Talk:Lecture - Mesoderm Development

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2014 Lecture 5 PDF

2011 Lecture 5 Audio

Mesoderm Development

Carnegie stage 9 showing somite formation

Carnegie stage 9 scanning electron microscope image showing somite formation

Carnegie stage 11 mesoderm

Introduction

File:Mesoderm_001_icon.jpg</wikiflv>

This animation shows the migration of mesoderm throughout the embryonic disc during gastrulation.

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).

Mesenchyme

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

Heart

• prechordal splanchnic mesderm forms cardiac mesoderm (week 4)
  • splanchnic mesoderm lying above the notochord
• initially as a simple tube
• first organ to form in the embryo

Chicken Model - Somite formation

Hamburger & Hamilton Stage 10 (33 hours)

• Chicken Stages -regular appearance of somites (somitomere to somite) allowed early experimenters to accurately stage the embryo Chicken Development
• 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 Hamburger Hamilton Stages
• Other vertebrate animal models - Fish (Zebrafish), Frog (Xenopus)

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
  • mainly growth of surrounding tissues not movement of sclerotome
• notochord forms nucleus pulposus of intervertebral disc (IVD)

Lecture Links

• Mesoderm Slides 2009 Lecture | Mesoderm Lecture 2008 - 1 slide/page | Lecture 3 2008 Slides - 4 slides/page | Mesoderm Lecture 2008 Slides - 6 slides/page

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