Bilaminar To Trilaminar Stages Flashcards
Cytotrophoblast differentiates into what two layers?
Epiblast layer - adjacent to aminotic cavity
Hypoblast - adjacent to the blastocyst cavity
Amniotic cavity function?
Location?
What is the surrounding location like?
Amniotic sac; protection
First appears within the epiblast as a small cavity and it grows larger
Endometrial stroma- because edematous and highly vascularized
__ + ___ = primitive yolk sac
Hypoblast + Heusers membrane
Function of sinusoids?
When are sinusoids formed?
They are filled with blood; exchange of nutrients (but never exchange of blood)
When synciotrophoblasts erode maternal capillaries
~ Day 11/12
What is the decidual rection
Thickening of the endometrium around the gestational sac
__ + ___ = primary villi
Purpose?
Cellular column + syncytial covering; surface defect is closed now
Increase surface area to increase supply of nutrients, oxygen, and waste removal
When is the secondary yolk sac formed?
Day 13
DAY 13
Epiblasts form?
Hypoblast forms?
Epiblast: floor of amniotic cavity
Hypoblast: roof of secondary yolk sac
~bilaminar germ disc
Prechordal plate is
Future mouth
So in summary, what is developed during the second week?
Decidual reaction, primary yolk sac, extraembryonic coelom (cavity), secondary yolk sac, amniotic cavity, bilaminar germ disc (epiblast/hypoblast) and prechordal plate
Migration of cells of epiblast forms?
When does it appear? Disappear?
Significance?
Primitive streak
Appears on day 15-16; disappears on day 26
Helps in identifying craniocaudal axis of embryo
Difference between what is happening at the cranial and caudal ends during invagination
Cranial - differentiation
Caudal- gastrulation (primitive streak continues to form mesoderm
- Cranial end of primitive streak gives rise to?
- Midstreak?
- Caudal end?
- Paraxial mesoderm (head and somite)(somite= skeletal muscle, dermatomes and cartilage)
- Intermediate mesoderm (kidney and gonads)
- Lateral plate mesoderm (splanchnic, somatic, extra embryonic)
Define gastrulation
What does it begin with?
What is the gastrula?
Process by which bilaminar embryonic discs convert to trilaminar embryonic discs; formation of embryonic mesoderm and endoderm
Begins with formation of the primitive streak
Embryo
- What does FGF8 stand for?
- What is it synthesized by?
- FGF8 controls what two processes?
- FGF8 downregulates? Which normally does?
- Fibroblast growth factor 8
- Streak cells
- Cell migration and specification
- E-cadherin which normally binds epiblast cells together
How do FGF8 control cell specification into mesoderm?
By regulating Brachyury (T) expression
- What do cells in the germ layers give rise to?
2. What is the source of all the germ layers?
- All of the tissues and organs in the embryo
2. Epiblast
The prechordal plate itself forms what two things?
Later, the prechordal plate is important for what?
What later becomes of the oropharyngeal membrane?
Notochord and oropharyngeal membrane
Induction of the forebrain
Its layers represent the future opening of the oral cavity
What is the extent of the notochord
In midline from prechordal plate caudally to the primitive streak
Neural cells proliferate beginning at which end?
When the notochord gets detached from embryonic endoderm, what does endoderm form?
Cranial and begins to fold
Roof of yolk sac
Notochord is basis for developing?
Remnants of notochord is?
Notochord induces overlying ectoderm to form?
Axial skeleton
Nucleus pulposus
Neural plate
What is the cloacal membrane?
Covers embryonic cloaca during development of urinary and reproductive organs
What is allantois?
What is it involved with
Small diverticulum from posterior wall of yolk sac
Involved with abnormality of bladder development
Derivatives of ectoderm
CNS, PNS, sensory of ear, nose and eye, epidermis, subcutaneous glands, mammary glands, pituitary gland, and enamel of teeth
Derivatives of endoderm
Liver, pancreas, parathyroid glands, thymus, thyroid, tonsils, auditory tube, and epithelial linings of GI, respiratory tract, urinary bladder/urethra
Derivatives of mesoderm
Spleen, cortical portion of suprarenal gland, kidneys, gonads, blood and lymph cells, walls of heart, striated and smooth muscles, and supporting tissue (connective tissue, cartilage, bone)
The anterior visceral endoderm expresses genes. What are the genes and what are they important for?
What do they inhibit?
Three transcription factors- OTX2, LIM1, and HESX1. Important for head formation; disfunction in these genes will make the body unable to develop axis’s
Inhibit nodal (a growth factor) in order to establish cranial end embryo before gastrulation
Function of BMP4 and FGF?
