Bone Growth and Development Flashcards
What is osteogenesis?
Process of bone formation
What are the two types of bone formation?
1) Endochondral Ossification
2) Intramembranous Ossification
What is endochondral ossification?
It is the bone formation from a cartilage template
What does endochondral ossification contribute to?
Contributes to increase bone length
What does endochondral ossification form?
All tubular and flat bones, vertebrae
Does endochondral ossification stop at a certain point?
Yes, it stops after skeletal maturity
What is intramembranous ossification?
It is the bone formation as a replacement of connective tissue, but in the absence of cartilage.
What does intramembranous ossification contribute to?
Contributes to increases in bone thickness
What does intramembranous ossification form?
Cortex of tubular and flat bones, facial bones, and most of cranial bones (skull)
Where does intramembranous ossification stop?
It doesn’t stop at any certain point - it remodels throughout life.
During development of the fetus, most bones of the skeleton have a ___________, which is gradually replaced by _________.
Cartilage template, bone
Describe the FIRST step in the fetal development of bone.
Loose connective tissue from the mesoderm called the mesenchyme condenses during embryogenesis.
Describe the SECOND step in the fetal development of bone.
Committed mesenchyme cells differentiate into chondrocytes that proliferate rapidly to form the model for bone.
- These chondrocytes produce a cartilage specific ECM
- The remaining mesenchymal cells surrounding the cartilage core form the perichondrium (outer membrane).
Describe the THIRD step in the fetal development of bone.
Centrally located chondrocytes stop dividing and undergo hypertrophy.
- Chondrocytes change to producing proteins that contribute to the mineralization of the matrix.
Describe the FOURTH step in the fetal development of bone.
Hypertrophic chondrocytes die by apoptosis (they die to leave space).
- This allows blood vessels to enter.
- There will be an invasion of osteoblasts and they will deposit bone matrix on partially degraded collagen.
Describe the FIFTH step in the fetal development of bone.
Perichondrium is converted to periosteum. Osteoblasts form a layer of bone around the diaphysis.
Describe the SIXTH step in the fetal development of bone.
Primary ossification center is established in the central portion of the diaphysis.
- Osteoblasts replace cartilage with spongy bone.
- Bone is formed until the diaphysis is filled.
- As bone grows, osteoclasts hollow out a marrow cavity
Describe the SEVENTH step in the fetal development of bone.
Bone formation and growth consists of ordered arrays of proliferating, hypertrophic, and mineralizing chondrocytes.
Describe the EIGHTH step in the fetal development of bone.
Secondary ossification centers form as blood vessels enter near the tips of bone.
Secondary centers of ossification:
1) Chondrocytes in the _____________ have been maturing and are invaded by _______________.
2) _____________ produce spongy bone that replaces ___________ cartilage.
3) Leaves ________ cartilage, and cartilage at ________________.
1) bone epiphyses, blood vessels
2) Osteoblasts, epiphyseal
3) articular, growth plate
What are the two basic processes of lengthening of long bones?
1) Growth of cartilage on the epiphyseal side of the growth plate.
2) Ossification of cartilage on the diaphyseal side of the growth plate.
What are the five zones of the epiphyseal growth plate?
1) Resting Zone
2) Proliferating Zone
3) Pre-Hypertrophic Zone
4) Hypertrophic Zone
5) Trabecular Zone
Describe the Resting Zone of the growth plate.
- Chondrocytes are closest to the epiphysis
- It is the source of chondrocytes that form the proliferation zone.
Describe the Proliferating Zone of the growth plate.
- Chondrocytes proliferate and flatten
- Chondrocytes are also laying down a cartilage matrix that will later serve as a scaffold for bone formation.
- This process pushes the epiphysis away from the diaphysis.
