BGDA Practical 7 - Week 3: Difference between revisions

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==Introduction==
==Introduction==
Key events of human development during the third week (week 3) following fertilization or Clinical week 5 (LMP). Note that during this time the conceptus cells not contributing to the embryo are contributing to placental membranes and the early placenta.
Key events of human development during the third week (week 3) following fertilization clinical {{GA}} week 5.


Note that during this time the conceptus cells not contributing to the embryo are contributing to placental membranes and the early placenta. This page describes the mechanical events and changes occurring in each of the 3 germ layers (some concepts will also be covered in later weeks).
===Gastrulation===
Through week 3 the process of {{gastrulation}} continues, as cells to migrate through the primitive streak contributing to {{mesoderm}}.
As the embryonic disc grows overall in size, the primitive streak appears to become more caudal as it does not increase in size.
[[File:Stage7_primitive_streak_labelled.jpg|400px]] [[File:Trilaminar_embryo.jpg|400px]]
===Folding===
===Folding===
Endoderm, mesoderm and ectoderm layers. There are two major folding processes that take place during this time.
Endoderm, mesoderm and ectoderm layers. There are two major folding processes that take place during this time.
# Folding of the whole embryonic disc ventrally, separates the endoderm to form the epithelial lining of the gut. Folding of the embryonic disc occurs ventrally around the notochord, which forms a rod-like region running rostro-caudally in the midline.  
# Folding of the whole embryonic disc ventrally, separates the endoderm to form the epithelial lining of the gut. Folding of the [[E#embryonic disc|embryonic disc]] occurs ventrally around the {{notochord}}, which forms a rod-like region running rostro-caudally in the midline.  
# Folding of the ecoderm  will form a neural groove, then closing to form a neural tube, separating the neural ectoderm from the embryo surface ectoderm.
# Folding of the ecoderm  will form a [[N#neural groove|neural groove]], then closing to form a [[N#neural tube|neural tube]], separating the neural ectoderm from the embryo surface ectoderm.


===Mesoderm Segmentation===
===Mesoderm Segmentation===
Different regions of mesoderm form early intermediate structures.
Different regions of mesoderm form early intermediate structures.
# [[S#somitogenesis|Somitogenesis]] -  when part of the mesoderm layer segments during week 3 to form balls of mesoderm called somites. The later migration of cells forms the mesoderm germ layer. An embryonic connective tissue ([[M#mesenchyme|mesenchyme]]) which forms nearly all the connective tissues of the body (the head is different). Somitogenesis is when part of this layer segments during week 3 to form balls of mesoderm called somites.
# [[Basic_-_Primitive_Heart_Tube|Cardiac development]] - forming the simple heart tube within splanchnic mesoderm.
# [[I#intraembryonic coelom|Intraembryonic coelom]] - Within the embryonic disc lateral plate mesoderm a space (coelom) forms, it lies within the embryo and so is called the '''intraembryonic coelom'''. This single "horseshoe-shaped" space will form the 3 major body cavities: '''pericardial''' (around the heart), '''pleural''' (around the lungs) and '''peritoneal''' (around the GIT and visceral organs).
# {{Somitogenesis}} -  when part of the mesoderm layer segments commences during week 3 to form balls of mesoderm called somites. The later migration of cells forms the mesoderm germ layer. An embryonic connective tissue ([[M#mesenchyme|mesenchyme]]) which forms nearly all the connective tissues of the body (the head is different). Somitogenesis is when part of this layer segments during week 3 to form balls of mesoderm called somites, note that the majority of somites form during week 4.
# {{Intra-embryonic coelom}} - Within the embryonic disc lateral plate mesoderm a space (coelom) forms, it lies within the embryo and so is called the '''intraembryonic coelom'''. This single "horseshoe-shaped" space will form the 3 major body cavities: '''pericardial''' (around the heart), '''pleural''' (around the lungs) and '''peritoneal''' (around the GIT and visceral organs).


