Difference between revisions of "Week 8"

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==Carnegie Stages==
 
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Historic [[Carnegie Stages]] 20 to 23.
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{{Carnegie stage 20 links}}
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{{Carnegie stage 21 links}}
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{{Carnegie stage 22 links}}
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{{Carnegie stage 23 links}}
  
 
==Timeline==
 
==Timeline==

Latest revision as of 10:34, 16 March 2020

Embryology - 4 Jun 2020    Facebook link Pinterest link Twitter link  Expand to Translate  
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A personal message from Dr Mark Hill (May 2020)  
Mark Hill.jpg
I have decided to take early retirement in September 2020. During the many years online I have received wonderful feedback from many readers, researchers and students interested in human embryology. I especially thank my research collaborators and contributors to the site. The good news is Embryology will remain online and I will continue my association with UNSW Australia. I look forward to updating and including the many exciting new discoveries in Embryology!

Key Events of Human Development during the eighth week (week 8) following fertilization or clinical gestational age GA week 10 (LMP). At the end of the embryonic period in week 8 about 90% of the adult anatomical structures have formed.

This is the final week of embryonic development, after this we describe all future development as Fetal Development.

Carnegie Stages: 20 | 21 | 22 | 23
Week 8 Links: stage 20 | stage 21 | stage 22 | stage 23 | Lecture - Head | Outflow Tract | Heart Valves | Category:Week 8 | GA week 10

Carnegie Stages

Week: 1 2 3 4 5 6 7 8
Carnegie stage: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23


Historic Carnegie Stages 20 to 23.

Stage 20 Links: Week 8 | System Development | Lecture - Limb | Lecture - Head Development | Lecture - Sensory | Science Practical - Head | Science Practical - Sensory | Science Practical - Urogenital | Historic - Skull Development | Carnegie Embryos | Category:Carnegie Stage 20 | Next Stage 21
  Historic Papers: 1914 head | 1954 Stage 19-23


Stage 21 Links: Week 8 | System Development | Lecture - Limb | Lecture - Head Development | Lecture - Sensory | Science Practical - Head | Science Practical - Sensory | Science Practical - Urogenital | Historic - Skull Development | Carnegie Embryos | Madrid Embryos | Category:Carnegie Stage 21 | Next Stage 22
  Historic Papers: 1897 Coelom | 1911 Larynx | 1954 Stage 19-23


Stage 22 Links: Week 8 | System Development | Lecture - Limb | Lecture - Head Development | Lecture - Sensory | Science Practical - Head | Science Practical - Sensory | Science Practical - Urogenital | Historic - Skull Development | Carnegie Embryos | Madrid Embryos | Category:Carnegie Stage 22 | Next Stage 23
Week 8, GA week 10, 54 - 56 days, CRL 23 - 28 mm, Carnegie Embryos
  Historic Papers: 1914 | 1954 Stage 19-23


Stage 23 Links: Week 8 | System Development | Lecture - Limb | Lecture - Head Development | Lecture - Sensory | Science Practical - Head | Science Practical - Sensory | Science Practical - Urogenital | Historic - Skull Development | Carnegie Embryos | Madrid Embryos | Category:Carnegie Stage 23 | Next Fetal Development
  Historic Papers: 1954 Stage 19-23

Timeline

Week 8 - Human Embryo Stages and Events (GA week 10) 
Embryo Week: Week 1 | Week 2 | Week 3 | Week 4 | Week 5 | Week 6 | Week 7 | Week 8 | Week 9
Day
Stage
Event
50
Stage 20 Stage20 bf1c.jpg

