Embryonic development Wks 3&4 Flashcards
At day ___ the primitive streak appears in the _____ surface of the ______. It elongates towards the _____ end of the _____ through continued additon of cells at its _____end.
15
caudal dorsal
embryonic disc
cranial
embryonic disc
caudal
At what end does the primitive node form?
the cranial end
How does the primitive groove form?
By what day is the primitive streak visible as a narrow groove w/ bulging sides?
Through the migration and invagination of epiblast cells.
Day 16
What is the function of the primitive streak?
It actively participates in the formation of embryonic ENDOderm and MESOderm until early wk 4
Describe the formation of the 3 germ layers in gastrulation.
Epiblast cells invaginate/migrate through the primitive streak to displace the hypoblast, and form the embryonic ENDODERM.
The FIRST SET of epiblast cells that migrate thru the streak form mesenchyme, some of which form mesoblasts (after ecto/endoderm are there) which will form the embryonic MESODERM.
The outermost layer of epiblast cells is renamed the embryonic ECTODERM.
During gastrulation, where are the 2 locations where the ectoderm and endoderm stay fused? What do these sites become?
The prechordal plate in the cranial end of the embryonic disc, which becomes the OROPHARYNGEAL MEMBRANE, the future site of the oral cavity.
Caudally, this becomes the CLOACAL MEMBRANE, the futures site of the anus.
What are the 5 fates of epiblast cells the migrate through the different parts of the primitive node/streak to form mesoderm structures?
Migrating at:__, Becomes:__
1) cranial-most part of primitive node, notochord
2) cranial-most part of prim. streak, paraxial mesoderm
3) next portion of streak, intermediate mesoderm
4) caudal portin of streak, lateral plate mesoderm
5) caudal-most portion, extraembryonic mesoderm
What is a sacrococcygeal tetroma?
What is sirenomelia and how does it happen?
A remnant of the primitive streak that develops into a benign tumor in the sacral region.
The fusion of lower limbs occuring because of insufficient mesoderm to form the caudal region of the embryo (caused by tetratogens)
Ectoderm differentiates into which 2 layers?
Surface ectoderm
Neuroectoderm
The surface ectoderm will give rise to….
Mammary glands
Adrenal medulla
Subcutaneous glands
Hair
Epidermis of skin
Enamel of teeth
Pharyngeal arch cartilages
Mneumonic: Ma Sheep
The neural ectoderm gives rise to:
Neural crest and Neural tube
From where does the notochordal process begin to develop?
What does it become?
The notochordal process lengthens by migration of cells from the primitive node. It lengthens as the mimitive streak shortens. It will become the notochord around day 21.
What are somitomeres and how are they formed?
What do the first 7 pairs form?
The paraxial mesoderm condenses into paired, loosely organized somitomeres. They appear from cephalic region and develop in a cranial to caudal direction.
The first SEVEN pairs of somitomeres DONT form somites but give rise to the musculature of the face, jaw, and throat.
At what day does the first somite appear? How many pairs are there after 5 wks?
What do they give rise to?
Day 20; There are 42-44 pairs but the caudal-most somites degenerate resulting in final total of 34 OR 38 pairs.
They give rise to most of the axial skeleton, the voluntary muscles, and part of the dermis of the skin.
What does the INTERMEDIATE mesoderm become?
It differentiates into the urinary system, portion of gonads, and male genital duct system.
What appears in the lateral mesoderm?
What are the 2 layers it makes?
Intraembryonic coelum (horse-shoe shaped). This space splits the intermediate mesoderm into 2 layers:
- VENTRAL splanchnic or VENTRAL mesoderm
- DORSAL somatic or PARIETAL mesoderm
What is the main thing that the embryonic endoderm forms?
The future digestive system
How does Fibroblast growth factor 8 (FGF8) secreted by the primitive node and streak induce expression of the protein Nodal ONLY on the left side?
The ventral surface of the prmitie node contains unique cilia which beat to the left creating a gradient of Nodal protein on the left side of the embryo.
What is Situs Inversus and how common is it?
A condition in which the body’s internal organs are transposed to the opposite side; It affects 1:8000
On what day is the neural groove formed?
Day 18
How is the neural tube formed?
By the end of the 3rd wk, the neural folds that form the neural groove above the notochord invaginate and fuse to form the neural tube.
Fusion begins in cervical region and proceeds cranially AND caudally (like a zipper closing both ways). 2 pores will form at the end.
What will give rise to the CNS (ie brain and spinal cord)?
The ectoderm of the neural plate
Approx. how many somites does the embryo have at the end of wk 3?
4-7 somites
When do the neuropores close?
Day 24: Rostral neuopore IS CLOSING
Day 26: Rostral neuropore has CLOSED
Day 28: Caudal neuropore has closed
How is the neural crest formed?
As the neural tube separates from the surface ectoderm, some cells lying along the neural folds detach and give rise to the neural crest. It will be lateral to neurotube(ie above tube, below amnion cavity).
It will give rise to the spinal ganglia (ie dorsal root ganglia)