===Ectoderm Segmentation===
==Ectoderm==
The central portion of the embryonic disc forms the neural plate, the edge of this plate forms neural crest and the edge forms the epitheium of the skin. This will be covered in week 4.
The central portion of the embryonic disc forms the '''neural plate''', the edge of this plate forms '''neural crest''' and outside of this again will contribute the epitheium of the skin. (this will be covered in more detail week 4).
 
<br>
<gallery>
{|
File:Stage7-sem2.jpg|[[Carnegie stage 7]]
! Neural Plate
File:Stage8_SEM1.jpg|[[Carnegie stage 8]]
! Neural Groove
File:Stage9 sem4c.jpg|[[Carnegie stage 9]]
|-
 
| [[File:Mesoderm-cartoon1.jpg|300px]]
</gallery>
| [[File::Mesoderm-cartoon2.jpg|300px]]
 
|}
==Folding==
<br>
 
{|
There are two major folding processes that take place during this time.
| [[File:Stage7-sem2.jpg|250px|link=Carnegie stage 7]]
 
| [[File:Stage8_SEM1.jpg|250px|link=Carnegie stage 8]]
# Folding of the ecoderm  will form a [[N#neural groove|neural groove]], then closing to form a [[N#neural tube|neural tube]], separating the neural ectoderm from the embryo surface ectoderm.
| [[File:Stage9 sem4c.jpg|250px|link=Carnegie stage 9]]
# Folding of the whole embryonic disc ventrally, separates the endoderm to form the epithelial lining of the gut. Folding of the [[E#embryonic disc|embryonic disc]] occurs ventrally around the [[N#notochord|notochord]], which forms a rod-like region running rostro-caudally in the midline.
|-
 
| [[Carnegie stage 7]]
[[File:Amnion 001 icon.jpg|120px|link=Development Animation - Amniotic Cavity]] [[File:Week3_folding icon.jpg|120px|link=Development Animation - Week 3]]
| [[Carnegie stage 8]]
 
| [[Carnegie stage 9]]
In relation to the notochord:  
|}
==Endoderm==
{|
| {{Week 3 movie}}
| {{Amnion movie}}
|-
| The major folding processes that take place during this time, in relation to the notochord:  


* '''Laterally''' (either side of the notochord) lies mesoderm.  
* '''Laterally''' (either side of the notochord) lies mesoderm.  
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* '''Dorsally''' (above the notochord) lies the neural tube then ectoderm.  
* '''Dorsally''' (above the notochord) lies the neural tube then ectoderm.  
* '''Ventrally''' (beneath the notochord) lies the mesoderm then endoderm.
* '''Ventrally''' (beneath the notochord) lies the mesoderm then endoderm.
| The ventral endoderm (shown yellow) has grown to line a space called the yolk sac. Folding of the [[E#embryonic disc|embryonic disc]] "pinches off" part of this yolk sac forming the first primative GIT.


The ventral endoderm (shown yellow) has grown to line a space called the yolk sac. Folding of the [[E#embryonic disc|embryonic disc]] "pinches off" part of this yolk sac forming the first primative GIT.
[[File:Endoderm_cartoon.jpg]]
|}


[[File:Endoderm_cartoon.jpg]]


==Mesoderm==
==Mesoderm==
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<gallery>
<gallery>
Image:Mesoderm cartoon1.gif|trilaminar embryo
File:Mesoderm-cartoon1.jpg|trilaminar embryo
Image:Mesoderm cartoon2.gif|mesoderm regions
File:Mesoderm-cartoon2.jpg|mesoderm regions
Image:Mesoderm cartoon3.gif|somite coelom
File:Mesoderm-cartoon3.jpg|somite
Image:Mesoderm cartoon4.gif|neural tube and neural crest
File:Mesoderm-cartoon4.jpg|somatic, coelom, splanchnic
</gallery>
</gallery>


