Growth And Development Unit A: The Nature Of Craniofacial Growth

Front 1

What are the three possibilities when growth occurs?

Back 1

(1) Hyperplasia
(2) Hypertrophy
(3) Secretion of extracellular material

Front 2

What is hyperplasia, hypertrophy, and secretion of extracellular material?

Back 2

hyperplasia - increase in number of cells
Hypertrophy - increase in cell size
Secretion of extracellular material - increase in size independent of the number or size of the cells themselves.

Front 3

How does soft tissue grow?

Back 3

Grwoth of soft tissues occurs mostly by a combination of hyperplasia nad hypertrophy. These processes go on within the tissues at all points - interstitially.

Front 4

Can bone growt interstitially?

Back 4

Yes, through endochondral ossification., in which cartilage is doing the growing and is then replaced by a bone.

Front 5

What grows interstitially?

Back 5

Interstitial growth is a characterstic of uncaclified cartilage and other soft tissues.

Front 6

If interstitial growth does not happen in calcified tissue, how does it grow?

Back 6

(1) Significant growth occurs only at surfaces, not within the calcified mass.
(2) Growth of hard tissue, therefore, occurs in two ways:
(a) Direct addition and (b) replacement

Front 7

What is direct addition?

Back 7

Direct addition to the calcified tissue on its free surfaces occurs through the activity of cells in the periosteum (the soft tissue membrane covering the bone). Formation of new cells occurs in the periosteum and the extracellular material is secreted and then calcifies into bone.

Front 8

How does "replacement" of soft tissue work?

Back 8

Many of the bones are modeled in cartilage originally, and then cartilage model is replaced by bone --> endochondrol ossification.

Front 9

Describe the process of endochondral ossification.

Back 9

(1) Bone formation on the surface of the cartilage.
(2) Invasion of blood vessels that produce a hollowed-out center with bone formation in that area

Front 10

The bone grows longer by what?
It growes wider by what?

Back 10

(1) The bone grows longer by endochondral ossification. and (2) It grows wider by direct formation of new bone on the surface.

Front 11

How does endochondral bone formation differ from direct bone formation?

Back 11

For endochondral bone formation, a complex maturational patter of cartilage is required. In direct bone formation by the periosteum, osteoblasts secrete their matrix directly in connective tissue, and it calcifies there without an intermediate formation of cartilage.

Front 12

What are the two major functions of the remodeling of the internal structure?

Back 12

(1) It serves as a means of adapting the bone to mechanical stress and (2) it also makes calcium and phosphate ions available for exchange with blood.

Front 13

Can the bone get bigger through remodeling?

Back 13

An Haversian System constantly remodels during life. This internal modeling, however does not significantly contribut to growth or change the shape of the bone. The bone cannot get bigger through remodeling.

Front 14

Describe the skeletal growth of the cranial vault.

Back 14

* Made up of a number of flat bones that are formed directly by periosteum
*No endochondral ossification.
*Apposition of bone at the sutures is the major mechanism for growth at the cranial vault

Front 15

What are fontanelles?

Back 15

Fontanelles are open spaces that are relatively widely separated by connective tissues. Their presence allows for considerable deformation at birth.

Front 16

Describe the skeletal growth of the cranial base.

Back 16

*Endochondral ossification - 8 weeks in utero: cartilage extends beneath the brain from the nasal capsule anteriorly to the occipital area posteriorly.
*Intramembranous Ossification-at 12 weeksossification centers have appeared in the midline cartilage structures.
*Lengthening of the cranial base is largely due to endochondral replacement.

Front 17

What are the three most important synchondroses?

Back 17

(1) spheno-occipital
(2) inter-sphenoid
(3) spheno-ethmoidal

Front 18

What is the difference between a suture and a synchondrosis?

Back 18

Similarities: both are thin, soft tissue areas between adjacent bones
Differences:
*Synchondroses is filled with cartilage; undergoes endochondral ossification, is actively growing. Sutures are filled with connective tissue; undergoes direct ossification; and grows reactively.

Front 19

Describe the skeletal growth of the maxilla.

Back 19

*bone moves downward and forward, new bone is added at the sutures and tuberosity.
*anterior surfaces resorb, while the roof of the mouth moves further down by remodeling
*remodeling of the roof of the mouth means,tooth eruption is unpredictable when judging how far away it is from the palatal vault.

Front 20

Describe the skeletal growth of the mandible.

Back 20

*Mandible has a cartilage model.
*Chin moves downard and forward
*Chin grows longer by apposition of bone on the posterior surface
*Ramus grows higher by endochondral replacement at the condyle and by surface remodeling.
*overall the mandible grows UPWARD And BACKWARD but the effect of this growth is a DOWNWARD and FORWARD translation of the chin.

Front 21

Describe the skeletal grwoth of the alveolar processes of the maxilla and the mandible.

Back 21

As the mandible grows downward, away from the maxilla, it creates more space between the jaws. As the jaws grow, the teeth are actively erupting. As they erupt they bring alveolar bone with them, so the alveolar processes become taller.