BGDA Lecture - Development of the Embryo/Fetus 2: Difference between revisions
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{{Header}} | |||
==Introduction== | ==Introduction== | ||
[[File:Human development timeline graph 02.jpg|thumb|400px]] | [[File:Human development timeline graph 02.jpg|thumb|400px]] | ||
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This lecture covers the period of Embryonic development, in Humans from week 3 to week 8 ({{GA}} week 5-10) and is divided into 23 Carnegie stages of embryonic development. There will also be a brief introduction to fetal development. Note, the period from week 9 to week 38 is considered Fetal development and will be covered in detail in the [[BGDA_Practical_-_Fetal_Development|Laboratory 12]]. | This lecture covers the period of Embryonic development, in Humans from week 3 to week 8 ({{GA}} week 5-10) and is divided into 23 Carnegie stages of embryonic development. There will also be a brief introduction to fetal development. Note, the period from week 9 to week 38 is considered Fetal development and will be covered in detail in the [[BGDA_Practical_-_Fetal_Development|Laboratory 12]]. | ||
[[Media:2019 BGDA Lecture - Development of the Embryo-Fetus 2.pdf|'''2019 Lecture PDF''']] | |||
===Lecture Objectives=== | ===Lecture Objectives=== | ||
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* Brief understanding of organ and system formation (functional / not functional). | * Brief understanding of organ and system formation (functional / not functional). | ||
* Brief understanding of critical periods of development. | * Brief understanding of critical periods of development. | ||
<br> | |||
{{OneMinuteClock}} | |||
[[One_Minute_Embryology#Human_Embryo|'''1 Minute Embryology''']] | [https://thebox.unsw.edu.au/video/1-minute-embryology-human-embryo UNSW theBox] | |||
<br><br> | |||
{| class="wikitable mw-collapsible mw-collapsed" | {| class="wikitable mw-collapsible mw-collapsed" | ||
! Lecture Archive | ! Lecture Archive | ||
|- | |- | ||
| [https://embryology.med.unsw.edu.au/embryology/index.php?title=BGDA_Lecture_-_Development_of_the_Embryo/Fetus_2&oldid=179651 2015] | [https://embryology.med.unsw.edu.au/embryology/index.php?title=BGDA_Lecture_-_Development_of_the_Embryo/Fetus_2&oldid=138489 2014] | [http://embryology.med.unsw.edu.au/embryology/index.php?title=BGDA_Lecture_-_Development_of_the_Embryo/Fetus_2&printable=yes 2014 PDF] | [[BGDA_Practical_-_Implantation_to_8_Weeks|Practical 6 Embryonic Development]] | [[BGDA_Practical_-_Fetal_Development|Practical 12 Fetal Development]] | | [https://embryology.med.unsw.edu.au/embryology/index.php?title=BGDA_Lecture_-_Development_of_the_Embryo/Fetus_2&oldid=339100 2018] | [Media:2018 BGDA Lecture - Development of the Embryo-Fetus 2.pdf 2018 PDF] | [https://embryology.med.unsw.edu.au/embryology/index.php?title=BGDA_Lecture_-_Development_of_the_Embryo/Fetus_2&oldid=286557 2017] | [[Media:2017 BGDA Lecture - Development of the Embryo-Fetus 2.pdf|2017 PDF]] | | ||
[https://embryology.med.unsw.edu.au/embryology/index.php?title=BGDA_Lecture_-_Development_of_the_Embryo/Fetus_2&oldid=228857 2016] | | |||
