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HESP645 Exam 1 > Embryology > Flashcards

Embryology Flashcards

1
Q

When does the trilaminar embryo form?

A

-First 3 weeks of development

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2
Q

What are the three layers of the trilaminar embryo?

A
  • Ectoderm
  • Mesoderm
  • Endoderm
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3
Q

What arises from the ectoderm?

A
  • Neural tissue

- Surface of epithelium

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4
Q

What arises form the mesoderm?

A

-Most connective tissues of the body: muscle, bone, cartilage

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5
Q

What arises from the endoderm?

A

-Lining epithelium of the gastrointestinal, urogenital, & respiratory tracts

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6
Q

What layers of the trilaminar embryo give rise to the sense of hearing?

A

-All three

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7
Q

What does the otic vesicle give rise to?

A
  • Give rise to all inner ear structures, including:
    • Cochleovestibular neurons from future CN VIII
    • Auditory system (cochlear duct)
    • Vestibular system (SSCs)
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8
Q

Describe early otic vesicle development.

A
  • Undergoes evagination (folding out) and takes on elongated shape
  • Divides into an utricular-saccular area and a tubular extension (endolymphatic duct)
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9
Q

The inner ear arises from what layer of the trilaminar embryo?

A

-Ectoderm

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10
Q

The middle ear arises from what layer of the trilaminar embryo?

A

-Endoderm

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11
Q

What do the pharyngeal arches (bracchial arches) form?

A

-Main anatomical structures of the head & neck, including components of the middle and outer ear

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12
Q

Describe pharyngeal (bracchial) arch development.

A
  • By week 4, 5 bracchial grooves or “gill slits” appear in the lower head and neck region on the lateral surfaces
  • Inside the embryo, corresponding pharyngeal pouches develop
  • The collective structures are identified as “arches” (series of 5)
  • Pharyngeal arches 1 and 2 are main contributors to the middle and outer ear
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13
Q

Describe where the ossicles arise from.

A
  • 1st branchial arch:
    • Responsible for most of the body structure of the malleus and incus
  • 2nd branchial arch:
    • Lenticular process of the incus
    • Handle of the malleus
    • Stapes
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14
Q

Describe ossicle development.

A

MALLEUS & INCUS

  • By 8.5 weeks, the incus and malleus have a cartilaginous adult-like form
  • By weeks 15-16, ossification begins to occur in the malleus and incus, which have nearly reached completion by the 32rd week

STAPES

  • Stapes continues to develop as a cartilaginous structure until week 15
  • Stapes does not begin to ossify until week 18 and continues to develop through life even after ossification is complete
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15
Q

Describe auricle development.

A
  • The auricle develops during the 3rd or 4th week from the 1st and 2nd bracchial arches
  • The auricle is derived primarily from the 2nd branchial arch (tragus arises from 1st)
  • Week 6: 6 tissue hillocks (thickenings) form which impacts the ultimate shape and configuration of the adult auricle
  • Weeks 7-20: Auricle continues to develop, moving form original ventromedial position to be slowly displaced laterally by the growth of the mandible and face
  • Week 20: Auricle is in the adult shape but continues to grow in size until 9 years of age
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16
Q

Describe external auditory meatus development.

A
  • Weeks 4-5: derived from 1st bracchial groove
  • Week 8: primary auditory meatus sinks toward the middle ear cavity and becomes the outer 1/3 of the auditory canal, surrounded ultimately by cartilage
  • The ectodermal groove deepens towards the tympanic cavity from the external surface until it meets a meatal plug
  • Mesenchyme grows between the meatal plug and the epithelial cells of the tympanic cavity
  • The solid meatal plug keeps the EAC closed until week 21
  • Meatal plug disintegrates and forms a canal, with the innermost layer of meatal plug epithelium becoming the squamous epithelial layer of the TM
  • The EAC continues to develop until the 9th year
  • At birth, the floor of the EAC has no bony portion (not completed until ~7 year)
  • In infants, the EAC is short and straight
  • In adults, the EAC is longer and curved
17
Q

What are the 3 categories of abnormalities?

A
  • Genetic
  • Environmental
  • Unknown
18
Q

Describe genetic abnormalities.

A
  • In human development, most major genetic abnormalities are thought to be within 1st 2 weeks of development as the zygote:
    • Chromosomal
    • Translocation of chromosomal segments
    • Single gene mutation
19
Q

Describe environmental abnormalities.

A
  • Teratogens (maternal effects)
  • Maternal behavioral factors (i.e. smoking, alcohol, drugs)
  • Bacteria, virus, parasites
  • Hyperthermia
  • Environmental contaminents
  • Radiation
20
Q

What external ear abnormalities could be indicative of middle ear bone abnormalities?

A
  • Thickened lobes: abnormal incus and stapes
  • Small cupped ears with absent cartilage: mennonite genetic absences of incus and stapes
  • Absent superior crus: congenital ossicle fixation
21
Q

What is anotia?

A
  • Unformed ear canal
  • Due to pharyngeal arch hillocks failing to form
  • Also impacts EAC and middle ear bones
  • Known genetic associations:
    • Manibulofacial dyostosis (Treacher Collins)
    • Hemifacial microsomia
    • Congenital aural atresia
22
Q

What are some physical features associated with Treacher Collins?

A
  • Downward slanting eyes
  • Small jaw and chin
  • Alters development of facial bones and tissues
23
Q

What is microtia?

A
  • Smaller cup ear or overfolded auricle
  • Over 40 different associations including syndromes:
    • Hearing and vision abnormalities
    • Neurological abnormalities
    • Clefting of the face and palate
    • Musculoskeletal abnormalities
  • May also be caused by maternal drugs (thalidomide, retinoic acid)
24
Q

What are some less common external ear abnormalities?

A
  • Auricular fistulas and sinuses
  • Auricular appendages
  • Stenosis of EAC
25
Q

What external ear characteristics are indicative of Fetal Alcohol Syndrome?

A
  • Lower or uneven external ear position

- “Railroad track” ear

26
Q

What is “railroad track” ear?

A

-Auricle has a curve at the top part of the ear, which is underdeveloped and folded over parallel to the curve beneath

27
Q

Describe absent ossicles.

A
  • Can be associated with a range of conditions/syndromes (i.e. dwarfism, achondrogenesis)
  • Most common bones to be absent: incus, stapes
28
Q

What cochlear abnormalities of the oval window are associated with stapes fixation?

A
  • X linked deafness
  • Branchio-oto-renal syndrome
  • Beckwith-Wiedemann Syndrome
29
Q

What prenatal infections could lead to inner ear abnormalities?

A
  • Rubella: cochlear duct, saccular development
  • Cytomegalovirus (CMV)
  • Toxoplasmosis
30
Q

What are some genetic conditions associated with cochlear and SSC abnormalities?

A
  • Trisomies
  • Michel aplasia: absence of inner ear labyrinth
  • Pendred syndrome: abnormalities of the cochlea, enlarged vestibular aqueduct, thyroid enlargement (goiter)
31
Q

How is persistent stapedial artery associated with middle ear abnormalities?

A
  • The stapedial artery initially lies between the foramen of the stapes and is lost before birth
  • If the regression fails, the persistent artery can affect conduction through the ossicular chain
  • May be seen in hemifacial microsomia
  • Middle ear cavity can be delayed in formation or size, leading to various conduction effects
  • May occur with BOR syndrome

HESP645 Exam 1 (10 decks)

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