2009 Lecture 5: Difference between revisions

From Embryology
 
(36 intermediate revisions by 2 users not shown)
Line 1: Line 1:
=Mesoderm Development=
=Mesoderm Development=
[[Image:Stage9sm.jpg|thumb|Carnegie stage 9 showing somite formation]]
[[Image:Stage9sm.jpg|thumb|Carnegie stage 9 showing somite formation]]
[[Image:Stage 9 SEM1.jpg|thumb|Carnegie stage 9 scanning electron microscope image showing somite formation]]
== Introduction ==
== Introduction ==
We have seen the following processes during early human development so far: fertilization and blastocyst development in the first week, implantation in the second week, early placentation and bilaminar to trilaminar in the third week. In the third to fourth week we will now follow the development of the trilaminar embryo as each layer begins to differentiate into the primordia of different tissues within the embryo. From this point onward the lectures will not be in a strict timeline format as we will have to follow each layer ('''ectoderm, mesoderm, endoderm''') forward through its early development, and then jump back to discuss the next layer.
We have seen the following processes during early human development so far: fertilization and blastocyst development in the first week, implantation in the second week, early placentation and bilaminar to trilaminar in the third week. In the third to fourth week we will now follow the development of the trilaminar embryo as each layer begins to differentiate into the primordia of different tissues within the embryo. From this point onward the lectures will not be in a strict timeline format as we will have to follow each layer ('''ectoderm, mesoderm, endoderm''') forward through its early development, and then jump back to discuss the next layer.
Line 10: Line 11:
'''Coelom''', meaning "cavity", and major fluid-filled cavities can be seen to form both within the embryo (intraembryonic coelom) and outside the embryo (extraembryonic coelom). The '''intraembryonic coelom''' is the single primitive cavity that lies within the mesoderm layer that will eventually form the 3 major anatomical body cavities ('''pericardial, pleural, peritoneal''').
'''Coelom''', meaning "cavity", and major fluid-filled cavities can be seen to form both within the embryo (intraembryonic coelom) and outside the embryo (extraembryonic coelom). The '''intraembryonic coelom''' is the single primitive cavity that lies within the mesoderm layer that will eventually form the 3 major anatomical body cavities ('''pericardial, pleural, peritoneal''').


* '''Lectopia Lecture Audio''' Lecture Date: 10-08-2009 Lecture Time: 12:00 Venue: CLB 5 Speaker: Mark Hill [http://lectopia.elearning.unsw.edu.au/ilectures/ilectures.lasso?ut=153&id=48825 Mesoderm]
* [[2010_Lecture_5|2010 Lecture - Mesoderm Development]] | [[ANAT2341_Course_Timetable_2010|Science 2010]]
== Objectives ==
== Objectives ==


Line 21: Line 24:
==UNSW Embryology Links==
==UNSW Embryology Links==


* [[2010_Lecture_5|2010 Lecture - Mesoderm Development]] | [[ANAT2341_Course_Timetable_2010|Science 2010]]
* '''Mesoderm Slides''' [http://embryology.med.unsw.edu.au/pdf/ANAT2341L6Mesoderms1.pdf Mesoderm Lecture 2008 - 1 slide/page ] | [http://embryology.med.unsw.edu.au/pdf/ANAT2341L6Mesoderms4.pdf Lecture 3 2008 Slides - 4 slides/page] | [http://embryology.med.unsw.edu.au/pdf/ANAT2341L6Mesoderms6.pdf Mesoderm Lecture 2008 Slides - 6 slides/page]
* '''Mesoderm Slides''' [http://embryology.med.unsw.edu.au/pdf/ANAT2341L6Mesoderms1.pdf Mesoderm Lecture 2008 - 1 slide/page ] | [http://embryology.med.unsw.edu.au/pdf/ANAT2341L6Mesoderms4.pdf Lecture 3 2008 Slides - 4 slides/page] | [http://embryology.med.unsw.edu.au/pdf/ANAT2341L6Mesoderms6.pdf Mesoderm Lecture 2008 Slides - 6 slides/page]


Line 27: Line 31:


== Lecture Summary ==
== Lecture Summary ==
The following text is extracted and modified from lecture slides and should be used as a "trigger" to remind you of key concepts.
The following text is extracted and modified from 2008 lecture slides and should be used as a "trigger" to remind you of key concepts.


