Craniofacial Biology Flashcards
What is Developmental Biology?
The study of the processes by which organs grow and develop.
Define mitosis
the process by which a cell replicates its chromosomes and then segregates them, producing two identical nuclei in preparation for cell division
Define meiosis
a type of cell division in sexually reproducing organisms that reduces the number of chromosomes in gametes
Define apoptosis
the process of programmed cell death
In embryology, what is induction?
the process in which an undifferentiated cell is instructed by specific organisers to produce a morphogenic effect
What are the 3 stages of prenatal development and their time lines?
preimplantation period (first week)
embryonic period (second to eighth week)
fetal period (third to ninth month)
Define the proliferation stage in the embryonic period
a physiological process of cell division that occurs in almost all tissues, resulting in an increase of the number of cells.
Define the differentiation stage in the embryonic period
the process of development during which embryonic cells specialise and diverse tissue structures arise.
Define morphogenesis in embryonic period
the process of development of specific tissue structure or shape
What point in time does the second period (embryonic period) of prenatal development start?
beginning of the 2nd week to the end of the 8th week
what physiological processes make up the embryonic period?
induction
proliferation
differentiation
morphogenesis
maturation
What is the purpose of the 5 processes of embryonic period?
cause the structure of the implanted blastocyst to become, with further development, an embryo.
they also allow the teeth, orofacial structures and other organ structures to develop in the embryo
Define cytodifferentiation
the development of different cell types
Define histodifferentiation
the development of different histologic tissue types within a structure
Define morphodifferentiation
the development of the differing morphology, which makes up its structure or shape, for each organ or system
When does the bilaminar embryonic disc develop from the blastocyst?
second week
when does the trilaminar embryonic disc develop from the bilaminar disc
third week
What week of prenatal development does the disc undergo embryonic folding?
week 4
Tissue interactions appear to be associated with atleast 2 general types of phenomena, what are they?
Instructive
Permissive
What is organogenesis?
the production and development of the organs of an animal or plant
define instructive tissue interactions
the ability of one tissue to determine specific patterns of morphogenesis and differentiation that will develop in an associated tissue. (tells other tissues what to do)
Define permissive tissue interactions
the ability of an interacting tissue to provide certain conditions that is necessary for its committed partner tissue to progress to full expression of its predetermined phenotype. (drives the devlopment of tissue)
an organ starts as an epithelial placode
placodes are embryonic structures that give rise to structures.
epithelial placode is a condensation of which germ layer
epithelial placode is a condensation of the ectoderm layer
What are the 3 distinct regions of the embryonic origins of the skull?
desmocranium
chondrocranium
viscerocranium
When does the posterior fontanelle close?
The posterior fontanelle usually closes by age 1 to 2 months
It may already be closed at birth
When does the anterior frontanelle close?
The anterior fontanelle usually closes sometime within 7 to 19 months
What are fontanelles?
soft spots on an infant’s head where the bony plates that make up the skull have not yet come together
What is craniosynostosis?
A group of disorders where there is a premature fusion of the sutures
What is Apert syndrome?
Brain is expanding at the front and back instead of transversely due to the premature fusion of the lambdoid and coronal sutures
What is turricephaly?
Turricephaly (Tower Head) is a descriptive term for a distinctive head shape often observed in children with syndromic forms of craniosynostosis, in particular, those with Apert syndrome
What is crouzon syndrome?
A type of craniosynotosis
Prevents the brain expanding resulting in protrusion of the eyes and expansion of the front area of the skull
What is plagiocephaly?
Due to premature sagittal and coronal fusion
The head is flattened on one side, causing it to look asymmetrical
What is Trigonocephaly?
premature closure of the metopic suture causing the inability of the frontal bones to grow laterally, thus forming a triangular forehead with an obvious or subtle osseous ridge
What is cloverleaf skull?
an abnormal configuration of the calvaria classified as craniosynostosis, consisting of premature ossification of cranial sutures
What is Treacher Collins Syndrome (TCS)?
A disorder of craniofacial development which effects the way the face develops,
What causes TCS?
the abnormal formation of the first and second branchial arches during 5-8th weeks of human fetal development, leading to profound facial dysmorphism
TCS is both genetically and phenotypically heterogenous, true or false?
True
What type of TC0F1 mutation, leading to TCS ,is the majority of cases?
Deletions
The loss-of-fuction mutations in which gene is responsible for most cases of TCS?
TCOF1
What may the TC0F1 mutations result in which is small and functional?
truncated treacle protein
What protein does TCOF1 encode for?
Treacle
Less common mutations in which genes can cause TCS
POLR1D and POLR1C
What do POLR1D and POLR1C encode for?
subunits of the enzymes RNA polymerase I and III, important in RNA synthesis
what is the importance of the treacle protein?
it is active during early embryonic development in structures that become bones and other tissues in the face.
it also plays a key role in pre-ribosomal processing and the making of the ribosome
What facial bones are most affected by TCS?
Underdeveloped cheek bones, eye sockets, small jaw and chin (micrognathia)
What facial features can be seen in someone with TCS?
eyes that slant downwards, sparse eyelashes, eyelid coloboma
What is the main concern in newborn TCS patients?
respiratory failure due to airway narrowing from craniofacial malformation
Which gene mutation involved in TCS are inherited via an autosomal pattern (not a sex chromosome)
TC0F1
What is the chondocranium also known as?
cranial base
When does the development of the head, face and oral cavity usually take place and end?
Starts around week 4
Usually finishes around week 10
What is the pharyngeal apparatus?
It is made up on the arch, the clefts (grooves), pouches and membranes and gives rise to muscle, cartilage, nerve and blood supply
What are the 4 fundamental aspects of developmental biology?
Proliferation/Growth size
Pattern formation
Morphogenesis - shape
Differentiation - type
What is pattern formation?
The cells differentiating into the correct tissues and the right place
What are dynamic, reciprocal and sequential interactions?
Sequentially - they happen at a specific time
Reciprocal - one cell will control what happens to another and vice versa
Dynamic - Happens between 4-10 weeks (very quick)
What are signalling centres?
the organiser of whats going to occur in that place
What is the signalling gradient?
Only at the right points will the cells make a tissue
What is true fusion?
2 things at either sides of the head need to fuse together, eg. palate fusion
What is cell migration?
Cells move into the area in order to produce what they need to
How many primary germ layers are there and what are they
3
Ectoderm
Mesoderm
Endoderm
Neural crest/Ecto-mesenchyme (not a true layer)
What is the ectoderm layer?
The outer most layer, gives rise to the skin and neural tube
Comes from the epiblast layer
What is the mesoderm layer?
Layer in between the ectoderm and endoderm
Forms from migratory cells of the epiblast layer
Forms just about everything else
What is the endoderm layer?
Innermost layer of the 3 primary germ layers
Forms the gut
Comes from the hypoblast layer
When do the branchial arches start to develop?
days 24/25
What effects how the branchial arches differentiate into different tissues?
The spinal column
What does pharyngeal arch 1 give rise to?
the mandible and maxilla (lower part of face)
Meckel’s cartilage
What does pharyngeal arch 2 give rise to?
Reichart’s cartilage
What is the purpose of Meckel’s cartilage?
Acts as a jaw support during early development and a template for the later forming bones
By week 20 there are only remnants of it left
What is the stomatodeum?
a depression between the brain and the pericardium in an embryo
This forms the oral cavity
