Trilaminar Embryo (week 3) Flashcards
when does hemangiogenesis begin?
end of week 3
where does hemangiogenesis begin?
in the extraembryonic mesoderm
what are blood islands?
hemangiogenic mesorderm within the wall of the yolk sac
what are hemangioblasts?
progenitor cells capable of differentiating into angioblasts and hematopoeitic stem cells
what are angioblasts precursors to?
endothelial cells of the blood vessels
what are the precursors of blood cells?
hematopoitic cells
what is angiogenesis
formation of new blood vessels by fusion of pre-existing blood vessels,
what does the blood island give rise to
angioblasts and hematopoeitic stem cells
when does primitive hemangiogenesis start?
beginning of week 3 in the yolk sac
when does definitive hemangiogenesis start?
2 days after primitive hemangiogenesis in the embryo
what is vasculogenesis?
process in which the primitive blood vessels form within the blood islands via fusion of endothelial cells (angioblasts)
what is the main event of week three of embryonic development?
gastrulation (formation of 3 embryonic germ layers)
what is gastrulation?
bilaminar embryo is transformed into a trilaminar embryo and the formation of three embryonic germ layers: embryonic ectoderm, mesoderm, and endoderm
at what end of the embryonic disk does gastrulation begin at? (caudal or cranial)
caudal
when does gastrulation begin (day number)
day 15
How does gastrulation start? (what is the first thing to begin to develop)
primitive streak
what does structures does the primitive streak consist of?
primitive groove + primitive node
what types of cells make up the primitive streak?
proliferating epiblasts
where is the primitive pit found?
it is the depression in the primitive node
what does the first wave of migrating epiblast cells through the primitive groove (during gastrulation) form?
embryonic endoderm (displaces the hypoblast)
what does the second wave of migrating epiblast cells through the primitive groove (during gastrulation) form?
embryonic mesoderm (moves between the endoderm and epiblast)
what does the remaining epiblast cells that don’t migrate during the first or second wave during gastrulation form?
embryonic ectoderm
what cells make up the primitive pit? what is their function?
ciliated cells; their cilia protrude toward the ventral side of the embryo and constantly rorate creating nodal flow to the left
Towards which side is nodal flow created? how?
to the left; via the ciliated cells in the primitive pit constantly rotating
what is responsible for the left-right embryo asymmetry?
the leftward gradient of the signaling protein Nodal (secreted by the primitive node)
what protein is secreted by the primitive node? what is it’s function?
nodal; its a signaling protein responsible for the left-right embryo asymmetry
where do the ectoderm and endoderm tightly adhere during gastrulation?
at the buccopharyngeal (oropharyngeal) membrane and at the cloacal membrane
Do the buccopharyngeal and cloacal membrane have any intervening mesoderm?
NO! they are only made up of tightly adhering ectoderm and endoderm
what does the buccopharyngeal membrane define? what future cavity does it make?
defines the cranial end of the embryo; gives rise to the future oral cavity (mouth)
what does the cloacal membrane define? what future cavity does it give rise to?
defines the caudal end of the embryo; gives rise to future cloaca (anus and urethra)
what is the notochord process?
a hollow tube, which grows cranially from the primitive pit between the ectoderm and endoderm until is it blocked by the prechordal plate
When does the notochord process stop growing?
once it reaches the prechordal plate
what is the prechordal plate? where is it located?
a condensation of the mesoderm, adjacent to the the buccopharyngeal membrane
What is the notochordal canal?
the hollow center of the notochordal process which is continuous with primitive pit
what makes up the notochord plate
the notochordal canal unzipped and fused with the endoderm
what is the neuroenteric canal?
a transient canal, which temporarily links the amniotic cavity with the yolk sac through the notochordal canal
As the three germ layers are established, the cells of the notochordal plate begin to proliferate and separate from the _________, forming the ________.
endoderm; definitive notochord
what does the notochord get incorporated into after notocord transformation?
vertebral bodies of the vertebral column during axial skeleton development
What are the main functions of the notochord?
- defines the dorsal-ventral and left-right axes of the embryo
- provides midline patterning signals for the surrounding tissues
- serves as a major skeletal element of the developing embryo
which cells make up the neural ectoderm?
epiblasts closest to the midline of the ectoderm layer
which cells make up the surface ectoderm?
epiblasts closes to the lateral surfaces of the ectoderm layer
what does the neural ectoderm give rise to?
- brain
- spinal cord
- all cranial and spinal MOTOR neurons
- retina
- neurohypophysis
- epithelium and muscles of the iris
- epithelium of the ciliary body of the eye
from which germ layer does the epithelium of the ciliary body of the eye arise from?
neural ectoderm
which germ layer gives rise to the epithelium and muscles of the iris?
neural ectoderm
which germ layer gives rise to the neurohypophysis?
neural ectoderm
which germ layer gives rise to the retina
neural ectoderm
which germ layer gives rise to all of the MOTOR cranial and spinal neurons?
neural ectoderm
which germ layer gives rise to the spinal cord and brain?
neural ectoderm
which germ layer gives rise to the epidermis and its appendages?
surface ectoderm
which germ layer gives rise to the epithelial lining of the cornea and conjunctiva?
surface ectoderm
which germ layer gives rise to the epithelial lining of the external ear?
surface ectoderm
which germ layer gives rise to the epithelial lining of the mouth and appendages?
surface ectoderm
which germ layer gives rise to the proctodeal epithelium and epithelium of terminal male urethra?
surface ectoderm
where are the cells that make up the mesoderm found?
between the ectoderm and endoderm during gastrulation
what layers does the mesoderm differentiate into?
paraxial, intermediate, and lateral mesoderm
Where is the paraxial mesoderm located?
caudal to the otic vesicles
what forms the somites?
paraxial mesoderm segmentation
what are somites?
symmetrical condensations of mesenchymal cells on both sides of the developing neural tube
are all parts of the paraxial mesoderm segmented? If not, what area(s) are not?
