Ossification And Development Of Bone - intramembranous ossification Flashcards
What are the 2 ways costal bone develops?
Intramembranous ossification
And endochondral ossification
What is intramembranous ossification?
Ossification in membrane
Direct replacement of the mesenchyme/ mesenchyme tissue with bone
What is endochondral ossification?
Ossification of cartilage
What does ossification involve?
In both cases replacement of connective tissue with woven bone = (osteoid) occurs
Is woven bone mineralised?
No
Describe the process from woven bone to lamellar bone?
Woven bone (immature unmineralised bone) then remodelled to lamellar bone (mature bone) which is impregnated with calcium salts – Ca hydroxyapatite crystals (mineralised)
What are the 4 forms of lamellar bone?
Compact
Cortical
Sponges
Alveolar bone
Is this woven or lamellar bone?
Woven
Is this woven or lamellar bone?
Lamellar
Where does endochondral ossification occur?
Within the long ones of the limbs
What is cortical bone?
The bone on the outside
The cortex of the bone
What bone is places inside of the cortical bone?
Compact bone
What is alveolar bone?
Specialised type of compact bone
Alveolar processes of the maxilla and mandible
How is the compact bone arranged?
Compact bone consists of closely packed osteons or haversian systems. The osteon consists of a central canal called the osteonic (haversian) canal, which is surrounded by concentric rings (lamellae) of matrix. Between the rings of matrix, the bone cells (osteocytes) are located in spaces called lacunae.
What is the structure of spongy bone?
Spongy (cancellous) bone is lighter and less dense than compact bone. Spongy bone consists of plates (trabeculae) and bars of bone adjacent to small, irregular cavities that contain red bone marrow. The canaliculi connect to the adjacent cavities, instead of a central haversian canal, to receive their blood supply.
What are examples of bone which use intramembranous ossification?
Vault of skull
Maxilla
Most of mandible
What is the mesenchyme of the skull?
In the head of an embryo, a layer of mesenchyme surrounds the brain underneath the surface ectoderm. This cranial mesenchyme gives rise to the meninges, the calvaria (top part of the skull), and the dermis of the scalp.
When does intramembranous ossification occur?
8th week of gestation
What is the process of intramembranous ossification in the skull?
During intramembranous ossification, what do the mesenchymal cells differentiate to?
Osteoblasts
What is the role of osteoblasts in intramembranous ossification?
Lay down organic/woven bone matrix (=osteoid)
What happens to the osteoid matrix during intramembranous ossification?
Becomes mineralise producing a number of centres of ossification
What cells are at the surface of the osteoid atria?
Osteoprojenitor cells
How do osteoprojentor cells divide?
Divide by mitosis and make more osteoblasts
What do osteoprojenitor cells divide to make?
More osteoblasts and repeat the above process
How do ossification centres enlarge?
By addition of more woven bone which then becomes ossified (mineralised)
What are m and b in the diagram?
M = mesenchyme
B = woven bone
What do the mesenchymal cells not forming woven bone become?
Become bone marrow cells
What are the 2 regions of skull bone?
Neurocranium
Vicerocranium
What are the 2 parts of the neurocranium?
Cranial vault (calvarium)
Base of skull (chondrocranium)
Which part of the neurocranium is developed by intramembranous ossification?
Cranial vault (calvarium)
Which part of the neurocranium is developed by endochondral ossification?
Bones at base of skull (Chondrocranium)
What are examples of calvarium bones developed by intramembranous ossification?
Frontal
Parietal
Squamous part of temporal bone
Occipital
What are examples of chondrocranium bones developed by endochondral ossification?
Ethmoid
Base of sphenoid
Petrous part of temporal
Base of occipital
What type of ossification develops the vicerocranium?
Intramembranous
What are examples of bones in the viscerocranium developed by intramembranous ossification?
Maxilla
Zygomatic bone
Palatine bone
Mandible