Head scalp vascular plexus visible

limb upper limbs begin to rotate ventrally

neural - amygdaloid body has at least four individual nuclei[1]

oculomotor nerve shows a dorsolateral and a ventromedial portion

rhombic lip (rhombencephalon) formation of the cerebellum (intermediate layer) and of the cochlear nuclei

cerebellum cell layer (future Purkinje cells) develops

choroid plexuses of the fourth and lateral ventricles

51
  Gastrointestinal Tract anal (cloacal) membrane perforates
52
Stage 21 Stage21 bf1c.jpg

neural - cortical plate appears in the area of future insula[2]

limb upper and lower limbs rotate

Intraembryonic Coelom pericardioperitoneal canals close

53
   
54
Stage 22 Stage22 bf1c.jpg

neural - neocortical fibres project to epithalamus, to dorsal thalamus, and to mesencephalon[2]

limb fingers and toes lengthen

Sense - Smell Stage 22 to early fetal period - migratory streams of neurons from the subventricular zone of the olfactory bulb towards the future claustrum[3]

55
Genital 8 Weeks Testis - mesenchyme, interstitial cells (of Leydig) secrete testosterone, androstenedione

Genital 8 to 12 Weeks - hCG stimulates testosterone production

Tongue Week 8 - nerves penetrate epitheilai basal lamina and synapse with undifferentiated, elongated, epithelial cells (taste bud progenitor cell)

56
Stage 23 Stage23 bf1c.jpg Stage 23 defines the end of the embryonic (organogenesis) period

mesoderm heart prominence, ossification continues

Head nose, eye, external acoustic meatus, eyelids, external ears, rounded head

Body - straightening of trunk, heart, liver, umbilical cord, intestines herniated at umbilicus

limb upper limbs longer and bent at elbow, hands and feet turned inward, foot with separated digits, wrist, hand with separated digits

Extraembryonic Coelom chorionic cavity is now lost by fusion with the expanding amniotic cavity

neural - rhombencephalon, pyramidal decussation present, nuclei and tracts similar to those present in the newborn cerebellum present as only a plate connected to midbrain and hindbrain through fibre bundles[4]

axial skeleton vertebral column 33 or 34 cartilaginous vertebrae (20-33 mm in total length), vertebral pedicles, articular and transverse processes identifiable (no spinous processes)[5]

 
Week 8 stomach - Week 8 - Gastrin containing cells in stomach antrum. Somatostatin cells in both the antrum and the fundus.
Note - the day timing of stages is only approximate, system names link to first page of that specific system, and events are based upon the literature cited below.
References
  1. Müller F & O'Rahilly R. (1990). The human brain at stages 18-20, including the choroid plexuses and the amygdaloid and septal nuclei. Anat. Embryol. , 182, 285-306. PMID: 2268071
  2. 2.0 2.1 Müller F & O'Rahilly R. (1990). The human brain at stages 21-23, with particular reference to the cerebral cortical plate and to the development of the cerebellum. Anat. Embryol. , 182, 375-400. PMID: 2252222
  3. Müller F & O'Rahilly R. (2004). Olfactory structures in staged human embryos. Cells Tissues Organs (Print) , 178, 93-116. PMID: 15604533 DOI.
  4. Müller F & O'Rahilly R. (1990). The human rhombencephalon at the end of the embryonic period proper. Am. J. Anat. , 189, 127-45. PMID: 2244584 DOI.
  5. O'Rahilly R, Muller F & Meyer DB. (1980). The human vertebral column at the end of the embryonic period proper. 1. The column as a whole. J. Anat. , 131, 565-75. PMID: 7216919


Day
Stage
Event
50
Stage 20 Stage20 bf1c.jpg

Head scalp vascular plexus visible

Limb upper limbs begin to rotate ventrally

Neural - amygdaloid body has at least four individual nuclei[1]

oculomotor nerve shows a dorsolateral and a ventromedial portion

rhombic lip (rhombencephalon) formation of the cerebellum (intermediate layer) and of the cochlear nuclei

cerebellum cell layer (future Purkinje cells) develops

choroid plexuses of the fourth and lateral ventricles

51
  Gastrointestinal Tract anal (cloacal) membrane perforates
52
Stage 21 Stage21 bf1c.jpg

Neural - cortical plate appears in the area of future insula[2]