'''Lecture Overview - Mesoderm '''
[[Image:Mesoderm cartoon1.gif]] [[Image:Mesoderm cartoon2.gif]]


* Axial mesoderm - notochord
[[Image:Mesoderm cartoon3.gif]] [[Image:Mesoderm cartoon4.gif]]
* Paraxial mesoderm- somites
 
* Intermediate mesoderm
 
* Lateral Plate mesoderm
===Notochord (Axial mesoderm)===
** Somatic, Splanchnic
<gallery>
* Cavity is called a Coelom (Intraembryonic, ?Extraembryonic)
Image:Stage7_800x700px.jpg|Stage 7 embryonic disc
** Intraembryonic Coelom forms in lateral plate mesoderm and forms 3 major body cavities
Image:Stage7_primitive-streak-node.jpg|Stage 7 primitive-streak-node
* partitioning and segmentation
Image:Stage7_cloacal-oral-membranes.jpg|Stage 7 cloacal-oral-membranes
* adult products, axes
Image:Stage7 notochord.jpg|Stage 7 notochord
** '''MH''' - Limb, Heart, Bone, connective tissue and later development will be covered in future lectures
</gallery>
* '''UNSW Embryology''' - Lecture Slides [http://embryology.med.unsw.edu.au/Science/ANAT2341lecture06.htm http://embryology.med.unsw.edu.au/Science/ANAT2341lecture06.htm]  
 
** Week 3 Development [http://embryology.med.unsw.edu.au/Notes/week3.htm http://embryology.med.unsw.edu.au/Notes/week3.htm]  
===Mesoderm===
** Week 4 Movies [http://embryology.med.unsw.edu.au/Movies/week4.htm http://embryology.med.unsw.edu.au/Movies/week4.htm]  
[[Image:Stage7_mesoderm.jpg|thumb|Stage 7 mesoderm]]
** Skeletal Muscle Development [http://embryology.med.unsw.edu.au/Notes/skmus.htm http://embryology.med.unsw.edu.au/Notes/skmus.htm]
* Text Book References
** Human Embryology (3rd ed.) ?Larson Ch11 p311-339
** The Developing Human: Clinically Oriented Embryology (6th ed.) Moore and Persaud Ch15,16: p405-423, 426-430
** Before We Are Born (5th ed.) Moore and Persaud Ch16,17: p379-397, 399-405
** Essentials of Human Embryology Larson Ch11 p207-228
** Human Embryology, Fitzgerald and Fitzgerald
** Human Embryology and Developmental Biology ?Carlson Ch9,10: p173-193, 209-222
* NCBI Books
** Developmental Biology. 6th ed. Gilbert, Scott F. Sunderland (MA): c2000.  
*** Part 3. Later embryonic development
*** 14. Paraxial and intermediate mesoderm
*** 15. Lateral plate mesoderm and endoderm
** Molecular Biology of the Cell
*** V. Cells in Their Social Context - 21. Development of Multicellular Organisms - Cell Movements and the Shaping of the Vertebrate Body Mesoderm Formation, Trilaminar Embryo- Axial Process Cell Sorting
* Mesenchyme
** Embryonic connective tissue
** Describes the cell morphology
** Histology - not epithelial
* Mesoderm
** generated from epiblast cells migrating through the primitive streak  
** generated from epiblast cells migrating through the primitive streak  
** epiblast cells expressing fibroblast growth factor (FGF2)  
** epiblast cells expressing fibroblast growth factor (FGF2)  
Line 69: Line 53:
** present before neural tube formation  
** present before neural tube formation  
* divides initially into 3 components  
* divides initially into 3 components  
** Paraxial
 
** Intermediate
<gallery>
** Lateral plate  
Image:Stage7_paraxial-mesoderm.jpg|Stage 7 paraxial mesoderm
* Intermediate Mesoderm
Image:Stage7_intermediate-mesoderm.jpg|Stage 7 intermediate mesoderm
** lies between paraxial and lateral mesoderm  
Image:Stage7_lateral-plate.jpg|Stage 7 lateral plate
** generates urogenital system
</gallery>
** Wolffian duct, kidney  
 
** '''MH''' - covered in Kidney Development Lecture/Laboratory
* Paraxial mesoderm - somites - musculoskeletal structures
* Lateral Plate Mesoderm  
* Intermediate mesoderm - kidney
** divides into 2 parts at about day 18-19
* Lateral plate mesoderm - body wall structures
* Intraembryonic coelom
 
