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Flashcards in Bone development and growth Deck (12):
1

Bone vs cartilage

-Matrix of bone: osteoid calcified by deposition of hydroxyapatite crystals, with type I collagen (covered by periosteum, vascular)
-Matrix of cartilage: proteoglycan (hyaluronic acid) aggregates covered by perichrodrium (avascular)
-Cells in bone: osteobasts, osteocytes, and osteoclasts
-Cells in cartilage: chrondroblasts, chrondrocytes
-Growth mode of bone: appositional
-Growth mode of cartilage: interstitial and appositional

2

Cartilage degeneration

-Normal part of endochondral bone formation
-Chrondrocytes die and matrix calcifies
-Normal process of aging as well

3

Intramembranous bone formation 1

-Bone is formed from vascularized condensed mesenchymal tissue
-Growth of flat bone
-Mesenchymal cells differentiate then clusters together to form ossification center
-Osteoblasts are generated secrete osteoid, which becomes crystalized by hydroyapatite on the surface of bone

4

Intramembranous bone formation 2

-The ostoblasts are trapped in the osteoid matrix and become osteocytes
-Trabeculae from osteocytes join together to create spongy bone (primary bone)
-Undifferentiated mesenchymal cells surrounding the trabeculae differentiate into BM

5

Endochondral bone formation 1

-Bone is formed from cartilage, mostly long bones
-Vascularization of perichondrium of the cartilage model at the midshaft (diaphysis) causes chondrogenic cells to differentiate into osteogenic cells
-These give rise to osteoblasts which lay down osteoid
-Osteoid at the diaphysis is calcified to form a (subperiosteal) bone collar around the diaphysis
-Chondrocytes in the center of the diaphysis undergo apoptosis and the area is vascularized and invaded by periosteum (periosteal bud) then lined w/ osteoblasts (ossification center)

6

Endochondral bone formation 2

-The osteoblasts divide and osteoid replaces the cartilage except for at the ends of the bone (epiphyses) which remain cartilaginous (calcified cartilage-bone complex)
-The epiphyses form secondary ossification centers after birth
-Proliferation and hypertrophy of chondrocytes w/in the epiphyseal plate followed by calcification of cartilage matrix leads to increase in bone length
-Bone deposition on the outer surface of bone collar and resorption of bone on the inner surface results in increase in diameter of diaphysis (width)

7

Epiphyseal (growth) plate

-Made of hyaline cartilage and only found in children/adolescents, allows for interstitial growth of cartilage-> bone via calcification
-Is replaced by epiphyseal line in adults
-Epiphyseal plate composed of 5 distant zones: zone of resting (reserve cartilage), proliferation (stacks of chondrocytes), maturation/hypertrophy (large chondrocytes in columns), calcification (thin layer of calcified dead chondrocytes, ossification (bone)
-Together these areas look like columns of enlarged chondrocytes

8

Formation of fracture hematoma

-Blood vessels are broken, clots form around the site of fracture (hematoma)
-Lack of circulation results in inflammation and cell death
-Dead bone and fragments will be resorbed by osteoclasts

9

Cartilaginous callus formation

-Capillaries, fibroblasts, and osteogenic cells from broken periosteum and BM resolve the fracture hematoma into granulation tissue
-Fibrous connective tissue btwn ends of fractured bone are formed from fibroblasts and osteogenic cells
-Some osteogenic cells in the CT become chondrogenic cells and produce a hyaline cartilage callus around the ends of the bones

10

Bony callus formation

-Osteogenic cells in fibrous lining of the callus produce bony trabeculae by intramembranous bone formation
-Blood supply to callus improves and endochondral ossification occurs in the cartilaginous callus
-This forms bony callus consisting of primary (woven) bone (weaker than secondary bone, found in fetal bones, eventually replaced by secondary)

11

Bone remodeling

-The primary bone in bony callus is remodeled into secondary bone
-Original bone architecture is restored

12

Synovial membrane

-Lines the synovial cavity, is a layer of squamous to cuboidal epithelial cells
-2 types of cells: type A (phagocytic) and type B (fibroblast-like)
-The membrane secretes viscous fluid (synovial fluid) rich in hyaluronic acid and proteins
-Bone surfaces within synovial cavity are lined by persistent layer of hyaline cartilage (articular cartilage)