BGDA Practical 7 - Week 8
Introduction
Practical 6: Week 3 | Week 4 | Week 5 | Week 6 | Week 7 | Week 8 |
Key Events of Human Development during the eighth week (week 8) following fertilization or clinical week 10 (GA week 10).
There are 4 Carnegie stages that show external embryo development during this week.
This page will give an overview of limb and neural development and look at other system organization compared with the earlier stages.
Head
Oral Cavity Region
Sensory
Parts of each sensory system formed from placodes. Each system has a complex embryonic origin.
Neural
Cortex development commences
choroid plexus
Note
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Body
Lungs, thymus, musculoskeletal. | vertebral column, spinal cord. |
Limbs
Week 8 Limb Development |
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Human Embryo (Stage19) limb rotation |
Gastrointestinal Tract
The gastrointestinal midgut remains herniated outside of the ventral body wall.
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Genital
- Testis - mesenchyme, interstitial cells (of Leydig) secrete testosterone, androstenedione.
- Genital 8 to 12 Weeks - hCG stimulates testosterone production.
- required for internal and external genital tract development.
Human Embryo Male Testis (stage 22) | |
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- Human Stage 22: Testis - labeled overview | Testis - unlabeled overview | Testis - unlabeled detail | Testis - labeled detail | testis | Carnegie stage 22 | Movie - Urogenital stage 22
Genital Development will be covered in detail in BGDB.
Extra-embryonic Coelom
- Chorionic cavity is now lost by fusion with the expanding amniotic cavity.
Covered in more detail in the Placenta practical.
Other Embryo Systems
Movies - Embryo Carnegie stage 22 - These are rotating animations based upon reconstruction of a human embryo (stage 22) serial slice images.
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Critical Periods
Critical Periods of Human Development | ||||||||||||||||||||
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Conceptus | Embryonic development (weeks) | Fetal period (weeks) | ||||||||||||||||||
Neural | ||||||||||||||||||||
Heart | ||||||||||||||||||||
Upper limbs | ||||||||||||||||||||
Lower limbs | ||||||||||||||||||||
Ear | ||||||||||||||||||||
Eye | ||||||||||||||||||||
Palate | ||||||||||||||||||||
Teeth | ||||||||||||||||||||
External genitalia | ||||||||||||||||||||
Loss | Major abnormalities | Functional and Minor abnormalities | ||||||||||||||||||
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Practical 6: Week 3 | Week 4 | Week 5 | Week 6 | Week 7 | Week 8 |
Additional Information
Additional Information - Content shown under this heading is not part of the material covered in this class. It is provided for those students who would like to know about some concepts or current research in topics related to the current class page. |
Timeline
Week 8 - Human Embryo Stages and Events (GA week 10) | ||
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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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Week 8 - Stage 22
These sections provide a detailed histological overview of the internal structures present within the embryo by the end of the embryonic period.
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Selected Embryo Histology - Week 8 (Stage 22) |
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Links: Carnegie stage 22 | Week 8 |
All Stage 22 Sections | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
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These are low resolution histology images, the section images start at the head (cranial) end of the embryo and run to the caudal (tail) end. There are available both labelled and unlabelled versions of each section.
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Practical 6: Week 3 | Week 4 | Week 5 | Week 6 | Week 7 | Week 8 |