Thoracic Cavity Development

Question 1

Pleural cavities

Answer 1

space where lungs develop and persist

Question 2

Pericadial cavity

Answer 2

space where heart develops and persists

Question 3

Peritoneal cavity

Answer 3

space where abdominal viscera develops and persists

Question 4

What will the septum transversum become?

Answer 4

central tendon of the thoracic diaphragm

Question 5

Where does the septum transversum come from?

Answer 5

head fold

Question 6

When and where does the horseshoe-shaped cavity develop?

Answer 6

during 4th week in the lateral mesoderm

Question 7

What body cavity does the cranial end become?

Answer 7

pericardial

Question 8

Where does the heart start out at in development? What must occur?

Answer 8

cranial end, embryo must undergo head fold to bring the pericardium ventrocaudally to take its position anterior to the foregut

Question 9

What do the mesenteries do during development?

Answer 9

1) convey blood vessels, nerves and lymphatics to organs
2) divides the peritoneal cavity into right and left halves
3) parietal peritoneum (covers body wall)
4) visceral peritoneum (covers organs)

Question 10

What splits lateral mesoderm into somatic plate and splanchnic plate?

Answer 10

coelomic cavity

Question 11

Briefly describe the events of lateral folding

Answer 11

1) 2 caudal limbs fold ventrally (big hug)
2) pinches off the yolk sac
3) 2 ends fuse giving rise to peritoneal cavity
4) the gut tube (remnant of yolk sac) is suspended by 2 layers of mesenteries (dorsal and ventral)

Question 12

What are mesenteries?

Answer 12

double layer of peritoneum that extends from the abdominal wall

Question 13

Which mesentery is the permanent structure that provides the route for vasculatures, nerves and lymphatics to the developing organs?

Answer 13

dorsal

Question 14

What happens to the ventral mesentery?

Answer 14

• disappears and becomes continuous with liver and becomes the falciform ligament and lesser omentum

Question 15

How does the peritoneal cavity form?

Answer 15

lateral folding and fusing of the 2 caudal limbs ventrally

Question 16

What term is used for intraembryonic coelom after embryonic folding?

Answer 16

pericardioperitoneal canals

Question 17

Where are the pericardioperitoneal canals?

Answer 17

• lies lateral to foregut (future esophagus)
• dorsal to septum transversum
• each canal forms different partition

Question 18

Partitions in each pericardioperitoneal canals are formed due to what event?

Answer 18

developing bronchial buds

Question 19

What are the two partitions the pericardioperitoneal canals will form?

Answer 19

1) cranial ridges - pleuropericardial folds

2) caudal ridges - pleuroperitoneal folds

Question 20

Which folds are superior to developing lungs?

Answer 20

pleuropericardial folds (cranial ridges)
- separate pleural from pericardial cavities

Question 21

Which folds are inferior to developing lungs

Answer 21

pleuroperitoneal folds (caudal ridges)
- separate pleural from peritoneal cavities

Question 22

Describe the development events that involve cranial ridges

Answer 22

• right and left cranial folds come out from the somatic wall of the thoracic cavity and become ridges
• the ridges merge to form the pleuropericardial membrane that separates the pericardial and pleural cavities
• phrenic nerve gets caught in the folds

Question 23

Describe the development events that involve caudal ridges

Answer 23

• develops after the cranial ridges
• right and left start on the caudal side and move cranially to form the right and left pleuroperitoneal membranes
• do not fuse together (unlike cranial ridges), but with dorsal mesentery of the esophagus and the septum transversum
• separates pleural cavity and peritoneal cavity

Question 24

What does the pleuroperitoneal membrane merge with to help form the diaphragm?

Answer 24

septum transversum

Question 25

Which layer does the phrenic nerve get caught up in and what happens to it?

Answer 25

- pleuropericardial | - becomes part of the fibrous pericardium (somatic mesoderm)

Question 26

Which pleuroperitoneal fold needs to close last?

Answer 26

left side

Question 27

What does the diaphragm develop from?

Answer 27

1) septum transversum 2) pleuroperitoneal membranes 3) dorsal mesentery of the esophagus (along with 2 vessels - vena cava and aorta) 4) muscular ingrowth from the lateral body walls

Question 28

What are the two congenital diaphragmatic hernia?

Answer 28

1) posterolateral defect - pleuroperitoneal of the left side did not fuse with the central tendon of the diagphragm 2) congenital hiatal hernia - can occur with esophagus or stomach (ie stomach may be up in the thorax)