CTB 8 – Early development of the human head and face Flashcards
What occurs with phase 1 (0-3 weeks) i.u?
Cell proliferation and migration
What occurs with phase 2 (3-8 weeks) i.u?
Morphogenesis and differentiation
Formation of organs and body structures
What are teratogens?
Substances that introduce birth defects
How many weeks i.u. do craniofacial defects can develop?
4-8 weeks
How does anencephaly develop?
Absence of brain tissue as neural tube fails to close
How can anencephaly develop?
Folic acid deficiency or high retinoic acid (vit A) levels can interfere with the Hox gene expression
How many days i.u. does the embryo head folding begin?
21 days
What organ develops at 16 days i.u?
Heart
What is the function of the yolk sac in an embryo?
Provides nutrients
What is formed from the neural plate in an embryo?
Brain
What organ develops at 18 days i.u?
- Oropharyngeal membrane develops, separating the future mouth from the pharynx
- This membrane acts as a transient cell signalling centre to oral cavity
What is the biological term for mouth?
Stomodeum
What organ occurs at 22 days i.u?
Formation of the stomodeum
Heart rotates
What length is an embryo at 30 days?
4mm
What happens at 30 days i.u?
- Rudiments (anlagen) of most organs are established
- Oropharyngeal membrane starts to breakdown
- Pharyngeal arches (PA) 1,2,3 become prominent
What cells are outcompeted by other cells in the PA, in the face?
Neural crest cells can out compete the mesodermal cells in the face
What cells from the pharyngeal arches form muscles and bones?
Mesodermal cells
What is the formation of neural crest cells?
- Cells are induced between neuroectoderm and epidermis induced by a morphogenic gradient
- Neural plate invaginates – forming neural folds and then an open tube
- Neural folds fuse forming the neural tube – neural crest cells migrate along predetermined pathways
- Migration continues and become specialised cell types
What is the function of the Hox gene in PA1?
There is a lack of Hox gene, therefore cranial neural crest cell are specified by Hox gene code
What type of bone is the hyoid bone?
Composite bone
What is eagles syndrome? And the symptoms?
Calcified/elongated styloid process
Causing pain and difficulty swallowing
What is the facial development at 4-5 weeks?
- Formation and growth of an unpaired frontonasal prominence – mesenchymal cells in the frontonasal prominence
- Nasolateral and nasomedial processes form the nasal pit
- Mandibular processes form grows and merge and the same for the maxillary processes
How is the nasal placode formed?
Thickening of the overlying ectoderm
What is the facial development at 5.5-6 weeks?
- Frontonasal prominence recedes as nasomedial processes grow strongly
- Nasolateral processes and maxillary processes grow – fusing to form the nasolacrimal duct, cheek and alar base of the nose
What is the facial development at 7-8 weeks?
- Merging of nasomedial processes
- Further growth of the maxillary processes
- Forming – central part of the nose, upper lip and primary palate
- Upper lip formed from the maxillary processes laterally and in the midline from the nasomedial processes (PHILTRUM)
How is the philtrum formed?
Fusion between the maxillary processes
Define merging.
- Elimination of a furrow between 2 processes – by mesenchymal cell proliferation
- Always been connected
Define fusion.
- 2 processes are separate to begin with
- Contact between epithelial cells of the process’s triggers fusion of the epithelial cell sheets and then elimination of epithelial cells
What does the maxillary process contribute to the facial structures?
- Maxilla
- Upper lateral lip
What does the mandibular process contribute to the facial structures?
- Mandible
- Lower lip
What does the medial nasal processes contribute to the facial structures?
- Medial part of the nose
- Upper medial lip
- Primary palate
What does the lateral nasal processes contribute to the facial structures?
Lateral part of the nose
What processes fail to come together in a median cleft lip?
Failure of merging of med nasal processes
What processes fail to come together in a bilateral cleft lip?
Failure of fusion between maxillary processes and med nasal processes
What is the most common cleft lip?
Bilateral cleft lip
What processes fail to come together in an oblique cleft lip?
Failure between maxillary and lateral nasal processes
What processes fail to come together in a lateral cleft lip?
Failure merger between mandibular and maxillary process
What is micrognathia?
Small mandible
What is agnathia?
No mandible
What is Pierre Robin Sequence presented in?
Micrognathia, cleft lip and glossoptosis
What is glossoptosis?
Medical condition and abnormality which involves the downward displacement or retraction of the tongue. It may cause non-fusion of the hard palate, causing cleft palate
What are the symptoms of teacher collins syndrome?
- Hypoplasia (under development) of mandible (macrostomia) and facial bones (e.g. cheek)
- Ear malformations
- Cleft palate
- Abnormal dentition
- Slanting of palpebral fissures
- Eyelid coloboma
How does treacher collins syndrome develop i.u?
Failure of neural crest cells to migrate into craniofacial region – cells apoptose
What is the mutation in treacher collins syndrome?
Heterozygous mut in Tcof1 in ribosome biogenesis