[https://embryology.med.unsw.edu.au/embryology/index.php?title=BGDA_Lecture_-_Development_of_the_Embryo/Fetus_2&oldid=179651 2015] | [https://embryology.med.unsw.edu.au/embryology/index.php?title=BGDA_Lecture_-_Development_of_the_Embryo/Fetus_2&oldid=138489 2014] | [http://embryology.med.unsw.edu.au/embryology/index.php?title=BGDA_Lecture_-_Development_of_the_Embryo/Fetus_2&printable=yes 2014 PDF] | [http://embryology.med.unsw.edu.au/embryology/index.php?title=BGDA_Lecture_-_Development_of_the_Embryo/Fetus_2&oldid=123345 2013] | [http://php.med.unsw.edu.au/embryology/index.php?title=BGDA_Lecture_-_Development_of_the_Embryo/Fetus_2&oldid=91874 2012] | [[2010_BGD_Lecture_-_Development_of_the_Embryo/Fetus_2|2010]] | [[BGDA_Practical_-_Implantation_to_8_Weeks|Practical 6 Embryonic Development]] | [[BGDA_Practical_-_Fetal_Development|Practical 12 Fetal Development]] | |||
|} | |} | ||
{| class="wikitable mw-collapsible mw-collapsed" | {| class="wikitable mw-collapsible mw-collapsed" | ||
! Textbooks | ! Textbooks | ||
|- | |- | ||
| | | | ||
===UNSW Embryology=== | ===UNSW Embryology=== | ||
{| | {| | ||
| [[File:Logo.png|90px]] | | [[File:Logo.png|90px]] | ||
| {{Embryo citation}} | | {{Embryo citation}} | ||
* {{human timeline}} | {{first trimester timeline}} | |||
* [[Week 3]] | [[Week 4]] | [[Week 5]] | [[Week 6]] | [[Week 7]] | [[Week 8]] | * [[Week 3]] | [[Week 4]] | [[Week 5]] | [[Week 6]] | [[Week 7]] | [[Week 8]] | ||
* | * {{fetal}} | ||
* | * {{abnormal development}} | {{birth}} | {{neonatal}} | [[Neonatal Diagnosis]] | ||
{{prenatal diagnosis}} | |||
|} | |} | ||
===The Developing Human: Clinically Oriented Embryology=== | ===The Developing Human: Clinically Oriented Embryology=== | ||
{{MPT2015APAcitation}} (links only function with UNSW connection) | |||
{| | {| | ||
|- | |- | ||
| [[File:The Developing Human, | | [[File:The Developing Human, 10th edn.jpg|90px]] | ||
| | | | ||
Chapter 5 [http://ebookcentral.proquest.com.wwwproxy1.library.unsw.edu.au/lib/unsw/reader.action?docID=2074364&ppg=104 Fourth to Eighth Weeks of Human Development] | |||
Chapter 6 [http://ebookcentral.proquest.com.wwwproxy1.library.unsw.edu.au/lib/unsw/reader.action?docID=2074364&ppg=132 Fetal Period] | |||
Chapter 20 [http://ebookcentral.proquest.com.wwwproxy1.library.unsw.edu.au/lib/unsw/reader.action?docID=2074364&ppg Human Birth Defects] | |||
{{UNSW textbook - The Developing Human}} | |||
|} | |||
===Larsen's Human Embryology=== | |||
{{Larsen2015APAcitation}}(links only function with UNSW connection) | |||
{| | |||
|- | |||
| [[File:Larsen's human embryology 5th ed.jpg|90px]] | |||
| | |||
Chapter 4 [http://ebookcentral.proquest.com.wwwproxy1.library.unsw.edu.au/lib/unsw/reader.action?docID=2074524&ppg=100 Fourth Week: Forming the Embryo] | |||
Chapter 6 [http://ebookcentral.proquest.com.wwwproxy1.library.unsw.edu.au/lib/unsw/reader.action?docID=2074524&ppg=151 Fetal Development and the Fetus as Patient] | |||
{{UNSW textbook - Larsen's Human Embryology}} | |||
|} | |} | ||
[[Embryology_Textbooks|More Textbooks?]] | [[Embryology_Textbooks|More Textbooks?]] | ||
|} | |} | ||
===BGDA Practical Classes=== | ===BGDA Practical Classes=== | ||
{{BGDAPracTable}} | {{BGDAPracTable}} | ||
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'''Mesoderm''' means the "middle layer" and it is from this layer that the body's connective tissues are derived (note that the head neural crest ectoderm also forms connective tissues) | '''Mesoderm''' means the "middle layer" and it is from this layer that the body's connective tissues are derived (note that the head neural crest ectoderm also forms connective tissues) | ||
In early mesoderm development a number of transient structures will form and then be lost as | In early mesoderm development a number of transient structures will form and then be lost as tissue structure is patterned and organised. | ||