===Mesoderm Development===
===Mesoderm Development===
 
{|
|
# [[E#epiblast|epiblast]] -> mesoderm + [[A#axial mesoderm|axial mesoderm]] ([[N#notochord|notochord]])  
# [[E#epiblast|epiblast]] -> mesoderm + [[A#axial mesoderm|axial mesoderm]] ([[N#notochord|notochord]])  
# [[L#lateral plate|lateral plate]] + [[P#paraxial mesoderm|paraxial mesoderm]] + [[A#axial mesoderm|axial mesoderm]]  
# [[L#lateral plate|lateral plate]] + [[P#paraxial mesoderm|paraxial mesoderm]] + [[A#axial mesoderm|axial mesoderm]]  
# [[L#lateral plate|lateral plate]] + [[I#intermediate mesoderm|intermediate mesoderm]] + [[S#somite|somites]] (body),  [[P#paraxial mesoderm|paraxial mesoderm]] (head) + [[A#axial mesoderm|axial mesoderm]]  
# [[L#lateral plate|lateral plate]] + [[I#intermediate mesoderm|intermediate mesoderm]] + [[S#somite|somites]] (body),  [[P#paraxial mesoderm|paraxial mesoderm]] (head) + [[A#axial mesoderm|axial mesoderm]]  
# [[S#somatic mesoderm|somatic mesoderm]] + [[I#intraembryonic coelom|intraembryonic coelom]] + [[S#splanchnic mesoderm|splanchnic mesoderm]] + [[I#intermediate mesoderm|intermediate mesoderm]] + [[S#somite|somites]] (body),  [[P#paraxial mesoderm|paraxial mesoderm]] (head) + [[A#axial mesoderm|axial mesoderm]]
# [[S#somatic mesoderm|somatic mesoderm]] + [[I#intraembryonic coelom|intraembryonic coelom]] + [[S#splanchnic mesoderm|splanchnic mesoderm]] + [[I#intermediate mesoderm|intermediate mesoderm]] + [[S#somite|somites]] (body),  [[P#paraxial mesoderm|paraxial mesoderm]] (head) + [[A#axial mesoderm|axial mesoderm]]
 
| [[File:Mesoderm cartoon.gif]]
|}
===Axial Mesoderm===
===Axial Mesoderm===
[[File:Sonic_hedgehog_expression.jpg|thumb|Notochord secreting sonic hedgehog]]
[[File:Sonic_hedgehog_expression.jpg|thumb|Notochord secreting sonic hedgehog]]
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# molecular role in patterning surrounding tissues
# molecular role in patterning surrounding tissues


{{Week 3 notochord 1 movie}} {{Week 3 notochord 2 movie}}




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|  
|  
* a "horseshoe shaped" space forms in the middle
* a "horseshoe shaped" space forms in the middle
* [[S#somatic mesoderm|somatic mesoderm]] - closest to ectoderm
* [[S#somatic mesoderm|somatic mesoderm]] - closest to ectoderm, forms connective tissue of the body wall and the skeletal elements of the appendicular skeleton and sternum.
* space - forms the 3 body cavities (pericardial, pleural, peritoneal)
* space - forms the 3 body cavities (pericardial, pleural, peritoneal)
* [[S#splanchnic mesoderm|splanchnic mesoderm]] - closest to endoderm
* [[S#splanchnic mesoderm|splanchnic mesoderm]] - closest to endoderm, forms heart and blood vessels; connective tissue and smooth muscle of the gastrointestinal tract
 




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|-
|-
|}
===Heart Development===
{|
| [[File:Early_Development_of_Heart_Tube.jpg|300px]]
| Splanchnic mesoderm lying above the notochord (prechordal splanchnic mesoderm) forms a pair of simple tubes, that will fuse to form the primordia of the heart tube.
More: [[Basic_-_Primitive_Heart_Tube|Primitive Heart Tube]]
|}
|}


===Somite Development===
===Somite Development===


[[File:Stage11 sem100c.jpg|stage 11 Embryo]]
[[File:Stage11 sem100.jpg|400px]]
 
