Mechanisms of post-natal growth

• why should the face grow during childhood?

  - increase ability for respiration for oxygen supply for growth

  - make room for permanent teeth
• What are the 3 regions of the craniofacial complex?

  - Cranial vault

  - Cranial Base

  - Face

  
• What is the ratio of the cranial vault to the face at birth?

  8:1

  
• What is the ratio of the cranial vault to the face in adulthood?

  3:1

  
• What is the cranial vault characterised by at birth?

  6 fontanelles

  
• What are fontanelles and why are they important?


  Space between infant skull bones, they allow for rapid brain growth and moulding of the skull for delivery through the birth canal

  
• Is the midline of the face united at birth?

  No, but it will do so within the first 2 years

  
• What are some other features of the craniofacial complex at birth?

  - bones are thin

  - Nasal septum & orbits align

  - Face is small- virtual absence of paranasal air sinuses & small facial bones

  - Base of mandible- obtuse

  
• Why is the cranial vault advanced relative to the face?

  Cranial vault reflects growth of brain, which is much faster. Face growth follows body growth

  
• when is most of cranial vault development complete at?

  by the age of 10
• What are endochondral bones?

  Most bones of the skeleton; they have been developed from cartilage.

  
  

  - resistant to force and pressure

  - respond very slowly (so are not altered)

  
• What are intramembranous bones?

  Broad, flat bones of the skull that form layers of connective tissue; bones that develop from embryonic membranes

  
  

  - respond quickly to tension and pressures so can be manipulated to increase growth rapidly

  
• the cranial vault is intramembranous.

  TRUE/FALSE

  TRUE
• What are the different mechanisms of growth?

  - Endochondral growth

  - intramembranous growth
• describe Endochondral growth


  Growth plates- interstitial growth

  Remodelling- appositional growth
• describe intramembranous growth

  growth at suture- important during early childhood

  Remodelling- most important method of growth in late childhood & adolescence

  Secondary cartilage- condylar cartilage (until adolescence)
• What do neural crest cells give rise to?

  All skeletal structures in your face
• What does the paraxial mesoderm give rise to?

  Cranial vault (except frontal bone)
• what are the two embryonic origins of the cranial vault?

  - neural crest

  - paraxial mesoderm
• What does cranial vault development look like?

  A- initial ossification of frontal and parietal bone

  B- bone expands

  C- coronal suture separates the frontal and parietal bone

  
• What are the different fontanelles and sutures?

  fontanelles: large gaps where several bones of the cranial bone meet

  (allows bones to slide over eachother when baby is born and allows the skull to be compressed)

  
  

  sutures: fibrous bands of tissue that connect the bones of the skull

  
• What is displacement in terms of bone growth?

  Soft tissues are growing, they displace the bone & the bone grows in compensation to fill the gap
• what two mechanisms are required for displacement?

  - sutural growth

  - remodelling
• What happens in sutural growth?

  The expanding brain forces the cranial vault bones apart, increasing the gap or width of the suture, and then the osteoblast progenitors within this suture grow & differentiate to fill in that gap

  
• What is remodelling?

  Osteoblasts deposit matrix on outside of bone and bone matrix is removed from inside. This hollows the bone, making it lighter & thicker

  
• brain defects linked to skull growth:

  
  

  What is microcephaly?


  Abnormally small head and brain

  
• brain defects linked to skull growth:

  
  

  What is macrocephaly?

  Abnormally large head and brain

  
  

  e.g. hydrocephaly- a neurological disorder caused by an abnormal buildup of cerebrospinal fluid in the ventricles (cavities) deep within the brain. This excess fluid causes the ventricles to widen, putting harmful pressure on the brain's tissues (expansion of the brain)

  
• brain defects linked to skull growth:

  
  

  How can hydrocephaly affect head size?

  There's an expansion of the brain and cranial vault so the head would be larger
• brain defects linked to skull growth:

  
  

  What is craniosynostosis?

  Non-uniform growth of brain and skull (brain grows but skull doesn't grow/expand appropriately)

  - Often from premature cranial suture closure
• brain defects linked to skull growth:

  
  

  What are the different types of craniosynostosis?

  which suture is affected will determine shape of the skull

  
• what type of bone is the cranial base?

  endochondral bone

  - so it develops through a cartilage intermediate
• what 3 pairs of cartilages does the cranial base in the embryo develop as?

  3 pairs of cartilages along the midline:

  
  

  Parachordal cartilage- gives rise to base of occipital bone

  Hypophyseal cartilage- develops into body of sphenoid

  Pre-chordal cartilage- will fuse & develop into ethmoid bone

  
• what bones are developing around sense organs?

  endochondral bones:

  - optic capsule

  - olfactory capsule

  - alisphenoid bone
• What does the otic capsule do?

  Protects the developing otic vesicle
• What does the olfactory capsule do?

  Protects the developing nose
• What does the alisphenoid bone do?

  Provides some protection to the eye
• what happens as the initial endochondral bones of the cranial base develop and grow?

  they will fuse along the midline and eventually mediolaterally

  - growth now begins limited to growth plates at particular regions of the growth plates
• What 3 growth plates does the cranial base grow at?

  Spheno-ethmoid (fused by 3-5 yrs)

  Intersphenoid (fused at birth)

  Spheno-occipital (closed by 20 yrs)

  
  

  - once the growth plate has closed and ossified there is no longer any growth

  
• where do the growth plates direct growth|?

  along the anterior-posterior axis
• Describe the growth & fusion of the spheno-occipital cartilage growth plate?


  - Growth is bidirectional

  - Fusion (synostosis) starts at 14yrs for females & 16yrs for males