Humans as vertebrates have a "backbone" and the first mesoderm structure we will see form after the notochord will be somites. | Humans as vertebrates have a "backbone" and the first mesoderm structure we will see form after the {{notochord}} will be {{somites}}. | ||
<gallery mode="packed-hover" caption="Mesoderm and Ectoderm Cartoons"> | <gallery mode="packed-hover" caption="Mesoderm and Ectoderm Cartoons"> | ||
File:Mesoderm-cartoon1.jpg|Trilaminar Embryo | File:Mesoderm-cartoon1.jpg|Trilaminar Embryo | ||
File:Mesoderm-cartoon2.jpg|Paraxial and Lateral Plate | File:Mesoderm-cartoon2.jpg|Paraxial and Lateral Plate | ||
File:Mesoderm-cartoon3.jpg| | File:Mesoderm-cartoon3.jpg|{{somites}} | ||
File:Mesoderm-cartoon4.jpg|Somatic and Splanchnic | File:Mesoderm-cartoon4.jpg|Somatic and Splanchnic | ||
</gallery> | </gallery> | ||
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'''Mesoderm organization:''' (left to right) | '''Mesoderm organization:''' (left to right) | ||
lateral plate - intermediate mesoderm - paraxial mesoderm - axial mesoderm - paraxial mesoderm - intermediate mesoderm - lateral plate | lateral plate - intermediate mesoderm - paraxial mesoderm - '''axial mesoderm''' - paraxial mesoderm - intermediate mesoderm - lateral plate | ||
{| | {| | ||
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===Paraxial Mesoderm=== | ===Paraxial Mesoderm=== | ||
{| | {| | ||
| [[ | | [[File:Stage7_paraxial-mesoderm.jpg|200px]] | ||
| | | | ||
* differentiates rostro-caudally (head to tail) | * differentiates rostro-caudally (head to tail) | ||
* head region - remains unsegmented | * head region - remains unsegmented | ||
* body region - segments to form pairs of '''somites''' along the length of the embryo. | * body region - segments to form pairs of '''{{somites}}''' along the length of the embryo. | ||
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* named by position (between paraxial and lateral plate) | * named by position (between paraxial and lateral plate) | ||
* differentiates rostro-caudally (head to tail) | * differentiates rostro-caudally (head to tail) | ||
* forms 3 sets of "kidneys" in sequence | * {{renal}} forms 3 sets of "kidneys" in sequence | ||
# pronephros | # pronephros | ||
# mesonephros | # mesonephros | ||
# metanephros | # metanephros | ||
'''Adult''' - metanephros forms the kidney | '''Adult''' - metanephros forms the {{renal}} kidney | ||
|} | |} | ||
===Lateral Plate Mesoderm=== | ===Lateral Plate Mesoderm=== | ||
{| | {| | ||
| [[ | | [[File:Stage7_lateral-plate.jpg|200px]] | ||
| | | | ||
* at edge of embryonic disc | * at edge of embryonic disc | ||
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File:Stage11 sem100.jpg|Stage 11 | File:Stage11 sem100.jpg|Stage 11 | ||
</gallery> | </gallery> | ||
<br> | |||
Somite initially forms 2 main components | Somite initially forms 2 main components | ||
* ventromedial- sclerotome forms vertebral body and intervertebral disc | * ventromedial- sclerotome forms vertebral body and intervertebral disc | ||
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File:Somite cartoon5.png|epaxial and hypaxial muscles | File:Somite cartoon5.png|epaxial and hypaxial muscles | ||
</gallery> | </gallery> | ||
<br> | |||
{{Somite parts table}} | |||
[[File:Mesoderm 001 icon.jpg|160px|link=Mesoderm Movie]] [[File:Somite 001 icon.jpg|160px|link=Somite_Musculoskeletal_Movie]] [[File:Vertabra 003 icon.jpg|160px|link=Vertebra Development Movie]] | [[File:Mesoderm 001 icon.jpg|160px|link=Mesoderm Movie]] [[File:Somite 001 icon.jpg|160px|link=Somite_Musculoskeletal_Movie]] [[File:Vertabra 003 icon.jpg|160px|link=Vertebra Development Movie]] | ||
