2010 BGD Practical 6 - 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 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.
===Practical Audio===
{| border='0px'
|-
| [[File:Mark_Hill.jpg|60px|left]]
|
BGD Cycle A 2010 Audio - Dr Mark Hill Monday 17th May 2010 3-5pm G2G4.
:Note - this is a live unedited recording from the practical and may contain errors in either descriptions or content.
[[Media:BGD2010-Embryo Lab 170510-601.mp3|listen Part 1]] | [[:File:BGD2010-Embryo Lab 170510-601.mp3|download]] (2.7 Mb MP3 20:39)
|-
|}


===Folding===
===Folding===
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===Mesoderm Segmentation===
===Mesoderm Segmentation===
Different regions of mesoderm form early intermediate structures.
Different regions of mesoderm form early intermediate structures.
# 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 (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.
# [[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.
# 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).  
# [[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).


===Ectoderm Segmentation===
===Ectoderm Segmentation===
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There are two major folding processes that take place during this time.
There are two major folding processes that take place during this time.


# 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.
# 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 [[N#notochord|notochord]], which forms a rod-like region running rostro-caudally in the midline.  


[[File:Amnion 001 icon.jpg|120px|link=Development Animation - Amniotic Cavity]] [[File:Week3_folding icon.jpg|120px|link=Development Animation - Week 3]]
[[File:Amnion 001 icon.jpg|120px|link=Development Animation - Amniotic Cavity]] [[File:Week3_folding icon.jpg|120px|link=Development Animation - Week 3]]
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* '''Laterally''' (either side of the notochord) lies mesoderm.  
* '''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.  
* '''Rostrally''' (above the notochord end) lies the [[B#buccopharyngeal membrane|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.  
* '''Caudally''' (below the notochord end) lies the primitive streak (where gastrulation occurred), below this again is the [[C#cloacal membrane|cloacal membrane]].  
* '''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 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]]


==Mesoderm==
==Mesoderm==
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</gallery>
</gallery>


'''Mesoderm organization:''' lateral plate - intermediate mesoderm - paraxial mesoderm - axial mesoderm - paraxial mesoderm - intermediate mesoderm - lateral plate
===Mesoderm Development===


<gallery>
# [[E#epiblast|epiblast]] -> mesoderm + [[A#axial mesoderm|axial mesoderm]] ([[N#notochord|notochord]])
Image:Stage7_paraxial-mesoderm.jpg|Stage 7 paraxial mesoderm
# [[L#lateral plate|lateral plate]] + [[P#paraxial mesoderm|paraxial mesoderm]] + [[A#axial mesoderm|axial mesoderm]]
Image:Stage7_intermediate-mesoderm.jpg|Stage 7 intermediate 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]]
Image:Stage7_lateral-plate.jpg|Stage 7 lateral plate
# [[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]]
</gallery>


===Axial Mesoderm===
===Axial Mesoderm===
* notochord
[[File:Sonic_hedgehog_expression.jpg|thumb|Notochord secreting sonic hedgehog]]
{|
| [[Image:Stage7 notochord.jpg|left|200px|Stage 7 notochord]]
|
The notochord
# mechanical role in embryonic disc folding
# mechanical role in embryonic disc folding
# molecular role in patterning surrounding tissues
# molecular role in patterning surrounding tissues


<gallery>
Image:Stage7_800x700px.jpg|Stage 7 embryonic disc
Image:Stage7_primitive-streak-node.jpg|Stage 7 primitive-streak-node
Image:Stage7_cloacal-oral-membranes.jpg|Stage 7 cloacal-oral-membranes
Image:Stage7 notochord.jpg|Stage 7 notochord
</gallery>


'''Adult''' - contributes to the nucleus pulposis of the intervertebral disc
 
'''Adult''' - contributes to the [[N#nucleus pulposus|nucleus pulposus]] of the intervertebral disc
|-
|}


===Paraxial Mesoderm===
===Paraxial Mesoderm===
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* differentiates rostro-caudally  (head to tail)
* differentiates rostro-caudally  (head to tail)
* forms 3 sets of "kidneys" in sequence
* forms 3 sets of "kidneys" in sequence
# pronephros
# [[P#pronephros|pronephros]]
# mesonephros
# [[M#mesonephros|mesonephros]]
# metanephros
# [[M#metanephros|metanephros]]






'''Adult''' - metanephros forms the kidney
'''Adult''' - [[M#metanephros|metanephros]] forms the kidney
|-
|-
|}
|}
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|  
|  
* a "horseshoe shaped" space forms in the middle
* a "horseshoe shaped" space forms in the middle
* somatic mesoderm - closest to ectoderm
* [[S#somatic mesoderm|somatic mesoderm]] - closest to ectoderm
* space - forms the 3 body cavities (pericardial, pleural, peritoneal)
* space - forms the 3 body cavities (pericardial, pleural, peritoneal)
* splanchnic mesoderm - closest to endoderm
* [[S#splanchnic mesoderm|splanchnic mesoderm]] - closest to endoderm






