Histology of developing bone part I
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embryogically, cartilage derive from
- the cells of connective tissue, such as chondroblasts, osteoblasts and
produce flat bone
how is chondroblast, osteoblast and fibroblast similar?
produce some kind of collagen
derive from mesenchyme
develops around the growing cartilage. This will contain the blood supply and stem cells for the cartilage.
type II collagen and cartilage-specific matrix components.
tendon is made up of
type I collagen produce by fibroblast in one direction
resist shear force
Type I vs type II
shear force vs compression force
fibroblast produce and found in
type I collagen
found in ligament, osteoblast in bone
Bone consist of
type I collagen (Strength) and mineralized matrix (hardness)
Flat bone consist of ...layers
3 layers: outer table, Diploe and inner table
intramembrananous ossification - process
1. Mesenchymal cells condense into a vascularized sheet of cells, and differentiate into osteoblasts.
2. osteoblast begin secreting and calcifying osteoid
3. Some osteoblasts become completely surrounded by osteoid, and differentiate into osteocytes. This process produces islands of woven bone.
4. Trabecular bone forms, a rudimentary periosteum forms from mesenchyme, blood vessels grow into bone islands.
5. Woven bone is remodeled to compact bone around the periphery to create inner, outer circumferential lamellae, which are represented by the outer and inner tables
Intramembranous Ossification - fontanelles
The process of forming the bones of the skull is not complete by birth.
As a result, the incompletely ossified areas between the bones are covered only by periosteum and primitive connective tissue.
- We know these areas as “soft spots” or fontanelles.
- Rationale: child birth and cerebral growth
unmineralized bone matrix
Woven bone end up becoming
cavity where bone marrow reside
Long bone - anatomy
- Development of a long bone – requires
- that the articular surface remain largely unchanged throughout process, plus subject must comply with birth canal size restrictions, but still have bones capable of being used and capable of
- increasing in length
Endochondral Ossification - process
1. The process of forming a long bone begins with the construction of a template made from cartilage.
2. Osteoblasts differentiate from cells in the perichondrium, secrete osteoid around the center of the cartilage, forming a bone collar.
3. The bone collar blocks nutrients from reaching chondrocytes located within the cartilage. These chondrocytes swell up and degenerate. They secrete alkaline phosphatase (a bone matrix mineralization enzyme) and enlarge their lacunae.
- 4. Blood vessels from the perichondrium
- infiltrate this tissue, they bring osteoprogenitor cells (these cells differentiate into osteoblasts).
- 5. . Osteoblasts adhere to the mineralized cartilaginous matrix and secrete osteoid,
- which is transformed into woven bone.
long bone - developing property
child birth: right shape but not big size
continue to development
Secondary Ossification center
- will form between the metaphysis and
- the epiphysis.
- –This process is initiated by the growth of blood vessels into the epiphysis, which
- brings a supply of osteoprogenitor
- cells into the center of the epiphyseal cartilage.
- –The cartilage in the epiphysis will be gradually replaced with bone marrow in a
- similar manner as the primary ossification center.
–The articular cartilage will be spared from ossification.
The Epiphyseal Plate
Located in the metaphysis
Site at which chondrocytes proliferate, degenerate, and are replaced by bone resulting in increases in bone length during adolescence and young adulthood.
Epiphyseeal plate: 4 layers
–1 Resting Zone
–2 Proliferating Zone: chondroblast
–3 Hypertrophic and Degenerative Zone: dying cell and enlarger lacunnae
–4 Calcification and Ossification Zone
Secondary site of ossification: time line
form after birth
vertical vs horizontal septa zone
vertical: maintain trabecullae integrity
Horizontal: got compressed and dense
evidence of growth
vertical and horizontal septa
hypertrophic and dying cell
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