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ChM > Chapter 4: Ocular Development > Flashcards

Chapter 4: Ocular Development Flashcards

1
Q

How many germ layers are present during gastrulation?

A
  • Ectoderm
  • Mesoderm
  • Endoderm
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2
Q

What germ layers do the eyes and orbit develop from?

A

The eyes and orbit develop from all three germ layers, with neural crest cells making a substantial contribution

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3
Q

What is the earliest sign of ocular development?

A

Formation of the Lens Placode is the first sign of ocular development

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4
Q

What is the Lens Placode?

A

small surface ectoderm thickenings on both sides of the developing head

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5
Q

What are optic vesicles? When during embryogenesis do they develop?

A

optic pits that fill up to form pouches that are derived from ectoderm. They connect to the forebrain via a narrow neck. They develop around the same time as the lens placode.

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6
Q

What is the optic cup?

A

bi-layered invagination of the optic vesicles that occurs after they come into contact with the surface ectoderm

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7
Q

What are the two layers of the optic cup?

A

the inner layer, which becomes the neurosensory retina

the outer layer, which becomes the RPE

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8
Q

How does the Lens begin to form?

A

As the optic cup forms, the surface ectoderm begins to invaginate

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9
Q

How does lens formation contribute to development of the anterior segment?

A

As the surface ectoderm is invaginating, the area b.w the optic cup and surface ectoderm is invaded by migrating mesodermal and neural crest cells

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10
Q

What are the steps in Lens Formation?

A

Lens Plate= proliferation of surface ectoderm
Lens Pit= inward invagination of lens plate
Lens Vesicle= Pit deepens, closes, and detaches from surface

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11
Q

What is the Lens Vesicle?

A

a single layered structure composed of cuboidal cells surrounding a large lumen

sits in the optic cup

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12
Q

Describe the formation of the primary lens fibers

A

Posterior Lens epithelium proliferates, elongates, and fills in the optic vesicle

Called the embryonal nucleus

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13
Q

How does the lens capsule form?

A

the remaining epithelial cells form the lens capsule, which is composed of type IV collagen

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14
Q

What do the zonular fibers develop from?

A

they develop as a part of the vitreous and ciliary body (via mainly ectomesenchymal cells)

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15
Q

What does the cornea develop from?

A

Corneal epithelium develops from surface ectoderm, and the stroma/endothelium develop from neural crest derived ectomesenchymal cells

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16
Q

What cell layers does the Uvea develop from?

A

Develops from a combination of neural ectoderm, mesoderm, and neural crest cells

Neural Crest cells–pigmented epithelial components

Mesoderm–spincter and dilator muscles, non-pigmented parts of the uvea (i.e. iris stroma and ciliary muscle)

17
Q

What are the initial two layers involved in retinal development?

A

Neural retina forms from the inner layer of the optic cup

RPE forms from the outer layer of the optic cup

18
Q

What germ layers are involved in formation of the vitreous?

A

Neural Ectoderm– contribute to primary vitreous CT fibers

Mesoderm–hyaloid vasculature

19
Q

Describe the formation of the primary vitreous?

A

Forms a central conical structure that contains the hyaloid vasculature and is surrounded by secondary vitreous

20
Q

What is the significant of the Neural Retina Leucine Zipper (Nrl)?

A

is a transcription factor of the Maf subfamily, is an intrinsic regulator of Rod photoreceptor development

21
Q

What are the first retinal cells to differentiate?

A

Ganglion Cells

22
Q

When do the ILM/ELM of the retina form?

A

They form when cells cease proliferating and begin to differentiate

23
Q

What is the only pigmented tissue in the body that does not form from neural crest cells?

A

RPE, which forms from proliferating pseudo stratified columnar epithelial cells

24
Q

What structures does the optic nerve develop from?

A

the optic stalk, which is the narrow neck that connects the optic cup to the forebrain

is initially formed from neuroectodermal cells surrounded by neural crest cells

25
Q

What germ layer/s form the Sclera?

A

formed from ectomesenchymal elements

26
Q

When do the scleral spur and Tenons Capsule form?

A

They begin to form at the time of EOM insertion

27
Q

Orbital development involves key contributions from which germ cell layers?

A

all of them–ectoderm, mesoderm, endoderm, and neural crest cells

28
Q

What are the EOMs formed from?

A

They form from paraxial and prechordal mesoderm

29
Q

Signals from what primitive ocular structure are necessary for proper migration of neural crest cells into the eye surrounding tissues?

A

The optic cup–interactions b.w optic cup, mesoderm, and neural crest cells are crucial for proper development and organization

30
Q

What are some consequences of delayed innervation of EOM during development?

A

Innervation by the wrong nerve (occurs in Marcus Gunn Jaw Winking syndrome and Duane Syndrome)

Can also cause premature differentiation into CT (i.e. fibrosis)

31
Q

When do bone/fat/cartilage/CT of the orbit develop? What do they develop from?

A

They develop by the 4th WGA from frontonasal and maxillary processes of neural crest cells that occupy the space around the optic cup

32
Q

What is the only bone that isn’t membranous during development? And what does it consist of?

A

The sphenoid bone is the only bone that isn’t membranous, and its made of cartilage instead.

33
Q

When does ossification of orbital bones occur during development?

A

Ossification occurs around the 3rd month of gestation

34
Q

What does the upper eyelid develop from?

A

it develops from a proliferation of surface ectoderm in the region of the future outer can thus at 4-5 WGA

35
Q

What type of cells eventually infiltrate the eyelids and form the palpebral muscles?

A

Mesodermal mesenchyme

36
Q

When does the lacrimal gland begin to develop?

A

6-7 WGA

37
Q

When does tear production by the lacrimal gland begin?

A

occurs >20 days after birth

38
Q

What are homeobox genes?

A

they are the blueprint for embryonic program–serve as the main regulators of downstream development

39
Q

What is the PAX6 gene? What is its significance relating to ocular development?

A

A homeobox gene that appears to be the master switch for ocular development

ChM (59 decks)

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