Embryo ([[Carnegie stage 11]]) SEM


Somite initially forms 2 main components
Somite initially forms 2 main components
Line 142: Line 170:
* dorsolateral - [[D#dermomyotome|dermomyotome]] forms dermis and skeletal muscle
* dorsolateral - [[D#dermomyotome|dermomyotome]] forms dermis and skeletal muscle


<gallery>
{|
Image:Somite cartoon1.png|paraxial mesoderm
|-
Image:Somite cartoon2.png|early somite
| [[File:Somite cartoon1.png|200px]]
Image:Somite cartoon3.png|[[S#sclerotome|sclerotome]] and [[D#dermomyotome|dermomyotome]]
| [[File:Somite cartoon2.png|200px]]
Image:Somite cartoon4.png|[[D#dermatome|dermatome]] and [[M#myotome|myotome]]
| [[File:Somite cartoon3.png|200px]]
</gallery>
| [[File:Somite cartoon4.png|200px]]
|-
| paraxial mesoderm
| early somite
| sclerotome and dermomyotome
| dermatome and myotome
|}


{{Somite parts table}}
===Sclerotome===
===Sclerotome===
{|
{|
|-
|-
| [[File:Vertabra 003 icon.jpg|200px|link=Development_Animation_-_Vertebra]]
| [[File:Vertabra 003 icon.jpg|200px|link=Vertebra Development Movie]]
|
|
* sclerotome from somites at the same segmental level contribute the right and left half of each vertebral and intervertebral element
* sclerotome from somites at the same segmental level contribute the right and left half of each vertebral and intervertebral element
Line 165: Line 200:
{|
{|
| [[File:Somite cartoon5.png|left|200px|epaxial and hypaxial muscles]]
| [[File:Somite cartoon5.png|left|200px|epaxial and hypaxial muscles]]
|
| [[File:Somite 001 icon.jpg|200px|link=Somite Musculoskeletal Movie]]
Forms 2 muscle groups in body and limbs
|-
| Forms 2 muscle groups in body and limbs
* Body - [[E#epaxial muscle|epaxial]] and [[H#hypaxial muscle|hypaxial muscle]] groups
* Body - [[E#epaxial muscle|epaxial]] and [[H#hypaxial muscle|hypaxial muscle]] groups
* Limbs - flexor and extensor muscles
* Limbs - flexor and extensor muscles
|-
| [[File:Somite 001 icon.jpg|200px|link=Development_Animation_-_Somite_Musculoskeletal]]
| Development of the sclerotome and myotome components of the somite.
| Development of the sclerotome and myotome components of the somite.
|-
|-
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* spreads throughout the body
* spreads throughout the body


'''Note''' - Dermatome is the term also used clinically postnatally to describe the region of skin supplied by a single spinal nerve.
'''Note''' - Dermatome is the term also used clinically postnatally to describe the [[:File:Dermatomes.png|region of skin supplied by a single spinal nerve]].


==Week 2 and 3 Movies==
==Week 2 and 3 Movies==
 
===Week 2===
{| border='0px'
{|
 
| {{Template:Week 2 implant movie}}
|-
| {{Template:Week 2 bilaminar movie}}
| [[File:Week2_001 icon.jpg|90px|link=Development_Animation_-_Implantation]]
|}
| [[File:Mesoderm 001 icon.jpg|90px|link=Development_Animation_-_Mesoderm]]
===Week 3===
| [[File:Chorion 001 icon.jpg|90px|link=Development Animation - Chorionic Cavity]]
{|
| [[File:Amnion 001 icon.jpg|90px|link=Development Animation - Amniotic Cavity]]
| valign="bottom"|{{Week 3 mesoderm movie}}
| [[File:Week3_folding icon.jpg|90px|link=Development Animation - Week 3]]
| valign="bottom"|{{Week 3 notochord 1 movie}}
|-
| valign="bottom"|{{Week 3 notochord 2 movie}}
| [[Development_Animation_-_Implantation|Implantation]]
| valign="bottom"|{{Nodal cilia movie}}
| [[Development_Animation_-_Mesoderm|Mesoderm]]
| [[Development Animation - Chorionic Cavity|Chorionic Cavity]]
| [[Development Animation - Amniotic Cavity|Amniotic Cavity]]
| [[Development_Animation_-_Week 3|Week 3]]
|-
|-
| valign="bottom"|{{Week 3 movie}}
| valign="bottom"|{{Amnion movie}}
| valign="bottom"|{{Quail gastrulation ECM movie}}
|}
|}


