Transcript 01-body cavities2008-02

4 occipital &
8 cervical &
12 thoracic &
5 lumbar &
5 sacral &
8 – 10 coccygeal
The parietal layer is lined by
Methothelium derived from somatic
Mesoderm. & the visceral layer is
Covered by mesothelium derived from
Splanchnic mesoderm .
Early in the 4th week, the intraembryonic coelom appears as a horseshoe-shaped cavity.
The curve at the cranial end of the embryo represents the future pericardial cavity &
limbs indicate future pleural ;peritoneal cavities . The distal part of each limb of
intraembryonic coelom is continuous with extraembryonic coelom at lateral edges of
embryonic disc .This communication is important to midgut development. At 6th W
herniation occure withen the umblical cord. And at 10th week this connection is lost .
The intraembryonic coelom becomes the embryonic body cavity during 4th week ( 22-28
days ) 1. Pericardial cavity 2. two pericardioperitoneal canals 3. peritoneal cavity .
During formation of
the head fold , the
heart& pericardial
cavity move
ventrocaudally, anter.
to the foregut As a
result , the pericardial
cavity opens into
pericardioperitoneal
canals, which pass
dorsal to the foregut &
on each side of it (
future esophagus ) and
dorsal to septum
transversum ( a thick
plate of mesodermal
tissue ) that occupies
the space between
Partitions is formed in each pericardioperitoneal canal that
thoracic cavity & yolk
separate pericardial cavity from pleural cavities & pleural
stalk )
cavities from peritoneal cavity. These partition are pair of
membranous ridges that is produced in the lateral wall of
each canal. The cranial ridges: pleuropericardial folds,
located superior to lungs. Caudal ridges: pleuroperitoneal
folds are located inferior to developing lungs .
An extention of the
visceral peritoneum
covering an organ form
the mesentery. So , the
mesentery is a double
layer of the peritonium .
It connect the organ to
the body wall & conveys
vessels & nerves to it .
The ventral and dorsal
mesenteries divide the
cavity into R & L halves
The venteral mesentere.
Disappears , except
where it is attached to
the caudal part of the
foregut ( primordium of
terminal part of
esophagus , stomach &
1st part of duodenum) .
After this level the
peritoneum cavity
becomes continuous
space
The venteral •
mesentery
degenerates ,
resulting in a
large embryonic
peritoneal cavity
extending from
the heart to the
pelvic region .
Pleuropericardial
Mermbranes
They project into the cranial
ends of the
pericardioperitoneal canal
The bronchial buds grow
laterally from the caudal end
of the trachea into
pericardioperitoneal canals (
future pleural canals). As the
primordial pleural cavities
expand ventrally around the
heart, they extend into the
body wall , spilitting the
mesenchyme into : An outer
layer that becomes the
thoracic wall .&
They contain the common cardinal veins & phrenic Ns.
They become mesentery like folds ( extending from the
lateral wall of thoracic wall ). This is due to 1. Growth of
common cardinal v., descend of heart ; expansion of
pleural cavities
An inner layer
(pleuropericardial
membrane), that becomes
the fibrous pericardium .
( the outer layer of the
pericardial sac enclosing the
heart )
The right pleuropericardial opening closes earlier than
the left one , probably because the right common
cardinal vein is larger than the left one, and produces a
larger pleuropericardial membrane.
By the 7th week , the
pleuropericardial
membranes fuse with
mesenchyme ventral to
esophagus, forming the
primordium of mediastinum
,separating the pericardial
cavity from the pleural
cavities.
The primordial
mediastinum consists of a
mass of mesenchym (
embryonic connective
tissue ) that extendes from
the sternum to the
vertebral column,
separating the developing
lungs.
Pleuroperitoneal Membrane
As the pleuroperitoneal folds
enlarge ,they project into the
pericardioperitoneal canals.
Gradually ,the folds become
membranous.. They are attached
dorsolaterally to abdominal wall
and their crescentic free edges
project into the caudal ends of the
canals.
