UNSW Embryology

Extraembryonic Coelom

© Dr Mark Hill (2008)

Acknowledgements

Introduction

The extraembryonic coelom are three separate fluid-filled spaces that lies outside the developing embryo: amniotic, yolk and chorionic. Begin by looking at week 2 and week 3 development notes which cover the initial formation of the extraembryonic coelom, then look at notes covering placental development.

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:

External Link requires Internet connection

• Body Cavities (Early Week 4)
• Body Cavities (Late Week 4)

Development Overview

Cartoon of the intraembryonic coelom forming in the lateral plate 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) (see neural dev notes)

Extraembryonic Coelom Stage 23 (day 56) – chorionic cavity is now lost by fusion with the expanding amniotic cavity.

Amniotic Sac

The amniotic sac initially at the early trilaminar embryo stage lies dorsally, above the ectoderm. With folding of the embryonic disc (ventrally) the amniotic space is also drawn ventrally. (More? amniotic model)

Increases in embryonic surface area during 5 to 14 weeks (clinical) of pregnancy is thought to be a factor in determining early expansion of the amniotic sac.

The data below is from a study of amniotic sac and extracelomic space changes occurring from 5 to 14 weeks of pregnancy were observed with transvaginal ultrasound ( embryo, amniotic sac, and gestational sac areas measured by best-fitted computer-generated elliptical view).

Mean gestational age (from CRL) - 9.6 (5.3-14.6) weeks (range)

Embryonic heart rate - 153 (100-188) beats per minute

Embryonic surface - 699.6 (5-2,199) mm(2)

Amniotic sac surface - 1,383 (5-5,335) mm(2)

Gestational sac surface - 1,517 (110-5,335) mm(2) "Significant correlations between gestational sac surface, amniotic sac surface, embryonic surface, heart rate and gestational age. ....Changes in the amniotic sac surface correlated with embryonic surface but not with heart rate even when multiple regression analysis was attempted."

Reference: Santolaya-Forgas J, De Leon-Luis J, D'Ancona RL, Morgan J, Kauffman RP. Evolution of the amniotic sac and extracelomic space as seen by early ultrasound examination. Fetal Diagn Ther. 2003 Jul-Aug;18(4):262-9.

Amniotic Sac Model

Imagine you are the embryonic disc and you are standing with your arms outstretched holding a bed sheet (the amniotic membrane) in your hands and it lies over your back. Ventral folding of the trilaminar embryonic disc can be carried out by moving your arms forward (in front of you) as this occurs the sheet, attached at the disc edges, is also drawn forward (this would also occur in your head region). Therefore you the embryo now lies wrapped within the sheet (the amniotic space) and will remain so through the rest of embryonic and fetal development.

Glossary of Terms

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Quick Links

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

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

Movies ----------------- Embryo Growth Ultrasound Week 1 Week 2 Week 3 Week 4 Stage 13/14 Stage 22 Neural Head and Neck Heart Vasculature Gastrointestinal Urogenital Other Embryos Larsen Internet

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

UNSW Embryology ISBN: 978 0 7334 2609 4

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