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===Heart=== | ===Heart=== | ||
{| class="wikitable mw-collapsible mw-collapsed" | {| class="wikitable mw-collapsible mw-collapsed" | ||
! Heart Development Movies | ! Heart Development Movies | ||
|- | |- | ||
| {{CVS cartoons}} | | {{CVS cartoons}} | ||
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* heart tube connects to blood vessels forming in splanchnic and extraembryonic mesoderm | * heart tube connects to blood vessels forming in splanchnic and extraembryonic mesoderm | ||
'''Week 2-3''' pair of thin -walled tubes | '''Week 2-3''' pair of thin-walled tubes | ||
'''Week 3''' tubes fused, truncus arteriosus outflow, heart contracting | '''Week 3''' tubes fused, truncus arteriosus outflow, heart contracting | ||
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===Neural=== | ===Neural=== | ||
<gallery mode="packed-hover" caption="Mesoderm and Ectoderm Cartoons"> | |||
File:Mesoderm-cartoon1.jpg|Trilaminar Embryo | |||
File:Mesoderm-cartoon2.jpg|Paraxial and Lateral Plate | |||
File:Mesoderm-cartoon3.jpg|{{somites}} | |||
File:Mesoderm-cartoon4.jpg|Somatic and Splanchnic | |||
</gallery> | |||
[[File:Stage10 neural sm.jpg|thumb|Stage 10 Week 4, 22 - 23 days]] | [[File:Stage10 neural sm.jpg|thumb|Stage 10 Week 4, 22 - 23 days]] | ||
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[[File: | [[File:Intermediate Heart Development Timeline.jpg|600px|link=Cardiac Embryology]] | ||
Atrial septa remains open, foramen ovale, septation continues (week 5-7), | |||
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</gallery> | </gallery> | ||
* Endocrine development | * Endocrine development | ||
** | ** {{pituitary}} - connecting stalk between pouch and oral cavity degenerates | ||
** | ** {{parathyroid}} - diverticulum elongate, hollow then solid, dorsal cell proliferation | ||
** | ** {{thymus}} - diverticulum elongate, hollow then solid, ventral cell proliferation | ||
** | ** {{adrenal}} - fetal cortex forms from mesothelium adjacent to dorsal mesentery, medulla {{neural crest}} cells from adjacent sympathetic ganglia | ||
==Week 7== | ==Week 7== | ||
[[File:Stage19_bf2b.jpg|thumb|Human week 7]] | [[File:Stage19_bf2b.jpg|thumb|Human week 7]] | ||
<gallery> | <gallery> | ||
File:Stage18_bf1c.jpg|Stage 18 | File:Stage18_bf1c.jpg|Stage 18 | ||
File:Stage19_bf1c.jpg|Stage 19 | File:Stage19_bf1c.jpg|Stage 19 | ||
</gallery> | </gallery> | ||
* | |||
* | * {{pancreas}} - Week 7 to 20 pancreatic hormones secretion begins and increases, small amount maternal insulin | ||
* {{limb}} bones form by endochondrial ossification and throughout embryo replacement of cartilage with bone (week 5 onward; {{bone timeline}}) | |||
<br> | |||
<gallery> | <gallery> | ||
File:Endochondral_bone.jpg|Endochondral ossification in limb | File:Endochondral_bone.jpg|Endochondral ossification in limb | ||
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==Week 8== | ==Week 8== | ||
<gallery> | <gallery> | ||
File:CNS_secondary_vesicles.jpg|Neural - secondary vesicles | File:CNS_secondary_vesicles.jpg|Neural - secondary vesicles | ||
File: | File:Stage 22 image 217.jpg|Neural - early developing cortex | ||
File:Gray0986.jpg|Gastrointestinal tract herniation | File:Gray0986.jpg|Gastrointestinal tract herniation | ||
</gallery> | </gallery> | ||
* Limb upper and lower limbs rotate in different directions (upper limb dorsally, lower limb ventrally) | {{Stage 23 MRI movie 7}} | ||
