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Anatomy & Physiology 2 > Embryology > Flashcards

Embryology Flashcards

1
Q

How many layers are there of the Trilaminar Disc?

A

Three

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2
Q

What are the layers of the Trilaminar Disc?

A
  • Ectoderm (outer)
  • Mesoderm (middle)
  • Endoderm (inner)
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3
Q

What do the trilaminar disc layers produce?

A

Everything comes from one of these three layers (i.e. organs and tissues). This is called the Trilaminar Layer or Disc. Cell layers that divide and turn in on themselves to become three layers.

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4
Q

What’s another term for the trilaminar disc layers?

A

Germinal Cell Layers

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5
Q

What does the Ectoderm (Germinal Cell Layer) produce?

A

Neural tissue, skin, nails & hair

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6
Q

What does the Mesoderm (Germinal Cell Layer) produce?

A

Muscle, bone, connective tissue, circulatory system

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7
Q

What does the Endoderm (Germinal Cell Layer) produce?

A

Internal organs

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8
Q

What does the ectoderm become after it invaginates?

A

Neuroectoderm (neural plate)

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9
Q

How is the Neuroectoderm (neural plate) formed?

A

Neuroectodermal tissues differentiate from the ectoderm and thicken into the neural plate. The neural plate border separates the ectoderm from the neural plate.

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10
Q

What has to happen for spinal vertebra to form in embryology?

A

Neuroectodermal tissues differentiate from the ectoderm and thicken into the neural plate. The neural plate border separates the ectoderm from the neural plate.

The neural plate bends dorsally with the two ends of the neural plate borders, which are now referred to as the neural crest

The closure of the neural tube causes disconnection of the neural crest from the epidermis. Neural crest cells differentiate to form most of the PNS.

The Notochord (mesoderm-derived) degenerates in the intervertebral discs.

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11
Q

Where do the eyes differentiate from?

A

From the neural tube we can get different areas. For the eyes we are interested in the Telencephalon but particularly the Diencephalon which are both in the Prosencephalon (forebrain) and contribute wholly to the cerebrum.

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12
Q

What is the brain split into in a 5wk old human embryo?

A
  • Prosencephalon (split into Telencephalon, Diencephalon)
  • Mesencephalon
  • Rhombencephalon (split into Metencephalon & Myelencephalon)
  • Neural Tube
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13
Q

What gives us the retina in embryology?

A

Forebrain (Prosencephalon) –> Diencephalon –> Retina (& thalamus & hypothalamus)

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14
Q

How many primary and secondary vesicles does the neural tube have?

A

3 Primary
5 Secondary

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15
Q

What is the Ectoderm split into?

A

Surface Ectoderm
Neuro-Ectoderm
Neural Crest Cells

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15
Q

What cells or layers contribute to ocular development in embryology?

A

Surface Ectoderm
Neuro-Ectoderm
Neural Crest Cells
Mesenchyme

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16
Q

What makes up the Mesenchyme?

A

Mesoderm and Ectoderm layer

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17
Q

When does the optic cup and lens vesicle form?

A

Day 22 is the first event in development of the eye. The primary optic (aka optic primordium) is the out pouching which appears in the neural fold when we start to develop the optic vesicle.

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18
Q

What is the Neuroectoderm?

A

Cross section through the diencephalon

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19
Q

How is the lens formed?

A

The Optic primordium (primary optic) appears in the neural fold. The Optic stalk is on the optic vesicle (formed on it after invagination), then they meet the surface ectoderm which cause each other to differentiate (form in different ways), which induces the surface ectoderm which becomes a thickened area in the middle called the lens placode (which forms the lens). As the lens placode and the lens invaginate on themselves (another folding) with the optic vesicle (invaginate) the lens placode becomes the lens vesicle and the optic vesicle becomes the optic cup.

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20
Q

What does the lens placode become?

A

The Lens Vesicle

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21
Q

What does the Optic Vesicle become?

A

The optic cup

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22
Q

What invaginate together to form the optic cup and lens vesicle?

A

Optic Vesicle & Lens Placode

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23
Q

Why is it important that the optic vesicle has 2 layers?

A

Optic vesicle has 2 layers because it starts as an invagination of neural ectoderm. This is important because it is 2 layered that contribute to different types of our retina = different origin, function and outcome. They are the Inner (neurosensory retina) and Outer layers (RPE - thinner) of the optic cup. This is why ectoderm gives us the retina.

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24
Q

What are the two layers of the optic cup called?

A

Inner - Neurosensory Retina
Outer - RPE (thinner)

This is how the ectoderm gives us the retina

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25
Q

How is the choroid fissure formed?

A

As the optic vesicle becomes the optic cup (with the optic stalk and cup forming by inwards invagination), they are sort of splitting left & right which forms a fissure within the optic vesicle called the Choroid Fissure.

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26
Q

What does invagination of the optic vesicle form?

A

The optic cup and optic stalk which also causes the vitreous body to form and a lens pit

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27
Q

What are neural crest cells and mesoderm together called?

