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47 Cards in this Set
- Front
- Back
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Compaction
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About 8-16 cells.
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What happens after compaction?
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Cells in the inner cell mass are no longer totipotent, only pluripotent
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Gastrulation
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Formation of 3 layers from 2 layers. Cells migrate through primitive groove. Hypoblast is replaced. First cells to ingress are endoderm, later cells are mesoderm. Cells which DO not ingress = Ectoderm
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Fate of Blastocyst
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The Blastocyst forms the the Inner Cell Mass (ICM) and trophoblast
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What do cells in ICM segregate to form?
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Epiblast and Hypoblast. Epiblast is dorsal to the hypoblast
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Epiblast
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Embryo proper. Dorsal to hypoblast
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Hypoblast
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primary extraembryonic endoderm - forms yolk sac
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Primitive Streak
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First marker of craniocaudal axis. From proliferation and migration of cells. Cranial end forms primitive node
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Primitive Node
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Signaling center. Fate is determined by their position and distance from node. Timing/location helps specify and refine cell fates.
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Primitive Groove
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Depression in middle of primitive streak. Cells migrate through this during gastrulation.
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Location of Node
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Located anterior end of primitive streak
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What growth factors do cells express?
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BMP4 (bone morphogenetic protein 4 - a TGFβ family member) and FGF (fibroblast growth factors)
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What do BMP4 and FGF cause?
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Mesoderm to ventralize into intermediate and lateral plate mesoderm.
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What does the inhibition of BMP4 cause?
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With FGF and anti-BMP4, the mesoderm dorsalizes to form notochord and somitic mesoderm (paraxial mesoderm)
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What does the node secrete?
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BMP antagonists (ex Chordin, Noggin)
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What is the neural plate formed from?
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Dorsal ectoderm overlying the presumptive notochord
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Generally, what does ectoderm form?
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epithelium and nervous system
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How does the neural groove form?
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Lateral edges of ectoderm become elevated to form neural folds, mid-region becomes depressed
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How is a neural tube formed?
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Neural folds move towards each other and fuse. The neural tube then detaches from the overlying ectoderm.
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What germ layer is the neural tube from?
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Ectoderm
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What germ layer is the notochord formed from?
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Mesoderm.
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What is the notochord
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A signaling node. Sends signals affecting ectoderm.
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What is neurulation?
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The formation of the neural tube.
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How does the neural tube form?
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The tube forms in the middle first (neck region). Then fusion proceeds away in both directions. (cranial and caudal)
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What are the transient openings at either end of the neural tube?
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cranial and caudal neuropores
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How long does neurulation take?
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About 27 days
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What does incomplete fusion of neuropores cause?
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Neural tube defects, such as spina bifida and anencephaly
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What interacts during formation of the neural tube?
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Folic acid/cholesterol and numerous genes (Pax3, sonic hedgehog..)
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Notochord
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Structure that defines the body axis and phylum. Provides rigidity to embryo. Acts as a signaling center. Precursor for axial skeleton.
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What is a source of sonic hedgehog (SHH?)
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notochord
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What does notochord SHH and BMP induce?
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They induce neural plate.
SHH induces the floorl plate, which becomes a source of SHH. SHH patterns ventral NT fate, while BMPS pattern dorsal NT fate. |
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What type of neurons arise from dorsal and ventral NT?
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Dorsal = sensory neurons
Ventral = motor neurons |
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Why is it important to have both BMP and SHH?
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There has to be a gradient. At the BMP side, there are anti-SHHs expressed, and anti-BMP at the SHH side. This is so the size of the tube or gradient doesn't matter when forming the neural tube.
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How is the neural crest formed?
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During the formation of the Neural tube, the dorsal most portion of the neural tube gives rise to the neural crest.
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Why is the neural crest important?
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These cells form the mesenchymal, which migrate through the mesoderm to form a variety of tissues/organs
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What are the 4 neural crest cell regions?
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Cranial neural crest
Cardiac Neural crest Vagal/sacral neural crest trunk neural crest (dorsolateral and ventromedial) |
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What does the cranial neural crest form?
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Migrate dorsolaterally to form craniofacial mesenchyme --> becomes cartilage, bone, neurons, glia, and connective tissue of face. Som enter pharyngeal arches, contribute to thymus, tooth primordia, and middle ear/jaw bone
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What is cardiac neural crest?
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Gives rise to outflow tract septum (separates pulmonary/aortic circulation), and smooth muscle around large arteries arising from heart
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Trunk Neural Crest
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Dorsolateral - melanocytes
ventromedial - (through anterior somite) - dorsal root ganglia/nerves |
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What are the 4 regions/types of mesoderm?
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Axial (chordamesoderm)
paraxial mesoderm intermediate mesoderm lateral plate mesoderm |
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Paraxial mesoderm
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Unsegmented mesoderm becomes somitomeres formed in craniocaudal sequence. Give rist to sclerotome -surrounds neural tube/notochord and becomes cartilage cells of vertebrae and ribs. --Dermamyotome -> forms skeletal muscle and skin
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Intermediate mesoderm
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Urogenital structures. Segmental in cervical/thoracic regions, becomes nephrotomes. Nephrogenic cord, and gonads
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Lateral plate Mesoderm: Parietal mesoderm
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lateral and ventral body walls, thins serous membranes lining body cavity
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Lateral Plate Mesoderm: Visceral mesoderm (splanchnic)
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with endoderm forms gut wall, and thins serous membrane around each organ
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Lateral plate mesoderm: Visceral mesoderm of yolk sac
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Angioblasts -- give rise to endothelial cells and blood cells
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Endoderm
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GI tract, epithelial lining of lung buds and trachea, liver, gall bladder, pancreas. Anterior foregut and posterior hindgut.
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Folding of embryo
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All occurs at the same time. Lateral folding and head/tail folding.
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