** forms 3 body cavities- pericardial, pleural, peritoneal
[[Image:Mesoderm cartoon1.gif]]
* Splanchnic
 
** heart and smooth muscle of GIT and blood vessels
===Mesenchyme===
* Somatic
* Embryonic connective tissue, describes the cell morphology (Histology is not epithelial organization)
** body wall osteogenic, chrondrogenic and fibrogenic
** epithelial to mesenchymal transitions
** except ribs and scapula
** mesenchymal to epithelial transitions
* Paraxial Mesoderm  
 
===Paraxial Mesoderm===
[[Image:Mesoderm cartoon2.gif]]
** lies adjacent to notochord  
** lies adjacent to notochord  
** Forms 2 components  
** Forms 2 components  
Line 103: Line 89:
* neural tube begins to close at 4th somite level  
* neural tube begins to close at 4th somite level  
* 44 pairs of somites  
* 44 pairs of somites  
* Somite Formation
 
** Somite formation - Chick embryo
=== Intermediate Mesoderm===
** Somitomere to Somite
[[Image:Mesoderm cartoon2.gif]]
** Chicken Stages -regular appearance of somites allowed early experimenters to accurately stage the embryo
* lies between paraxial and lateral mesoderm
** Advantages - accessible, easy to manipulate, limb grafts/removal, chimeras, developmental processes
* generates urogenital system
* Chicken
** Wolffian duct, kidney
** taxon-Gallus gallus
** '''MH''' - covered in Kidney Development Lecture/Laboratory
** develops and hatches in 20-21 days
 
** Fertilized eggs easily maintained in humidified incubators
===Lateral Plate Development===
** Embryo Staged growth
[[Image:Mesoderm cartoon3.gif]]
** Series of Embryonic Chicken Growth
 
** Hamburger & Hamilton J. Morphology, 88 49 - 92, 1951
The intraembryonic coelom divides the lateral plate into 2 portions
** [http://embryology.med.unsw.edu.au/OtherEmb/chick1.htm]  
* '''Somatic mesoderm'''- closest to ectoderm
* See also UNSW Embryology - Other Embryos
** body wall osteogenic, chrondrogenic and fibrogenic
* Zebrafish, Xenopus
** except ribs and scapula 
* Paraxial Segmentation
* '''Splanchnic mesoderm''' - closest to endoderm
* Stage 13/14 Embryo
** heart and smooth muscle of GIT and blood vessels
* Somites
 
** ball forms through epithelialization and interactions (cell-cell, cell-extracellular matrix, ECM) fibronectin, laminin  
===Intraembryonic Coelom===
** has 2 populations of cells  
[[Image:Mesoderm cartoon4.gif]]
*** peripheral columnar  
* small spaces (vacuoles) begin appearing within the lateral plate mesoderm
*** central mesenchymal  
* small spaces enlarge forming a single cavity within the lateral plate mesoderm
** early somite has cavity- somitocoel  
** divides into 2 parts at about day 18-19
*** cavity is lost  
* this cavity is called the '''Intraembryonic Coelom'''
*** will contribute to sclerotome
** coelom is a general term for a "cavity" and can lie within the embryo (intraembryonic) and outside the embryo (extraembryonic)
** later anatomical spaces within the embryo and fetus can also be described as coeloms
* later when the embryonic disc folds the intraembryonic coelom in the lateral plate mesoderm will later form all 3 major body cavities
** Pericardial
** Pleural
** Peritoneal
 
===Somite Formation===
[[Image:Somite cartoon1.png]]  [[Image:Somite cartoon2.png]] [[Image:Somite cartoon3.png]] [[Image:Somite cartoon4.png]] [[Image:Somite cartoon5.png]]
 
[http://embryology.med.unsw.edu.au/Movies/mesoderm.htm Mesoderm Movies]
 
* ball forms through epithelialization and interactions (cell-cell, cell-extracellular matrix, ECM) fibronectin, laminin  
* has 2 populations of cells - peripheral columnar and central mesenchymal  
* early somite has cavity- somitocoel, cavity is lost during growth
* somite enclosed by ECM connected to nearby tissues  
* somite enclosed by ECM connected to nearby tissues  
* Somite Specification  
 
** Different segmental level somites have to generate different segmental body structures?  
Somite Specification  
** somite has to form different tissues?  
* Different segmental level somites have to generate different segmental body structures?  
* Segmental Plate Mesoderm
* somite has to form different tissues?
* Somite Differentiation  
* Somite Differentiation  
* Compartmentalization accompanied by altered patterns of expression of Pax genes within the somite  
* Compartmentalization accompanied by altered patterns of expression of Pax genes within the somite  
* forms 2 main components  
 
