Embryology Flashcards
(70 cards)
What is the embryonic period?
Week 3-8
What are the 3 germ layers and in what process do they appear?
Endoderm
Mesoderm
Ectoderm
Formed in gastrulation
When does gastrulation occur?
Third week of development- the start of the embryonic period
Why is week 2 the week of twos?
Trophoblast splits into two layers- cytotrophoblast and the syncytiotrophblast
Embryoblast gives rise to to cell layers-Bilaminar disc- epiblast and hypoblast
Hypoblast gives rise to two cavities - amniotic and primary yolk
List the germ layers and their derivatives
Endoderm- hypoblast
Mesoderm- epiblast
Ectoderm- epiblast
Outline the mesoderm organisation
The mesoderm sits between the ecto and end term apart from in one small area at each end of the body.
Which two future areas lack mesoderm?
Anus and mouth
What does ectodermal tissue give rise to?
Organs and structures that contact the outside world
- epidermis
- nervous tissue
Muscle, cartilage, bone and the CVS system are all formed from which germ layer?
Mesoderm
On day 16 what feature appears?
Primative streak and primative node appear on the dorsal surface of the epiblast at causdal end
How is a third layer formed from the bilaminar disc?
Epiblast cells migrate to the primitive streak and invaginate epiblast to displace the hypoblast- the new middle layer is the mesoderm. The epiblast is the ectoderm and the hypoblast is now called endoderm
How does gastrulation give left to right asymmetry?
The primitive node gives signalling molecules off that are moved more to the left by ciliated cells. This means that to the left of the notochord left sided signals are send and to the right side signals for right sidedness are sent.
List some anatomical left/right assymetry.
Liver on right
Stomach and spleen on left
Right lung 3 lobes left 2
Where does the primitive streak form?
caudal epiblast
What does gastrulation achieve?
3 germ layers
precursor tissue in correct place for subsequent morphogenesis.
What determines the fate of invaginating epiblast cells in gastrulation?
Position of invagination on the streak
What is the notochord?
Solid rod of cells running in the midline that has a signalling role.
What happens to the ectoderm that overlies the notochord?
Differentiates to neuro-ectoderm
Describe neural tube formation.
Ectoderm over notochord thickend and forms a slipper shaped neural plate.
The edges lift and curl toward each other, joining to make the neural tube.
Describe neuralation.
Ectoderm over notochord thickend and forms a slipper shaped neural plate.
The edges lift and curl toward each other, joining to make the neural tube.
Splancnic mesoderm sits adjacent to which other germ layer?
Endoderm
Where is the paraxial mesoderm found and what does it form?
Found adjacent to the notochord.
It segments into somites in a cranio-caudal sequence.
How many somites are lost?
42-44 present at end of week 5
Final count is 31
11-13 lost
What do somites give rise to?
Musculo-skeletal system
Dermis
