Second And Third Week Of Development Flashcards
What 2 layers does the trophoblast differentiate in to
Cytotrophoblast
Syncytiotrophoblast
What does the Syncytiotrophoblast do
Erodes maternal sinusoids and maternal blood enters luncar network and by end of second week a primitive utero placental circulation begins
What does the cytotrophoblast do
Forms primary villi
What does inner cell mass differentiate in to
Epiblast and hypoblast forming the bilaminar disc
What do epiblasts do
Give rise to aminoblasts that line the amniotic cavity superior to epiblast layer
What does hypoblast do
Cont. with exocoelomic membrane and together surround the primitive yolk sac
How does chorionic cavity/extra embryonic coelom form
Vacuoles develop in tissue formed by the filling of extra embryonic mesoderm the space between trophoblast externally and amnion and excoelomic membrane internally
Why is the second week known as week of 2s
Trophoblast differentiates in 2 layers
Inner cell mass differentiates in 2 layers
Primary mesoderm splits in to somatopleuric and splanchopleuric primary mesoderm
Starting of formation of amniotic and yolk sac cavities
What are the properties of embryonic stem cells
Self renewal
Potency:capacity to differentiate
What is gastrulation
Process by in which bilaminar disc becomes trilaminar
Describe gastrulation
▪️Formation of primitive streak on surface of epiblast
▪️cephalic end is celled the primitive node and a groove appears called the primitive pit
▪️cells of ectoderm migrate in direction of primitive streak and slip under epiblast layer through primitive streak to replace hypoblast and form endoderm
▪️then some cells are used to form mesoderm
How is the notochord formed
Mesenchymal cells migrate cranially from primitive node and pit forming a median cellular cord: the notochord
What are the functions of the notochord
▪️Forms the axis around which the axial skeleton develops
▪️stimulate overlying ectoderm to form CNS
▪️degenerates and disappears as bodies of vertebrae form
What is caudal dysgenesis
Could be due to genetic abnormalities or toxic insults
Insufficient mesoderm is formed in the caudal most region of embryo
Abnormalities occur in lower limbs urogenital system, and lumbosacral vertebrae
What are sacrococcygealtertomas
By end of fourth week primitive streak shows regressive changes
Sometimes remnants of primitive streak persist in sacrococcygeal region
Cells proliferate and form these tumors