* Limb - upper and lower limbs rotate in different directions (upper limb dorsally, lower limb ventrally) | |||
[[File:Stage20-23 limbs a.jpg]] | [[File:Stage20-23 limbs a.jpg]] | ||
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==Fetal== | ==Fetal== | ||
[[File:Fetal_length_and_weight_change.jpg|thumb|Fetal length and weight changes]] | [[File:Fetal_length_and_weight_change.jpg|thumb|Fetal length and weight changes]] | ||
'''Note''' - Fetal development topic will be covered in detail in [[BGDA Practical - Fetal Development|practical 12 - Fetal]]. Information below is only a brief summary and may not be covered in this lecture. | |||
* First Trimester (1 - 12 weeks) - embryonic and early fetal | * First Trimester (1 - 12 weeks) - embryonic and early fetal | ||
* Second Trimester (13 - 24 weeks) - organ development | * Second Trimester (13 - 24 weeks) - organ development, function, and growth (length) | ||
* Third Trimester (25 - 40 weeks) - organ function and rapid growth (weight) | * Third Trimester (25 - 40 weeks) - organ function and rapid growth (weight) | ||
===Fetal Neural=== | ===Fetal Neural=== | ||
[[File:Neural-development.jpg|thumb|Timeline of events in Human Neural Development]] | [[File:Neural-development.jpg|thumb|Timeline of events in Human Neural Development]] | ||
* During the fetal period there is ongoing growth in size, weight and surface area of the brain and spinal cord. Microscopically there is ongoing: cell migration, extension of processes, cell death and glial cell development. | * During the fetal period there is ongoing growth in size, weight and surface area of the brain and spinal cord. Microscopically there is ongoing: cell migration, extension of processes, cell death and glial cell development. | ||
* Brain - folding of the initially smooth surface ( | * Brain - folding of the initially smooth surface (insular cortex, gyral and culcal development) | ||
* Neural development will continue after birth with substantial growth, death and reorganization occuring during the postnatal period | * Neural development will continue after birth with substantial growth, death and reorganization occuring during the postnatal period | ||
:'''Links:''' [[ | |||
:'''Links:''' {{neural}} | [[BGDA Lecture - Development of the Nervous System|BGDA Lecture - Nervous System]] | |||
===Lung Stages=== | ===Lung Stages=== | ||
{{respiratory}} | |||
* week 4 - 5 embryonic | * week 4 - 5 embryonic | ||
* week 5 - 17 pseudoglandular | * week 5 - 17 pseudoglandular | ||
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* late fetal - 8 years alveolar | * late fetal - 8 years alveolar | ||
:'''Links:''' [[Respiratory System Development]] | {| class="wikitable mw-collapsible mw-collapsed" | ||
! Lung Stages (detailed) | |||
|- | |||
| {{Lung stage table}} | |||
|} | |||
:'''Links:''' {{respiratory}} | [[SH Lecture - Respiratory System Development|SH Lecture - Respiratory]] | |||
===Fetal Genital=== | ===Fetal Genital=== | ||
* ovary and testis development | {{genital}} | ||
* | * Gonad - ovary and testis development | ||
* | * Internal genital tract - uterus and ductus deferens | ||
* External genital tract - genital folds development | |||
* Testis descent | |||
:'''Links:''' [[Genital | :'''Links:''' {{genital}} | [[BGD Lecture - Sexual Differentiation|BGDB Lecture - Genital]] | ||
===Fetal Renal=== | ===Fetal Renal=== | ||
{{renal}} | |||
* week 32-34 nephron development completed | * week 32-34 nephron development completed | ||