{{BGDA Practical 6 - Week 3 Interactive}}


{{Template:2010BGDLab6}}
{{Template:2010BGDLab6weeks}}
===Embryo Stages and Events===
{| class="prettytable"
| width= "50px" |'''Day'''
| width= "100px" |'''Stage'''
| '''Event'''
|-
| <center>15</center>
|
|
|-
| <center>16</center>
| [[Carnegie stage 7|Stage 7]] 
| [[Image:Stage7.jpg|120px|left]] '''Primitive node''' (Hensen's node, primitive knot) The small circular region located at the cranial end of the primitive streak, where gastrulation occurs, and is a controller of this process. The second role is to act as an initial generator of the left-right (L-R) body axis.
|-
| <center>17</center>
| &nbsp;
| &nbsp;
|-
| <center>18</center>
| [[Carnegie stage 8|Stage 8]]
| [[Image:Stage8_human.jpg|120px|left]] [http://embryology.med.unsw.edu.au/Notes/neuron.htm Neural]  neurogenesis, neural groove and folds are first seen
|-
| <center>19</center>
| &nbsp;
| [[Image:Stage8_SEM1.jpg|120px|left]]


|-
{{BGDALab7}}
| <center>20</center>
| [[Carnegie stage 9|Stage 9]]
| [[File:Stage9_bf1c.jpg|200px|link=Carnegie stage 9]] [http://embryology.med.unsw.edu.au/Notes/skmus6.htm Musculoskeletal]  somitogenesis - first somites form and continue to be added in sequence caudally


[http://embryology.med.unsw.edu.au/Notes/neuron.htm Neural] - three main divisions of the brain, which are not cerebral vesicles, can be distinguished while the neural groove is still completely open
==Additional Information==
 
{{Med Prac additional Information}}
 
|-
| <center>21</center>
| &nbsp;
| [http://embryology.med.unsw.edu.au/Notes/heart.htm Heart]  cardiogenesis - week 3 begins as paired heart tubes.
 
|}


===Timeline===
{{Week 3 Embryo Stages and Events table}}




{{Template:BGDAFooter}}
{{BGDAFooter}}


[[Category:Week 3]]
[[Category:Week 3]]

Latest revision as of 20:50, 12 May 2019

BGDsmall.jpg
Practical 6: Week 3 | Week 4 | Week 5 | Week 6 | Week 7 | Week 8


Introduction

Key events of human development during the third week (week 3) following fertilization clinical GA week 5.

Note that during this time the conceptus cells not contributing to the embryo are contributing to placental membranes and the early placenta. This page describes the mechanical events and changes occurring in each of the 3 germ layers (some concepts will also be covered in later weeks).

Gastrulation

Through week 3 the process of gastrulation continues, as cells to migrate through the primitive streak contributing to mesoderm.

As the embryonic disc grows overall in size, the primitive streak appears to become more caudal as it does not increase in size.

Stage7 primitive streak labelled.jpg Trilaminar embryo.jpg

Folding

Endoderm, mesoderm and ectoderm layers. There are two major folding processes that take place during this time.

  1. Folding of the whole embryonic disc ventrally, separates the endoderm to form the epithelial lining of the gut. Folding of the embryonic disc occurs ventrally around the notochord, which forms a rod-like region running rostro-caudally in the midline.
  2. Folding of the ecoderm will form a neural groove, then closing to form a neural tube, separating the neural ectoderm from the embryo surface ectoderm.