During the 6th week these
memberanes extend
ventromedially until their free
edges fuse with the dorsal
mesentery of esophagus &
septum transversum. This
process separates pleural cavities
from peritoneal cavity
Closure of the pleuroperitoneal openings is assisted by the migration of myoblasts
(primordial muscle cells ) into the membranes . The right opening closes before the left
one. This may be due to large size of the right lobe of the liver
Development of the
Diaphragm
1- septum transversum
2- pleuroperitoneal
membranes .
3- Dorsal mesentery of
esophagus
4- Muscular ingrowth from
lateral body walls
Septum Transversum
This septum is the primordium of the central tendon of
the diaphragm. It does not separate the thoracic &
abdominal cavities completely. Because there is
pericardioperitoneal canal . It expands and fuses with
the mesenchyme ventral to esophagus &
pleuroperitoneal memberanes
It is first identifiable at the end
of the third week as a mass of
mesodermal tissue cranial to
the pericardial cavity . After
head folds at 4th week, it
forms a thick incomplete
partition between pericardial &
abdominal cavities . There is a
large opening on each side of
the esophagus (
pericardioperitoneal canal ) .
The transverse septum grows dorsally
from the ventrolateral body wall and
forms a semicircular shelf which
separates the heart from the liver . A
large part of the liver is embeded in the
septum .It is located caudal to the
pericardial cavity and partially
separates it from the developing
peritoneal cavity
Pleuroperitoneal
Memberanes
It forms the primordial diaphragm
It forms large portion of fetal
diaphragm . But they form small
portion of the newborn infant’s
diaphragm . At the end of the 6th
week it fuse with the other 2
components( 9 to 12 ws ) .
Dorsal Mesentry of esophagus
It forms the median portion of the
diaphragm . The crura .( a leglike
pair of muscle bundles that cross
in the median plane anterior to
the aorta . It develop from
myoblasts that grow into the
dorsal mesentery of esophagus
.
As the 4 parts of the diaphragm fuse mesenchyme in
the septum transversum extends into the other 3 parts It
forms myoblasts that differentiate into the skeletal
muscle of the diaphragm .
muscular ingrowth from
lateral body walls
During 10th to 12 th
weeks, the lungs and
pleural cavities enlarge,
into the lateral body walls .
During this process the
body- wall tissue is split
into 2 layers :
An external layer that
becomes part of the
definitive abdominal wall .
An internal layer that
contributes to peripheral
parts of the diaphragm ,
external to the parts
derived from the
pleuroperitoneal
membranes .
Positional Changes
Durind the 4th week ( A ) & At 6 week it is at the level of the thoracic somites & by the beginning
of the 8th week , the dorsal part of the diaphragm lies at the level of the 1st lumbar vertebra
Innervation of the diaphragm
During the 5th week , myoblasts from 3,4;5 somites migrate into the developing diaphragm ( S. T. )
bringing their nerve fibers with them ( phrenic n. ) which arise from the venteral primary rami of the
3rd, 4th; 5th cervical spinal nerves. The embryonic phrenic ns. Enter the diaphragm by passing
through the pleuropericardial membranes . This explain why phrenic ns. Lie on the fibruos
pericardium. Hence it is motor to diaphragm and also sensory , but the costal rim receives sensory
supply from the lower intercostal ns. Because of the origin of the peripheral part of the diaphragm
from the lateral body walls.
In severe lung hypoplasia , some primordial alveoli
rupture, causing air to enter the pleural cavity ,
pneumothorax, Also, fetal lung maturation may be
delayed.
Prenatal diagnosis of CDH: ultrasound& magnetic
resonance imaging. It can repair prenatally between 22 &
28 Ws. But there is risk to fetus and mother .
Posterolateral defect of
the diaphragm is a
common congenital
anomaly of it . It occurs
about once in 2200. In
congenital diaphragmatic
hernia ,CDH, herniation of
stomach, spleen; most of
intestines herniate.
Usually, unilateral CDH
results from devective
formation and or fusion of
the pleuroperitoneal
membrane with other 3
parts of the diaphragm.
CDH, occurs on the left
side in 85 to 90 % of cases
This may be due to earlier
closure of the right
pleuroperitoneal opening .
CDH, is the most common
cause of polyhydramnios
& pulmonary hypoplasia
that because the lug is
copressed