** ventral- sclerotome  
Somite initially forms 2 main components  
*** forms vertebral body and intervertebral disc  
** ventromedial- '''sclerotome''' forms vertebral body and intervertebral disc  
** dorsal- dermomyotome  
** dorsolateral - '''dermomyotome''' forms dermis and skeletal muscle  
*** forms dermis and skeletal muscle  
 
* Somite Axial Specification  
Somite Axial Specification  
** rostro-caudal axis appears regulated by Pax/Hox expression  
* rostro-caudal axis appears regulated by Pax/Hox expression, family of DNA binding transcription factors  
** family of DNA binding transcription factors  
* Movie: Somite Development  
* Movie: Somite Development  
* Sclerotome  
 
** sclerotome later becomes subdivided  
Sclerotome  
** rostral and caudal halves separated laterally by von Ebner's fissure  
* sclerotome later becomes subdivided  
*** half somites contribute to a single vertebral level body  
* rostral and caudal halves separated laterally by von Ebner's fissure  
*** other half intervertebral disc  
** half somites contribute to a single vertebral level body  
** therefore final vertebral segmentation “shifts”
** other half intervertebral disc  
* Muscle  
* therefore final vertebral segmentation ‚"shifts"
** MyoD is first expressed in the dorsomedial quadrant of the still epithelial somite whose cells are not yet definitely committed  
 
** MyoD myoblast determining transcription factor
Muscle  
* Myoblast determining transcription factor MyoD is first expressed in the dorsomedial quadrant of the still epithelial somite whose cells are not yet definitely committed  
** basic Helix Loop Helix  
** basic Helix Loop Helix  
** form myotome  
** form myotome  
* Myotome component of Somite  
* Myotome component of Somite  
** epaxial myotome (dorsomedial quarter)  
** epaxial myotome (dorsomedial quarter) forms the dorsal epimere (erector spinae)  
*** dorsal epimere (erector spinae)  
** hypaxial myotome (dorsolateral quarter) forms the ventral hypomere, 3 primary muscle layers which are different at neck, thorax and abdomen
** hypaxial myotome (dorsolateral quarter)  
[[Image:Stage14 somites limbbuds.png|thumb|Stage 14 Embryo showing somites and limb buds (Week 5)]]
*** ventral hypomere  
 
*** 3 primary muscle layers  
 
** different at neck, thorax and abdomen  
* Chick Embryo Mesoderm  
* Chick Embryo Mesoderm  
* Body Musculature - Myotome derivatives-mouse embryo  
* Body Musculature - Myotome derivatives-mouse embryo  
Line 173: Line 172:
*** not movement of sclerotome, growth of surrounding tissues  
*** not movement of sclerotome, growth of surrounding tissues  
*** notochord forming nucleus pulposus of IVD  
*** notochord forming nucleus pulposus of IVD  
* Dermomyotome  
 
** lateral myotome edge migrates at level of limbs  
Dermomyotome  
** upper limb first then lower  
* lateral myotome edge migrates at level of limbs  
** mixes with somatic mesoderm  
* upper limb first then lower  
** dermotome continues to contribute cells to myotome  
* mixes with somatic mesoderm  
* Muscle Development Abnormalities  
* dermotome continues to contribute cells to myotome  
** Duchenne Muscular Dystrophy  
 
*** Embryonic muscle development normal and changes occur postnatally  
Muscle Development Abnormalities  
*** X-linked dystrophy, large gene encoding cytoskeletal protein - Dystrophin  
* Duchenne Muscular Dystrophy  
*** progressive wasting of muscle, die late teens  
** Embryonic muscle development normal and changes occur postnatally  
** Becker Muscular Dystrophy, milder form, adult onset  
** X-linked dystrophy, large gene encoding cytoskeletal protein - Dystrophin  
* Axial Segmentation  
** progressive wasting of muscle, die late teens  
* Somite Specification Signals
* Becker Muscular Dystrophy, milder form, adult onset  
* Mesoderm Movies
 
