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In embryology, 'Carnegie stages' are a standardized system of 23 stages used to provide a unified developmental chronology of the vertebrate embryo.
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. It only covers the first 60 days of development; at that point the term embryo is usually replaced with the term fetus.
It was based on work by Streeter (1942) and O'Rahilly and Müller (1987). The name "Carnegie stages" comes from the Carnegie Institute.
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 model organisms in developmental biology, such as the Hamburger-Hamilton stages in the chick.
Stages
Days are approximate, and reflect the days since the last ovulation before pregnancy ("Postovulatory age").
Stage 1: 1 days
★ fertilization
★ polar bodies
Stage 2: 3 days
★ cleavage
★ morula
★ compaction
Stage 3: 4 days
★ blastocyst and blastocoele
★ embryonic disk
★ trophoblast and embryoblast
Stage 4: 5-6 days
★ syncytiotrophoblast
★ cytotrophoblast
★ amniotic ectoderm
Stage 5 (a-c): 7-12 days
★ implantation
★ bilaminar germ disk
★ primary yolk sac
★ amniotic cavity
Stage 6: 13-15 days
★ primitive streak
★ primitive groove
★ chorionic villi
★ secondary yolk sac
Stage 7: 15-17 days
★ gastrulation
★ neural plate
★ start of hematopoiesis
★ notochord
Stage 8: 17-19 days
★ primitive pit
Stage 9: 19-21 days
★ neural groove
★ neural folds
★ septum transversum
★ placode
★ early heart
Stage 10: 21-23 days
★ pharyngeal arches #1 and #2
★ cardiac loop
★ intermediate mesoderm
Stage 11: 23-26 days
★ sinus venosus
★ mesonephric duct
Stage 12: 26-30 days
★ upper limb buds
Stage 13: 28-32 days
★ septum primum
★ foramen primum
Stage 14: 31-35 days
★ ureteric bud
Stage 15: 35-38 days
Stage 16: 36-42 days
Stage 17: 42-44 days
Stage 18: 44-48 days
★ septum secundum
Stage 19: 48-51 days
Stage 20: 51-53 days
Stage 21: 53-54 days
Stage 22: 54-58 days
Stage 23: 56-60 days
See also
★ Mammalian embryogenesis
External links
★
★
★ Photos at unsw.edu.au
★ Overview at umich.edu
★ Details on stages at lsuhsc.edu
★ List of structures by week, at mrc.ac.uk
★ Diagrams at actual size at Visible Embryo
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