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Embryology > Embryology Week 3 > Flashcards

Embryology Week 3 Flashcards

1
Q

What is gastrulation

What happens 1st at 3rd week

A
  • formation of all three germ layers

- primitive streak forms at caudal region at day 15-16

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2
Q

Describe primitive streak and node and where found

A
  • found on surface of epiblast
  • narrow groove bulging at either side

-cephalic ( cranial ) end of streak which is elevated ( the organizer )

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3
Q

Describe ingression / invagination

Function of FGF8 and where made and how does it do it’s function

A

/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
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4
Q

What do mesoderm cells do to hypoblast

What happens to ingressed cells that lie between hypo and epiblast

A

/displace it and diff into endoderm

-diff into mesoderm

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5
Q

How are all the germ layers formed

A

/ingression of epiblast cells through gastrulation

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6
Q

Where do mesoderm cells spread to ( laterally and cranially )

Where is prechordal plate found

A
  • 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
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7
Q

Function of prechordal plate

Describe structure of oropharanygeal and cloacal membrane and their functions

A

/induction of forebrain

-tightly adhered ectoderm and endoderm cells with no mesoderm in between

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8
Q

How do prenotochordal cells arrive to midline of epi and hypoblast

Name of node during prenotochordal cell migration

A
  • epiblast cells move caudally and ingress at node then move cranially until they reach prechordal plate
  • nuerenteric canal
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9
Q

How is notochord formed

When is it formed ( what else is occurring )

A
  • cells ingress to prechordal plate
  • attach to endoderm
  • proliferate and detach
  • form into definitive notochord

-occurs as hypoblast is being displaced by endoderm cells

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10
Q

In what direction is notochord formed definitively

Where does notochord extend to

A

/cranial to Caudal

-from prechordal plate cranially to caudal of primitive pit

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11
Q

When does it form and function of nueretenric pit

How is prechordal plate formed

A

/when pit forms indentation in epiblast

  • connects amniotic and yolk sac temporarily
  • some cells migrate ahead of prenotochordal and diff into prechordal plate
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12
Q

What happens when cloacal membrane is formed

-what structure is formed , describe it , name it and when formed !?

A
  • posterior to of yolk sac forms a diverticulum that extends into connecting stalk called Allantois / allantoenteric diverticulum
  • 16th day
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13
Q

List body axes established during development

A

1 anterior , posterior ( A-P craniocaudal )

2 Dorso- ventral ( D-V )

3 left right ( L-R )

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14
Q

When is A-P axis made and what happens during the process

Name the genes in the process and the transcription factors

A
  • 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 )
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15
Q

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

A
  • inhibit nodal activity thereby establishing cranial end of embryo
  • nodal expression continues thus maintaining primitive streak
  • once streak is formed by NODAL
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16
Q

Function of BMP4

What secrets it

A

—bone morphogenetic protein 4 will ventralize mesoderm which contribute to kidneys , blood and body wall mesoderm with FGF

-by embryonic disc

17
Q

Which factors antagonize BMP4 and what activates them

Function of HNF-3beta

Function of goosecoid and effects of over or under production

A

-CHORDIN , noggin and folistatin
( GOOSECOID )

-maintains node and later induces regional specificity for forebrain

  • inhibits BMP4 and contributes to head development
  • head region malformation
18
Q

What regulates dorsal mesoderm in midline and caudal regions and what secrets it

Function of BRACHYURY ( T )

A
  • BRACHYURY ( T ) expressed in node, notochord precursor and notochord
  • essential for migration through streak
19
Q

What does BRACHYURY do

What causes assymtry early in organ development

A
  • encodes a specific DNA binding protein that is a transcription factor in F box
  • Cascade of signal molecules and genes
20
Q

How is nodal expresses and limited to the left

A

-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

21
Q

Midline genes expressed and what they do

A
  • Sonic hedgehog ( SHH ) , lefty 1, ZIC3
  • code for zinc finger transcription factor
  • establish midline
  • prevent nodal from crossing to the right
22
Q

What induces lefty 2 and function of l2

A

Nodal

-unregulates PITX2 ( a home box transcription factor ) master gene for establishing left sideness

23
Q

What happens if PITX2 expressed ectopically

A

-lateral defects

24
Q

SNAIL function and location

A
  • found at right side of gastrula

- establishes right side

25
Q

What happens to cells that ingress cranially , at lateral edge , midstreak and at caudal and at most caudal

A
  • become prechordal plate and notochord
  • paraxial mesoderm
  • intermediate mesoderm
  • lateral plate mesoderm
  • extra embryonic mesoderm
26
Q

Describe growing structure of mesoderm

Why does cranial end grow more

When does ingression stop

A
  • 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

27
Q

Why does embryo develop cephalocaudally

A

/cephalic cells begin to diff by 3rd week and caudal end still ingresing up until 4th week

28
Q

Describe villi by beginning and end of 3rd week

A
  • 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
29
Q

What does the forming capillaries of definitive villi do !?

A

-contact developing mesoderm and connective stalk and intra embryonic circulation system connecting placenta and embryo

Embryology (5 decks)

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