Embryology Flashcards
What surrounds the blastomeres after first mitotic divide?
Zona pellucida
When does the first mitotic divide occur?
30 hours after fertisilation
What is created in day 3?
Morula - totipotent cells
What happens to the morula?
Compaction occurs to create blastocyst (formation of first cavity)
What are the four components of the blastocyst?
Zona pellucida
Outer cell mass - trophoblast
Inner cell mass - embryoblast
Blastocyst cavity
What occurs after the formation of the blastocyst?
Hatching from zona pellucida
After implantation begin, what occurs?
Formation of bilaminar disc
What does the embryoblast form?
Epiblast and hypoblast
What does the trophoblst form?
Cytotrophoblast and syncytiotrophoblast
Name the components present after the formation of the bilaminar disc
Epiblast, hypoblast - forming bilaminar disc
Cytotrophoblast, synctiotrophoblast
Amniotic cavity
Blastocyst cavity
What occurs after the formation of the bilaminar disc?
Formation of primitive yolk sac by hypoblast development
What happens to the primitive yolk sac that is connected to the cytotrophoblast?
It is pushed away from the cytotrophoblast
Extraembryonic mesoderm fills its place
What occurs after primitive yolk sac is pushed away from cytotrophoblast?
Uteroplacental circulation begins
How does uteroplacental circulation occur?
Invasion of maternal sinusoid to syncytiotrophoblast
What occurs after uteroplacental circulation?
Formation of secondary yolk sac
How does the secondary yolk sac form?
Pinches off from primitive yolk sac
In terms of embryology, what is the present at the end of week 2?
Bilaminar disc composed of epiblast and hypoblast Amniotic cavity of epiblast cells Primary yolk sac of hypoblast cells Secondary yolk sac of hypoblast cells Chorionic cavity Connecting stalk
Where is the ideal location of implantation?
Posterior uterine wall
What is the different between topipotent and pluripotent cells? When does the change occur?
Totipotent - capacity to become anything
Pluripotent - capacity to become one of many cell types
Change occurs during compaction
What occurs during gastrulation?
Process of establishing the 3 germ layers (trilaminar disc)
Sets axes
From where does the primitive streak develop?
Develops from caudal end of epiblast layer
Describe the formation of the primitive streak, node and pit
The primitive streak is a narrow groove with bulging edges
The primitive node is at the end with the pit lying between it and the streak
What occurs after the formation of the primitive streak, node and pit?
Migration and invagination of epiblast layer, spreading laterally and cephalad between epiblast and hypoblast
Displacement of the hypoblast layer with creation of third layer
Trilaminar disc is formed
What are the 3 layers of the trimlaminar disc?
Ectoderm
Mesoderm
Endoderm
Describe the formation of the notochord
Prenotochordal cells of the spiblast migrate through the cranial part of the primitive pit to form solid rod of cells
Why is the notochord important?
Defines midline
Axial skeleton forms around it
Drives neurulation
Why is the primitive node important?
Emits molecular signals which ensure correct dorso-ventral and left-right orientation
What is ultimately derived from the ectoderm?
Organs and structures with contact to the outside world (nervous, epidermis)
What is ultimately derived from the mesoderm?
Supporting tissues (muscles, cartilage, bone & vascular system)
What is ultimately derived from the endoderm?
Internal structures (GI, respiratory & urinary tract)
How is left and right asymmetry formed?
Action of cilated cells at node results in leftward flow of signalling molecules - side specific signalling cascades initiated
What occurs during the fourth week?
Neurulation
Mesoderm differentiation
Folding
What is neurulation?
Notochord driven induction of ectoderm to form nervous system
How does neurulation occur?
Notochord signals for overlying ectoderm to thicken to form neural plate
Edges elevate out of plane of disc and then curl towards each other to form neural tube
What is the first step in mesoderm diffrentiation?
Mesoderm organises into paraxial mesoderm, lateral mesoderm (somatic mesoderm, splanchnic mesoderm) and intermediate mesoderm
What does the paraxial mesoderm form?
Somites which develop craniocaudal - 31 pairs
Describe organised degeneration of the somite
Degeneration of the ventral wall of somite forms sclerotome
Further organisation occurs to form combined dermomyotome
Myotome proliferates and migrates and dermatome disperses
What do the dermatome, myotome and sclerotome give rise to?
Dermatome - Skin section (dermis)
Myotome - Muscle section (muscle)
Sclerotome - Hard tissue (bone)
What do somites ultimately give rise to?
Repeating structures e.g. vertebrae, ribs, intercostal muscles, spinal cord segments
Also guides innervation
What does the paraxial mesoderm ultimately give rise to?
Axial skeleton, dermis, muscles
What does the intermediate mesoderm ultimately give rise to?
Urogenital system
What does the lateral mesoderm ultimately give rise to?
Somatic - connective tissues of limbs
Splanchnic - Smooth masculature, connective tissue and vascularture of gut
How does the embryo fold?
Driven by lateral plate mesoderm pulling downwards and encompassing all the primitive yolk sac creating the embryo suspended within aminotic sac