Mesoderm Segmentation

Different regions of mesoderm form early intermediate structures.

  1. Cardiac development - forming the simple heart tube within splanchnic mesoderm.
  2. somitogenesis - when part of the mesoderm layer segments commences during week 3 to form balls of mesoderm called somites. The later migration of cells forms the mesoderm germ layer. An embryonic connective tissue (mesenchyme) which forms nearly all the connective tissues of the body (the head is different). Somitogenesis is when part of this layer segments during week 3 to form balls of mesoderm called somites, note that the majority of somites form during week 4.
  3. intra-embryonic coelom - Within the embryonic disc lateral plate mesoderm a space (coelom) forms, it lies within the embryo and so is called the intraembryonic coelom. This single "horseshoe-shaped" space will form the 3 major body cavities: pericardial (around the heart), pleural (around the lungs) and peritoneal (around the GIT and visceral organs).

Ectoderm

The central portion of the embryonic disc forms the neural plate, the edge of this plate forms neural crest and outside of this again will contribute the epitheium of the skin. (this will be covered in more detail week 4).

Neural Plate Neural Groove
Mesoderm-cartoon1.jpg [[File::Mesoderm-cartoon2.jpg|300px]]


Stage7-sem2.jpg Stage8 SEM1.jpg Stage9 sem4c.jpg
Carnegie stage 7 Carnegie stage 8 Carnegie stage 9

Endoderm

Week3 folding icon.jpg
 ‎‎Week 3
Page | Play
Amnion 001 icon.jpg
 ‎‎Amniotic Cavity
Page | Play
The major folding processes that take place during this time, in relation to the notochord:
  • Laterally (either side of the notochord) lies mesoderm.
  • Rostrally (above the notochord end) lies the buccopharyngeal membrane, above this again is the mesoderm region forming the heart.
  • Caudally (below the notochord end) lies the primitive streak (where gastrulation occurred), below this again is the cloacal membrane.
  • Dorsally (above the notochord) lies the neural tube then ectoderm.
  • Ventrally (beneath the notochord) lies the mesoderm then endoderm.
 The ventral endoderm (shown yellow) has grown to line a space called the yolk sac. Folding of the embryonic disc "pinches off" part of this yolk sac forming the first primative GIT.

Endoderm cartoon.jpg


Mesoderm

Mesoderm means the "middle layer" and it is from this layer that nearly all the bodies connective tissues are derived. In early mesoderm development a number of transient structures will form and then be lost as tissue structure is patterned and organised. Humans are vertebrates, with a "backbone", and the first mesoderm structure we will see form after the notochord will be somites.

Facts: Week 4, 22 - 23 days, 2 - 3.5 mm, Somite Number 4 - 12

View: This is a dorsal view of the human embryo, the amniotic membrane has been removed. Top embryo is an early stage 10, bottom is late stage 10.

  • Early stage 10

    Early stage 10

  • Late stage 10

    Late stage 10

  • Labeled stage 10

    Labeled stage 10

  • trilaminar embryo

    trilaminar embryo

  • mesoderm regions

    mesoderm regions

  • somite

    somite

  • somatic, coelom, splanchnic

    somatic, coelom, splanchnic

Mesoderm Development

  1. epiblast -> mesoderm + axial mesoderm (notochord)
  2. lateral plate + paraxial mesoderm + axial mesoderm
  3. lateral plate + intermediate mesoderm + somites (body), paraxial mesoderm (head) + axial mesoderm
  4. somatic mesoderm + intraembryonic coelom + splanchnic mesoderm + intermediate mesoderm + somites (body), paraxial mesoderm (head) + axial mesoderm
 Mesoderm cartoon.gif

Axial Mesoderm

Notochord secreting sonic hedgehog
Stage 7 notochord

The notochord

  1. mechanical role in embryonic disc folding
  2. molecular role in patterning surrounding tissues
Notochord 01 icon.jpg
 ‎‎Week 3 Notochord
Page | Play
Notochord 02 icon.jpg
 ‎‎Week 3 Notochord
Page | Play


Adult - contributes to the nucleus pulposus of the intervertebral disc

Paraxial Mesoderm

Stage 7 paraxial mesoderm
  • differentiates rostro-caudally (head to tail)
  • remains unsegmented in the head region.
  • segments in the body region to form pairs of somites along the length of the embryo.


