L52. Embryology Flashcards
What is a fertilised ovum called?
Zygote
After what period of time is a zygote formed?
24h
What is the mass of cells formed from 4-6 days called?
Morula
What is the hollow ball of cells formed from 6-10 days called?
Blastocyst
What are the components of a blastocyst?
Outer layer of cells (trophoblast) and an inner cell mass.
At 10 days, what does the trophoblast contain?
2 layered-embryo
Name the 2 layers of the 2 layered embryo.
Epiblast (inner layer)
Hypoblast (outer layer)
What do the epiblast and hypoblast do?
Epiblast gives rise to the embryonic ectoderm, mesoderm and endoderm.
Hypoblast helps form the endoderm.
How many placentas are present in identical twins?
1 placenta
How many placentas are present in fraternal twins?
2 placentas
What is the groove called which forms during development?
The primitive streak
Where are mesodermal cells found?
Between the epiblast and the hypoblast
What do mesodermal cells do?
Push through the primitive streak and spread out to form the 3rd layer
What is organogenesis?
When organs (including CNS) develop between weeks 3-8
Describe the flow chart of how the neural tube develops.
Neural fold -> neural groove -> neural tube
What is the condition called when the neural tube persists?
Spina bifida
What happens around 25 days old?
Front and back ends of the embryo fold in the middle (folds around yolk sac) and heart, liver and lungs appear.
Name the 3 embryonic layers and their positions.
Ectoderm (outer covering)
Mesoderm (middle)
Endoderm (inner lining)
What is the ectoderm involved in producing?
Skin, oral mucous membranes, CNS, enamel
What is the mesoderm involved in producing?
Connective tissue, blood vessels, reproductive system
What is the endoderm involved in producing?
Respiratory system, alimentary (pharynx to anus)
What is the ectomesenchyme?
A “4th layer” which develops the peripheral nervous system (sensory and autonomic nerves) and oral structures (except enamel)
