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What is gastrulaiton?
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What are the 3 germ layers?
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Embryology II

Gastrulation, neurulation, folding

QuestionAnswer
What is gastrulaiton? Process by which three germ layers are established
What are the 3 germ layers? Ectoderm, mesoderm, and endoderm
What is the bilaminar layer? Hypoblast and epiblast
What does the bilaminar embryonic disc turn into? Trilaminar embryonic disc
What is the embryo referred to as during gastrulation? Gastrula
What is occuring at the beginning of the 3rd week? Formation of primitive streak
What is the primitive streak Thickened linear band in the median plane of the dorsal aspect of the embryonic disc
How is the primitive streak formed? Results from proliferation and movement of cells of epiblast to the median plane of the embryonic disc
What happens to the cranial end of the primitive streak? Proliferates to form a primitive node
What happens to the primitive streak? End proliferates to form a primitive node, narrow groove (primitive groove) develops in primitive streak that is continuous with a small depression in the primitive node - primitive pit
How is the mesoderm formed? Cells leave deep surface of streak and start to move between epiblast and hypoblast - forming mesenchyme which forms mesoblast which forms the embryonic mesoderm
What is mesenchyme? Embryonic CT which forms supporting tissues of the embryo such as CT
What is mesoblast? Undifferentiated mesoderm
What does the mesoblast have the potential to form? Muscles, vessels, and CT
What is the mesoderm derived from? Epiblast
How is the endoderm formed? Cells from epiblast, as well as from primitive node and other parts of primitive streak, displace hypoblast, forming embryonic endoderm in roof of umbilical vesicle
How is the ectoderm formed? Cells remaining in epiblast form embryonic ectoderm
What are all 3 germ layers derived from? Epiblast
What can mesenchymal cells derived from primitive streak differentiate to? They are pluripotential cells that can differentiate into diverse types of cells - fibroblast, chondroblast, osteoblast
What eventually happens to the primitive streak? Diminishes in relative size and becomes an insignificant structure in the sacrococcygeal region
When does the primitive streak disappear? By end of 4th week
How is the notochordal process formed? Some mesenchymal cells dive into the primitive pit and migrate cranially to form cord
How is the notochordal canal formed? Notochordal process acquires a lumen and becomes the notochordal canal
What is the role of the notochord? Gives rigidity, provides signals for development of axial muscoloskeletal structures and CNS, contributes to intervertebral discs
How does the notochordal process grow? Cranially between ectoderm and endoderm until it reaches the prechordal plate
What is the prechordal plate Small circular area of columnar endodermal cells where ectoderm and endoderm are fused
what does the prechordal plate give rise to? Endoderm of oropharyngeal membrane located at future site of oral cavity
How does the notochordal process elongate? Invagination of cells from the primitive pit
How does the primitive pit help form the notochordal canal? Extends into notochordal process forming notochordal canal
What shape is the notochordal process after forming the canal? Cellular tube that extends cranially from the primitive node to the prechordal plate
What happens to the floor of the notochordal process? Fuses with underlying embryonic endoderm
What happens after the layers of the notochordal process have fused Degenerate, resulting in formation of openings in the floor of the notochordal process -
What do the openings in the floor of the notochordal process allow? Allows communication with umbilical vesicle
Do the openings in the floor of the notochordal process remain? No, become confluent and floor of notochordal canal disappears
What happens after the floor of the notochordal canal disappears? Remains of the notochordal process form a flattened grooved notochordal plate
How is the notochord formed? Beginning at the cranial end of embryo, notochordal cells proliferate and notochordal plate infolds to form notochord
What happens to the notochord after it is formed? Becomes detached from endoderm of the umbilical vesicle, which again becomes a continuous layer
What is the function of the notochord in the beginning of embryo? Primary inductor (signaling center)
What happens to the notochord later in embryo? Developing notochord induces overlying embryonic ectoderm to thicken and form neural plate
What is the primordium of the CNS? Neural plate
What is the functio of the prechordal plate? Will become oropharyngeal membrane, prevents further notochord growth, signaling center for controlling development cranial structures
How is the cardiogenic mesoderm formed? Mesenchymal cells from primitive streak that migrate around prechordal plate to form
What is the premordium of the heart? Cardiogenic mesoderm
How is the cloacal membrane formed? Forms caudally to primitive streak
What is the future site of the anus? Cloacal membrane
What is the alantois Small, vascularized diverticulum from the caudal wall of umbilical vesicle, extending into connecting stalk