Axial Segmentation - Somite Specification Signals
 
Chicken Model - Somite formation
* Somitomere to Somite  
* Chicken Stages -regular appearance of somites allowed early experimenters to accurately stage the embryo 
* Chicken
** Advantages - accessible, easy to manipulate, limb grafts/removal, chimeras, developmental processes
** taxon-Gallus gallus
** develops and hatches in 20-21 days
** Fertilized eggs easily maintained in humidified incubators
** Embryo Staged growth
** Series of Embryonic Chicken Growth
** Hamburger & Hamilton J. Morphology, 88 49 - 92, 1951  [http://embryology.med.unsw.edu.au/OtherEmb/chick1.htm]
* Zebrafish, Xenopus
* Paraxial Segmentation
* Stage 13/14 Embryo
 
==Take the Quiz==
<quiz display=simple>
 
{Mesenchyme refers to the middle layer of the trilaminar embryo
|type="()"}
- true
+ false
|| The  the middle layer of the trilaminar embryo is the '''mesoderm''' (meaning middle layer), while most of these cells are mesemchymal in appearance, this term is used to describe the cell histological appearance/organization.
 
{The intraembryonic coelom forms within :
|type="()"}
- somites
+ lateral plate
- neural tube
- intermediate mesoderm
||The intraembryonic coelom forms initially small spaces  in the mesoderm layer and coalesce to form a single large "horseshoe-shaped" space within the '''lateral plate mesoderm''' around the embryonic disc. Both young somites (somitocoels) and the neural tube (neural tube lumen) do have cavities, but neither is called the intraembryonic coelom.
 
{All paraxial mesoderm segments into somites.
|type="()"}
- true
+ false
|| While somites do form within paraxial mesoderm, this region remains unsegmented at the level of the head and therefore does not incorporate into somites.
 
 
{Somites are developmental structures that contribute the following adult structures :
|type="()"}
- vertebra, notochord, dermis, skeletal muscle
+ vertebra, intervertebral discs, dermis, skeletal muscle
- kidney, body wall connective tissue, sensory ganglia
- kidney, gastrointestinal tract smooth muscle, mesentry
||Each somite has specific regions that contribute different components of the embryo. Sclerotome contributes the vertebral column ('''vertebra, intervertebral discs'''). Dermotome contributes the connective tissue layers of the skin ('''dermis''', hypodermis). Myotome ontributes the '''skeletal muscle''' of the body and limbs.
 
 
</quiz>


== References ==
== References ==
Line 208: Line 258:
* '''Bookshelf'''  [http://www.ncbi.nlm.nih.gov/sites/entrez?db=Books&cmd=search&term=mesoderm mesoderm] | [http://www.ncbi.nlm.nih.gov/sites/entrez?db=Books&cmd=search&term=coelom coelom] |  [http://www.ncbi.nlm.nih.gov/sites/entrez?db=Books&cmd=search&term=somite somite] | [http://www.ncbi.nlm.nih.gov/sites/entrez?db=Books&cmd=search&term=coelomic_cavity coelomic cavity]
* '''Bookshelf'''  [http://www.ncbi.nlm.nih.gov/sites/entrez?db=Books&cmd=search&term=mesoderm mesoderm] | [http://www.ncbi.nlm.nih.gov/sites/entrez?db=Books&cmd=search&term=coelom coelom] |  [http://www.ncbi.nlm.nih.gov/sites/entrez?db=Books&cmd=search&term=somite somite] | [http://www.ncbi.nlm.nih.gov/sites/entrez?db=Books&cmd=search&term=coelomic_cavity coelomic cavity]


* '''Pubmed''' [http://www.ncbi.nlm.nih.gov/sites/gquery?itool=toolbar&cmd=search&term=mesoderm mesoderm] | [http://www.ncbi.nlm.nih.gov/sites/gquery?itool=toolbar&cmd=search&term=coelom coelom] | [http://www.ncbi.nlm.nih.gov/sites/gquery?itool=toolbar&cmd=search&term=somite somite] |
* '''Pubmed''' [http://www.ncbi.nlm.nih.gov/sites/gquery?itool=toolbar&cmd=search&term=mesoderm mesoderm] | [http://www.ncbi.nlm.nih.gov/sites/gquery?itool=toolbar&cmd=search&term=coelom coelom] | [http://www.ncbi.nlm.nih.gov/sites/gquery?itool=toolbar&cmd=search&term=somite somite]
 
==Movies==
{| border='0px'
 
|-
| [[File:Mesoderm 001 icon.jpg|90px|link=Development_Animation_-_Mesoderm]]
| [[File:Somite 001 icon.jpg|90px|link=Development_Animation_-_Somite_Musculoskeletal]]
| [[File:Vertabra 003 icon.jpg|90px|link=Development_Animation_-_Vertebra]]
|
|-
| [[Development_Animation_-_Mesoderm|Mesoderm]]
| [[Development_Animation_-_Somite_Musculoskeletal|Somite Structures]]
| [[Development_Animation_-_Vertebra|Vertebra]]
|
|-
|}