Cause mesoderm to be ventralized which contributes to the formation of kidneys, blood and body wall mesoderm
What blocks BMP4?
Why?
Genes expressed by the node; if not, all mesoderm would be ventralized (so node is considered the organizer)
- What 3 things antagonize the activity of BMP4?
2. What does this cause?
- Chordin, noggin, and follistatin
- Causes cranial mesoderm is dorsalized into notocord, somites, and somitomeres; also important for neural induction in the cranial region
Function of HNF-3 beta
What would happen without HNF-3beta
Maintains the node and later induces regional specificity in the forebrain and midbrain
Embryos fail to gastrulate properly and lack midbrain/forebrain structures
What acts as an inhibitor of BMP4?
Contributes to regulation of?
Goosecoid; head development
Brachyury encodes a transcription factor that causes?
So absence of Brachyury results in?
Mesoderm formation in the middle and caudal regions
Shortening of embryonic axis (caudal dysgenesis)
When the primitive streak appears, what is secreted and what does it do?
FGF8 is secreted by cells in the node and primitive streak to induce expression of Nodal
How is left and right sidedness established?
Nodal expression is restricted to the left side of the embryo by accumulation of serotonin (5-HT) on the left
High concentration of 5-HT on left activates expression of? Which does what?
Name 3 genes that are involved in establishing the midline and prevent Nodal expression from crossing over to the right side
MAD3- restricts nodal expression to the left side of the primitive node
SHH, Lefty1 and ZIC3
Lefty2 upregulates PITX2 which is ?
So a defect in this gene would look like what in the body?
A master gene that establishes left sidedness for heart, stomach, and gut primordia
For example, if the heart was on the right side instead of the left (if gene is expressed ectopically)
- 5HT is a neurotransmitter that helps establish ?
2. Issues with 5HGT signaling are seen in patients that?
- Laterality (heterotaxy)
2. Take SSRIs (antidepressants)(selective serotonin reuptake inhibitors)
Cells that migrate to the following areas become?
- Epiblast cells that enter through cranial region?
- To the lateral edges of the node?
- Through the midstreak
- Through caudal part of streak?
- Caudalmost part of streak?
- Notochord
- Paraxial mesoderm (somites and somitomeres)
- Intermediate mesoderm (urogenital)
- Lateral plate mesoderm (body wall)
- Extraembryonic mesoderm (primitive yolk sac, hypoblast)
Cartilage cells are formed from?
Folding and invagination of surface cells
What does it mean that the embryo develops cephalocaudally?
Gastrulation is continuing in caudal segments while cranial structures are differentiating
Differentiation into blood vessels and blood cells happens during which week?
When does heart begin to beat?
Third week
Fourth week (primary villus to tertiary villus)
Conjoined heads/head duplication would be caused by?
Overexpression of goosecoid
What is situs inversus?
Condition where the organs of the thorax and abdomen are transposed or reversed
Sacrococcygeal teratoma?
Remnants of primitive streak persist in the sacrococcygeal region
Function of FGF8?
What increases the expression of FGF8?
Name another function of nodal gene
Expresses nodal gene from primitive node but only on the left side
Serotonin (5-HT)
It initiates and maintains the primitive streak (same as HNF 3 beta)
So serotonin expresses FGF 8 which expresses nodal and ___ which expresses ___
Nodal and lefty 1 express PITX2 which is responsible for left sidedness
~absence in any of these can lead to situs inversus
Why does serotonin not work on the right side?
MAD is present on the right side which destroys it. But it is not present on the left side
What is the only gene present on the right side?
Snail
What is located on the notochord that prevents left sided genes from going over to the right side
Shh
Absence of HNF 3 beta will stop what two things?
Will prevent gastrulation and formation of forebrain/midbrain
4 genes for head formation
OTX2, LIM1, HESX1, cerebrus
What do homeobox genes do
Separate forebrain/midbrain/hindbrain
Main function of BMP4
Same family as ?
Ventralization of mesoderm
Nodal gene
Why does BMP4 need to be controlled
What 3 genes control BMP4
Or else it will ventralize all mesoderm
Chordin, noggin, and follistatin
What activates chordin?
Goosecoid (important for head development)
What is brachyury gene responsible for?
What is it under the control of?
Absence of brachyury leads to
Dorsalization of middle and caudal mesoderm
FGF8
Caudal dysgenesis (lower part of spine is abnormal)
If primitive streak does not close what can happen
Sacrococcygeal tetratoma
Primitive streak grows in what direction
Cranial to caudal
