Embryology Flashcards
Abnormal ear shape or size
Microtia
Agenesis of the ear
Anotia
What are some causes of congenital neurosensory deafness?
- Abnormal development of cochlea, cranial nerve VIII or brain stem
- Rubella in first trimester will damage the organ of Corti in 30% of case
What are some causes of congenital conduction deafness?
- Persistent meatal plug; seen in first arch syndrome
- Fixation of footplate of stapes
- Malleus and incus often involved in first arch syndrome
Rare disorders where one or both eyes are small and absent.
Anopthalmia and microphthalmia
Defective closure of the choroid or optic fissure.
Postioned in the infero-nasal quadrant, reflective of the location of the optic fissure during fetal development.
Congenital coloboma.
Cloudy cornea from abnormally high intraocular
pressure usually due to malformed drainage apparatus. Genetic mutations
account for ~85% of cases. May also result from rubella infection.
Congenital glaucoma
Cloudy or opaque lens. May be inherited, caused by rubella virus or a result of congenital galactosemia.
Congenital cataracts
Surrounds the developing foregut. It is the source of mesenchymal tissue that will form the head & neck, face, palate & nasal cavity structures. Pouches are evaginations on this inside of this.
Pharyngeal apparatus
What is formed from Meckel’s cartilage, all First Arch derivatives?
- Mandible
- Malleus
- Incus
- Spine of the sphenoid
- Sphenomandibular ligament
First arch syndrome caused by deficiency of neural crest cells migrating into the arch. Results in mandibulofacial dystosis, abnormal first arch structures. Hypoplasia of upper and lower jaw. Conductive hearing loss.
Treacher Collins Syndrome
First Arch Syndrome. Micrognathia + large posteriorly placed tongue resulting in airway obstruction.
Pierre Robin Sydrome
What is formed from Reicherts cartilage?
- Stapes
- Styloid process
- Stylohyoid ligament
- Lesser cornu
What is derived from the first pharyngeal pouch?
- Auditory tube (epithelial lining)
- Tympanic or middle ear cavity (epithelial lining)
- Mastoid air cells
What is derived from the second pharyngeal pouch?
Palatine tonsils (epithelial component)
What is derived from the third pharyngeal pouch?
- Thymus (ventral)
- Inferior parathyroid glands (dorsal); these have the farthest to travel, thus there terminal location is highly variable. Tough to locate surgically.
What is derived from the fourth pharyngeal pouch?
- Superior parathyroid glands (dorsal)
- Ultimobranchial bodies (ventral) AKA parafollicular cells of the thyroid.
Genetic and/or environmental micro deletion of Chr. 22q11.2 No thymus or parathyroids.
“CATCH 22” – a partial list of symptoms
Cardiac abnormality
Abnormal facies
Thymic hypoplasia
Cleft palate
Hypocalcemia
22 - deletion/abnormality of chromosome 22
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DiGeorge Syndrome.
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What pharyngeal membrane (separates pouches from clefts) is the only one that persists?
1st membrane becomes the tympanic membrane.
What are the muscles and nerve associated with the first pharyngeal arch?
Trigeminal nerve
- Muscles of mastication
- Tensor tympani
- Tensor veli palatini
- Mylohyoid
- Anterior belly of digastric
*Meckel’s cartilage
What are the muscles and nerve associated with the second pharyngeal arch?
Facial nerve
- Muscles of facial expression
- Posterior belly of digastric
- Stylohyoid
- Stapedius
*Reichert’s cartilage
What are the muscles and nerve associated with the third pharyngeal arch?
Glossopharyngeal nerve
-Stylopharyngeus
What are the muscles and nerve associated with the 4th and 6th pharyngeal arch?
Vagus nerve
4th arch: Superior Laryngeal Nerve
- Muscles of the soft palate (except tensor veli palatini)
- Muscles of the pharynx (except stylopharyngeus)
- Cricothyroid
- Cricopharyngeus
6th arch: Recurrent branch of the laryngeal nerve
- Intrinsic muscles of the larynx (except cricothyroid)
- Striated (upper) muscles of esophagus
What is derived from the first cleft?
External auditory meatus (epithelial lining)
What happens to the 2nd, 3rd, and 4th clefts?
They normally disappear; lateral cervical (branchial) cyst or fistula occurs when it persists
What pharyngeal arch is the tongue derived from?
Arches 1-4. This is why you get the innervations of Trigeminal, Facial, Glossopharyngeal, and superior branch of laryngeal nerve (vagus).
