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Respiration tract

Introduction

The human body possesses two large cavities (pleural and peritoneal) and a smaller cavity (pericardial), all of which are covered with a mesothelium. One speaks of visceral mesothelium that coats the organs and parietal mesothelium that coats the somatic walls delimiting the cavitiy towards the inside and also the outside.

Origin of the pleural cavities

In stage 10 (28 days) the cranial section of the intraembryonic coelom consists of a middle part, the pericardial cavity, and two thin canals laterally, the pericardioperitoneal canals.

Fig. perikardfruh01 - Cardiac development in stage 8
media/module16/p1_pericardfruh8.gif

  1. Cardiac anlage (cardiogenetic plate
  2. pericardial cavity (part of the intraembryonic coelom)
  3. Embryo
  4. Edge of the umbilical vesicle section
  5. Edge of the amniotic cavity section
  6. Coelom opening

Legend
Fig. perikardfruh01

The embryo is disk-shaped. During the transition from the amniotic cavity to the umbilical vesicle a horseshoe-shaped gap forms in the cranial region, the intraembryonic coelom, probably due to unequal growth.
The cranial part of this gap, the pericardial cavity is located above the cardiogenenetic plate in front of the embryo. At this point, this coelom has no connection to the extraembryonic coelom (chorionic cavity).

Fig. perikardfruh02 - Cardiac development in stage 9
media/module16/p1_pericardfruh9.gif

  1. Cardiac anlage (cardiogenetic plate
  2. pericardial cavity (part of the intraembryonic coelom)
  3. Embryo
  4. Edge of the umbilical vesicle section
  5. Edge of the amniotic cavity section
  6. Coelom opening

Legend
Fig. perikardfruh02

With the extension of the amniotic cavity and the cranial flexion of the embryo the whole cranial primordium goes through a rotation of 180 degrees with the pericardial cavity.
The cardiac primordium lies dorsally to the pericardial cavity (with relation to the embryo).

Fig. perikardfruh03 - Cardiac development in stage 10
media/module16/p1_pericardfruh10.gif

  1. Cardiac anlage (cardiogenetic plate
  2. pericardial cavity (part of the intraembryonic coelom)
  3. Embryo
  4. Edge of the umbilical vesicle section
  5. Edge of the amniotic cavity section
  6. Coelom opening

Legend
Fig. perikardfruh03

The pericardial cavity is bent over forwards and has enclosed the cardiac primordium (myoepicardium, cardiac jelly and the endocardiac tube) in the front.
Dorsally, the cardiac primordium forms the two layers of the pericardial bilaminar structure of a folded envelope, the mesocardium.

They connect the pericardial cavity with the part of the intraembryonic coelom that is open towards the outside, the future peritoneal cavity. At this point no pleural cavity yet exists because the lungs have not yet begun to develop.

Fig. 14 - Intraembryonic coelom in stage 12
media/module18/r4a_zoelom12.gif

  1. Pharyngeal pouch
  2. Aortic arch
  3. Pericardioperitoneal canal
  4. Peritoneal cavity
  5. Aortic sac
  6. Pericardial cavity (without heart)
  7. Venous sinus
  8. Liver bud
  9. Umbilical coelom

Legend
Fig. 14

In stage 12 the peritoneal cavity is connected with the pericardial cavity via the pericardio-peritoneal canals.
From the foregut in the middle, the lung buds will soon sprout on both sides into the pericardio-peritoneal canals.
Observe the proximity of the heart and liver anlagen

 

In stage 13 (32 days), the lung buds grow into the pericardioperitoneal canals and dent them. Thereby the pericardioperitoneal canals are subdivided on both sides by these lung buds that are sprouting in from the medial direction.

Fig. 15 - Schematic cross-section through an embryo in stage 14
media/module18/r4b_koerperhohlen14.gif

  1. Arm buds
  2. Pleuropericardial membrane
  3. Development of the pleural cavity in the pericardioperitoneal canal
  4. Esophago-tracheal septum
  5. Esophagus
  6. Trachea
  7. Lung buds
  8. Bulbus cordis
  9. Heart
  10. Pericardial cavity

Legend
Fig. 15

The cross-section of this embryo in stage 14 shows the lung buds that grow into the pericardio-peritoneal canal on both sides.