A

Mesenchyme

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28
Q

Where does the choroidal fissure extend?

A

Extends the length of the forming eye from the anterior surface of the optic cup through to the optic stalk (which becomes the optic nerve)

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29
Q

What is the purpose of the choroidal fissure?

A

Within the choroidal fissure we have space for an artery (hyaloid artery) which is then enclosed by the choroidal fissure.

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30
Q

What is the purpose of the Hyaloid Artery?

A

To provide layers nutrition (blood supply) to the anterior structures of the eye.

At this point the stalk is still at the wall of the diencephalon

31
Q

Are the cornea and eyelids formed at the same layers?

A

Yes

32
Q

What happens to the hyaloid artery?

A

It degenerates and becomes the hyaloid artery just before birth.

Once the structures are fully formed we break down (degenerate) the hyaloid artery as we have blood vessels from tributaries; Central retinal artery and vein now supply. We get the hyaloid canal; non-pathological floaters is seeing the empty hyaloid canal like small squiggly lines. Pathological floaters will be pieces of retina falling into retina and new floaters.

33
Q

What is Cloquet’s Canal?

A

Cloquet’s canal, also known as the hyaloid canal or Stilling’s canal, is a transparent canal that runs from the optic nerve disc to the lens traversing the vitreous body.

34
Q

What else is the Hyaloid Canal known as?

A

Cloquet’s Canal or Stilling’s Canal

35
Q

Of the retina, how much has sensory properties?

A

Posterior 4/ 5th has sensory properties that perceive light (becomes the neurosensory layer, inner layer), anterior 1/5th does not contribute towards sensation (no nervous tissue; it overlaps the lens)

36
Q

What is Ora Serrata?

A

The demarcation between the anterior 1/5th and posterior 4/5th is visible in the adult eye which is known as the ora serrata

Ora Serrata doesn’t contribute to light and we don’t need it to because it’s too anterior. Posterior is the best part of vision which is the macular and fovea.

37
Q

When does macular development start?

A

4.5 months where the ganglion cell increases temporally to the optic disc

But foveal depression is seen at 7 months

By 4 months post-partum, the fovea is only 1 layer thick (cone nuclei)

38
Q

How does light travel through the retina?

A

Light travels UP through the retina before moving to the optic disc

39
Q

Why do we have pitting of the fovea?

A

Pitting = high resolution to stop the other layers from refractive=ng the light which is why it’s only one cell layer thick (only several microns)

40
Q

How does the optic nerve develop?

A

1) Hollow optic stalk connects the third ventricle of the forebrain and the cavity of the optic vesicles

2) As the choroidal fissure closes, a double layer of neuroectoderm is produced and closes in the optic disc and hyaloid artery)

3) Ganglion cell axons from the retina pass along the inner layer of the stalk

4) Eventually, the cavity between the inner and outer layers closes completely, forming the optic nerve

5)The optic nerve is a formation of ganglion cell layer axons that all travel and become the optic nerve which is surrounded by the meninges

41
Q

How does the lens form from the lens vesicle?

A

Starts as a vesicle, divides into itself to form the longitudinal primary lens fibres and then in a mature lens secondary fibres that are circular in shape develop.

42
Q

When do the lids, conjunctiva and lacrimal gland begin to develop?

A

From around day 42

43
Q

What do the lids, conjunctiva and lacrimal gland develop from?

A

Surface ectoderm which folds in itself around day 42

44
Q

How does the ciliary muscle develop?

A

From migrating neural crest cells (NCCs)

45
Q

At which point do the extraocular muscles develop? & from what layer?

A

Between days 28 and 70 from mesoderm

46
Q

How does the nasolacrimal system develop?

A

From neural crest cells (NCCs) cannulation at day 120

47
Q

When does the primary vascular vitreous start to develop?

A

As soon as the choroidal fissure closes

48
Q

What does the secondary avascular vitreous replace?

A

Replaced by secondary avascular vitreous as hyalocytes produce hyaluronic acid (mesodermal origin) and vascular vitreous regresses (day 210)

49
Q

When does the retina stop maturing?

A

The retina continues to mature until term (day 270)

50
Q

What starts developing around day 42?

A

Lids, conjunctiva and the lacrimal gland

51
Q

What develops from migrating neural crest cells?

A

Ciliary Muscle

52
Q

What develops between days 28 and 70 from the mesoderm?

A

Extraocular muscles

53
Q

What develops from neural crest cells (NCCs)?

A

Nasolacrimal system, cannulation at day 120

54
Q

What continues to mature until term (day 270)?

A

The retina

55
Q

What starts to develop as the choroidal fissure closes?

A

Primary vascular vitreous

56
Q

What are the neuroectroderm derivatives?

A
  • Retina
  • Optic Nerve
  • Epithelium of the Iris
  • Epithelium of Ciliary Body
  • Iris Smooth Muscle (Sphincter & Dilator Pupillae)
57
Q

What are the surface ectoderm derivatives?