==UNSW Embryology Links==
==UNSW Embryology Links==
* [http://embryology.med.unsw.edu.au/Science/ANAT2341lecture06.htm Lecture 6 2008]
* [http://embryology.med.unsw.edu.au/Science/ANAT2341lecture06.htm Lecture 6 2008]
* '''Mesoderm''' [http://embryology.med.unsw.edu.au/Movies/week4.htm Week 4 Movies] | [http://embryology.med.unsw.edu.au/Movies/mesoderm.htm Mesoderm Movies]
* '''Mesoderm Notes''' [http://embryology.med.unsw.edu.au/Notes/week4.htm Week 4] | [http://embryology.med.unsw.edu.au/Notes/week4_4.htm Week 4 - Somites] | [http://embryology.med.unsw.edu.au/Notes/coelom.htm Coelomic Cavity Development] | [http://embryology.med.unsw.edu.au/Notes/skmus.htm Musculoskeletal Development]
* [http://embryology.med.unsw.edu.au/sysnote.htm System Notes]
* [http://embryology.med.unsw.edu.au/sysnote.htm System Notes]
* [http://embryology.med.unsw.edu.au/week/weekbyweek.htm Development Timeline]
* [http://embryology.med.unsw.edu.au/week/weekbyweek.htm Development Timeline]


== Glossary Links ==
{{Template:2009ANAT2341}}
 
[[A|A]]  | [[B|B]] | [[C|C]] | [[D|D]] | [[E|E]] | [[F|F]] | [[G|G]] | [[H|H]] | [[I|I]] | [[J|J]] | [[K|K]] | [[L|L]] | [[M|M]] | [[N|N]] | [[O|O]] | [[P|P]] | [[Q|Q]] | [[R|R]] | [[S|S]] | [[T|T]] | [[U|U]] | [[V|V]] | [[W|W]] | [[X|X]] | [[Y|Y]] | [[Z|Z]]
 
== Next Lecture ==
 
[[2009 Lecture 6|Lecture 6]] | [[ANAT2341_Embryology_2009#Course_Timetable|Course Timetable]]
 
:''Dr Mark Hill 2009'' UNSW CRICOS Provider Code No. 00098G


[[Category:2009ANAT2341]] [[Category:Science-Undergraduate]] [[Category:Week 3]] [[Category:Week 4]] [[Category:Mesoderm]] [[Category:Coelomic Cavity]]
[[Category:2009ANAT2341]] [[Category:Science-Undergraduate]] [[Category:Week 3]] [[Category:Week 4]] [[Category:Mesoderm]]  [[Category:Somite]] [[Category:Coelomic Cavity]]

Latest revision as of 02:53, 28 August 2010

Mesoderm Development

Carnegie stage 9 showing somite formation
Carnegie stage 9 scanning electron microscope image showing somite formation

Introduction

We have seen the following processes during early human development so far: fertilization and blastocyst development in the first week, implantation in the second week, early placentation and bilaminar to trilaminar in the third week. In the third to fourth week we will now follow the development of the trilaminar embryo as each layer begins to differentiate into the primordia of different tissues within the embryo. From this point onward the lectures will not be in a strict timeline format as we will have to follow each layer (ectoderm, mesoderm, endoderm) forward through its early development, and then jump back to discuss the next layer.

This lecture will look at mesoderm development and formation of the body cavities.

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.

Coelom, meaning "cavity", and major fluid-filled cavities can be seen to form both within the embryo (intraembryonic coelom) and outside the embryo (extraembryonic coelom). The intraembryonic coelom is the single primitive cavity that lies within the mesoderm layer that will eventually form the 3 major anatomical body cavities (pericardial, pleural, peritoneal).

Objectives

  • Understanding of events during the third week of development
  • Understanding the process of notochord formation
  • Understanding the process of early somite development
  • Understanding the process of body cavity formation
  • Understanding the future fate of mesoderm components
  • Brief understanding of early heart formation

UNSW Embryology Links

Lecture Summary

The following text is extracted and modified from 2008 lecture slides and should be used as a "trigger" to remind you of key concepts.