* term birth nephron number per kidney about 1 million (300,000 to 2 million) | * term birth nephron number per kidney about 1 million (300,000 to 2 million) | ||
:'''Links:''' | :'''Links:''' {{renal}} | ||
===Fetal Endocrine=== | ===Fetal Endocrine=== | ||
{{endocrine}} | |||
* Many endocrine organs begin to function in the early fetal period. | * Many endocrine organs begin to function in the early fetal period. | ||
* Pituitary | * Pituitary hormones - HPA axis established by week 20, pituitary functional throughout fetal development | ||
* Thyroid | * Thyroid hormone - important for neural development, required for metabolic activity, also in the newborn | ||
Remember that the Placenta also has important endocrine functions during development. | Remember that the Placenta also has important endocrine functions during development. | ||
:'''Links:''' | :'''Links:''' {{endocrine}} | {{placenta}} | ||
==Critical Periods== | ==Critical Periods== | ||
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[[File:Human-critical_periods_of_development.jpg|thumb]] | [[File:Human-critical_periods_of_development.jpg|thumb]] | ||
{{Critical Periods table}} | |||
==Additional Information== | |||
See the associated [[BGDA_Practical_-_Implantation_to_8_Weeks|BGDA Practical 6]] class. | |||
'''Links:''' {{human timeline}} | {{first trimester timeline}} | {{second trimester timeline}} | {{third trimester timeline}} | {{fetal}} | {{movies}} | |||
| | |||
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| | |||
{{Abnormality Links}} | |||
{| class="wikitable mw-collapsible mw-collapsed" | |||
! First Trimester Timeline | |||
|- | |- | ||
| '''Embryonic Weeks/Stages''' | |||
{{Carnegie_stage_table_1}} | |||
|- | |- | ||
| | | {{First Trimester Timeline}} | ||
|- | |- | ||
| '''References''' | |||
<references/> | |||
|} | |} | ||
{{BGDAFooter}} | {{BGDAFooter}} |
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Introduction
This lecture covers the period of Embryonic development, in Humans from week 3 to week 8 (GA week 5-10) and is divided into 23 Carnegie stages of embryonic development. There will also be a brief introduction to fetal development. Note, the period from week 9 to week 38 is considered Fetal development and will be covered in detail in the Laboratory 12.
Lecture Objectives
- Understand key structures and events in embryonic development.
- Understanding of the dynamic changes internal and external structures.
- Brief understanding of organ and system formation (functional / not functional).
- Brief understanding of critical periods of development.
1 Minute Embryology | UNSW theBox
Lecture Archive |
---|
[Media:2018 BGDA Lecture - Development of the Embryo-Fetus 2.pdf 2018 PDF] | 2017 | 2017 PDF |
2016 | 2015 | 2014 | 2014 PDF | 2013 | 2012 | 2010 | Practical 6 Embryonic Development | Practical 12 Fetal Development |
BGDA Practical Classes
Practical 3 - Fertilization to Implantation | Practical 6 - Implantation to 8 Weeks | Practical 12 - Fetal Period |
First 8 Weeks
The Carnegie stages of the first 8 week of human development.
Week 3
Mesoderm means the "middle layer" and it is from this layer that the body's connective tissues are derived (note that the head neural crest ectoderm also forms connective tissues)
In early mesoderm development a number of transient structures will form and then be lost as tissue structure is patterned and organised.
Humans as vertebrates have a "backbone" and the first mesoderm structure we will see form after the notochord will be somites.
