Craniofacial embryology Flashcards
How do transcription factors lead to congenital malformations?
TF bind to DNA to control expression of genes
TF bind to regulatory DNA (promotores and enhancers) to influence the level of expression of downstream genes.
How are many different body parts organised during development?
Segments - different segments having a different fate for example the spinal cord and mesodermal somites, our medull and the pharyngeal arches
This in influenced by patterning - spatial significant gene expression influencing the function of tissue based on its location relevant to secretion sites of signalling hormones.
What is the basic link between developmental genes and cancer?
Cancer is developmental genes turned on in the right place but at the wrong time, causing inappropriate and uncontrolled division.
What is the process of gastrulation?
When the bilaminar embryo disk develops into the trilaminar disk.
The primitive streak forms: composed of the primitive groove (gap), the primitive pit (cranial end) and the primitive node (thickening).
The epiblast invaginates through the primitive groove (this is regression)- resulting in the formation of three layers - replacing the hypoblast and epiderm layer - the ectoderm, the mesoderm and the endoderm
What is the process of neuralation?
The neural plate is a thickening of ectodermal cells (neuroectoderm).
The edges of the plate begin to grow upwards and inwards - this forms the neural folds and the neural groove
At the tip of the folds are neural crest cells
The folds eventually join together - forming a tube like structure - called the neural tube
Before fusion - migratory neural crest cells are released - these contribute to structures in the face, SANS and peripheral nervous system.
The cranial and caudal core at the end of the tube will eventually fuse - this is the formation of the CNS.
What is the role of placodes in craniofacial development?
Placodes are ectodermal thickenings
Differentiate into neurons - forming specialised sense organs
Examples - lens (eyes), otic (ear), olfactors (nose)
What are neural crest cells and what are some important structures that they become?
Is a population of multipotent neuroectodermal cells that migrate from the dorsal neural tube
Pax7 helps regulate neural crest developments - peripheral nervous system, DRG, Schwann cells, pericytes etc, PANS post ganglion neurons, some cranial nerve ganglia
In the head what structures are importantly formed from the neural crest cells?
Musculoskeletal tissues - through an epithelial to mesenchymal transition - forming ectomesenchyme (cartilage and bone)
(Note vagal, trunk and sacral neural crest cells do not)
Describe the complex morphogenesis of the face
Cranial NC and placodes undergoe extensive meopthogenesis - cell migration and shaping regulated by transcription factors - mainly migrate anteriorly and fuse on the midline.
Forms the pharyngeal arches - separated by pharyngeal clefts on the ectodermal surface and pharyngeal pouches on the endodermal surface.
What structures are associated with each pharyngeal arch? (generalised)
A pharyngeal artery
An arch cranial nerve
Arch cartilage
How many pharyngeal arches are found in humans?
five - these are labelled
1,2,3,4,6 (five disappears early in development)
Why in relation to its emrbyology is the innervation of the face so complicated?
The pharyngeal arches are innervated when they are formed by the respective cranial nerves
This innervation is the carried during the complex morphogenesis - when the arches may overlap and form different structures.
What is the key role of the 1st pharnygeal arch?
Innervates muscles of mastication - trigeminal nerve.
What is the role of the 2nd pharyngeal arch?
Innervates the muscles of facial expression - the facial nerve
With reference to the pharyngeal arches explain why the innervation of the tongue is so complicated?
Arches 1-4
Formed from the 1st - trigeminal nerve for general sensation to enter 2/3 of tongue
3rd pharyngeal arch - facial nerve (tase to anterior 2/3)
4th pharyngeal arch - glossopharyngeal (tase and general sensation to post 1/3)
What is important about the spectrum of Shh activity?
Normal
Less than normal - cyclopia - fusion of structures in midline (failure of midline prominence to develop and lateral features move inwards/fuse)
More than normal - hypertelorism/disprosopus - duplication of structures move away from the midline