Adult - contributes vertebral column (vertebra and IVD), dermis of the skin, skeletal muscle of body and limbs

Intermediate Mesoderm

Stage 7 intermediate mesoderm
  • named by position (between paraxial and lateral plate)
  • differentiates rostro-caudally (head to tail)
  • forms 3 sets of "kidneys" in sequence
  1. pronephros
  2. mesonephros
  3. metanephros


Adult - metanephros forms the kidney

Lateral Plate Mesoderm

Stage 7 lateral plate
  • a "horseshoe shaped" space forms in the middle
  • somatic mesoderm - closest to ectoderm, forms connective tissue of the body wall and the skeletal elements of the appendicular skeleton and sternum.
  • space - forms the 3 body cavities (pericardial, pleural, peritoneal)
  • splanchnic mesoderm - closest to endoderm, forms heart and blood vessels; connective tissue and smooth muscle of the gastrointestinal tract


Adult - body and limb connective tissues, gastrointestinal tract (connective tissues, muscle, organs), heart

Heart Development

Early Development of Heart Tube.jpg Splanchnic mesoderm lying above the notochord (prechordal splanchnic mesoderm) forms a pair of simple tubes, that will fuse to form the primordia of the heart tube.

More: Primitive Heart Tube

Somite Development

Stage11 sem100.jpg

Embryo (Carnegie stage 11) SEM

Somite initially forms 2 main components

  • ventromedial- sclerotome forms vertebral body and intervertebral disc
  • dorsolateral - dermomyotome forms dermis and skeletal muscle
Somite cartoon1.png Somite cartoon2.png Somite cartoon3.png Somite cartoon4.png
paraxial mesoderm early somite sclerotome and dermomyotome dermatome and myotome
  Sclerotome   Dermatome
  • sclerotome later becomes subdivided
    • rostral and caudal halves separated laterally by von Ebner's fissure
  • half somites contribute to a single vertebral level body
  • other half intervertebral disc
  • therefore final vertebral segmentation “shifts”
  • connective tissue underlying epidermis
  • begins as a dorsal thickening
  • spreads throughout the body
  Myotome
  • Body - epaxial and hypaxial muscles
  • Limbs - flexor and extensor muscles

Sclerotome

Vertabra 003 icon.jpg
  • sclerotome from somites at the same segmental level contribute the right and left half of each vertebral and intervertebral element
  • sclerotome later becomes subdivided into rostral and caudal halves (separated by von Ebner's fissure)
  • half somites contribute to a single vertebral level body
  • other half intervertebral disc
  • therefore final vertebral segmentation “shifts”

Myotome

epaxial and hypaxial muscles
 Somite 001 icon.jpg
Forms 2 muscle groups in body and limbs Development of the sclerotome and myotome components of the somite.

Dermatome

  • connective tissue underlying epidermis
  • begins as a dorsal thickening
  • spreads throughout the body

Note - Dermatome is the term also used clinically postnatally to describe the region of skin supplied by a single spinal nerve.

