Embryology Week 3 Flashcards
What is gastrulation
What happens 1st at 3rd week
- formation of all three germ layers
- primitive streak forms at caudal region at day 15-16
Describe primitive streak and node and where found
- found on surface of epiblast
- narrow groove bulging at either side
-cephalic ( cranial ) end of streak which is elevated ( the organizer )
Describe ingression / invagination
Function of FGF8 and where made and how does it do it’s function
/this is when cells of epiblast migrate to streak become flask shaped and detach and slip beneath streak
- controls invaginations and specifications. Made by streak cells themselves
- it down regulates E-Cadherin a protein which joins epiblast cells together
- also regulates BRACHYURY ( T ) expression to control specification into mesoderm
What do mesoderm cells do to hypoblast
What happens to ingressed cells that lie between hypo and epiblast
/displace it and diff into endoderm
-diff into mesoderm
How are all the germ layers formed
/ingression of epiblast cells through gastrulation
Where do mesoderm cells spread to ( laterally and cranially )
Where is prechordal plate found
- laterally migrate and spread until they contact extra embryonic mesoderm covering yolk sac and amnion
- cranially they pass on either side of prechordal plate
- tip of notochord and oropharnygeal membrane
Function of prechordal plate
Describe structure of oropharanygeal and cloacal membrane and their functions
/induction of forebrain
-tightly adhered ectoderm and endoderm cells with no mesoderm in between
How do prenotochordal cells arrive to midline of epi and hypoblast
Name of node during prenotochordal cell migration
- epiblast cells move caudally and ingress at node then move cranially until they reach prechordal plate
- nuerenteric canal
How is notochord formed
When is it formed ( what else is occurring )
- cells ingress to prechordal plate
- attach to endoderm
- proliferate and detach
- form into definitive notochord
-occurs as hypoblast is being displaced by endoderm cells
In what direction is notochord formed definitively
Where does notochord extend to
/cranial to Caudal
-from prechordal plate cranially to caudal of primitive pit
When does it form and function of nueretenric pit
How is prechordal plate formed
/when pit forms indentation in epiblast
- connects amniotic and yolk sac temporarily
- some cells migrate ahead of prenotochordal and diff into prechordal plate
What happens when cloacal membrane is formed
-what structure is formed , describe it , name it and when formed !?
- posterior to of yolk sac forms a diverticulum that extends into connecting stalk called Allantois / allantoenteric diverticulum
- 16th day
List body axes established during development
1 anterior , posterior ( A-P craniocaudal )
2 Dorso- ventral ( D-V )
3 left right ( L-R )
When is A-P axis made and what happens during the process
Name the genes in the process and the transcription factors
- at blastocyst stage
- the cells determined for anterior visceral endoderm ( AVE ) at cranial migrate to cranial end and express genes essential for head function
- OTX2 , LIM1 , HESX1
- Lefty 1 , Cerberus ( TGF-Beta family )
What do the AVE transcription factors do
Effect of lack of AVE transcription factors at caudal end
When are genes for dorsal and ventral structures upregulated and by what structure
- inhibit nodal activity thereby establishing cranial end of embryo
- nodal expression continues thus maintaining primitive streak
- once streak is formed by NODAL
Function of BMP4
What secrets it
—bone morphogenetic protein 4 will ventralize mesoderm which contribute to kidneys , blood and body wall mesoderm with FGF
-by embryonic disc
Which factors antagonize BMP4 and what activates them
Function of HNF-3beta
Function of goosecoid and effects of over or under production
-CHORDIN , noggin and folistatin
( GOOSECOID )
-maintains node and later induces regional specificity for forebrain
- inhibits BMP4 and contributes to head development
- head region malformation
What regulates dorsal mesoderm in midline and caudal regions and what secrets it
Function of BRACHYURY ( T )
- BRACHYURY ( T ) expressed in node, notochord precursor and notochord
- essential for migration through streak
What does BRACHYURY do
What causes assymtry early in organ development
- encodes a specific DNA binding protein that is a transcription factor in F box
- Cascade of signal molecules and genes
How is nodal expresses and limited to the left
-when steak appears it releases growth factors which induce expression of NODAL and accumulation of seratonin ( 5-HT ) actives MAD3 limiting it to the left
Midline genes expressed and what they do
- Sonic hedgehog ( SHH ) , lefty 1, ZIC3
- code for zinc finger transcription factor
- establish midline
- prevent nodal from crossing to the right
What induces lefty 2 and function of l2
Nodal
-unregulates PITX2 ( a home box transcription factor ) master gene for establishing left sideness
What happens if PITX2 expressed ectopically
-lateral defects
SNAIL function and location
- found at right side of gastrula
- establishes right side
What happens to cells that ingress cranially , at lateral edge , midstreak and at caudal and at most caudal
- become prechordal plate and notochord
- paraxial mesoderm
- intermediate mesoderm
- lateral plate mesoderm
- extra embryonic mesoderm
Describe growing structure of mesoderm
Why does cranial end grow more
When does ingression stop
- initially flat and round
- becomes elongated more at cranial end but streak region more the same due to continuous migration of cell from streak towards cephalic direction
-by 4th week
Why does embryo develop cephalocaudally
/cephalic cells begin to diff by 3rd week and caudal end still ingresing up until 4th week
Describe villi by beginning and end of 3rd week
- initially has 1• villi but mesoderm later penetrates and extends towards decidau to form 2• villi
- mesoderm diff’s into blood cells and vessels forming villous capillary system and villi now called definitive placental villi
What does the forming capillaries of definitive villi do !?
-contact developing mesoderm and connective stalk and intra embryonic circulation system connecting placenta and embryo
