Body Cavities

Question 1

Extraembrionic cavitation

Answer 1

the chorionic (extraembryonic) cavity is being formed;

above the trilaminar disc the amniotic cavity is formed;

under the disk – the cavity of definitive yolk sac is formed.

Chorionic cavity is lined with the extraembryonic mesoderm.

The extraembryonic mesoderm forms the connecting stalk and covers the amniotic cavity and the yolk sac.

Question 2

Lateral folding and body wall closure

Answer 2

the endodermal layer rolls down and incorporates a part of the yolk sac forming the gut tube.

The lateral plate mesoderm splits into visceral (splanchnic) and parietal (somatic) layers.

The visceral layer rolls ventrally and is intimately connected to the gut tube.

The parietal layer forms the lateral body wall folds.
Folds move ventrally, meet in the midline, close the ventral body wall.

Question 3

The intraembryonic coelom

Answer 3

appears in the lateral plate mesoderm in the form of several isolated vacuoles.

Question 4

During the lateral unfolding of the embryo

Answer 4

these vacuoles fuse and form a U-shaped cavity:

the intraembryonic coelom.

Question 5

The space between visceral and parietal layers of lateral plate mesoderm

Answer 5

the primitive body cavity (intraembryonic coelom).

Question 6

Cells of the parietal layer of the lateral plate mesoderm

Answer 6

form the parietal layer of the serous membranes.

Question 7

Cells of the visceral layer of the lateral plate mesoderm

Answer 7

form visceral pericardium, pleurae and peritoneum.

Question 8

Visceral and parietal layers are continuous with each other as the

Answer 8

dorsal mesentery.

Question 9

Septum transversum

Answer 9

a plate of mesodermal tissue between the thoracic cavity and omphaloenteric duct;

it is the primordium of the central tendon of the diaphragm.

Question 10

After formation of the head fold, the intraembryonic coelom is reshaped into:

Answer 10

a ventral cranial expansion (primitive pericardial cavity)

2 narrow canals called pericardioperitoneal canals (future pleural cavities) that lie dorsal to the septum transversum,

2 more caudal areas (future peritoneal cavities) where the intraembryonic and extraembryonic coeloms are broadly continuous.

Question 11

Pericardioperitoneal canals

Answer 11

develop partitions;

these separate the pericardial cavity from the pleural cavities, and the pleural cavities from the peritoneal cavity.

Question 12

The bronchial buds grow into the pericardioperitoneal canals, producing a pair of membranous ridges in the lateral wall of each canal:

Answer 12

the cranial ridges - pleuropericardial folds - are located superior to the developing lungs;

the caudal ridges - pleuroperitoneal folds - are located inferior to the lungs.

Question 13

pleuropericardial folds enlarge;

Answer 13

form pleuropericardial
membranes;

separate the pericardial cavity from the pleural cavities by week 7;

contain the common cardinal veins;

Question 14

the bronchial buds grow laterally from the caudal end of the trachea into

Answer 14

the pericardio-peritoneal canals (future pleural canals);

Question 15

mesenchyme of pleuropericardial membrane splits into

Answer 15

an outer layer that becomes the thoracic wall;

an inner layer (pleuropericardial membrane) that becomes the fibrous pericardium.

Question 16

pleuroperitoneal folds enlarge;

Answer 16

project into the pericardioperitoneal canals;

gradually become membranous, forming the pleuroperitoneal membranes.

membranes are produced as the developing lungs and pleural cavities expand and invade the body wall;

week 6: the pleuroperitoneal membranes extend ventromedially until their free edges fuse with the dorsal mesentery of the esophagus and septum transversum;

closure of the pleuroperitoneal openings is assisted by the migration of myoblasts into the pleuroperitoneal membranes.

Question 17

The diaphragm is a composite structure that develops from 4 embryonic components:

Answer 17

septum transversum;

pleuroperitoneal membranes;

dorsal mesentery of esophagus

muscular ingrowth from lateral body walls.

Question 18

The septum transversum grows dorsally from the ventrolateral body wall and forms

Answer 18

a semicircular shelf, which separates the heart from the liver.

Question 19

The septum transversum and pleuroperitoneal membranes fuse with

Answer 19

the dorsal mesentery of the esophagus

Question 20

The crura of the diaphragm develop from myoblasts that

Answer 20

grow into the dorsal mesentery of the esophagus.

Question 21

Further extension of the developing pleural cavities into the lateral body walls forms

Answer 21

the costodiaphragmatic recesses.

Question 22

Posterolateral defect of the diaphragm (foramen of Bochdalek)

Answer 22

results from defective formation and/or fusion of the pleuroperitoneal membranes with the other three parts of the diaphragm

associated with congenital diaphragmatic hernia.

Question 23

Congenital diaphragmatic hernia

Answer 23

it is the most common cause of pulmonary hypoplasia;

• usually unilateral;
• fetal lung maturation may be delayed;
• polyhydramnios may also be present;
• the abdominal organs are most often in the left side of the thorax;
• the heart and mediastinum are usually displaced to the right.

Question 24

Eventration of the diaphragm and congenital hiatal hernia

Answer 24

eventeration results mainly from failure of muscular tissue from the body wall to extend into the pleuroperitoneal membrane on the affected side;

clinical manifestations may simulate congenital diaphragmatic hernia.

Question 25

Herniations through the sternocostal hiatus (foramen of Morgagni)

Answer 25

the opening for the superior epigastric vessels in the retrosternal area (uncommon).

Herniation of intestine into pericardial sac, or part of heart descends into peritoneal cavity in epigastric region

Question 26

Gastroschisis

Answer 26

a congenital fissure in the anterior abdominal wall: usually there is protrusion of viscera

occurs in the median plane between the xiphoid process and umbilicus;

result from failure of the lateral body folds to fuse completely in week 4.

Question 27

As the face develops, the nasal placodes become depressed, forming

Answer 27

nasal pits.

Question 28

Proliferation of the surrounding

mesenchyme forms the medial and lateral nasal prominences, which results in deepening of the nasal pits and formation of

Answer 28

primordial nasal sacs.

Question 29

At first, the sacs are separated from the oral cavity by the

Answer 29

oronasal membrane

Question 30

The regions of continuity between the nasal and oral cavities are the

Answer 30

primordial choanae .

Question 31

The ectodermal epithelium in the roof of each nasal cavity becomes specialized to form

Answer 31

olfactory epithelium

Question 32

Development of the paranasal sinuses

Answer 32

mostly form from diverticula of the walls of the nasal cavities;

the original openings of the diverticula persist as the orifices of the adult sinuses;

expansion of sinuses after their formation is called secondary pneumatization

Question 33

maxillary sinuses begin to develop

Answer 33

during 3rd fetal month by initial invagination (primary pneumatization);

Question 34

sphenoid sinus forms by

Answer 34

closure of sphenoethmoidal recess during 4th fetal month;

Question 35

ethmoidal sinuses form during

Answer 35

5th fetal month;

Question 36

frontal sinuses are not radiologically visible

Answer 36

until 5-6 postnatal years.