Thoracic Development

Question 1

Describe the Intraembryonic Coelom.

Answer 1

• week 4 of development
• horseshoe cavity that exists between the somatic and splanchnic layers of lateral mesoderm.
• It is lined by mesothelium and will become the body cavities.

Question 2

Organization of the intraembryonic Colem:

Answer 2

• cranial end = pericardial cavity
• Caudal limbs - cranially, this is the site of the Pericardio-peritoneal canal (future plueral cavity), caudally this is the future peritoneal cavity.

Question 3

Characteristics at week 5:

Answer 3

• Cranial folding occured at week 4
• no true cavities exist yet.
• Bronchial buds (future lungs) grow into the pericardioperitoneal canal and develop ventral and caudal walls of the pericardioperitoneal canals. (plueropericadial folds and the plueroperitoneal folds)

Question 4

At week 5, this structure separates the pleural cavity at the cranial ridges.

Answer 4

• Pleuralpericardial folds/membranes- located superior to the future lungs. They develop into membranes by week 6
• this structure contains the phrenic nerve and common cardinal veins.
• eventually forms the fibrous pericardium

Question 5

At week 5, this structure forms the caudal ridges of the pleural cavity.

Answer 5

• Pleuroperitoneal fold/membrane.
• Located inferior to the future lungs.
• contributes to diaphragm in the future.

Question 6

Defining characteristics of week 6:

Answer 6

• further enlargement of the developing lungs widens pericardioperitoneal canals (future plueral cavities.. later separated by the pleurocardial membrane.

Question 7

Defining characteristics of week 7/8:

Answer 7

• Expansion of the lungs anteriorally and ventrally results in the heart being emcompassed by the lungs.
• Also, the pleuropericardial membrane begin to engulf the heart to form the fibrous pericardium.

Question 8

Lateral folding of the embryo occurs at week _______, and results in the formation of the _______.

Answer 8

• week 4
• Peritoneal cavity
• this fusion forms the gut tube suspended by mesentery (doubled layers) note: the ventral mesentery eventually goes away. Dorsal mesentery sticks around to support nerves and arteries into adulthood.

Question 9

The mesothelium of the peritoneal cavity

Answer 9

the peritoneum

Question 10

Mesothelium lining the body walls of the abdominal and peritoneal cavity

Answer 10

Parietal Peritoneum

Question 11

Mesothelium that lines the outer walls of abdominal organs.

Answer 11

Visceral Peritoneum

Question 12

Two layers of peritoneum is called:

Answer 12

Mesentery

Question 13

The Ventral mesentery largely dissapears but remains into adulthood as these what structures?

Answer 13

The lesser omentum of the stomach and the falciform ligament of the liver.

Question 14

After later folding the peritoneal cavity will still communicate with the extra-embryonic coloem via an opening in the umbilicus. This is important for…

Answer 14

It allows the herniation of the intestines into the umbilical cord, allowing further growth and movement of the abdominal structures.

Question 15

Congenital Diaphragmatic Hernia results if…

Answer 15

The fusion of the septum transversum, dorsal mesentery of the esophagaus and the left pleurperitoneal membrane fails to occur before week 10. The result is inadequate closure of the Pericardioperitoneal canals. Note: right canal usually closes before left.

Question 16

The precursor of the central tendon is the…

Answer 16

The septum transversum

Question 17

Typical fusion of these 3 structures with the addition of _____ results in formation of the diaphragm, and occurs at ___ weeks.

Answer 17

• Pleuroperitoneal membranes, the dorsal mesentery, and the septum transversus
• muscular ingrowth from the lateral body walls occurs at this time ot contribute to the diaphragm formation.
• 6 weeks

Question 18

Describe the innervation pattern for the phrenic nerve.

Answer 18

• C3-C5
• Because of the original location of the septum transversum prior to cranial folding, myoblast migration is from neighboring somites at the level of cervical myotomes 3-5.
• As diaphragmatic structures grow and extend they drag these nerves with them
• While the diaphramgm is located inferiorly by the lumbar, it maintains innervation from the phrenic nerves of C3-C5.
• NOTE: the phrenic nerve will travel through the pleuropericardial membranes during its descent to the diaphragm

Question 19

What early embryonic membrane houses the phrenic nerve?

Answer 19

The pleuropericardial membrane.