Bone formation & Repair 20 Flashcards
What are the 4 principal situations ossification occurs in?
1) Initially in embryo & foetus.
2) Growth
3) Remodelling
4) Repair of fractures
What are the 2 bone formation mechanisms?
1) Intramembranous ossification (simplest)
2) Endochondral ossification.
Explain intramembranous ossification.
Simplest. Bone forms directly in mesenchyme layers ( membrane like). Mesenchyme (one of embryonic tissue layers) model is replaced with bone.
Explain endochondral ossification.
Forms within hyaline cartilage developed from mesenchyme.
Name & describe stage 1 of Intramembranous Ossification.
‘Development of ossification centre’. Where mesenchyme cells differentiate becoming osteogenic, further becoming osteoblasts which secrete organic matrix.
Name & describe stage 2 of intramembranous ossification.
‘Calcification- cells become osteocytes’ In lacunae they extend cytoplasmic processes to each other. Deposits calcium & other minerals.
Name & describe stage 3 of intramembranous ossification.
‘Formation of Trabeculae’ - spongy bone tissue. Blood vessels grow in & red marrow is formed.
Name & describe stage 4 of intramembranous ossification.
‘Development of the periosteum’, Mesenchyme condenses at periphery’ - becoming periosteum. EG flat bones of skull and mandible.
Name & describe stage 1 of endochondral ossification.
Develop a cartilage model - mesenchyme cells crowd together in shape of bone, called chondroblasts.
What is the name of mesenchyme cells crowded together in the shape of a bone?
Chondroblasts.
Name & describe stage 2 of endochondral ossification.
‘Growth” - chondroblasts secrete cartilage.
Perichondrium forms on surface of chondrobasts.
Internal chondrocytes in lacunae die and form small cavities.
Name & describe stage 3 of endochondral ossification. (long answer, take notes)
‘Development of primary ossification centre’ - Ossification proceeds inwards with nutrient artery from surface perichondrium.
In disintegrating cartilage osteogenic cells = osteoblasts creating a ‘primary ossification centre’.
As bone forms perichondrium = periosteum.
First spongy bone is formed.
Name & describe stage 4 of endochondral ossification.
‘Development of the medullary (marrow) cavity’.
osteoblasts break some bone down, developing a medullary cavity in centre of bone.
Outer wall of diaphysis = compact bone.
Describe stage 5 of endochondral ossification.
Near birth, blood vessels enter epiphysis, developing secondary ossification centre. Hyaline cartilage at end of bone > articular cartilage. Prior to adulthood, hyaline remains in epiphyseal plates to allow bones to grow.
What happens to hyaline cartilage before adulthood?
It remains in the epiphyseal plates to allow growth in bone length.
Explain growth of bones before adulthood.
Chondrocytes in the epiphyseal plate divide and increase the cartilage layer. Later dying on the diaphysial side being replaced by bone.
Periosteum supports surface growth for thickness.
Name the 4 zones of the epiphyseal plate.
Proliferation zone
Hypertrophic zone
Calcification zone
Ossification zone
What happens at the proliferation zone in the epiphyseal plate?
Chondrocytes divide rapidly (mitosis) forming columns of stacked cells parallel to the axis of the bone.
What happens at the hypertrophic zone in the epiphyseal plate?
Older chondrocytes and their lacunae enlarge.
What happens at the calcification zone in the epiphyseal plate?
Matrix becomes calcified, begins deteriorating, chondrocytes die, leaving behind large empty holes.
What happens at the ossification zone in the epiphyseal plate?
The bone matrix is formed.
When bones are remodelled, they are reabsorbed by what cell?
Osteoclasts.
When bones are remodelled, they are dispositioned by what cell?
Osteoblasts.
What are the steps to repair a fracture?
1) Dead tissue is removed
2) Chondroblasts become fibrocartilage…
3) > spongy bone by osteoblasts
4) >remodelled to compact bone
What are the types of fractures?
Partial/greenstick -incomplete break, children (crack)
Complete- bone in two or more pieces
Closed (simple)- not through skin
Open (compound)- broken ends break skin
Transverse, spiral, comminuted, vertebral, compression- elderly
Describe osteoporosis.
Bones become brittle and lose calcium. Mainly occurs after menopause & men after 60.
