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41 Cards in this Set
- Front
- Back
zygote
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male and female pronuclei join
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zona pellucida
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membrane + ova
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Cleavage
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mitotic division without growth, occuring as it moves the uterine horn
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blastomers
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ball of cells
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morula
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ball of blastomeres
when morula reaches the uterine cavity the zona pellucida dissolves, influx of fluid creates a cavity in the morula and it is now called a blastocyst |
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development of the blastocyst:
trophoblast: Inner Cell Mass (ICM) |
= single layer of cells surrounds the blastocyst cavity. Will form an extraembryonic membrane (placenta), and will undergo further differentiation
ICM = at one of the blastocyst will form embryo |
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6 days after fertilization
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blastocyst contacts uterine wall and beings inplantation
trophoblast differentiates into inner cytotrophoblast and outer invasive layer called syncytiotrophoblast, they both develop into placenta |
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Formation of primative germ layers and cavities
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Amniotic fluid
hypoblast epiblast primative yolk sac |
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Amniotic Cavity
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space develops b/w ICM and trophoblast
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hypoblast
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ICM cells facing blastocyst layer
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epiblast
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cells b/w the hypoblast and amniotic cavity segregate to this, all tissue from the embryo are derived from this
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Primative Yolk Sack
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hypoblast line the blastocyst forming this, lined by extraembryonic endoderm
epiblast cells line the amniotic cavity and form the extraembryonic ectoderm hypoblast cells stream out and form the extraembryonic mesoderm layer surrounding the amnion and yolk sac now have a small bi-layered embryonic disc situatied between the yolk sac and amnion |
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Gastrulation (3 weeks po)
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Main Events:
1. formation of the primative streak 2. formation of 3 embryonic germ layers (trilaminer disc) 3. formation of the notochord |
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formation of the primative streak
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epiblast cells migrate medially and form the middle thickening = primative streak,
cranial end of the streak = primative node - important for organizing center of embryo depressions form the primative pit in the node and primative groove in the streak |
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formation of the trilaminar disc
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epiblast cells migrate inwards at primative groove and pit and form new layer (3rd layer) b/w epiblast and hypoblast = embryonic mesoderm
some epiblast cells migrate in and replace hypoblast cells forming a new layer below the mesoderm and above the yolk sac = embryonic endoderm surface epiblast cells = embryonic ectoderm |
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Migrating mesodermal cells follow distinct migration routes and will form
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precordal plate
notochord different layers of mesoderm |
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precordal plate
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first cells to migrate, migrate cranially from primative pit
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notochord
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cells follow precordal plate cells, migrate cranially from pit and form medial cord of cells extending from pit to precordal plate
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cells migrating in at the primative streak form: (from cranial to caudal)
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paraxial mesoderm - most medial
intermediate mesoderm lateral mesoderm extraembryonic mesoderm - most lateral |
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oropharyngeal (buccopharyngeal) membrane
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at cranial and caudal ends of the embryo, mesoderm cells do not migrate between endoderm and ectoderm. in these areas, the ectoderm is fused to the endoderm forming this membrane cranialy and the clocal membrane caudally
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Caudal Dysgenesis
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epiblast cells stop migration to soon and caudal end of the embryo does not develop properly
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sirenimelia
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most severe form of caudal dysegenesis
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Notochord Development
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cells migrate cranially from the primative pit and form midline cord of cells extending from the node to precordal plate. Primative pit extends into the cord creating a canal. Floor of canal fuses with endoderm forming the notochrodal plate, short transient neuroenteric canal
notochordal plate proliferates and infolds forming notochord. Notochord detaches from the underlying endodern notochord is the primary inducer of differentiation of embryonic tissues. vertebral column forms around notochord and most of it degenerates except for a small portion that form the nucleus pulposus of ithe IV disc it is a transient structure for the development of the neural tube |
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notochordal plate
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fused layers degenerative leaving roof of canal
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neuroenteric canal
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short transient communication betwen the two divisions, yolk sac and amnion, if persists results in a rare defect where central canal of spinal cord communicates with intestines
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Primative Node
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genes in this area determine the organization of the embryo and development of the embryo axes cranial-caudal, dorsal-ventral, left-right
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Reversal of Laterality Sequences
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Partial: partial defects in left and right sideness
Situs Inversis: complete reversal of left and right |
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Neuralation (complete by 4 weeks po): formation of the neural tube
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ectoderm over notochord (mesoderm) thickens and forms neural plate (neuroectoderm)
neural plate invaginates forming neural folds on either side of the neural grove neural folds approach each other and fuse forming neural tube. closure starts in the cervical area and extends cranially and caudally anterior and posterior neuropores: anterior closes first (25 days po), then posterior (28 po) as neural folds approach each other, neural creast cells seperate from the creast of neural folds and form clusters dorsolateral to neural tube ectoderm closes over the surface and mesoderm surrounds the neural tube Mesoderm - vertebrae and meninges Neural Tube - CNS Neural Crest - PNS, meninges, head, mesenchyme, melanocytes, adrenal medulla |
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Neural Tube Defects
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can occur if neural tube doesnt close or defects in induction of other tissues
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neaural tube does not close
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anencephaly - lack of brain
spina bifida cystica rachischisis - most severe, no brain,loss of spinal cord |
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neural tube closes but other tissue defects
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protrusion of the meninges = meningocele
protrusion of the meninges + neural tissue = encephalocele and myelomeningocele vertebral defects = spina bifida occulta, least severe |
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Mesoderm migration, organization, and its derivatives
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1. precordal plate cells - induce forebrain development
2. notochord 3. cardiogenic area - mesoderm cells that migrate around precordal plate, lie cranial to neural tube but will be drawn ventral caudally with embryo folding 4. paraxial mesoderm - closest to neural tube, gives rise to somites, in the cranial region referred to as somatomeres |
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somite formation
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paraxial mesoderm proliferates and segregates
head region: remains loosely arranged = somatomeres neural crest + somatomeres form head mesenchyme head mesenchyme - pharyngeal arches, bones and CT of cranical facial structures from occipital reigion to caudal region paraxial mesoderm segregates and forms paired somites on either side of the developing neural tube, by week 5 po 42-44 pairs of somites somite mesoderm organizes further (from paraxial mesoderm) |
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Scelrotome
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ventral medial region to- bone forming cells of vertebra and ribs
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Epimere
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dorsolateral region to - muscles, CT of the back proper muscles (dorsal muscles)
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hypomere
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dorsolateral region to - muscles of the CT body wall and extremities, ventral muscles and limbs
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dermatome
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dorsal most region to - dermis of skin
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Intermediate mesoderm
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urogenital organs, ducts and glands
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lateral (plate) mesoderm
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forms layer extending from intermediate mesoderm to edges of embryonic disc (starts out as a solid and then spaces appear)
spaces apprear in lateral mesoderm and seperate into 2 layers with a space inbetween somatic (parietal) layer: lines inner body wall (under the mesoderm) splanchnic (visceral) layer:gut organ muscles + CT , gut organ derivatives |
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intraembryonic cavity (coelom)
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space betwen layers, body cavities
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Folding of the embryo
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folding of cranial and caudal ends occur simultaneously with later foldings and results in:
1. head and tail folds tuck under, cardiogenic area brought in ventrally 2. endoderm forms gut tube surrounded by splanchinic mesoderm, small caudal outpocket = allantosis, gut tube connected to yolk sac by vitrelline duct 3. amnion is pulled ventrally and surrounds entire embryo 4. "purse string" effect draws vitrillene duct, allantosis and body stalk together to form an umbillica ring |