Mesoderm organization: (left to right)
lateral plate - intermediate mesoderm - paraxial mesoderm - axial mesoderm - paraxial mesoderm - intermediate mesoderm - lateral plate
|
Axial Mesoderm
Adult - contributes to the nucleus pulposis of the intervertebral disc |
|
Paraxial Mesoderm
|
Intermediate Mesoderm
Adult - metanephros forms the renal kidney |
Lateral Plate Mesoderm
Adult - body connective tissues, gastrointestinal tract (connective tissues, muscle, organs), heart |
Week 4
Somite Development
Somite initially forms 2 main components
- ventromedial- sclerotome forms vertebral body and intervertebral disc
- dorsolateral - dermomyotome forms dermis and skeletal muscle
Sclerotome | Dermatome |
---|---|
|
|
Myotome | |
|
Heart
Heart Development Movies | ||||||||||||||||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
|
- forms initially in splanchnic mesoderm of prechordal plate region - cardiogenic region
- growth and folding of the embryo moves heart ventrallly and downward into anatomical position
- week 3 begins as paired heart tubes that fuse to form single heart tube
- begins to beat in Humans- day 22-23
- heart tube connects to blood vessels forming in splanchnic and extraembryonic mesoderm
Week 2-3 pair of thin-walled tubes
Week 3 tubes fused, truncus arteriosus outflow, heart contracting
Week 4 heart tube continues to elongate, curving to form S shape
Week 5 Septation starts, atrial and ventricular
- Links: Cardiac Embryology
Neural
Neural Plate
|
Neural Groove
- forms in the midline of the neural plate (day 18-19)
- either side of which are the neural folds which continues to deepen until about week 4
- neural folds begins to fuse, beginning at 4th somite level
Neural Tube
Failure for the neural tube to close correctly or completely results in a neural tube defect. |
Neural - 3 primary vesicles
Neural Crest
- population of cells at the edge of the neural plate that lie dorsally when the neural tube fuses
- dorsal to the neural tube, as a pair of streaks
- pluripotential, forms many different types of cells
- cells migrate throughout the embryo
Neural Crest Derivatives: dorsal root ganglia, autonomic ganglia, adrenal medulla, drg sheath cells, glia, pia-arachnoid sheath, skin melanocytes, connective tissue of cardiac outflow, thyroid parafollicular cells, craniofacial skeleton, teeth odontoblasts
Head
- branchial arch (Gk. branchia= gill)
- arch consists of all 3 trilaminar embryo layers (ectoderm- outside, mesoderm - core of mesenchyme, endoderm - inside)
- Humans have 5 arches - 1, 2, 3, 4, 6 (Arch 5 does not form or regresses rapidly)
- from in rostro-caudal sequence, Arch 1 to 6 from week 4 onwards
- arch 1 and 2 appear at time of closure of cranial neuropore
- Face - mainly arch 1 and 2
- Neck components - arch 3 and 4 (arch 4 and 6 fuse)
Sensory Placodes
- During week 4 a series of thickened surface ectodermal patches form in pairs rostro-caudally in the head region.
- These sensory placodes will later contribute key components of each of our special senses (vision, hearing and smell).
- Note that their initial postion on the developing head is significantly different to their final position in the future sensory system
- Otic placode - istage 13/14 embryo the otic placode sunk from the surface ectoderm to form a hollow epithelial ball, the otocyst, which now lies beneath the surface surrounded by mesenchyme (mesoderm). The epithelia of this ball varies in thickness and has begun to distort, it will eventually form the inner ear membranous labyrinth.
- Lens placode - lies on the surface, adjacent to the outpocketing of the nervous system (which will for the retina) and will form the lens.
- Nasal placode - has 2 components (medial and lateral) and will form the nose olefactory epithelium.
Upper and Lower Limb
|
Gastrointestinal Tract
- Begins at buccopharyngeal membrane
- Ends at cloacal membrane
- 3 distinct portions (fore-, mid- and hind-gut)
- liver earliest forming organ
Germ layer contributions
- Endoderm - epithelium and associated glands
- Mesoderm (splanchnic) - mesentry, connective tissues, smooth muscle, blood vessels
- Ectoderm (neural crest) - enteric nervous system
Both endoderm and mesoderm will contribute to associated organs.
