Bone formation Flashcards
What is intramembranous ossification? Where might you find intramembranous ossification in an adult?
This is the process of forming bone from a connective tissue precursor. In the embryo, this precursor is a condensation of primitive mesenchyme. In adults, this continues in the periosteum and, therefore, a large percentage of every bone in the body is formed from intramembranous ossification. Also, fractures heal by intramembranous ossification of a fibrous “scar” called callous.
Where do osteoblasts come from during intramembranous ossification?
Osteoblasts differentiate from primitive mesenchymal cells.
What would you find within canaliculi in the bone?
The processes of osteocytes would be in the canaliculi. They contact the cytoplasmic processes of adjacent osteocytes and have gap junctions whereby they pass nutrients back and forth.
What are the steps in intramembranous ossification?
Osteoblasts develop from mesenchymal osteoprogenitor cells. Cancellous bone (immature) is laid down. This bone undergoes compaction into cortical bone (immature) and remodeling then occurs with maturation of the bone.
What bones originally develop by intramembranous ossification?
Much of the skull (except the bones at the base), the shaft of the clavicle and much of the scapula and pelvis originate in an intramembranous ossification process. FLAT BONES.
What are spicules? How do they contact one another?
Islands of developing bone. Through trabecular networks
How do osteoblasts receive nourishment? Osteocytes?
Osteoblasts receive nourishment from the blood vessels surrounding the tissues. Osteocytes receive nourishment from the blood vessels through the canaliculi
How do you form spongy bone vs. compact bone?
Spongy: the spaces between the trabeculae will give rise to bone marrow cells
Compact: the trabecular will thicken until the intervening spaces are gone
What is endochondral ossification?
This is the process whereby a cartilage model is replaced by bone. Most bones begin as cartilage models.
What are the steps in endochrondral ossification?
- Cartilage model
- Appositional or interstitial growth
- Formation of bone collar (perichondral cells stop producing chondroblasts and instead produce osteoblasts)
- Chondrocytes hypertrophy
- Death of chondrocytes and breakdown of matrix
- Blood vessels invade through the bone collar. These bring other cells into the model.
- Osteoclasts break down the calcified cartilage, forming a marrow cavity. Osteoblasts lay down bone on calcified cartilage “spicules”. Secondary ossification centers forms at the epiphyses.
What happens to the cartilage in the epiphyses?
It is not replaced by bone and becomes articular cartilage
What are mixed spicules?
Spicules are islands of developing bone. Mixed spicules have cartilage (basophilic) and bone (eosinophilic)
How does a bone increase in length?
The bone can only increase in length at the cartilage growth plate zones (epiphyseal plates). The growth in length of the bone is due to interstitial growth of cartilage (bone can not grow interstitially). There are zones of cartilage cells in the epiphyses. These include: a resting zone; a zone of proliferation; a zone of hypertrophy; a zone of calcification; and a zone of resorption. Osteoblasts will lay bone down on spicules of calcified cartilage and osteoclasts will break down calcified cartilage and the early bone in order to allow for production of mature bone.
Describe steps of epiphyseal plate growth
- Resting zone: Hyaline cartilage
- Zone of proliferation: Chondrocytes divide rapidly; form column of cells
- Zone of hypertrophy: Cells hypertrophy; secrete X collagen;
- Zone of calcification: Matrix becomes calcified; chondrocytes die
- Zone of ossification: where blood vessels invade and bring osteoprogenitor cells-> osteoblasts deposit bone matrix on calcified matrix
Bone deposition occurs on the ….. plate?
Diaphyseal
