Week 8
Embryology - 1 Dec 2023    Expand to Translate
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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 | |||
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| 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 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 |
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 | ||
| Event | ||
| Stage 20 |
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 | |
| Gastrointestinal Tract anal (cloacal) membrane perforates | ||
| Stage 21 |
neural - cortical plate appears in the area of future insula[2] limb upper and lower limbs rotate Intraembryonic Coelom pericardioperitoneal canals close | |
| Stage 22 |
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] | |
| 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) | ||
| Stage 23 | 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
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| Event | ||
| Stage 20 |
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 | |
| Gastrointestinal Tract anal (cloacal) membrane perforates | ||
| Stage 21 |
Neural - cortical plate appears in the area of future insula[2] Limb upper and lower limbs rotate Intraembryonic Coelom pericardioperitoneal canals close | |
| Stage 22 | Neural - 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] | |
| 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) | ||
| Stage 23 | 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
- ↑ 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
- ↑ 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
- ↑ 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
- ↑ Müller F & O'Rahilly R. (2004). Olfactory structures in staged human embryos. Cells Tissues Organs (Print) , 178, 93-116. PMID: 15604533 DOI.
- ↑ 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.
- ↑ 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. (2023, December 1) Embryology Week 8. Retrieved from https://embryology.med.unsw.edu.au/embryology/index.php/Week_8
- © Dr Mark Hill 2023, UNSW Embryology ISBN: 978 0 7334 2609 4 - UNSW CRICOS Provider Code No. 00098G
