Microanatomy lecture 2 - Ossification Flashcards
what are the two different types of ossification and how do they differ?
(2)
1- Intramembraneous Ossification –> forms directly from mesenchymal (STEM cell) tissue =flat bones of the face, most of the cranial bones, and the clavicles (collarbones)
2-Endochodral ossification
In endochondral ossification, bone develops by replacing hyaline cartilage =Instead, cartilage serves as a template to be completely replaced by new bone. Endochondral ossification takes much longer than intramembranous ossification.
Outline intramembraneous ossification ?
4
1-Mesenchymal cell are a template for the future bone , they GET REPLACED
2-Mesenchymal cell–>Osteoprogentor cells = 1 ossification centre –>Osteoblast –>Osteoid (Matrix)
3-minerilastion occurs
4-several osteoids unite around 1 capillary = TRABECULAR MATRIX + Trabeculae form and so does periosteum (osteoblast on surface = external covering of bones ) = SPONGY BONE has no OSTEON ( more porous ,has lots more blood vessels , red bone marrow = RBC production )
Outline Endochondral ossification?
5
1) first Intramembraneous ossification occurs to make bony collar around the CT template
2) Chondrocytes are in the diaphysis (center of the bone) = template
3) THE matrix becomes calcified, causing loss of minerals and OXYGEN into the matrix = CHONDROCYTES DIE = cavities in matrix
- HYPOXIC GRADIENT = causes blood vessels to enter
4) The blood vessels bring OsteoPROGENITOR cells = causes DENSE irregular CT around bone = Periosteum
- Osteoprogenitor cells =>Osteoblasts =>primary ossification complete
5) Capillaries penetrate the Epiphyses ( end of a long bone)= step 1 -4 occurs again
- osteoprogenitor cell –>osteoblasts –>osteoid + mineralised = bONE
how does bone grow
( 3 areas )
(3)
epiphyseal Plate:
1- Epiphyseal side : the chondrocytes start to divide to produce matrix
2-Diaphysis side : Zone of calcification , chondrocytes have died , osteoblasts invade
3-Zone of ossification = osteoblast start Laying down new bone