A
  • Lens
  • Epithelium of Cornea
  • Epithelium of Conjunctiva
  • Epithelium of Skin of Eyelids
  • Glands of Eyelid, Lacrimal Gland
58
Q

What are the mesoderm derivatives?

A
  • Extraocular muscles, orbicularis oculi & LPS
  • Endothelium of the Ocular Blood Vessels
  • Sclera (temporal portion) & Schlemm’s Canal
  • Vitreous (secondary, from hyalocytes)
59
Q

What are the Neural Crest Cell (NCCs) derivatives?

A
  • Corneal Stroma & Endothelium
  • Sclera
  • Trabecular Meshwork
  • Ciliary Muscles
  • Melaoncytes
  • Schwann Cells
  • Meningeal Sheath of Optic Nerve
  • Vitreous (primary)
60
Q

Is a newborn hypermetropic or myopic?

A

Hypermetropic as the eyeball is relatively short

61
Q

When does the cornea reach adult size?

A

2 years old

62
Q

What structure of the eye continues growing throughout adult life?

A

Lens grows rapidly

63
Q

When does pigmentation of the iris stroma occur?

A

In the first few years of life and so eye colour can change in this time

64
Q

When do the embryonic membranes in the nasolacrimal system open at birth/shortly after?

A

Embryonic membranes in nasolacrimal system open at birth/shortly after which allows tearsto begin to flow

65
Q

Why do retinal ganglion cells overlying fovea migrate?

A

Retinal ganglion cells overlying fovea migrate allowing for improved VA

66
Q

What is Coloboma?

A

Happens when part of the tissue that makes up the eye is missing. It comes from the word “curtailed”. The eye develops quickly during a fetus’ first three months of growth. A gap, known as the choroidal fissure, appears at the bottom of the stalks that eventually forms the eye. This fissure generally closes by the seventh week of pregnancy. If it does not close, a coloboma or space forms.

67
Q

What can Coloboma affect?

A
  • Eyelid coloboma.
    A piece of the upper or lowereyelidis missing.
  • Lens coloboma.
    A piece of thelensis missing.
  • Macular coloboma.
    In this coloboma, themaculafails to develop normally.
  • Optic nerve coloboma.
    In this coloboma, theoptic nerveis hollowed out, reducing vision.
  • Uveal coloboma.
    Theuveais the middle layer of the eye. This coloboma can affect the iris, the colored part of the eye, giving it a distinct keyhole or cat-eye appearance.
  • Chorio-retinal coloboma.
    In this coloboma, part of theretinais missing.
68
Q

What issues do people with Coloboma experience?

A

Usually affects the inferonasal quadrant

Sometimes people are asymptomatic with Coloboma but others may experience problems with their vision such as visual loss, blindness, low vision or sensitivity to light (photophobia), keyhole or cat-eyed shaped pupil, nystagmus, larger than usual blind spot, reduced peripheral vision, difficulty with depth perception.

69
Q

What causes Coloboma?

A

Sometimes a coloboma is part of a genetic syndrome e.g. cat eye syndrome is a rare disorder that’s named after the distinctive shape of an iris coloboma is caused by a specific genetic mutation and occurs along with other physical abnormalities.

Can be caused by the PAX6 gene being mutated. Associated with the CHD7 gene

Can be present as part of CHARGE syndrome (coloboma, heart disease, atresia choanae, retardation of growth, genital hypoplasia, ear malformation)

70
Q

What is the PAX6 gene for?

A

ThePAX6gene belongs to a family of genes that play a critical role in the formation of tissues and organs during embryonic development.

During embryonic development, the PAX6 protein is thought to turn on (activate) genes involved in the formation of the eyes, the brain and spinal cord (central nervous system), and the pancreas.

71
Q

What happens if you don’t have a PAX6 gene?

A

Mutations can lead to:

  • Anophthalmia (no eye),
  • Anterior segment dysgenesis (anterior segment different from anterior chamber! It’s the anterior segment that’s affected which is anything to the lens which is divided into the anterior and posterior chambers; so anything from lens forward that’s the issue),
  • Congenital glaucoma (really big eyes on a baby can be a sign of glaucoma),
  • Aniridia (without iris or incomplete iris = can’t focus light) – depends on mutation level of which mutation we get
72
Q

What does OD, OS or OU stand for?

A

O D = Ocular Dexter = Right
O S = Ocular Sinister = Left (used to think the left was sinister in ye olden days)
O U = Both Eyes

73
Q

Which part of the optic cup gives rise to the neural retina?

A

Posterior portion of the inner layer (think of the eye as a closed system from sclera (outer) to inner eye (inner)

74
Q

What happens if the lens loses its transparency?

A

Halo around lights or almost night blindness if the lens loses its transparency. Not exclusive to cataracts.

75
Q

How does the cornea stay transparent?

A

Dehydrated & stroma layers at 90 degrees to each other

76
Q

How does the lens stay transparent?

A

Lens gets its transparency from both crystalline (uniform in terms of makeup) proteins and a lack of nucleus and organelles

Anatomy & Physiology 2 (12 decks)

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