UNSW Embryology

Coelomic Cavity Development

© Dr Mark Hill (2011)

Acknowledgements

Introduction

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 body cavities (pericardial, pleural, peritoneal). The other major cavity seen within the embryo is within the neural tube and is not covered in these current notes (More? Neural Notes - Ventricular System).

Extraembryonic Coelom cavity surrounding the developing embryo	coelomic portals transient communication between extra/intracoelom	Intraembryonic Coelom horseshoe shaped structure forms 3 main cavities	Neural Tube
		percardial cavity	Ventricular space
		L/R pleural cavities	Spinal canal
		peritoneal cavity	(More? Neural Notes)

Peritoneal Cavity (stage 13/14) surrounding the stomach

The coelom forms very early in embryogenesis and is much later paritioned inferiorly by the diaphragm and pleuroperitoneal membrane; and superiorly initially by the pleuropericardial fold between the heart and lungs.

The intraembryonic coelom communicated through coelomic portals (at the level of midgut herniation) with the extraembryonic coelom.

All cavities are fluid filled and developing organs push against a wall of the cavity, generating a double coat (serosal/adventital) surrounding an organ (for example the lungs). The serous membrane is the epithelium (squamous) and its associated underlying loose connective tissue.

Page Links: Introduction | Some Recent Findings | Reading | Objectives | Computer Activities | Development Overview | Molecular Factors | References | Glossary

Other Pages: Abnormalities | Stage 13/14 | Stage 22 | Selected Stage 22 | Extraembryonic Coelom | Text only | Web Links

Some Recent Findings

Reading

• Human Embryology (2nd ed.) Larson
  • Ch6 p127-146
• The Developing Human: Clinically Oriented Embryology (6th ed.) Moore and Persaud
  • Ch9: p174-184
• Before we Are Born (5th ed.) Moore and Persaud
  • Ch10 p181-195
• Essentials of Human Embryology Larson
  • Ch6 p81-93
• Human Embryology Fitzgerald and Fitzgerald
  • Ch5 p29-32, Ch7 p47,48
• Additional References
• Search PubMed- Medline

Objectives

• Describe the development of the intra- and extra-embryonic coeloms.
• Describe the processes involved in the development of the three divisions of the intra-embryonic coelom; pericardium, pleural cavities and peritoneum.
• Describe the fate of the extra embryonic coelom.
• Describe the development of the diaphragm.

Learning activities

• Review the development of the 3-layered embryo, with particular reference to the antero-posterior and lateral folding processes.
• Examine the 6mm pig and 27mm human embryo microfiche cards identifying the main features of the developing coelom.
• Identify the diaphragm in the 27mm human embryo and relate this to the development of the diaphragm.
• Discuss the developmental anomalies associated with the formation of the diaphragm.

Computer Activities

UNSW Embryology: Pig coelom sections (st13/14) | Human coelom sections (st22) | Selected Human highpower (st22)

Human Embryology Movies:

Embryo Images Unit: Body Cavities (Early Week 4) | Body Cavities (Late Week 4)

Development Overview

Cells migrate through the primitive streak to form mesodermal layer. Extraembryonic mesoderm lies adjacent to the trilaminar embryo totally enclosing the amnion, yolk sac and forming the connecting stalk.

Paraxial mesoderm accumulates under the neural plate with thinner mesoderm laterally. This forms 2 thickened streaks running the length of the embryonic disc along the rostrocaudal axis. In humans, during the 3rd week, this mesoderm begins to segment. The neural plate folds to form a neural groove and folds.

Segmentation of the paraxial mesoderm into somites continues caudally at 1 somite/90minutes and a cavity (intraembryonic coelom) forms in the lateral plate mesoderm separating somatic and splanchnic mesoderm.

Note intraembryonic coelomic cavity communicates with extraembryonic coelom through portals (holes) initially on lateral margin of embryonic disc.

Somites continue to form. The neural groove fuses dorsally to form a tube at the level of the 4th somite and "zips up cranially and caudally and the neural crest migrates into the mesoderm.

Extraembryonic Coelom cavity surrounding the developing embryo	coelomic portals transient communication between extra/intracoelom	Intraembryonic Coelom horseshoe shaped structure forms 3 main cavities	Neural Tube
		percardial cavity	Ventricular space
		L/R pleural cavities	Spinal canal
		peritoneal cavity	(not part of this section) (More? )

Mesothelia

The epithelial covering of coelomic organs and also line their cavities.

Contribute to the vasculature of the heart and the intestinal tract. Undergo epithelial-mesenchymal transition (EMT), migration, and differentiation into endothelial cells, vascular smooth muscle cells, and pericytes.

Development Terms

• atresia- obstruction.
• eppiglottis- develops from hypobrachial eminence.
• fistula- abnormal comunication.
• hypopharyngeal eminence- fusion of 3rd pharyngeal arches, precursor of root of tongue.
• laryngotracheal groove- forms on anterior (ventral) wall of pharynx, gives rise to larynx, trachea, respiratory tree.
• larynx- lining from endoderm, cartilage from pharyngeal arch 4 and 6.
• lung buds- primordia of lungs.
• parietal pleura-outer lining of pleural cavity derived from epithelia of pericardioperitoneal canals from intraembryonic coelom.
• pleural cavity- walls derived from pericardioperitoneal canals -> intraembryonic coelom ->coelomic spaces -> lateral mesoderm -> mesoderm.
• pleuropericardial fold- restricts the communication between pleural cavity and pericardiac cavity, contains cardinal vein and phrenic nerve.
• pleuroperitoneal membrane- forms inferiorly at transverse septum to separate peritoneum from pleural cavity.
• septum transversum- mesoderm separating thoracic cavity and yolk sac, forms central tendon of diaphragm (and some of liver?).
• stenosis- narrowing
• surfactant- a detergent secreted by Type 2 alveolar cells between alveolar epithelium. Functions to lower surface tension, allowing lungs to remain inflated.
• visceral pleura- inner lining of pleural cavity derived from contact epithelia with lung bud of pericardioperitoneal canals from intraembryonic coelom.

Glossary

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Quick Links

Development Notes ----------------- Menstrual Cycle Week 1 Week 2 Week 3 Week 4 Placenta Serial Images Molecular Dev Abnormal Dev Postnatal Dev Notes Index

System Notes ----------------- All Systems Heart/Cardiovascular Respiratory Coelomic cavity Gastrointestinal Tract Head and Neck Neural Neural Crest Eye Ear Nose Endocrine Renal Genital Musculoskeletal Integumentary

Movies ----------------- Movies Quicktime Flash Audio Week 1 Week 2 Week 3 Stage 13 Stage 22 Neural Heart Gastrointestinal Renal Genital Other Embryos

Other Embryos ----------------- All Animals Chicken Fly Frog Mouse Rabbit Rat Worm Zebrafish Guinea Pig

UNSW Embryology ISBN: 978 0 7334 2609 4

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