Week 5
- Heart - septation starts, atrial and ventricular
- Vascular - 3 vascular systems (systemic, placental, vitelline) extensively remodelled
- Respiratory - left and right lung buds push into the pericardioperitoneal canals (primordia of pleural cavity)
- Sense - Hearing cochlear part of otic vesicle elongates (humans 2.5 turns)
Atrial septa remains open, foramen ovale, septation continues (week 5-7),
<html5media height="720" width="560">File:Heart septation 003.mp4</html5media>
Week 6
- Endocrine development
- pituitary - connecting stalk between pouch and oral cavity degenerates
- parathyroid - diverticulum elongate, hollow then solid, dorsal cell proliferation
- thymus - diverticulum elongate, hollow then solid, ventral cell proliferation
- adrenal - fetal cortex forms from mesothelium adjacent to dorsal mesentery, medulla neural crest cells from adjacent sympathetic ganglia
Week 7
- pancreas - Week 7 to 20 pancreatic hormones secretion begins and increases, small amount maternal insulin
- limb bones form by endochondrial ossification and throughout embryo replacement of cartilage with bone (week 5 onward; bone timeline)
Week 8
Sagittal GIT |
Page | Play |
- Limb - upper and lower limbs rotate in different directions (upper limb dorsally, lower limb ventrally)
Links: Embryonic Development | Timeline human development
Fetal
Note - Fetal development topic will be covered in detail in practical 12 - Fetal. Information below is only a brief summary and may not be covered in this lecture.
- First Trimester (1 - 12 weeks) - embryonic and early fetal
- Second Trimester (13 - 24 weeks) - organ development, function, and growth (length)
- Third Trimester (25 - 40 weeks) - organ function and rapid growth (weight)
Fetal Neural
- During the fetal period there is ongoing growth in size, weight and surface area of the brain and spinal cord. Microscopically there is ongoing: cell migration, extension of processes, cell death and glial cell development.
- Brain - folding of the initially smooth surface (insular cortex, gyral and culcal development)
- Neural development will continue after birth with substantial growth, death and reorganization occuring during the postnatal period
- Links: neural | BGDA Lecture - Nervous System
Lung Stages
- week 4 - 5 embryonic
- week 5 - 17 pseudoglandular
- week 16 - 25 canalicular
- week 24 - 40 terminal sac
- late fetal - 8 years alveolar
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- Links: respiratory | SH Lecture - Respiratory
Fetal Genital
- Gonad - ovary and testis development
- Internal genital tract - uterus and ductus deferens
- External genital tract - genital folds development
- Testis descent
- Links: genital | BGDB Lecture - Genital
Fetal Renal
- week 32-34 nephron development completed
- term birth nephron number per kidney about 1 million (300,000 to 2 million)
- Links: renal
Fetal Endocrine
- Many endocrine organs begin to function in the early fetal period.
- Pituitary hormones - HPA axis established by week 20, pituitary functional throughout fetal development
- Thyroid hormone - important for neural development, required for metabolic activity, also in the newborn
Remember that the Placenta also has important endocrine functions during development.
Critical Periods
The term "Critical Periods" refers to periods of development when specific systems are more sensitive to teratogen exposure or developmental insults.
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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Additional Information
See the associated BGDA Practical 6 class.
Links: human timeline | first trimester timeline | second trimester timeline | third trimester timeline | fetal | Template:Movies
Abnormality Links: abnormal development | abnormal genetic | abnormal environmental | Unknown | teratogens | ectopic pregnancy | cardiovascular abnormalities | coelom abnormalities | endocrine abnormalities | gastrointestinal abnormalities | genital abnormalities | head abnormalities | integumentary abnormalities | musculoskeletal abnormalities | limb abnormalities | neural abnormalities | neural crest abnormalities | placenta abnormalities | renal abnormalities | respiratory abnormalities | hearing abnormalities | vision abnormalities | twinning | Developmental Origins of Health and Disease | ICD-11 | ||
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First Trimester Timeline | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
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Embryonic Weeks/Stages
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References
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BGDA: Lecture 1 | Lecture 2 | Practical 3 | Practical 6 | Practical 12 | Lecture Neural | Practical 14 | Histology Support - Female | Male | Tutorial
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. (2024, May 4) Embryology BGDA Lecture - Development of the Embryo/Fetus 2. Retrieved from https://embryology.med.unsw.edu.au/embryology/index.php/BGDA_Lecture_-_Development_of_the_Embryo/Fetus_2
- © Dr Mark Hill 2024, UNSW Embryology ISBN: 978 0 7334 2609 4 - UNSW CRICOS Provider Code No. 00098G