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TEM inspection of in vitro blastocysts has allowed us to identify two types of cells that the developing embryo apparently discards. These are sequestered cells and isolated cells. Sequestered cells are groups of cells that are located in between the zona pellucida and the trophoblast. Isolated cells
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Primordial embryo. All the genetic material necessary for a new individual, along with some redundant chromosomes, are present within a single plasmalemma. Penetration of the fertilising sperm allows the oocyte to resume meiosis and the polar body is extruded.
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Ectoderm: sensory placodes, lens pit, otocyst, nasal pits moved ventrally, fourth ventricle of brain
Mesoderm: heart prominence, ossification continues Head: forebrain, eye, external acoustic meatus Body: straightening of trunk, heart, liver, umbilical cord
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Pronuclear embryo. Two separate haploid components are present - the maternal and paternal pronuclei. The pronuclei move towards each other and eventually compress their envelopes where they lie adjacent near the centre of the wall.
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Head: forebrain, eye, external acoustic meatus hearing - otic capsule connected with the basal plate and with the future exoccipitals. Tip of the cochlea is elongated and curled. Tensor tympani and stapedius present.
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The stages are delineated through the development of structures, not by size or the number of days of development, and so the chronology can vary between species, and to a certain extent between embryos. In the
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While the
Carnegie stages provide a universal system for staging and comparing the embryonic development of most vertebrates, other systems are occasionally used for the common
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This process is seen in vitro and it is not known whether this occurs in vivo. In vitro, the blastocyst rapidly collapses and slowly re-expands before hatching from the
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The initiation of cavitation indicates the start of CS3. This process leads to the differentiation of blastocysts into outer trophoblast cells and inner embryoblasts.
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Syngamic embryo. The last phase of fertilisation. The pronuclear envelopes disappear and the parental chromosomes come together in a process called
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During this process, the blastocyst breaks through and escapes from the zona pellucida. This process must occur prior to implantation into the
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There are four characteristic processes that CS3 embryos go through cavitation, collapse and expansion, hatching, and discarding of cells.
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Ectoderm: sensory placodes, nasal pits moved ventrally, fourth ventricle of brain
Mesoderm: heart prominence, ossification continues
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Limb: upper limbs longer and bent at elbow, foot plate with digital rays begin to separate, wrist, hand plate with webbed digits
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The cleavage divisions of CS2 embryos do not occur synchronously. And the fate of the blastomeres is not yet determined.
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Final embryonic stage, after this development is described as "fetal" through the entire second and third trimester.
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Limb: upper limbs longer and bent at elbow, foot plate with webbed digits, wrist, hand plate with separated digits
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It was based on work by
Streeter (1942) and O'Rahilly and MĂĽller (1987). The name "Carnegie stages" comes from the
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Ectoderm: sensory placodes, lens pit, otocyst, nasal pits moved ventrally, fourth ventricle of brain
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are a standardized system of 23 stages used to provide a unified developmental chronology of the
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Carnegie stage 2 begins when the zygote undergoes its first cell division, and ends when the
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Carnegie stage 1 is the unicellular embryo. This stage is divided into three substages.
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forms a cavity and comprises more than 16 cells. At this point, it is called a
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Hill, M.A. (2016) Embryology
Carnegie Stages. Retrieved August 19, 2016, from
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Development of the
Olfactory nerve and the early stage foot and hand plates
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On approximately day 3, at the eight-cell stage, compaction usually begins.
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https://embryology.med.unsw.edu.au/embryology/index.php/Carnegie_Stages
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The two-cell embryo is spherical and surrounded by the transparent
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when the embryo makes contact with the endometrial lining of the
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Body: straightening of trunk, intestines herniated at umbilicus
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There are only two stage 3 embryos in the
Carnegie collection.
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Body: straightening of trunk, heart, liver, umbilical cord
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Body: straightening of trunk, heart, liver, umbilical cord
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Carnegie stage 3 begins when a cavity first appears in the
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Days are approximate and reflect the days since the last
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601:Mesoderm: heart prominence, ossification continues
572:Mesoderm: heart prominence, ossification continues
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539:implementation embryo in posterior uterus wall
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275:are mainly found in the blastocystic cavity.
624:Head: eyelids, external ears, rounded head
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604:Head: nose, eye, external acoustic meatus
587:Head: nose, eye, external acoustic meatus
760:Diagrams at actual size at Visible Embryo
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755:List of structures by week, at mrc.ac.uk
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765:Virtual human embryo detailing stages
220:and ends after the hatching from the
630:Limbs: hands and feet turned inward
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55:Carnegie Institution of Washington
46:is usually replaced with the term
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688:"Carnegie Stage 3-1 Introduction"
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674:"Carnegie Stage 2 Introduction"
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803:in the first three weeks
313:bilaminar embryonic disc
302:Stage 5 (a-c): 7-12 days
730:iperiodembry/carnegie02
640:Mammalian embryogenesis
92:("Postovulatory age").
966:Regional specification
246:Collapse and expansion
1072:Intraembryonic coelom
745:Overview at umich.edu
565:Stage 20: c. 49 days
451:intermediate mesoderm
66:developmental biology
614:Stage 23: c. 56 days
597:Stage 22: c. 53 days
556:Stage 19: c. 46 days
544:Stage 18: c. 44 days
534:Stage 17: c. 41 days
524:Stage 16: c. 39 days
516:Stage 15: c. 36 days
504:Stage 14: c. 33 days
487:Stage 13: c. 32 days
474:Stage 12: c. 30 days
457:Stage 11: c. 29 days
434:Stage 10: c. 28 days
580:Stage 21: c. 51days
401:Stage 9: c. 25 days
389:Stage 8: c. 23 days
361:Stage 7: c. 19 days
330:Stage 6: c. 17 days
285:syncytiotrophoblast
270:Discarding of cells
417:septum transversum
356:early gastrulation
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192:Stage 3: 4-5 days
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202:blastocoele
40:human being
1109:Embryology
1055:Somitomere
942:Blastopore
906:Trilaminar
856:Blastocyst
851:Blastocoel
846:Cavitation
836:Blastomere
646:References
350:secondary
238:Cavitation
198:blastocyst
169:blastocyst
162:compaction
29:vertebrate
21:embryology
888:Hypoblast
879:Bilaminar
481:limb buds
442:#1 and #2
383:notochord
376:start of
294:amniotic
134:Stage 1 c
125:Stage 1 b
116:Stage 1 a
90:pregnancy
86:ovulation
1103:Category
1045:Paraxial
1032:Mesoderm
1014:Endoderm
976:Ectoderm
954:Gastrula
893:Epiblast
831:Cleavage
634:See also
352:yolk sac
319:yolk sac
317:primary
296:ectoderm
258:Hatching
152:cleavage
902:Week 3
875:Week 2
422:placode
140:syngamy
88:before
72:in the
1050:Somite
841:Morula
826:Zygote
809:Week 1
723:, and
715:(from
479:upper
426:early
226:uterus
218:morula
173:morula
157:morula
80:Stages
44:embryo
32:embryo
428:heart
74:chick
48:fetus
209:and
200:and
64:in
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