What is the function of alantois? Early blood formation and bladder development - blood vessels become umbilical arteries. Small portion persists as urachus that extends from bladder to umbilical region - becomes umbilical ligaments in adults
What does the ectoderm of the neural plate give rise to? CNS and retina
What does the neural plate correspond to at first? Corresponds in length to underlying notochord (rostral to primitive node)
What happens to the neural plate as the notochord elongates? Neural plate broadens and extends cranially as far as the oropharyngeal membrane
What happens on day 18 to the neural plate? Invaginates along its central axis to form a longitudinal median neural fold and then neural groove
What is happening at the end of the 3rd week to the neural plate? The neural folds move together and fuse, converting the neural plate into the neural tube
What is the primordium of the CNS? Neural tube
What are neural crest cells? Subset of neuroectoderm cells that lose affinity to epithelium and neighboring cells
How do neural crest cells migrate? Dorso-laterally on each side of the tube
Where do neural crest cells migrate to? Widely throughout mesenchyme
What is the neural crest Flattened mass of neural crest cells
When is neurulation complete? 4th week
How are paraxial mesoderm formed? Cells derived from primitive node form thick longitudinal column of cells - each column is continuous laterally with intermediate mesoderm
What is lateral mesoderm continuous with? Extraembryonic mesoderm covering umbilical vesicle and amnion
What happens to the paraxial mesoderm? Differentiates, condenses, and begins to divide into paired cuboidal bodies - somites
Where are the somites located? Each side of the developing neural tube
What do somites give rise to? Axial skeleton and associated musculature as well as to the adjacent dermis of skin
How does the primordium of the intraembryonic coelom appear? Isolated coelmoic spaces in the lateral mesoderm and cardiogenic mesoderm
How is the intraembryonic coelom formed Isolated spaces in lateral mesoderm and cardiogenic mesoderm soon coalesce to form a single horseshoe shaped cavity -
What does the intraembryonic coelom divide? Lateral mesoderm into two layers
What are the two layers of the lateral mesoderm? Somatic (parietal) and splanchnic (visceral) layers
What is the somatic (parietal) layer? Lateral mesoderm located beneath ectodermal epithelium and continuous with extraembryonic mesoderm covering amnion
What is the splanchnic (visceral) layer? Lateral mesoderm located adjacent to endoderm and continuous with extraemryonic mesoderm covering umbilical vesicle
What is the somatopleure? Somatic mesoderm and overlying embryonic ectoderm that forms embryonic body wall (somatopleure)
What is the splanchnopleure? Splanchnic mesoderm and underlying embryonic endoderm forming the embryonic gut (splanchnopleure)
What happens during the 2nd month to the intraembryonic coelom? Divided into 3 body cavities - pericardial, pleural, peritoneal
How does the embryo fold during the 3rd week? Along cranial caudal direction and laterally - resembling more like a tube than flat disk
As the embryo folds cranially, what begins to appear Brain vesicles and a few somites
As the embryo folds laterally, what begins to appear? Body wall is formed
What forms the foregut? Part of endoderm of umbilical vesicle incorporated into embryo
Where is the foregut located Between brain and heart
What separates the foregut from the stomoderum Oropharyngeal membrane
What is the stomodeum? Primordium of the mouth
Where is the septum transversum and what does it do? Lies caudal to heart where it develops into central tendon of the diaphragm and separates abdominal cavity from thoracic cavity
Where is the pericordial coelom after folding? Ventral to heart and cranial to the septum transversum
What projects over the cloacal membrane as embryo grows? Caudal eminence
What makes up the hindgut? Part of endodermal germ layer
What is the connecting stalk attached to? Ventral surface of embryo and the allantois is partially incoporated into embryo
What is the primordium of the umbilical cord? Connecting stalk
What produces lateral folding? Growing spinal cord and somites
How is the midgut formed? As abdominal walls form, part of endoderm germ layer is incorporated as midgut
Is there still a wide connection between the midgut and umbilical vesicle after lateral folding? No, it is reduced to an amphaloenteric duct
What happens to the region of attachment of the amnion to the central surface of the embryo after lateral folding? Reduced to a relatively narrow umbilical region
What does the ectoderm give rise to? CNS, PNS, sensory epihelia (eyes, ears, nose), epidermis and its appendages, mammary/pituitary/subcutaneous glands, enamel of teeth, melanocytes, muscle, CT, bones of pharyngeal arch origin, suprerenal medulla, meninges
What is neural crest cells derived from? Ectoderm
What does mesoderm give rise to? CT, cartilage, bone, striated and smooth muscle, heart, blood, lymphatics, KD, ovaries/testes, genital ducts, seroud membranes, spleen, cortex of suprarenal glands
What does endoderm give rise to? Epithelial lining of the Gi and respiratory tracts, urinary bladder, most of ureter, tympanic cavity; tympanic antrum; pharyngotympanic tube; parenchymal of tonsils; thyroid and parathyroid glands; thymus; LV; pancrease;
Created by: nnguyen44
 

 



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