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


|-
|-
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Somite initially forms 2 main components
Somite initially forms 2 main components
* ventromedial- sclerotome forms vertebral body and intervertebral disc
* ventromedial- [[S#sclerotome|sclerotome]] forms vertebral body and intervertebral disc
* dorsolateral - dermomyotome forms dermis and skeletal muscle
* dorsolateral - [[D#dermomyotome|dermomyotome]] forms dermis and skeletal muscle


<gallery>
<gallery>
Image:Somite cartoon1.png|paraxial mesoderm
Image:Somite cartoon1.png|paraxial mesoderm
Image:Somite cartoon2.png|early somite
Image:Somite cartoon2.png|early somite
Image:Somite cartoon3.png|sclerotome and dermomyotome
Image:Somite cartoon3.png|[[S#sclerotome|sclerotome]] and [[D#dermomyotome|dermomyotome]]
Image:Somite cartoon4.png|dermatome and myotome
Image:Somite cartoon4.png|[[D#dermatome|dermatome]] and [[M#myotome|myotome]]
Image:Somite cartoon5.png|epaxial and hypaxial muscles
</gallery>
</gallery>


===Sclerotome===
===Sclerotome===
* sclerotome later becomes subdivided
{|
** rostral and caudal halves separated laterally by von Ebner's fissure
|-
| [[File:Vertabra 003 icon.jpg|200px|link=Development_Animation_-_Vertebra]]
|
* 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 [[V#von Ebner's fissure|von Ebner's fissure]])
* half somites contribute to a single vertebral level body
* half somites contribute to a single vertebral level body
* other half intervertebral disc
* other half intervertebral disc
* therefore final vertebral segmentation “shifts”
* therefore final vertebral segmentation “shifts”
|-
|}


===Myotome===
===Myotome===
* Body - epaxial and hypaxial muscles
{|
| [[File:Somite cartoon5.png|left|200px|epaxial and hypaxial muscles]]
|
Forms 2 muscle groups in body and limbs
* 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.
|-
|}


===Dermatome===
===Dermatome===
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* spreads throughout the body
* spreads throughout the body


[[File:Mesoderm 001 icon.jpg|160px|link=Development_Animation_-_Mesoderm]] [[File:Somite 001 icon.jpg|160px|link=Development_Animation_-_Somite_Musculoskeletal]]  [[File:Vertabra 003 icon.jpg|160px|link=Development_Animation_-_Vertebra]]
'''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 and 3 Movies==
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|-
|-
|}
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{{Template:2010BGDLab6}}
{{Template:2010BGDLab6}}

Latest revision as of 17:27, 16 May 2014

BGDsmall.jpg

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


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.

Practical Audio

Mark Hill.jpg

BGD Cycle A 2010 Audio - Dr Mark Hill Monday 17th May 2010 3-5pm G2G4.

Note - this is a live unedited recording from the practical and may contain errors in either descriptions or content.

listen Part 1 | download (2.7 Mb MP3 20:39)


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. 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 (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.
  2. 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).

Ectoderm Segmentation

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.

Folding

There are two major folding processes that take place during this time.

  1. 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.
  2. 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.

Amnion 001 icon.jpg Week3 folding icon.jpg

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.

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

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


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
  • space - forms the 3 body cavities (pericardial, pleural, peritoneal)
  • splanchnic mesoderm - closest to endoderm


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

Somite Development

stage 11 Embryo

Somite initially forms 2 main components

  • ventromedial- sclerotome forms vertebral body and intervertebral disc
  • dorsolateral - dermomyotome forms dermis and skeletal muscle

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

Forms 2 muscle groups in body and limbs

Somite 001 icon.jpg 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

Week2 001 icon.jpg Mesoderm 001 icon.jpg Chorion 001 icon.jpg Amnion 001 icon.jpg Week3 folding icon.jpg
Implantation Mesoderm Chorionic Cavity Amniotic Cavity Week 3


BGDsmall.jpg

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


   

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.


Detailed Week by Week

The following information is a detailed timeline of embryonic development between week 3 to 8 and content does not form part of the current practical class.

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

Embryo Stages and Events

Day Stage Event
15
16
Stage 7
Stage7.jpg
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.
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

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


21
  Heart cardiogenesis - week 3 begins as paired heart tubes.


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
2010 BGD: Lecture 1 | Lecture 2 | Practical 3 | Practical 6 | Practical 12

Cite this page: Hill, M.A. (2024, March 28) Embryology 2010 BGD Practical 6 - Week 3. Retrieved from https://embryology.med.unsw.edu.au/embryology/index.php/2010_BGD_Practical_6_-_Week_3

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