Ortho module 1 part B Flashcards
How does endochondral ossification work?
Cartilage is growing and then replaced by bone.
How does cartilage grow during endochondral ossification?
Hyperplasia occurs in the area below the fibrocartilage that covers the surface of the bone.
Below that hypertrophy occurs with the increasing size of maturing cartilage cells.
The cartilage cells being formed release extracellular material that lies between cells and separates them.
Can bone grow in the same way as cartilage?
No, the calcified surroundings make it hard for the cells of the hard tissue to grow..
How does hard tissue grow?
2 ways:
Direct addition of calcified tissue on free surfaces. (through activity of cells in the periosteum)
Replacement of soft tissue that grew before calcification occured.
How does endochondral ossification take place?
Bone formation occurs on the surface of the cartilage followed by invasion of blood vessels creating a center of bone formation.
Ingrowth of blood vessels leads to an ossification center in the cartilaginous caps on either end but a band of cartilage remains between the diaphysis and epiphysis. This is called the epiphyseal plate.
The bone grows longer as the cartilage of the epiphyseal plate grows, matures, and is replaced by bone.
Eventually cartilage growth slows down compared to bone formation and the bone reaches maximum size.
How is bone growth during endochondral ossification different to periosteal apposition of bone?
For endochondral bone formation, a complex maturational pattern of the cartilage is required. In direct bone formation by the periosteum, osteoblasts secrete their matrix directly in connective tissue, and it calcifies there without any intermediate formation of cartilage.
How do complex shapes form at the tips of long bones such as at the tuberosities and the heads?
Growth at the epiphyseal plate requires corresponding changes in the surface of the bone. Not all the surface changes can be met by adding new bone. Because the contour of the long bones calls for a knob on the end, a continuous remodeling of the surface is required as endochondral growth occurs, meaning that bone must be added to the surface in some areas and removed in others.
The periosteum, therefore, must and does contain cells whose purpose is to remove bone as well as cells to make it, and there is a balance between apposition of bone in some areas and resorption in others. Addition of bone in some areas while old bone is removed in others is an essential component of the growth process.
This entire process is bone remodeling.
What are the functions of remodeling?
2 major functions:
Adapting bone to mechanical stresses.
Makes calcium and phosphate available for exchange in the blood.
Where does exchange of calcium and phosphate ions occur with the blood in bones?
Near periosteal surfaces and around haversian systems
What are the divisions used for the cranium and the face when discussing growth?
The cranium is divided into the cranial vault and base
The face is divided into the naso-maxillary complex and the mandible.
What is the cranial vault made up of? How does it grow?
It is made up of a number of flat bones that are formed directly by periosteum.
No endochondral bone formation, instead there periosteal activity at the surface of the flat bones both inner surface and outer surfaces and the periosteum lined spaces between them.
What are fontanelles and how do they close up?
Bones in a baby’s head are widely separated by open spaces with connective tissues. The spaces are called fontanelles. The presence of fontanelles allows considerable deformation at birth to allow passage through birth canal.
They close up by apposition of bone along the edges of the fontanelles which eliminate these open spaces quickly after birth.
How does the cranial base form and grow?
The bones of the cranial base are initially formed in cartilate then transformed into bone. This happens at about 8 weeks in utero before any bone formation has begun.
An essentially solid bar of cartilage extends beneath the brain from the nasal capsule anteriorly to the occipital area posteriorly. This cartilage is called the chondrocranium.
Laterally beneath the brain, growth at sutures and surface remodeling becomes more important but the cranial base is essentially a midline structure and the synchondroses are important growth sites.
What is the difference between a synchondrosis and a suture?
Both are thin soft tissue areas between adjacent bones however:
Synchondroses have cartilage inside. A band of proliferating cartilage cells are located in the center of the synchondroses and a band of maturing cartilage extends in both directions away from the center.
A suture only has periosteum and connective tissue.
The cartilage at
synchondroses is capable of active, independent growth while the connective tissue at sutures only reacts to what happens in its surroundings.
How does the maxilla grow?
Postnatally, the face grows downward and forward from the cranium, and the maxilla must move a considerable distance.
In the case of the maxilla, there is no pre-existing cartilage, so maxillary growth is a matter of sutures and surface remodeling.