Limb upper and lower limbs rotate

Intraembryonic Coelom pericardioperitoneal canals close

53
   
54
Stage 22 Stage22 bf1c.jpgNeural - neocortical fibres project to epithalamus, to dorsal thalamus, and to mesencephalon[3]

Limb fingers and toes lengthen

Sense - Smell Stage 22 to early fetal period - migratory streams of neurons from the subventricular zone of the olfactory bulb towards the future claustrum[4]

55
Genital 8 Weeks Testis - mesenchyme, interstitial cells (of Leydig) secrete testosterone, androstenedione

Genital 8 to 12 Weeks - hCG stimulates testosterone production

Tongue Week 8 - nerves penetrate epitheilai basal lamina and synapse with undifferentiated, elongated, epithelial cells (taste bud progenitor cell)

56
Stage 23 Stage23 bf1c.jpg Stage 23 defines the end of the embryonic (organogenesis) period

Mesoderm heart prominence, ossification continues

Head nose, eye, external acoustic meatus, eyelids, external ears, rounded head

Body - straightening of trunk, heart, liver, umbilical cord, intestines herniated at umbilicus

Limb upper limbs longer and bent at elbow, hands and feet turned inward, foot with separated digits, wrist, hand with separated digits

Extraembryonic Coelom chorionic cavity is now lost by fusion with the expanding amniotic cavity

Neural - rhombencephalon, pyramidal decussation present, nuclei and tracts similar to those present in the newborn cerebellum present as only a plate connected to midbrain and hindbrain through fibre bundles[5]

Axial Skeleton vertebral column 33 or 34 cartilaginous vertebrae (20-33 mm in total length), vertebral pedicles, articular and transverse processes identifiable (no spinous processes)[6]

 
Week 8 Stomach - Week 8 - Gastrin containing cells in stomach antrum. Somatostatin cells in both the antrum and the fundus.

References

  1. Müller F & O'Rahilly R. (1990). The human brain at stages 18-20, including the choroid plexuses and the amygdaloid and septal nuclei. Anat. Embryol. , 182, 285-306. PMID: 2268071
  2. Müller F & O'Rahilly R. (1990). The human brain at stages 21-23, with particular reference to the cerebral cortical plate and to the development of the cerebellum. Anat. Embryol. , 182, 375-400. PMID: 2252222
  3. Müller F & O'Rahilly R. (1990). The human brain at stages 21-23, with particular reference to the cerebral cortical plate and to the development of the cerebellum. Anat. Embryol. , 182, 375-400. PMID: 2252222
  4. Müller F & O'Rahilly R. (2004). Olfactory structures in staged human embryos. Cells Tissues Organs (Print) , 178, 93-116. PMID: 15604533 DOI.
  5. Müller F & O'Rahilly R. (1990). The human rhombencephalon at the end of the embryonic period proper. Am. J. Anat. , 189, 127-45. PMID: 2244584 DOI.
  6. O'Rahilly R, Muller F & Meyer DB. (1980). The human vertebral column at the end of the embryonic period proper. 1. The column as a whole. J. Anat. , 131, 565-75. PMID: 7216919



Embryo Week: Week 1 | Week 2 | Week 3 | Week 4 | Week 5 | Week 6 | Week 7 | Week 8 | Week 9


Carnegie Stages: 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | 11 | 12 | 13 | 14 | 15 | 16 | 17 | 18 | 19 | 20 | 21 | 22 | 23 | About Stages | Timeline


Glossary Links

Glossary: A | B | C | D | E | F | G | H | I | J | K | L | M | N | O | P | Q | R | S | T | U | V | W | X | Y | Z | Numbers | Symbols | Term Link

Cite this page: Hill, M.A. (2020, June 4) Embryology Week 8. Retrieved from https://embryology.med.unsw.edu.au/embryology/index.php/Week_8

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© Dr Mark Hill 2020, UNSW Embryology ISBN: 978 0 7334 2609 4 - UNSW CRICOS Provider Code No. 00098G