4 - Ocular Development Flashcards
2 feuillets embryonnaires impliqués dans le développement de l’oeil
Ectoderme
Mésoderme
Feuillet embryonnaire le plus impliqué dans le développement de l’oeil et ses sous-types
Most of the eye forms from different types of ectoderm:
* Surface ectoderm
* Neuroectoderm
* Neural crest cells (très grande contribution)
Causes de misactivation of genetic cascade (3)
- Gene mutations
- Oocyte abnormalities
- Exposure to teratogens
Conséquences de misactivation of genetic cascade (2)
Embryologic abnormalities that, in the most severe cases, are embryonic lethal or, in less severe cases, give rise to congenital abnormalities
Feuillets embryonnaires (et localisation)
- Ectoderm (superficial layer of cells)
- Mesoderm (middle layer)
- Endoderm (inner layer)
In addition, vertebrate embryos have an ectomesenchymal cell population that arises from neuroectoderm at the dorsal edge of the neural tube.
* These cells, known as neural crest cells, are transient migratory stem cells that can form tissues with ectodermal and mesodermal characteristics
D’où proviennent les neural crest cells?
In addition, vertebrate embryos have an ectomesenchymal cell population that arises from neuroectoderm at the dorsal edge of the neural tube.
- These cells, known as neural crest cells, are transient migratory stem cells that can form tissues with ectodermal and mesodermal characteristics.
Pourquoi les syndromes that arise from neural crest maldevelopment often involve the eye as well as facial, dental, and calvarial abnormalities (ex. Goldenhar syndrome)?
Neural crest cells make key contributions to eyes, orbital tissues, facial, dental, and cranial structures.
Nom de l’étape où il y a création des 3 feuillets embryonnaires durant le développement
Gastrulation
Que se passe-t-il a/n de l’ectoderm après l’étape de la gastrulation
Following gastrulation, the ectoderm separates into
* Surface ectoderm
* Neuroectoderm
À quel AG début le développement de l’oeil?
At 22 days, the optic primordium appears in neural folds.
Décrire les étapes de la neurulation
- Optic pits
- Optic vesicules
- Optic stalk (futur NO)
- Optic cup (invagination)
À quel AG début l’embryogénèse des yeux
Semaine 4
Que se passe-t-il au Jour 27 de l’embryogénèse?
By day 27,
* The optic vesicle starts to form in the neural ectoderm
* The lens placode forms in the surface, ectoderm
* The primary vitreous then extends to the future posterior lens has the hyaloid artery
Que se passe-t-il au Jour 29 de l’embryogénèse?
- The neural ectoderm invaginates to form the bilayer optic cup
- The surface ectoderm invaginates to form the lens vesicle
Que se passe-t-il au Jour 37 de l’embryogénèse?
By day 37,
The optic cup becomes more defined.
* The inner layer forms the neural retina
* The outer layer forms the retinal pigment epithelium.
The surface ectoderm has fully invaginated to form the lens and is separated from the future corneal epithelium.
* The posterior lens cells grow forward (as the primary lens fibers) which will form the embryo nucleus.
Next, the neural crest cells form additional corneal layers in two waves.
* The first wave for the future corneal endothelium.
* The second wave forms the future corneal stroma.
Que se passe-t-il au Jour 44 (sem 7) de l’embryogénèse?
By day 44, the conjunctival fornix in the eyelids start to form.
Que se passe-t-il au Jour 55 (sem 8) de l’embryogénèse?
Over the next 11 days (Jour 55, sem 8),
* The eyelids then come together and fuse, maintaining a conjunctival sac.
Que se passe-t-il 4e mois de l’embryogénèse?
By the fourth month,
- Folds of the ciliary processes appear.
- The iris sphincter develops.
- The hyaloid system starts to regress
- The Schlemm canal appears.
Que se passe-t-il 5e mois de l’embryogénèse?
At month five,
* The eyelid starts separate
* The eye has really taken shape.
* You can see the layers of the cornea, the anterior chamber, the lens, the sclera, the choroid, and the extra ocular muscles.
Tissu embryonaire du cristalllin
Surface ectoderm
Comment évolue/se développe le cristallin une fois la lens vesicle formée (post invagination de l’ectoderme de surface)
- The lens vesicle is a single- layer structure composed of cuboidal cells surrounding a large lumen, and it sits within the optic cup.
- The anterior cells remain cuboidal and single layered throughout life
- The rest of the lens epithelium cells become elongated, and their proliferation fills the optic vesicle.
- These posterior cells form the primary lens fibers that eventually form the embryonal nucleus.
- The remaining outer cells create a true basement membrane known as the lens capsule
Location of fissure closure
The location of fissure closure correlates with the inferonasal quadrant, which is where colobomas are clinically found.
Structure précédant le NO
The optic nerve develops from the optic stalk, the narrow stalk that connects the optic vesicle with the forebrain.
Tissu embryonaire de la vascularisation hyaloïde
The hyaloid vasculature develops from mesodermally derived cells.
Stades de développement du vitré
- The mesoderm gives rise to the hyaloid artery, which is contrained within the primary vitreous. (This vascular system supplies the tuinca vasculosa lentis).
- The secondary vitreous form from hyalocytes as the primary vitreous regresses.
- The zonular fibers develop from the tertiary vitreous.
À quel âge début le lacrimal gland (reflex) tear production?
- Lacrimal gland (reflex) tear production does not begin until 20 or more days after birth.
- Therefore, newborn infants cry without tears.