Mesoderm cartoon1.gif Mesoderm cartoon2.gif

Mesoderm cartoon3.gif Mesoderm cartoon4.gif


Notochord (Axial mesoderm)

Mesoderm

Stage 7 mesoderm
    • generated from epiblast cells migrating through the primitive streak
    • epiblast cells expressing fibroblast growth factor (FGF2)
    • forms a layer between ectoderm and endoderm with notochord down midline
    • present before neural tube formation
  • divides initially into 3 components
  • Paraxial mesoderm - somites - musculoskeletal structures
  • Intermediate mesoderm - kidney
  • Lateral plate mesoderm - body wall structures

Mesoderm cartoon1.gif

Mesenchyme

  • Embryonic connective tissue, describes the cell morphology (Histology is not epithelial organization)
    • epithelial to mesenchymal transitions
    • mesenchymal to epithelial transitions

Paraxial Mesoderm

Mesoderm cartoon2.gif

    • lies adjacent to notochord
    • Forms 2 components
      • Head - unsegmented paraxial mesoderm
      • Body - segmented paraxial mesoderm
    • Generates trunk muscles, skeleton, dermis of skin, blood vessels, connective tissue
  • Segmented Paraxial Mesoderm
    • segments called somites
    • first pair of somites (day 20)
    • segmentation imposes a pattern on
    • nerves, vasculature, vertebra....
    • somites appear in ordered sequence cranial to caudal
    • appearance so regular used to stage the embryo
    • Hamburger & Hamilton 1951- chicken
  • thought to be generated by a "clock" (1 pair every 90 minutes)
  • neural tube begins to close at 4th somite level
  • 44 pairs of somites

Intermediate Mesoderm

Mesoderm cartoon2.gif

  • lies between paraxial and lateral mesoderm
  • generates urogenital system
    • Wolffian duct, kidney
    • MH - covered in Kidney Development Lecture/Laboratory

Lateral Plate Development

Mesoderm cartoon3.gif

The intraembryonic coelom divides the lateral plate into 2 portions

  • Somatic mesoderm- closest to ectoderm
    • body wall osteogenic, chrondrogenic and fibrogenic
    • except ribs and scapula
  • Splanchnic mesoderm - closest to endoderm
    • heart and smooth muscle of GIT and blood vessels

Intraembryonic Coelom

Mesoderm cartoon4.gif

  • small spaces (vacuoles) begin appearing within the lateral plate mesoderm
  • small spaces enlarge forming a single cavity within the lateral plate mesoderm
    • divides into 2 parts at about day 18-19
  • this cavity is called the Intraembryonic Coelom
    • coelom is a general term for a "cavity" and can lie within the embryo (intraembryonic) and outside the embryo (extraembryonic)
    • later anatomical spaces within the embryo and fetus can also be described as coeloms
  • later when the embryonic disc folds the intraembryonic coelom in the lateral plate mesoderm will later form all 3 major body cavities
    • Pericardial
    • Pleural
    • Peritoneal

Somite Formation

Somite cartoon1.png Somite cartoon2.png Somite cartoon3.png Somite cartoon4.png Somite cartoon5.png

Mesoderm Movies

  • ball forms through epithelialization and interactions (cell-cell, cell-extracellular matrix, ECM) fibronectin, laminin
  • has 2 populations of cells - peripheral columnar and central mesenchymal
  • early somite has cavity- somitocoel, cavity is lost during growth
  • somite enclosed by ECM connected to nearby tissues

Somite Specification

  • Different segmental level somites have to generate different segmental body structures?
  • somite has to form different tissues?
  • Somite Differentiation
  • Compartmentalization accompanied by altered patterns of expression of Pax genes within the somite

Somite initially forms 2 main components

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

Somite Axial Specification

  • rostro-caudal axis appears regulated by Pax/Hox expression, family of DNA binding transcription factors
  • Movie: Somite Development

Sclerotome

  • 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"

Muscle

  • Myoblast determining transcription factor MyoD is first expressed in the dorsomedial quadrant of the still epithelial somite whose cells are not yet definitely committed
    • basic Helix Loop Helix
    • form myotome
  • Myotome component of Somite
    • epaxial myotome (dorsomedial quarter) forms the dorsal epimere (erector spinae)
    • hypaxial myotome (dorsolateral quarter) forms the ventral hypomere, 3 primary muscle layers which are different at neck, thorax and abdomen
Stage 14 Embryo showing somites and limb buds (Week 5)


