PG1007 Lecture 8 Forma2on of The Body Cavi2es Dr. Neil Docherty My Teaching Objec/ves • To revise initial body wall closure and describe the structure and"
function of serous membranes"
• To describe the separation of the abdominal and thoracic "
cavities and development of the diaphragm"
• To provide examples of defects in body wall closure and "
Abdominal-thoracic compartmentalisation "
Extraembryonic Cavitation
How many cavities
can we see?
Chorionic cavity



Also known as
–  Extraembryonic coelom
Later known as
–  Extraembryonic cavity
–  (Why??)
Later still
–  Is obliterated
–  (see later lecture on foetal
period)
Chorionic cavity"
Extraembryonic mesoderm
–  Lines

Chorionic cavity
–  Forms

Connecting stalk
–  Covers
Amniotic cavity
  Yolk sac

Sagittal Midline Sections of Embryo!
(Day 17-28)!
17d!
22d!
in situ
in uterus
24d!
28d!
Foregut
Hindgut
Growth in the head and tail region leads to cephalocaudal folding!
Lateral Folding and Body Wall Closure!
Pinched to a narrow channel by folding"
Lateral folding of the embryo proceeds to body wall closure"
by end of week 4"
Transverse Section of Gut and Embryonic !
Body Cavity Formation (Mouse)!
Intraembryonic cavity


Lined by mesoderm
Surface cells are epithelial
–  Mesothelium

Serous
–  Parietal layer
–  Visceral layer
–  Dorsal mesentery


Two layers
Pathway for vessels and
nerves
Division of the Intra-embryonic cavity


Later, this is divided into
–  The thoracic cavity
  Pleural cavities (right and
left)
  Pericardial cavity
–  The abdominal cavity
Each cavity will have a mesothelial
lining
–  Parietal layer (lining its walls)
–  Visceral layer (on its organs)
–  Mesenteries or their equivalents
The Ventral Body Cavities (RE:PG1006)
Organs are suspended inside chambers termed
cavities
-Protection and room for expansion
N.B. Although the kidney and pancreas are in the
abdominal cavity they lie behind the peritoneum and
are thus described as retroperitoneal
Spinal Chord"
Gastroschisis"

Failure of abdominal wall
closure
1/7,500
  Associated problems
uncommon


Mortality ~ 5%
Ventral View of Embryo (24 days)
Note the septum transversum at
day 24 and 28 (right-longitudinal)
This marks a point for division of
the intraembryonic cavity
Septum transversum
Mesoderm
  Begins to divide the
intraembryonic cavity
into

Thoracic cavity
  Abdominal cavity


The division is
incomplete
–  Channels remain on
each side

Pericardioperitoneal
canals
Ventral View of Embryo (24 days)
septum transversum
Note the pericardioperitoneal canals
-Lungs grow in to these
-They must be sealed to separate
abdomen and thorax!
Thoracic Development (5 weeks)
Looking down in cross section
• Note growth of lungs
• Formation of pleuropericardial folds
We are on our way to forming the thoracic
cavity
Thoracic Development Ctd.
Pleuropericardial folds approach, fuse as membranes
and then form pleural and pericardial cavities
Diaphragmatic Development
Looking in cross section
Weeks 5 to 7
• Note growth of folds
• Fusion with septum transversum and oesophageal mesentery
• \Muscular ingrowth from somite from cervical segments C3-C5
We have sealed the thoracic cavity and created a muscular diaphragm
Elements of the Diaphragm"




Septum transversum
–  Central tendon
Pleuroperitoneal folds (membranes)
Oesophageal mesentery
Muscular ingrowth
–  From cervical somites 3, 4, 5
Congenital Diaphragmatic Hernia

Incidence 1/2,000
Left 85%
  Right 12%
  Bilateral 3%

–  Mortality ~50%
Congenital diaphragmatic hernia"
Today’s Learning Objec/ves Your learning from today should focus on being able to;"
1)  Explain the sequence of changes that cause closure of the "
body wall and the formation and compartmentalisation of the "
intraembryonic cavity "
2) Describe the development of the diaphragm"