Lecture - Mesoderm Development
Objectives
- Understanding of events during the third week of development
- Understanding the process of early somite development
- Understanding the process of body cavity formation
- Brief understanding of the future fate of mesoderm components
- Brief understanding of early heart formation
Notochord (Axial mesoderm)
Stage 7 embryonic disc
Stage 7 primitive-streak-node
Stage 7 cloacal-oral-membranes
Stage 7 notochord
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
Stage 7 paraxial mesoderm
Stage 7 intermediate mesoderm
Stage 7 lateral plate
- Paraxial mesoderm - somites - musculoskeletal structures
- Intermediate mesoderm - kidney
- Lateral plate mesoderm - body wall structures
Mesoderm Development
The four images below beginning at week 3 show cross-sections of the trilaminar embryo and the sequence of mesoderm development.
Mesenchyme
- Embryonic connective tissue, describes the cell morphology (Histology is not epithelial organization)
- epithelial to mesenchymal transitions
- mesenchymal to epithelial transitions
Paraxial Mesoderm
- lies adjacent to notochord and 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
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Intermediate Mesoderm
- lies between paraxial and lateral mesoderm
- generates urogenital system
- Wolffian duct, kidney
- MH - covered in Kidney Development Lecture/Laboratory
Lateral Plate Development
- lying at the surrounding edge of he embryonic disc
- a cavity begins in this week to form within the mesoderm itself
Intraembryonic Coelom
- small spaces (vacuoles) begin appearing within the lateral plate mesoderm
- small spaces enlarge forming a single cavity within the lateral plate mesoderm
- divides lateral plate mesoderm 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
- when the embryonic disc folds the intraembryonic coelom will form all 3 major body cavities:
- Pericardial
- Pleural
- Peritoneal
Somatic Mesoderm
The intraembryonic coelom divides the lateral plate into 2 portions
- closest to ectoderm
- body wall osteogenic, chrondrogenic and fibrogenic
- except ribs and scapula
Splanchnic Mesoderm
- closest to endoderm
- heart, smooth muscle of GIT and blood vessels
Co-ordinator Note
Dr Mark Hill |
ANAT2341 Embryology S2 2011
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Course Content 2011
2011 Timetable: | Embryology Introduction | Fertilization | Cell Division/Fertilization | Week 1 and 2 Development | Week 3 Development | Week 1 to 3 | Mesoderm Development | Ectoderm, Early Neural, Neural Crest | Trilaminar Embryo to Early Embryo | Early Vascular Development | Placenta | Vascular and Placenta | Endoderm, Early Gastrointestinal | Respiratory Development | Endoderm and Respiratory | Head Development | Neural Crest Development | Head and Neural Crest | Musculoskeletal Development | Limb Development | Musculoskeletal | Renal Development | Genital | Kidney and Genital | Sensory | Stem Cells | Stem Cells | Endocrine Development | Endocrine | Heart | Integumentary Development | Heart and Integumentary | Fetal | Birth and Revision | Fetal
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, June 2) Embryology Lecture - Mesoderm Development. Retrieved from https://embryology.med.unsw.edu.au/embryology/index.php/Lecture_-_Mesoderm_Development
- © Dr Mark Hill 2024, UNSW Embryology ISBN: 978 0 7334 2609 4 - UNSW CRICOS Provider Code No. 00098G
