16 - Body Cavities

Question 1

When does the intraembryonic coelom (or body cavity) appear during development? How does it form?

Answer 1

Late in the third week as small spaces within the lateral mesoderm coalesce and split it into the:

Somatic mesoderm which associates with the ectoderm and

The Splanchnic mesoderm that associates with the endoderm.

Question 2

What is the somatic mesoderm continuous with initially? How is this relationship lost?

Answer 2

The extraembryonic mesoderm that coats the amnion.

Lost during folding.

Question 3

What is the splanchnic mesoderm continuous with initially? How is this relationship lost?

Answer 3

The mesoderm that coats the umbilical vesicle (yolk sac).

Lost during folding.

Question 4

What happens to the intraembryonic coelom as the embryo folds?

What is located on either side of the gut tube at this point?

Answer 4

It becomes a U-shaped space within the embryo.

The legs of the U, on either side of the gut tube, are called the pericardioperitoneal (pleural) canals.

Question 5

What change reflects the definitive arrangement in which the pericardial cavity is median and somewhat ventral to the pleural cavities?

Answer 5

Folding of the embryo in the sagittal plane, which causes the transverse portion of the coelom to become ventral with respect to the longitudinal portions.

Question 6

What is the result of folding in the horizontal plane?

Answer 6

Longitudinal portions of the ceolom approach each other and become ventral to the neural tube and surround the primitive gut tube.

Question 7

Initially, the longitudinal portions of the intraembryonic coelom are continuous with the ________? When is this lost?

Answer 7

Extraembryonic coelom, or chorionic cavity.

Lost when ventral body wall forms during folding in the horizontal plane.

Question 8

What is the septum transversum?

Answer 8

A semicircular shelf of mesenchyme.

After folding, it’s located caudal to the forming heart and cranial to the abdominal cavity.

During growth, it expands and helps form the diaphragm.

Question 9

Where is the ventral mesentery during development?

Answer 9

It’s attached only to the foregut and organs derived from it: stomach, liver, part of the esophagus, and part of the duodenum.

Question 10

Each layer derived from the lateral mesoderm forms a _______ _____ located adjacent to the lumen of the coelom.

Answer 10

Serous membrane.

Question 11

The serous membrane derived from somatic mesoderm is located where? What is it called?

Answer 11

Lines the wall of the coelom cavity - parietal layer that becomes the parietal pleura in the thorax and parietal peritoneum in the abdomen.

Question 12

The serous membrane derived from the splanchnic mesoderm is located where? What is it called?

Answer 12

Covers organs extending into the cavity - visceral layer that becomes the visceral pleura in the thorax and visceral peritoneum in the abdomen.

Question 13

What are anterior (ventral) body wall defects? What are some common causes?

Answer 13

When the body wall fails to close ventrally.

May be insufficient migration of the folds ventrally or a fusion problem.

Question 14

What is ectopia cardia? What is Gastroschisis? What is cloacal exstrophy?

Answer 14

Ectopia cardia: externalized heart

Gastroschisis: externalized bowel.

Exystrophy: externalized bladder

All anterior body wall defects.

Question 15

What is Omphalocele?

Answer 15

Considered to be an anterior body wall defect, but isn’t caused by a failure of the body wall closure.

Intestinal contents herniated out of umbilical cord.

Question 16

What is the transverse portion of the inverted U-shapped intraembryonic coelom called? What occurs here?

Answer 16

The primitive pericardial cavity, in which the heart-forming region lies within the splanchnic mesoderm.

Question 17

How do the lungs grow?

Answer 17

Dorsal to the pericardial cavity, lung buds grow laterally from the respiratory diverticulum (derivative of the foregut).

Question 18

What is located in the pleuropericardial folds created by the expansion of the lungs?

Answer 18

The common cardinal vein and the phrenic nerve.

Question 19

What does the mesenchyme of the pleuropericardial folds become?

Answer 19

The fibrous and serous layers of the parietal pericardium.

Question 20

After separated from the pericardial cavity, what do the pericardioperitoneal canals remain open to? When does this close?

Answer 20

The forming abdominal cavity caudally.

Crescent-shaped folds are drawn out and fuse with the mesentery dorsal to the forming esophagus.

Question 21

The diaphram forms from the merger of what three primordia?

Answer 21

The septum transversum, the dorsal mesentery of the esophagus, and the paired pleuroperitoneal folds.

Question 22

What is the most common defect of the diaphragm?

Answer 22

Posterolateral defect of the diaphragm, most often unilateral, is a result of incomplete formation/fusion of the pleuroperitoneal membrane with the septum transversum.

Question 23

What is congenital diaphragmatic hernia (CDH)?

Answer 23

When abdominal organs herniate into the thoracic cavity.

Usually occurs when there is a posterolateral defect of the diaphragm when the GI organs return to the abdomen during week 10.

Question 24

What effect does a congenital diaphragmatic hernia have on other organs?

Answer 24

Often shifts the heart and mediastinum to the right.

The abdomen becomes narrow and the anterior wall is sunken (scaphoid abdomen).