Embryology

Question 1

Gastrulation week 3

Answer 1

Epiblast is yolk sac
Hypoblast is embryo
Epiblast on caudal midline invaginate through primitive streak displacing hypoblast turning it into endoderm.
Epiblast becomes ectoderm
Primitive streak is initial gastrulation event as establishes embryo body axis
creates ectoderm, mesoderm,endoderm

Question 2

Neurulation day 18-28

Answer 2

formation of neural tube
from sheet of ectoderm
Neural tube is precursor to CNS
Neural ectoderm aka neural plate- includes neural crest cells and neural tube
Forebrain of neural tube is where eye development happens

Question 3

Development of eye weeks 3-10

Answer 3

Eye is derived from neural tube
Day 22- optic vesicles which expand laterally have stalk like connections to CNS which will narrow and become optic nerves
Contact of optic vesicles with surface ectoderm induces formation of lens placed
Optic vesicle invaginate- becomes optic cup
Lens placoderms invaginates - becomes less vesicles

Question 4

Optic cup

Answer 4

Optic cup - outer layer- RPE layer produces melanin
inner layer- neural retina contains ganglion cells, interneurons, photoreceptors
Mesoderm enclosed in cup which forms hyaloid artery
Choroid fissure also involved

Question 5

Hyaloid artery

Answer 5

Provides nutrients to developing lens
regresses in 3rd trimester- 7th month
Regresses and leaves croquets canal in vitreous and becomes central retinal artery
Persistent hyaloid artery- Remnants on optic disk is Bermeisters pupila
Mittendorfs dot- pin point like scar on posterior surface of lens
Free remnants in vitreous can be seen as floaters

Question 6

Somites

Answer 6

Paired segments along the neural tube
develop into muscles of body
Indicator of precise embryo age

Question 7

Where sections come from

Answer 7

Surface ectoderm - lens and cornea
Mesenchyme- choroid and sclera - transpired into optic cup through choroid fissure- becomes cornea fibrous layer- corneal stroma
Anterior neural plate- retina and iris and ciliary body epithelia
neural crest cells- iris and ciliary body stroma
and formation of cornea sclera and melanocytes
All under the control of transcription factors eg pax 6 gene
Retinal ganglion cells- neutrons that send retinal electrical signals converge at optic disk toward optic stalk forming optic disk