Week 2 and 3 Movies

Week 2

Week2 001 icon.jpg
 ‎‎Week 2 - Implant
Page | Play
Chorion 001 icon.jpg
 ‎‎Week 2 - Bilaminar
Page | Play

Week 3

Mesoderm 001 icon.jpg
 ‎‎Week 3 Mesoderm
Page | Play
Notochord 01 icon.jpg
 ‎‎Week 3 Notochord
Page | Play
Notochord 02 icon.jpg
 ‎‎Week 3 Notochord
Page | Play
Nodal-cilia-001-icon.jpg
 ‎‎Nodal Cilia
Page | Play
Week3 folding icon.jpg
 ‎‎Week 3
Page | Play
Amnion 001 icon.jpg
 ‎‎Amniotic Cavity
Page | Play
Quail HH stage 2 fibronectin movement.jpg
 ‎‎Gastrulation ECM
Page | Play

Week 3 Interactive Component

Attempt the Quiz - Week 3  
BGDsmall.jpg

Here are a few simple Quiz questions that relate to Week 3 (GA week 5) from the lecture and practical.

See your Quiz Result - Answer all the questions, then click "submit" to complete. The page will reload and you can then reopen this table to see your result and feedback.

  

1 During embryonic disc folding in week 3 only the ectoderm layer folds ventrally left, right and above and below the notochord.

  true
  false

2 Which of the following is the most correct statement about the primitive streak:

  extends from the primitive node to the parachordal plate
  is a primary inducer during organogenesis
  is a site of migration of epiblast cells to form the mesoderm
  persists as the parachordal plate
  all of the above are correct

3 The migration of intra-embryonic mesoderm occurs between the ectoderm and endoderm to give rise to:

 the buccopharyngeal membrane
 the cloacal membrane
 the allantois
 the somites
 all of the above

4 The buccopharyngeal membrane is made up of:

 embryonic ectoderm, mesoderm and endoderm
 endoderm fused with mesoderm
 ectoderm fused with mesoderm
 ectoderm fused with endoderm
 the cephalic end of notochordal process

5 The intraembryonic coelom finally forms

  pericardial, pleural and peritoneal cavity.
  single pericardial cavity and two pleural and two peritoneal cavities.
  neural tube lumen, gastrointestinal tract lumen and neural crest.
  the paired dorsal aortas running the embryo.

6 The amniotic cavity appears initially as a slit-like space within the:

  exocoelomic (Heuser’s) membrane
  extra-embryonic mesoderm
  ectoderm
  connecting stalk
  endoderm

7 Which of the following processes are necessary for the early development of the human embryo?

  cell proliferation
  cell migration
  cell fusion
  differential growth
  all of the above


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Practical 6: Week 3 | Week 4 | Week 5 | Week 6 | Week 7 | Week 8



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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 3 - Human Embryo Stages and Events (GA week 5) 
Embryo Week: Week 1 | Week 2 | Week 3 | Week 4 | Week 5 | Week 6 | Week 7 | Week 8 | Week 9
Day
Stage
 Event
15
16
 Stage 7
Stage7.jpg
Gastrulation primitive node (Hensen's node, primitive knot) The small circular region located at the cranial end of the primitive streak, where gastrulation occurs, and is a controller of this process. The process establishes the 3 germ cell layers: Endoderm, Mesoderm and Ectoderm. The second role is to act as an initial generator of the left-right (L-R) body axis.
17
    
18
 Stage 8
Stage8 human.jpg
Neural - neurogenesis, neural groove and folds are first seen
19
  
Stage8 SEM1.jpg
20
 Stage 9
Stage9 bf1c.jpg
Musculoskeletal - somitogenesis, first somites form and continue to be added in sequence caudally (1 - 3 somite pairs).

Neural - the three main divisions of the brain, which are not cerebral vesicles, can be distinguished while the neural groove is still completely open

Neural Crest - mesencephalic neural crest is visible[1]

21
   Heart - cardiogenesis, week 3 begins as paired heart tubes.
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. ↑ <pubmed>17848161</pubmed>


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Cite this page: Hill, M.A. (2024, April 16) Embryology BGDA Practical 7 - Week 3. Retrieved from https://embryology.med.unsw.edu.au/embryology/index.php/BGDA_Practical_7_-_Week_3

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© Dr Mark Hill 2024, UNSW Embryology ISBN: 978 0 7334 2609 4 - UNSW CRICOS Provider Code No. 00098G
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