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Embryology Exam III > Eye Development > Flashcards

Flashcards in Eye Development Deck (21)
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What are the major placoderms and what do they form?

-hypophyseal placode: primordium for Ratheke's pouch -> adenohypophysis

-olfactory placode: primordium for olfactory epithelium

-lens placode: primordium for lens

-trigeminal placode: primordium for CN V

-otic placode: primordium for inner ear

-epibrachial placode:primordium for sensory neurons supplying visceral structures (CN VII, IX, X)


What is the preplacodal region?

-encircles cranial plate

-induced by cranial mesoderm and neural tube

-involves activation of FGF pathway and inhibition of Wnt and BMP


What is the optic stalk?

-lateral evaginations of the diencephalon which enlarges distally to form the optic vesicle


What does the optic vesicle do?

-optic vesicle asymmetrically invaginate a to form a cup-like structure with a groove along one side of it

-the groove is the choroid fissure and it is continuous with the groove in the optic stalk

-the groove in the optic stalk is continuous with the posterior chamber of the eye

-the hyaloid artery uses the choroid fissure and optic stalk to pass into the posterior chamber of the eye


What does the initial expression of Pax6 produce?


-nasal placodes



What does Pax6 do in Drosophilia?

-turns of gene sequence needed for eye development

-absence of gene leads to eyeless mutant


What does Pax6 do in mammals?

-absences of gene results in early optic vesicle formation, but the rest of eye formation does not occur

-prospective lens ectoderm does not respond to induction by optic vesicle


How does Pax6 affect the optic stalk?

-high conc of Shh inhibit expression of Pax6

-low conc of Shh in distal optic stalk permits expression of Pax6 and development of optic vesicle -> leads to formation of retina

-high conc of Shh in proximal optic stalk decreases expression of Pax6 and induces expression of Pax2 -> this will provide guidance of axons of ganglion cells from retina


Explain how the lens is form.

-formed by lens. Fibers derived from inner pole of lens vesicle

-lens fiber cells are postmitotic, elongated cells made up mostly of crystalline proteins alpha, beta, and gamma

-rest of lens fiber cells are derived from mitotic activity of cuboidal cells of anterior lens epithelium

-retinal secretions, esp FGF, accumulate in the vitreous humor and stimulate formation of lens fibers


Explain how the cornea is formed.

-Pax6 is necessary for corneal induction

-underlying lens vesicle induces overlying ectoderm to transform from bilayered epithelium (simple cuboidal basal layer +flattened periderm) to transport multilayered structure


The invaginate optic cup forms both the _________ and ________ ____________.

-pigmented and neural retina


What is the pigmented retina?

-outer thin layer of the optic cup after invagination occurs


What is necessary for the differentiation of the pigmented retina?

-Otx2 stimulated by Shh


In terms of the fixation of retinal polarity, what is formed first?

-nasotemoral (anterior-posterior) axis is fixed first


How is the nasotemoral axis produced?

-established by gradients composed of ephrins and receptors

-ganglion cells differentiate first and bipolar neurons and cones differentiate last

-the spread of the gradient is from the center to the periphery

-Notch gene expression keeps cells from differentiating too early


What retinal axis is fixed second?

-dorsoventral axis


How is he dorsoventral axis fixed?

-established by the antagonistic actions of Shh and BMP, along with V entropic, Tbx-5, Pax2, and Vax2


What is anophthalmos?

-the absence of one of both eyes


What is microphthalamos?

-birth defect where one of both of the eyes are abnormally small, eye may be missing but tissue is still there


What is a coloboma?

-a hole in one of the structures of the eye, such as the iris, retina, choroid, or optic disc


What are ectodermal placodes?

-local thickening in the embryonic ectodermal layer that generally constitutes a primordial group of cells from which a sense organ or ganglion will develop