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Craniofacial Dev
Face formation, syndromes, skull dev
| Term | Definition |
|---|---|
| What tissue type is thyroid gland and what is it's development? | Endodermal proliferation, originates at tip of foramen caecum of developing tongue (caudal to 1st arch) -> mgirates inferiorly to final site (anteroinferior to larynx) |
| What is the failure of thyroid migration? | Lingual thyroid -> gland remains at tongue base -> thyroglossal cysts form in midline as thyroglossal duct remnants -> moves up/down when swallowing |
| What is a branchial cyst? | Failure of 2nd arch to overgrow 3rd/4th arches -> cervical sinus remnant -> swelling anterior to SCM -> may form a fistula that is asymptomatic until infection -> opening elevates upon swallowing |
| Function and formation of parathyroid glands? | Regulate extracellular Ca2+ uptake HOM, form from pharyngeal pouch endoderm (3rd/4th pouches) -> express Gcm2 TF (glial cells missing-2) for development -> produce PTH |
| When does face formation take place? | Wk 3 -> oropharyngeal membrane appears, wk 4 -> oropharyngeal membrane breaks down to form stomodeum, wk 5-10 facial processes develop |
| What is the stomodeum? | Opening btwn future oral cavity and foregut |
| What are the facial processes? | Frontonasal process -> medial/lateral nasal processes, pair of mandibular and maxillary processes |
| What is the frontonasal process? | Covers forebrain -> NCC mesenchyme origin -> medial nasal process contributes to medial nasal tissue and philtrum, lateral nasal process contriubtes to lateral nasal tissue |
| What are the tissues of the 1st pharyngeal arch? | Pair of mandibular processes (mandibular tissue), pair of maxillary processes (maxillary tissue and palatal processes) |
| What is the cause of a missing philtrum? | Defect in fusion of 2 medial nasal processes in midline |
| What is the cause/consequence of a cleft-lip? | Maxillary swelling doesn't fuse w/ medial nasal process -> problems when feeding/speaking (articulation) -> otitis media (oral cavity continuous w/ nasal cavity -> infections spread to middle ear) |
| What is the cause/consequence of a cleft-palate? | Incomplete (maxillary processes) palatine shelf fusion -> velopharyngeal insufficieny (air leaks into nasal cavity -> hypernasal voice/articulation errors) -> delayed teeth development -> trouble feeding (upright - gravity prevents milk through nose) |
| What is the cause/consequence of facial cleft? | Maxillary swelling doesn't fuse w/ lateral nasal process -> macrostomia (wide mouth) -> eye on affected side is drawn down |
| What is the process of palate formation? | Wk 5 -> Maxillary/lateral/medial processes meet, wk 6/7 -> primary palate too short to separate oral/nasal cavities, wk 7-8 -> medial palatal processes extend from maxillary processes -> fuse in midline by wk 10 as definitive palate |
| What is holoprosencephaly? | Forebrain of embryo fails to develop into 2 hemispheres in wk 5 due to failure of neural tube segmentation -> fetal death in utero -> synophthalmia (cyclops eye), hypotelorism (reduced distance btwn eyes), cebocephaly (single nostril), no corpus callosum |
| What are consequences of fetal alcohol syndrome? | Maternal alcohol during pregnancy (teratogen) -> short height, low body weight, poor cordination, small head, learning difficulties, hearing/visual problems, smooth philtrum -> can cause holoprosencephaly |
| What is the cause of Treacher Collins syndrome? | Mutations in TCOF1 gene -> ribosome biogenesis, chr segregation, O2 stress regulation -> autosomal dominant mandibulofacial dysostosis -> NCC deficit in 1st/2nd arches -> underdevelopment of facial bones/mandible |
| What are the symptoms of Treacher Collins syndrome? | Cleft palate, ear abnormalities -> EAM atresia (1st pharyngeal cleft - conductive hearing loss), absent ossicles (malleus/incus from 1st cleft, stapes from 2nd cleft - bilateral conductive hearing loss), choanal atresia (blocked nasal/nasopharynx route) |
| What is the cause of CHARGE syndrome? | Heterozygous mutation in CHD7 gene -> autosomal dominant -> transcriptional regulator for NCC formation -> failure of choroid fissure fusion (coloboma - missing iris) |
| What are the symptoms of CHARGE syndrome? | Coloboma of eye, heart defects, atresia of choanae, retardation of growth/development, genital hypoplasia, ear anomalies (external ear defects, malformed ossicles, hypoplastic cochlea, missing semicircular canals) |
| What is the cause of diGeorge syndrome? | Chr 22q11 deletion -> Tbx1 gene expressed in pharyngeal ecto/endo/mesoderm -> NCCs misrouted |
| What are the symptoms of diGeorge syndrome? | Minor craniofacial defects, thymus/parathyroid gland agenesis -> vulnerable to infections, cardiovascular abnormalities (persistent truncus arteriosus -> failure to form aorticopulmonary septum) |
| What bones have chondrocranium contribution? | NCC derived olfactory capsule -> ethmoid, NCC derived optic capsule -> sphenoid bone lesser/greater wing, mesoderm derived otic capsule -> sphenoid body, occipital base, petrous temporal |
| Flate plate bone development process? | Develop as intramembranous/dermal bones of skull vault -> ossify directly from dermis w/out cartilage IM in utero -> connect at sutures |
| Which dermal bones are NCC derived? | Frontal, nasal, lacrimal, zygomatic, maxilla, incisive, mandible, sphenoid, squamous temporal, hyoids |
| Which bones are mesoderm derived? | Parietal, petrous temporal, occipital |
| What is the purpose of the fontanelles? | Membranous structures separating vault bones -> allow skull molding during birth, protect cranial base, allow skull reshaping/brain growth |
| Anterior fontanelle description and clinical observations | Large rhomboid shaped gap palpable at junction of parietal/frontal bones -> closes mid 2nd year -> indicative of child health (increased intracranial Pa -> scalp bulges, dehydration -> tissues sucked down) |
| Posterior fontanelle description | Small triangular shaped gap at junction of parietal/occipital bones -> closes 3 months after birth |
| Skull development timeline | 3 months -> posterior fontanelle closes, mid-2nd yr -> anterior fontanelle closes, 5th yr -> skull increased to almost adult size (accommodates rapidly enlarging brain), 4th decade -> sutures ossify |
| What determines skull shape/size? | Determined by early brain growth, sutures widen in response to tension from intracranial Pa -> no genetic contribution (only dependent upon internal cranial environment) |
| What is microcephaly? | Brain grows inadequately due to mutations/external toxins -> small cranial vault did not expand to reflect small brain -> scalp fails to grow while face develops at normal rate -> intellectual impairment, disturbance in motor functions |
| What are symptoms of hydrocephalus? | CSF accumulation in brain -> increased intracranial Pa -> cranial contents excessively voluminous -> enlarged cranial vault -> headaches, double vision, poor balance, mental impairment |
| What is the cause and treatment of hydrocephalus? | Neural tube defects/aqueductal stenosis, meningitis, brain tumours -> shunt surgical placement, 3rd ventriculostomy alows CSF to flow directly to basal cisterns |
| What is craniosyntosis? | Premature suture closure (before 4th decade) -> closure at 1 suture causes increased growth at other suture -> deforms brain/skull, early fusion of multiple sutures -> increase brain Pa |
Created by:
vykleung
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