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KPE 365 early development of skeletal system
Transcript of KPE 365 early development of skeletal system
1. Molecular Development
2. Primary Ossification Centers
3. Secondary Ossification Centers
4. Appositional Bone Growth
There are two types of ossification centers - Primary and Secondary.
-A primary ossification center is the first area of a bone to start ossifying.
-It usually appears during prenatal development in the central part of each developing bone.
-In long bones the primary centers occur in the diaphysis/shaft.
-In irregular bones the primary centers occur usually in the body of the bone.
-Most bones have only one primary center but some irregular bones have multiple primary centers.
-A secondary ossification center is the area of ossification that appears after the primary ossification center has already appeared.
-most of which appear during the postnatal and adolescent years.
-Most bones have more than one secondary ossification center.
-In long bones, the secondary centers appear in the epiphyses.
-The secondary centers of endochondral ossification are located at the growing ends of the bone where the cartilage plates are located.
Appositional Bone Growth
• Before week 8 the skeleton is completely made up of fibrous membranes and hyaline cartilage.
• At this time bone tissue begins to develop and replace fibrous or cartilage structures.
• Intramembranous ossification – bone development from fibrous membrane. Results in membrane bone.
• Endochondral ossification – bone development from hyaline cartilage. Results in endochondral bone, or cartilage.
Molecular Bone Growth
• Intramembranous ossification forms the cranial bones of the skull and the clavicles.
• Most bones formed this way are flat bones.
• Essentially all bones of the skeleton below the base of the skull are formed by endochondral ossification.
• Begins in the second month of development.
• More complex than intramembranous ossification because the hyaline cartilage must be broken down as ossification continues.
The Process by which a tree increases in girth and the process by which a human bone increases in girth are very similar.
-Growth accomplished by the addition of new layers to those previously formed resulting in an increase in diameter/girth.
- The growth in diameter of bones around the diaphysis occurs by deposition of bone beneath the periosteum.
- Osteoclasts in the interior cavity continue to break down bone until its appropriate thickness is achieved - at which point the rate of formation on the outside and degradation from the inside is constant.
- This constant modification of bone occurs in response to the forces acting upon it. i.e. Wolff’s Law, “Bone in a healthy person or animal will adapt to the loads under which it is placed.” - Julius Wolff (1836–1902)
-Increase in load = remodeling to resist load = Increase in thickness
-Decrease in load = decreased need to maintain bone mass = decrease in thickness.