The intraembryonic coelom begins developing in the 3rd week as a horseshoe-shaped cavity in the cardiogenic and lateral mesoderm. By the 4th week, the coelom divides into three cavities - the pericardial cavity and two pericardioperitoneal canals that connect to the large peritoneal cavity. During the 5th-7th weeks, folds form that separate these cavities, with the pericardioperitoneal canals closing off. Meanwhile, the diaphragm develops from the fusion of the septum transversum, pleuroperitoneal membranes, dorsal mesentery of the esophagus, and muscular ingrowth from the body walls.

1. THE DEVELOPMENT OF THE BODY
CAVITIES
1

2. THE DEVELOPMENT OF THE BODY
CAVITIES
• The intraembryonic coelom begins to develop
near the end of the 3rd week.
• By the 4th week it appears as a horseshoe-
shaped cavity in the cardiogenic and lateral
mesoderm.
2

3. Drawing of a dorsal view of a 22-day embryo showing the outline of the horseshoe-shaped intraembryonic
coelom. The amnion has been removed, and the coelom is shown as if the embryo were translucent. The
continuity of the intraembryonic coelom, as well as the communication of its right and left limbs with the
extraembryonic coelom, is indicated by arrows. B, Transverse section through the embryo at the level shown in
A
3

4. 2 Midsagittal sections of embryos at various stages of development showing cephalocaudal folding and its
effects upon position of the heart, septum transversum, yolk sac, and amnion. Note that, as folding progresses,
the opening of the gut tube into the yolk sac narrows until it forms a thin connection, the vitelline (yolk sac)
duct, between the midgut and the yolk sac (D). Simultaneously, the amnion is pulled ventrally until the
amniotic cavity nearly surrounds the embryo. A. 17 days. B. 22 days. C. 24 days. D. 28 days. 4

5. THE EMBRYONIC BODY CAVITY
• The intraembryonic coelom becomes the
embryonic body cavity, which is divided into
three well-defined cavities during the fourth
week which are:
• A pericardial cavity
• Two pericardioperitoneal canals
• A peritoneal cavity
5

6. Figure 8-3 Illustrations of the mesenteries and body cavities at the beginning of the fifth week. A, Schematic
sagittal section. Note that the dorsal mesentery serves as a pathway for the arteries supplying the developing
gut. Nerves and lymphatics also pass between the layers of this mesentery. B to E, Transverse sections through
the embryo at the levels indicated in A. The ventral mesentery disappears, except in the region of the terminal
esophagus, stomach, and first part of the duodenum. Note that the right and left parts of the peritoneal cavity,
separate in C, are continuous in E
6

7. Body Cavities
Thoracic cavity
contains:
• One pericardial
&
• Two pleural cavities
Abdominopelvic cavity
contains:
• One large peritoneal
cavity
7

8. Body Cavities
• These body cavities have a parietal wall lined by
mesothelium (future parietal layer of peritoneum) derived
from somatic mesoderm and a visceral wall covered by
mesothelium (future visceral layer of peritoneum) derived
from splanchnic mesoderm.
• The peritoneal cavity (the major part of intraembryonic
coelom) is connected with the extraembryonic coelom at
the umbilicus.
• The peritoneal cavity loses its connection with the
extraembryonic coelom during the 10th week as the
intestines return to the abdomen from the umbilical cord.
8

9. Intraembryonic Coelom
• Appears as a horseshoe-
shaped cavity in the
cardiogenic area and
lateral mesoderm by the
4th week
• The bend in this cavity
indicates the future
pericardial cavity & the
limbs indicate the future
pleural and peritoneal
cavities
• The greater part of each
limb opens laterally into
the extra-embryonic celom
(EEC)
EEC
9

10. • The curve of the cavity represents the future
pericardial cavity and its lateral extensions
represent the future pleural and peritoneal
cavities
10

11. Folding of embryo
• In the 4th week also the embryonic disc will
fold.
• Lateral parts of the intraembryonic coelom
move together on the ventral aspect of the
embryo.
• When the caudal part of the ventral
mesentery disappears, the right and left parts
of the intraembryonic coelom merge to form
the peritoneal cavity
11

12. Folding of embryo
• During cranial folding of embryo,
the pericardial cavity comes to lie
ventral to the foregut
• The pericardioperitoneal canals:
• arise from the dorsal wall of
the pericardial cavity
• pass on each side of the
foregut (future esophagus)
• lie dorsal to septum
transversum
• open into the peritoneal
cavity
12

13. • During horizontal folding, the
limbs of the coelom are brought
together on the ventral aspect of
the embryo
• The coelom is lined by
mesothelium derived from the
somatic mesoderm (parietal layer)
and the splanchnic mesoderm
(visceral layer)
• The peritoneal cavity looses its
connection with the
extraembryonic coelom during the
10th week
Parietal
layer
Visceral
layer
13

14. THE DEVELOPMENT OF THE BODY
CAVITIES
• Until the 7th week, the embryonic pericardial
cavity communicates with the peritoneal
cavity through paired pericardioperitoneal
canals.
• During the 5th and 6th weeks, folds (later
membranes) form near the cranial and caudal
ends of these canals.
14

15. Division of Embryonic Coelom
• Partitions appear to separate the
pericardioperitoneal canals from
• the pericardial cavity and
• the peritoneal cavity
15

16. • As the lung buds grow into the pericardioperitoneal
canals, a pair of membranous ridges is produced in
the lateral wall of each canal:
 The pleuropericardial folds cranial to the
developing lungs
 The pleuroperitoneal folds caudal to the
developing lungs
16

