Lec2_Growth & Development Concepts Flashcards
Define ontogenetic plasticity:
Ability of structure to become variably expressed without adversely affecting function.
Based on growth pattern, does the head stay proportionate to the body over time?
No, the growth pattern reflects a changing proportionality.
The physical arrangement of body is a pattern of spatially proportioned parts at any time point.
Basically, you grow into your head size. By the time one reaches adulthood, the head is 12% decreased in terms of proportion to the rest of the body.
In our lecture, what two structures do we compare for cephalocaudal gradient of growth.
What is the general rule for cephalocaudal gradient of growth?
We compare the maxilla and the mandible. They have different growth patterns.
Cephalocaudal gradient of growth = the further from the top of the head, the more that structure grows.
What is differential tissue growth?
In general, this is a growth rate and duration that is cell specific.
The example we use is a part of the cephalocaudal gradient of growth: maxilla growth vs mandibular growth.
Maxilla @ same rate as head, mandible @ same rate as body.
Can you predict growth?
Yes, based on the known patterns. However, there is variability.
Look at the genetics to aid predictability. There is similar facial form to the growth of other family members and others of the same ethnicity.
Note that 1 std deviation contains all the normal variations.
How might you predict an obese child will grow differently than a non-obese child?
Obese children:
- normal to accelerated growth rate
- lower levels GH, normal levels of IGF-1 = grow faster
- Advanced craniofacial growth
- increased mand length (aka prognathic jaw)
- reduced upper ant. face height
What is endochondral bone formation? Where does it take place in the skull (just purely endochondral)?
In the skull, the cranial base results from endochondral bone formation.
Cartilage models the area first.
Also takes place in the long bones of the body.
What is intramembranous bone formation? Where does it take place in the skull (just purely intramembranous)?
In the skull, the maxilla and cranial vault result from intramembranous bone formation.
Coalescing cells populations and periosteal tissue form the bone. There is never a cartilage model or template.
With what type of growth is the mandible made?
BOTH via endochondral and intramembranous ossification.
The mandible is intramembranous (like the maxilla) everywhere EXCEPT the condyle.
The condyle is endochondral.
What does Meckel’s cartilage form?
Forms the mandible body, but NOT the condyle.
Summary:
By which process are flat bones of the skull and the cranial volt formed?
The mandible?
The cranial base?
Flat bones & cranial volt: By intramembranous ossification.
Mandible: both intramembranous and endochondrial.
Cranial base: endochondral.
What are the growth SITES on the cranium?
The area of active bone deposition, at the periosteum.
There are many growth sites!
What are the growth CENTERS on the cranium?
Growth centers are the area of growth control.
Force to separate tissue.
There are very few growth centers!
Ex: epiphysis of long bone
synchondrosis of cranial base (allows the skull to grow appropriately)
Growth site vs growth center: which is which when the brain grows and the skull grows with it?
Growth center = the brain! The brain causes the bone growth (or is it only the synchondrosis –> this is the debate!)
Growth site = cranial bones.
Note that a synchondrosis can be both a center and a site.
What are the growth sites on the maxilla?
The maxilla has 2 growth sites:
- the lateral portion (intramembranous ossification)
- the nasal septum (chondrocranium)
What are the growth sites on the mandible?
The mandible is a bit complicated. Formed from periosteum of developing mandible.
There are growth sites at the borders:
- Posterior border of ramus, inferior and superior borders of the body grow with appositional growth.
- The anterior portion of the ramus has resorption.
This combination is what results in a lengthening of the jaw. Relative to the temporal fossa, there is growth at the condyle upward and backward.
What is translational growth of the mandible?
This combination of apposition and resorption growth is what results in a lengthening of the jaw.
Relative to the temporal fossa, there is growth at the condyle upward and backward.
Note: a child’s radiograph might show a molar inside the ramus. This is ok because the anterior ramus will be resorbed and the translational growth pushes the ramus back and the jaw lengthens so that the molar is in the correct place at the correct time.
What is a the mandibular condyle? A growth site or center?
Studies show it is NOT a growth center.
Take the cartilage out of condyle = no growth.
What are other main growth CENTERS (control)?
The epiphyseal plates of long bones. Cartilage extends and then is ossified to create length.
Synchondrosis of the cranial base. Double growth plates where there is cartilage on both opposing sides.
–> The most important 3 are spheno-ethmoid, inter-sphenoid, and sphen-occipital chrondroses.
What type of growth is cortical drift?
Appositional growth (addition and subtraction). Forms the correct shape/size.
- Apposition on the outside (at perioteum)
- Resorption on the inside (intramedullary)
What type of growth is translocation?
Displacement growth. Helps place bone in correct position (like the mandible).
What are the 3 theories of growth control?
What are the 3 theories of growth centers:
- Bone/Periosteum
- Cartilage
- Soft Tissue/epigenetics
- Define the bone growth control theory:
1960s, Sicher
Genetic control at bone/periosteum, so growth modification isn’t possible.
–> now discarded because we CAN modify the growth of bone (ex: just separate sutures)
- Define the cartilage growth control theory:
Scott
Genetic control at cartilage level.
Experiments to remove cartilage and see if growth stops.
Long bones = cartilage control
Synchondroses = some cartilage control
Nasal septum = cartilage control
Condylar cartilage = NO cartilage control
–>not conclusive for all cases, but still important.
