitial growth; the growth in length of long bones depends on epiphyseal plates
does calcified cartilage become bone?
no; is replaced by bone
What are the zones of the epiphyseal plate?
- Zone of reserve cartilage (resting or quiescent) chondrocytes quiescent, no cellular proliferation or matrix production
- Zone of proliferation chondrocytes undergo division by mitosis and produce collagen types II and XI, cells become organized into columns
- Zone of hypertrophy (maturation) chondrocytes enlarge (hypertrophy), store glycogen, secrete collagen type II, X. Secrete VEGF that stimulate vascular invasion.
- Zone of calcified cartilage matrix calcifies and cells die. Chondrocytes undergo apoptosis
- Zone of resorption vessels invade and bring in osteogenic cells, bone deposition begins > ossification zone (zone of mixed spicules) bone
deposited on dead cartilage then remodeled
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zones of epiphyseal plate
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Intramembranous Ossification (bony spicule)
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Endochondral Ossification (mixed spicule)
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Compact adult bone contains Haversian system of varying age
and size. Bone Remodeling is a continuous process.
Microradiograph of the cross section of a bone. This 200-μm-thick cross section of bone from a healthy
19-year-old male shows various degrees of mineralization in different osteons. Mature compact bone is
actively replacing immature bone, which is seen on the periosteal. Very light areas represent the highly
mineralized tissue that deflects the X-rays and prevents them from striking the photographic film.
Conversely, dark areas contain less mineral and, thus, are less effective in deflecting the X-rays
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3-week-old bone fracture, stained with H&E, shows the fibrocartilage of the soft callus. (Fractured long bone undergoing repair)
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Higher magnification of the callus from the area indicated shows osteoblasts lining bone trabeculae (Fractured long bone undergoing repair)
identify
Higher magnification of the callus shows site by the periosteum. It will be removed by osteoclast activity