17. Pleuropericardial Membranes
• The bronchial buds grow
laterally from the caudal end
of the trachea into the
pericardioperitoneal canals
(future pleural cavities)
• As the pleural cavities expand
ventrally, they grow into the
body wall in the angle
between the body wall and a
ridge raised by the common
cardinal vein and the phrenic
nerve
17

18. • This results in splitting the
mesenchyme into:
 An outer layer that
forms the thoracic wall
 An inner layer that
forms the pleuro-
pericardial membrane
18

19. • With the growth and
descent of the heart
and expansion of the
pleural cavities, the
pleuro-pericardial
membranes expand
and move medially
19

20. • By 7th week, the membranes fuse with the
mesenchyme ventral to the esophagus
forming the primordial mediastinum, thus
closing the pleuropericardial openings .
20

21. • The right
pleuropericardial
opening closes
slightly earlier
than the left (right
common cardinal vein
is larger than the left
and so raises a bigger
fold) Phrenic nerve
21

22. Pleuroperitoneal Membranes
• Develop from the
pleuroperitoneal folds that
are attached dorsolaterally to
the body wall and their free
edges project into the caudal
part of the
pericardioperitoneal canals
• As the developing lung enlarges cranially and liver expands caudally,
these folds become more prominent and gradually become
membranous which will be invaded by the myoblasts (primitive
muscle cells).
22

23. • During 6th week, the
pleuroperitoneal
membranes extend
ventromedially and fuse
with the dorsal mesentery
of the esophagus and the
septum transversum
This results in closure of the
pericardioperitoneal openings. The right
opening closes slightly earlier than the left
23

24. Primitive Mesenteries
24

25. After embryonic folding……..
25

26. What is a mesentery?
• Double layer of
peritoneum enclosing a
mass of mesoderm
• Connects the organ to the
body wall
• Carries vessels, nerves &
lymphatics for the organ
• Is the site where the
visceral peritoneum
continues as parietal
peritoneum
26

27. After embryonic folding……..
27

28. • The caudal part of the
foregut is connected to
the anterior and
posterior abdominal
walls by the ventral &
dorsal mesentery
respectively
28

29. • The midgut and the
hindgut are
suspended in the
peritoneal cavity
from the posterior
abdominal wall by
the dorsal mesentery
29

30. • The ventral
mesentery
degenerates in the
region of the future
peritoneal cavity,
extending from the
heart to the pelvic
region
30

31. Development of the Diaphragm
31

32. • The diaphragm develops
from four embryonic
components:
1. Septum transversum
2. Pleuroperitoneal
membranes
3. Dorsal mesentery of
esophagus
4. Muscular ingrowth
from lateral body walls
1
3
2
4
32

33. Septum Transversum
• A thick plate of
mesodermal tissue
• Lies:
 Between the pericardial
cavity and the yolk sac
 Ventral to the foregut
and the pleuro-
peritoneal canals
• Grows dorsally from the
ventrolateral body wall
33

34. • Forms an incomplete
partition between the
thoracic cavity and the
abdominal cavity
• Expands and fuses with
the pleuroperitoneal
membranes and the
mesenchyme ventral to
the esophagus
Septum transversum is the primordium of
the central tendon of the diaphragm
34

35. • During 6th week, the
three basic components:
–Pleuroperitoneal
membranes
–Mesoesphagus
–Septum transversum
1
1
3
2
fuse with each other and form a complete
partition between the thoracic and abdominal
cavities
35

36. • During 9th – 12th weeks the
lungs and pleural cavities
enlarge, burrowing into the
body wall, splitting it into:
 External layer that becomes
part of the body wall
 Internal layer that contributes
muscles to peripheral portions
of diaphragm, extending to the
parts derived from the
pleuroperitoneal membranes
36

37. Body wall: peripheral
muscular part
Pleuroperitoneal
membranes: form large
portion of fetal
diaphragm but
represent a smaller
portion in infants
Septum transversum:
Central tendon
Dorsal mesentery of
esophagus: Crura
37

38. Positional Changes & Innervation of the Diaphragm
• During the 4th week, the
septum transversum lies
opposite the 3rd – 5th
cervical somites
• During 5th week, myoblasts
from these somites move
to the developing
diaphragm bringing their
nerve fibers with them
38

39. • Rapid growth of the body of
embryo result in further
descent of diaphragm
• By the 6th week, the
diaphragm lies at the level
of the thoracic somites
• By the end of 8th week the
dorsal end of diaphragm
lies at the level of first
lumbar vertebra
39

40. • When the 4 parts of the
diaphragm fuse, the
mesenchymal cells from the
septum transversum extend
into the other three parts,
change into myoblasts, and
give rise to the muscles of the
diaphragm.
• Thus phrenic nerve supplies
all the muscles of diaphragm
The phrenic nerve also supplies sensory fibers to
diaphram except in the peripheral region which is
derived from the body wall and brings its nerve supply
(lower intercostal nerves) with it
40

41. Gastroschisis and Congenital Epigastric
Hernia
• This uncommon hernia occurs in the median
plane between the xiphoid process and
umbilicus.
• Gastroschisis and epigastric hernias result from
failure of the lateral body folds to fuse completely
when forming the anterior abdominal wall during
folding in the fourth week.
• The small intestine herniates into the amniotic
cavity, which can be detected prenatally by
ultrasonography.
41

42. Congenital Hiatal Hernia
• There may be herniation of part of the foetal
stomach through an excessively large
oesophageal hiatus-the opening in the
diaphragm through which the oesophagus and
vagus nerves pass; however, thi.
• Although hiatal hernia is usually an acquired
lesion occurring during adult life, a
congenitally enlarged esophageal hiatus may
be the predisposing factor in some cases
42

43. Congenital Pericardial Defects
Defective
• Fusion of the pleuropericardial membranes
separating the pericardial and pleural cavities
results in a congenital defect of the
pericardium.
43