Embryology of the Eye and Ear

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Where do ears develop from embrologically?

Rhombencephalon
What is otic placode and when does it start to develop?
- First indicator of developing ears
- About 3-4 weeks gestation
What characterizes otic placode?

Thickening of the surface ectoderm on both sides of the rhombencephalon
What are otic pits and when does it develop?
- When otic placodes invaginates it become otic pits
- At about 4 weeks
What do otic pits become with further development?

Otic vesicles (aka auditory vesicles)
What do otic vesicles later develop into?

Membranous labyrinth- ventral and dorsal structures of inner ear: saccule, cochlear and utricle, semicircular canals, endolymphatic duct
What structures are part of the external ear?
- Auricle
- External auditory meatus
- Tympanic membrane
What does auricle develop from?

Six small swellings or proliferations of the 1st and 2nd pharyngeal arches called auricular hillocks
When does the eardrum form?

By the 7th month
What are the layers that make up the tympanic membrane?
- Ectodermal lining of the floor (meatal plug)
- Intermediate layer of mesoderm that forms fibrous stratum
- Endodermal epithelial lining of tympanic cavity
Where is tympanic cavity of the middle ear derived from?

First pharyngeal pouch
What forms the eustachian tube?

Medial portion of the tympanic cavity narrows
Which two ossicles were initially derived from mesenchymal condensation and cartilage from 1st pharyngeal arch?

Malleus and incus
What is stapes derived from

Same mechenchymal condensation as malleus and incus but cartilage from the 2nd arch instead of 1st
When do the ossicle show?

8th month, prior to that they were embedded in the mesenchyme
What does the cochlear duct form?

It forms the organ of corti
What is the function of the organ of corti?

Balance and equilibrium
When do eye start to develop embryologically?

Day 22 from a pair of shallow optic grooves
What are optic vesicles?

Optic grooves on the sides of the forebrain which later forms elevations that are the optic vesicles
What makes up the lens placode?

Optic vesicle make contact with the overlying surface epithelium make up the lens placode
What is the optic cup?

Optic vesicles and lens placode invaginate and forms the optic cup
What other structure beside the optic cup do the invagination of the lens placode and optic vesicle form?

Underlying pigment and neural layers of the retina: including rods and cones, ganglion and bipolar cells
When does the optic cup start to form?

Around week 4-5
Which is the master gene in eye development that is expressed in optic cup and lens placode?

PAX 6
What is the gene expressed predominantly in the optic stalk?

PAX 2
Where is the iris develop from?

Anterior portions of the outer pigment and inner neural layers of the optic cup
What is the histologic appearance of the iris?

Two layers of columnar epithelium
What differentiates into the sclera?

Mesenchyme that surrounds the optic cup
What is the name of the outer vascular layer that is next to the cup and below the sclera?

choroid abuts
What forms the cornea and what is its outer layer tissue derived from embryologically?
- Mesenchyme,
- Outer layer is derived by ectoderm
Where is the vitreous chamber found and what is the fluid inside of it called?

Behind the lens and it is a gelatinous fluid called vitreous humor
What embryological layer forms the eyelid and conjunctival sac?

Ectoderm

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Embryology of the Eye and Ear

Description

NMSK Exam 4

Updated

2018-11-28T19:50:55Z