No! The area cranial to the otic vesicles remains unsegmented
what are the four specialized regions of the somite?
- dermotome
- myotome
- lateral somite
- sclerotome
which region of the somite loses its compact organization first?
the sclerotome
where do the sclerotome cells migrate toward?
toward the notochord and neural tube
what do the sclerotomal cells form?
the vertebral column (later in development)
what area of the somite gives rise to the dermatome, myotome, and lateral somite regions?
dorsal portion of the somite
what does the dermatome give rise to?
dermis of the skin over the dorsal region of the trunk
what does the lateral somite give rise to?
ALL voluntary striated muscles of the body wall and limbs (hypaxial muscles)
what does the myotome give rise to?
segmented muscles of the axial skeletome (epaxial muscles)
what does the unsegmented area of the paraxial mesoderm give rise to?
straiated muscles of the head
What does the intermediate mesoderm give rise to
connective tissue and the smooth muscle cells of the gonads, urinary system, and reproductive tracts
what layers of mesoder does the lateral mesoderm divide into?
somatic (parietal) and splanchnic (visceral) mesoderm
where is somatic mesoderm found?
adjacent to the surface of the ectoderm
where is splanchnic mesoderm found?
adjacent to the endoderm
what makes up somatopleure?
surface ectoderm + somatic mesoderm
what makes up splanchnopleure?
visceral mesoderm + endoderm
which germ layer (specific) gives rise to the skeleton of the limbs?
somatic mesoderm
which germ layer (specific) gives rise to the connective tissues of the limbs and trunk?
somatic mesoderm
which germ layer (specific) gives rise to the dermis of the ventral body wall and limbs?
somatic mesoderm
which germ layer (specific) gives rise to the connective tissues of the external genitalia?
somatic mesoderm
which germ layer (specific) gives rise to the smooth muscle and connective tissue of the blood vessels?
somatic mesoderm
which germ layer (specific) gives rise to the smooth muscle and connective tissues of the intestinal tract, associated glands, and abdominal mesenteries?
visceral mesoderm
which germ layer (specific) gives rise to the smooth muscle and connective tissues of the respiratory tract and associated glands?
visceral mesoderm
which germ layer (specific) gives rise to the smooth muscles and connective tissues of the blood vessels?
visceral mesoderm
which germ layer (specific) gives rise to the cardiac muscle?
visceral mesoderm
where do the first blood islands appear?
in the splanchnopleuric mesoderm surrounding the definitive yolk sac
how is primitive vasculature formed?
the angioblasts of blood islands differentiate into the endothelial cells that fuse to form primitive vasculature filled with primitive blood (found within the yolk sac)
where is primitive vasculature found?
within the yolk sac
where are hemangioblasts found?
in the blood islands
where are the definitive hematpoeitic stem cells formed?
within the hemangiogenic mesoderm
what do angioblasts originating within the hemangiogenic mesoderm form?
endothelial lining of the vessels (including aorta and heart)
where are primitive hematpoeitic stem cells formed?
within the blood islands located in the walls of the definitive yolk sac
what do definitive hematpoeitic stem cells give rise to?
the embryonic liver
what is the function of the embryonic liver? how does this change after birth?
it is the main site of hematopoiesis during embryonic development; after birth, hematopoiesis shifts to the bone marrow
what does the septum transversum give rise to?
the mesenchyme of the developing liver, epicardium, the central portions of the diaphragm, and the esophageal mesentery
what does the endoderm give rise to largely?
epithelial lining of the developing gut and its appendages (foregut, midgut, hindgut, and allantois)
what germ layer gives rise to the epithelial lining of the gut?
endoderm
what germ layer gives rise to the epithelial lining of the respiratory tract?
endoderm
what germ layer gives rise to the hepatocytes of the liver?
endoderm
what germ layer gives rise to the bilary tract?
endoderm
what germ layer gives rise to the endocrine and exocrine cells of the pancreas?
endoderm
what germ layer gives rise to the epithelium of the middle ear and auditory tube?
endoderm
what germ layer gives rise to the urinary bladder
endoderm
what germ layer gives rise to the epithelial lining of the vagina?
endoderm
what germ layer gives rise to the epithelial lining of the urethra?
endoderm
what germ layer gives rise to the secretory cells of the prostate and urethral glands?
endoderm
what is primary ciliary dyskinesia (PCD)?
a rare autosomal recessive genetic disorder in which genetic mutations affect genes encoding various proteins comprising motile cilia; results in cilia which do not rotate, causing disruption of leftward flow of fluid in the primitive node during gastrulation, leading to disruption in the normal signaling cascade responsible for the establishment of left-right body asymmetry
what is a common result of primary ciliary dyskinesia (PCD)?
sius inversus– karatagener syndrome
what is sius inversus– karatagener syndrome?
a PCD where the laterality of the internal organs is the mirror-image of normal
what are PCD symptoms?
- susceptibility to chronic recurrent respiratory infections due to absent mucus clearance from the resp. system
- infertility in both males and females (due to diminished sperm motility in males or defective ciliary action in the fallopian tubes in females)
what is situs ambiguus?
organ placement is neither typical (situs solitus) nor totally reversed (situs inversus)
