MSK physiology Flashcards
Where does endochondral ossification take place?
All bones below the skull except for the clavicle
When does endochondral ossification start
2 months in utero
What does endochondral ossification use as a blueprint
Hyaline cartilage for ossification
1st stage of endochondral ossification
Perichondrium becomes vascularised:
Blood vessels supply new nutrients to mesenchymal cells, causing differentiation
Newly formed osteoblasts gather at the diaphysis wall to form a bone collar.
The starting point for ossification
Primary ossification centre
2nd phase of endochondral ossification
Chondrocytes within a central cavity enlarge causing the matrix to calcify
Calcified matrix impermeable to nutrients, causing cell death
Central clearing forms where cells have died (supported by the bone collar)
Healthy chondrocytes elsewhere cause elongation
3rd phase of endochondral ossification
Periosteal bud invades cavity-causing formation of spongy bone
Bud consists of artery, vein, lymphatics and nerves. It also delivers osteogenic cells.
Osteoclasts degrade cartilage matrix while osteoblasts deposit new spongy bone
Bone continues to elongate elsewhere
4th phase of endochondral ossification
The primary ossification centre continues to enlarge
Osteoclasts break down the newly formed spongy bone
The medullary cavity begins to form
Cartilaginous growth now only with epiphysis
The bony epiphyseal surface begins to form
A secondary ossification centre may appear at one or both epiphysis
5th phase of endochondral ossification
Epiphyses ossify
Secondary ossification centres usually only appear after birth
Longer bones more likely to have two secondary centres
Short bones have only one centre irregular bones may have several
Cartilage now remains on bone surfaces and at epiphyseal plates
When does intramembranous ossification occur
In utero before week 8
From what does intramembranous ossification occur
All bone formed from hyaline cartilage and fibrous membrane
What bones are formed from intramembranous ossification
Cranial bones and clavicles formed this way mostly flat bones
First stages of intramembranous ossification
Early in development, you have mesenchymal stem cells that aggregate to form osteoblast by differentiate
Form an ossification centre
Osteoblasts begin to secrete osteoid (unmineralised bone)
2nd stages of intramembranous ossification
Peripheral mesenchymal cells continue to differentiate.
Osteoblasts secrete osteoid inward towards the ossification centre.
Osteoblasts become trapped in osteoid, causing differentiation into osteocytes.
Osteoid calcified and hardened after several days
3rd stages of intramembranous ossification
Osteoid continues to be deposited and assembles in a random manner around the embryonic blood vessels
Finely woven trabeculae formed
Mesenchyme begins to differentiate into periosteum
4th stages of intramembranous ossification
Lamellar (compact) bone replaces woven bone at the outer edge
Layered
Internal spongy bone remains
Vascular tissue within trabecular spaces forms red marrow
Osteoblasts remain on bone surfaces to remodel when needed
Summary of intramembranous ossification
Bone forms from membrane or cartilage
Mostly flat bones
Mesenchymal cells differentiate
Osteoblasts direct growth
Woven bone forms
Lamellar bone and outer periosteum forms
Surface osteoblasts remodel as reacquired (stress)
What is cartilage
Type of connective tissue
Function of bones
Storage of minerals (eg. calcium hydroxyapatite)
Transmission of body weight
Protection of vital organs and structures
Anchorage - lever system for movement
Determination of body shape
Raises body from the ground against gravity
Houses bone marrow to facilitate haematopoiesis
Types of bones
Long bones
Short bones
Flat bones
Sesamoid bones
Irregular bones
Pneumatic bones
Bone Development classification
Bones are classified into three groups according to their method of development (ossification)
3 groups include:
- membranous bones
- cartilaginous bones
- Membrocartilaginous bones
Membranous bones
Also called dermal bone
These bones have an Intramembranous method of ossification
Membranous sheets formed by condensation of mesenchyme
Example of membranous bones
Flat bones of the skull
Bones of face
Maxilla
Zygomatic
Cartilaginous bones + example
Have Intracartilaginous method of ossification
Example:
Ribs
Vertebrae
Bones of limb