With the increase in size of the lung anlage the pericardioperitoneal canal widens to become the pleural cavity that is separated from the pericardial cavity by the pleuropericardial membrane and from the peritoneal cavity by the pleuroperitoneal membrane.

Fig. 16 - Lateral section of an embryo in stage 14
media/module18/r4c_zoelom14_kyoto.gif

  1. Pericardial cavity
  2. Pleuro-pericardial canal / pleuro-pericardial membrane
  3. Pleural cavity
  4. Peritoneal cavity
  5. Pelvic part of the peritoneal cavity

Legend
Fig. 16

Intraembryonic coelom projected on an embryo in stage 14.

In the region of the peritoneal cavity and the umbilical coelom, the left and right peritoneal tubes join ventrally to form a common cavity, the peritoneal cavity, that goes over into the umbilical coelom. In the dorsal region they form the meso of the guts.

Fig. 17 - Cut-open cavities with view the with visceral serosa-coated organs
media/module18/r4d_zoelom14.gif

  1. Pericardial cavity
  2. Pleuro-pericardiac canal / pleuro-pericardial membrane
  3. Lungenanlage
  4. Peritoneal cavity
  5. Pelvic part of the peritoneal cavity
  6. Urogenital ridge
  7. Stomach
  8. Liver

Legend
Fig. 17

Enlarged, more detailed view of insert A from Fig. 16.
In the cut-open coelom cavity one sees the intraperitoneal organs that are coated with mesothelium: the stomach and liver, as well as the urogenital ridge

The lungs become covered by the visceral layer of the pleural cavity, the pleura visceralis. Towards the outside, the pleural cavity is bounded by the parietal layer, the pleura parietalis. Through their rapid increase in size the two lungs, left and right, enclose the heart that is in their middle.

In the following interactive diagram (development of the pleural cavity in various stages) the intraembryonic coelom can be seen in various stages. One distinguishes the pericardial cavity in the middle from the two pleural cavities and, in the intestinal region, the peritoneal cavity.

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Fig. zoelom14 - Development of the pleural cavity in various stages
media/module18/r4d_zoelom14_detail.gif

  1. Pleuro-pericardial membrane
  2. Left lung with serosa covering (pleura visceralis)
  3. Stomach with serosa covering (visceral)
  4. Mesonephros with serosa covering (visceral)
  5. Peritoneal cavity
  6. Aortic sac
  7. Pericardial cavity
  8. Venous sinus
  9. Liver
  10. Intestines with serosa covering (visceral)
  11. Umbilical coelom
  12. Pleuro-peritoneal membrane

Legend
Fig. zoelom14
Fig. zoelom16 - Development of the pleural cavity in various stages
media/module18/r4e_zoelom16.gif

  1. Pleuro-pericardial membrane
  2. Left lung with serosa covering (pleura visceralis)
  3. Stomach with serosa covering (visceral)
  4. Mesonephros with serosa covering (visceral)
  5. Peritoneal cavity
  6. Aortic sac
  7. Pericardial cavity
  8. Venous sinus
  9. Liver
  10. Intestines with serosa covering (visceral)
  11. Umbilical coelom
  12. Pleuro-peritoneal membrane

Legend
Fig. zoelom16
Fig. zoelom18 - Development of the pleural cavity in various stages
media/module18/r4f_zoelom18.gif

  1. Pleuro-pericardial membrane
  2. Left lung with serosa covering (pleura visceralis)
  3. Stomach with serosa covering (visceral)
  4. Mesonephros with serosa covering (visceral)
  5. Peritoneal cavity
  6. Aortic sac
  7. Pericardial cavity
  8. Venous sinus
  9. Liver
  10. Intestines with serosa covering (visceral)
  11. Umbilical coelom
  12. Pleuro-peritoneal membrane

Legend
Fig. zoelom18