Coelomic Cavity Development

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coelom - (Greek, koilma = cavity) Term used to describe a fluid-filled cavity or space. Placental vertebrate development have both extraembryonic (outside the embryo) and intraembryonic (inside the embryo) coeloms. The extraembryonic coeloms include the yolk sac, amniotic cavity and the chorionic cavity. The initial single intraembryonic coelom located in the lateral plate mesoderm will form the 3 major body cavities: pleural, pericardial and peritoneal.

The intraembryonic coelom is the primitive cavity that lies within the developing embryo that will form the 3 major body cavities: pericardial, pleural, peritoneal. 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.

Coelom Links: Introduction | Lecture - Week 3 Development | Lecture - Mesoderm Development | Placenta - Membranes | Category:Coelomic Cavity
Historic Embryology: 1891 peritoneal | 1897 human coelom | 1910 | 1924 serous

| original page

System Links: Introduction | Cardiovascular | Coelomic Cavity | Endocrine | Gastrointestinal Tract | Genital | Head | Immune | Integumentary | Musculoskeletal | Neural | Neural Crest | Placenta | Renal | Respiratory | Sensory | Birth

Some Recent Findings

  • Embryo-fetal erythroid megaloblasts in the human coelomic cavity[1] "The coelomic cavity is part of the extraembryonic mesoderm, surrounding amniotic cavity, embryo, and yolk sac in the early gestation. It is now believed to represent an important transfer interface and a reservoir of nutrients for the embryo. Coelocentesis by ultrasound-guided transvaginal puncture offers an easier access to the early human embryo, from 28 days post-fertilization. However, despite some studies about its biochemical composition being reported, our knowledge about the presence of cellular elements and their quality in this compartment are still limited. Here we studied human coelomic fluids sampled from 6.6 (48 days) to 10 weeks of gestation, demonstrating the presence of functional embryonic erythroid precursors, that is, megaloblasts in the coelomic cavity."


  • 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.

Development Overview

Extraembryonic Coelom
cavity surrounding the developing embryo
coelomic portalstransient 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 System Development)

Extraembryonic Coelom

Amniotic cavity

The fluid-filled (amniotic fluid) extraembryonic coelom (cavity) formed initially by epiblast and then lined by ectoderm and surrounding extraembryonic mesoderm. In humans, it forms the innermost fetal membrane, produces amniotic fluid expanding to eventually fuse with the chorionic membrane during week 8 of development. This fluid-filled sac initially lies above the trilaminar embryo disc and with embryonic disc folding this sac is drawn ventrally to enclose (cover) the entire embryo, then fetus. The presence of this membrane led to the description of reptiles, bird, and mammals as "amniotes".

Chorionic cavity

The fluid-filled extraembryonic coelom (cavity) formed initially from trophoblast and extraembryonic mesoderm that forms placenta. Chorion and amnion are made by the somatopleure. The chorion becomes incorporated into placental development. The avian and reptilian chorion lies beside the egg shell and allows gas exchange. In humans, this cavity is lost during week 8 when the amniotic cavity expands and fuses with the chorion.

Yolk sac

An extraembryonic membrane which is endoderm origin and covered with extraembryonic mesoderm. Yolk sac lies outside the embryo connected initially by a yolk stalk to the midgut with which it is continuous with. The endodermal lining is continuous with the endoderm of the gastrointestinal tract. The extra-embryonic mesoderm differentiates to form both blood and blood vessels of the vitelline system. In reptiles and birds, the yolk sac has a function associated with nutrition. In mammals the yolk sac acts as a source of primordial germ cells and blood cells. Note that in early development (week 2) a structure called the "primitive yolk sac" forms from hypoblast, this is an entirely different structure.

Intraembryonic Coelom

peritoneal and retroperitoneal

Percardial Cavity

Links: Cardiovascular System Development

Pleural Cavity

Links: Respiratory System Development

Peritoneal Cavity

Week 8


Stage 22 image 200.jpg


Stage 22 image 203.jpg

Carnegie stage 22

Mesentery and Retroperitoneal


Stages in the development of the bursa omentalis, the greater omentum, and the fusion of the latter with the transverse mesocolon.


Links: Gastrointestinal Tract Development


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.
    • contribute most of the vascular smooth muscle to the respiratory and gastrointestinal tract. (Remainder derived from endothelium?)


  1. <pubmed>20533375</pubmed>




Search PubMed

Search Pubmed: Coelomic Cavity Development | pericardial cavity development | pleural cavity development | peritoneal cavity development

Additional Images


  • 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.

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Cite this page: Hill, M.A. (2020, June 4) Embryology Coelomic Cavity Development. Retrieved from

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© Dr Mark Hill 2020, UNSW Embryology ISBN: 978 0 7334 2609 4 - UNSW CRICOS Provider Code No. 00098G