  • Chick Embryo Mesoderm
  • Body Musculature - Myotome derivatives-mouse embryo
  • Lateral Plate Mesoderm
  • Limb Musculature
  • Dermomyotome- Muscle (MyoD)
  • MyoD Pax 3
  • Somite Differentiation
    • migrating neural crest cells enter cranial half, will form dorsal root ganglia (DRG)
    • sclerotome bulges ventro-medially towards notochord, then surround and engulf notochord
      • not movement of sclerotome, growth of surrounding tissues
      • notochord forming nucleus pulposus of IVD

Dermomyotome

  • lateral myotome edge migrates at level of limbs
  • upper limb first then lower
  • mixes with somatic mesoderm
  • dermotome continues to contribute cells to myotome

Muscle Development Abnormalities

  • Duchenne Muscular Dystrophy
    • Embryonic muscle development normal and changes occur postnatally
    • X-linked dystrophy, large gene encoding cytoskeletal protein - Dystrophin
    • progressive wasting of muscle, die late teens
  • Becker Muscular Dystrophy, milder form, adult onset

Axial Segmentation - Somite Specification Signals

Chicken Model - Somite formation

  • Somitomere to Somite
  • Chicken Stages -regular appearance of somites allowed early experimenters to accurately stage the embryo
  • Chicken
    • Advantages - accessible, easy to manipulate, limb grafts/removal, chimeras, developmental processes
    • taxon-Gallus gallus
    • develops and hatches in 20-21 days
    • Fertilized eggs easily maintained in humidified incubators
    • Embryo Staged growth
    • Series of Embryonic Chicken Growth
    • Hamburger & Hamilton J. Morphology, 88 49 - 92, 1951 [1]
  • Zebrafish, Xenopus
  • Paraxial Segmentation
  • Stage 13/14 Embryo

Take the Quiz

1 Mesenchyme refers to the middle layer of the trilaminar embryo

true
false

2 The intraembryonic coelom forms within :

somites
lateral plate
neural tube
intermediate mesoderm

3 All paraxial mesoderm segments into somites.

true
false

4 Somites are developmental structures that contribute the following adult structures :

vertebra, notochord, dermis, skeletal muscle
vertebra, intervertebral discs, dermis, skeletal muscle
kidney, body wall connective tissue, sensory ganglia
kidney, gastrointestinal tract smooth muscle, mesentry


References

Textbooks

  • The Developing Human: Clinically Oriented Embryology (8th Edition) by Keith L. Moore and T.V.N Persaud - Mesoderm Ch15,16: p405-423, 426-430 Body Cavities Ch9: p174-184
  • Larsen’s Human Embryology by GC. Schoenwolf, SB. Bleyl, PR. Brauer and PH. Francis-West - Mesoderm Ch11 p311-339 Body Cavities Ch6 p127-146

Additional Textbooks

  • Before We Are Born (5th ed.) Moore and Persaud Ch16,17: p379-397, 399-405
  • Essentials of Human Embryology Larson Ch11 p207-228
  • Human Embryology Fitzgerald and Fitzgerald Body Cavities Ch5 p29-32, Ch7 p47,48
  • Human Embryology and Developmental Biology ?Carlson Ch9,10: p173-193, 209-222 Body Cavities Ch5 p29-32, Ch7 p47,48

Online Textbooks

Search

Movies

Mesoderm 001 icon.jpg Somite 001 icon.jpg Vertabra 003 icon.jpg
Mesoderm Somite Structures Vertebra

UNSW Embryology Links

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

Course Content 2009

Embryology Introduction | Cell Division/Fertilization | Cell Division/Fertilization | Week 1&2 Development | Week 3 Development | Lab 2 | Mesoderm Development | Ectoderm, Early Neural, Neural Crest | Lab 3 | Early Vascular Development | Placenta | Lab 4 | Endoderm, Early Gastrointestinal | Respiratory Development | Lab 5 | Head Development | Neural Crest Development | Lab 6 | Musculoskeletal Development | Limb Development | Lab 7 | Kidney | Genital | Lab 8 | Sensory - Ear | Integumentary | Lab 9 | Sensory - Eye | Endocrine | Lab 10 | Late Vascular Development | Fetal | Lab 11 | Birth, Postnatal | Revision | Lab 12 | Lecture Audio | Course Timetable


Cite this page: Hill, M.A. (2024, March 29) Embryology 2009 Lecture 5. Retrieved from https://embryology.med.unsw.edu.au/embryology/index.php/2009_Lecture_5

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