Lecture 2: Body Folding and Body Cavities

Question 1

What causes body folding?

Answer 1

Up/downregulation of cell junctions and growth of cells allow embryo to fold a certain way

Question 2

What happens in these phases of embryo development?
Growth
Morphogenesis
Differentiation

Answer 2

• cell division and elaboration of cell products
• develops features of organs/part of body
• cells form patterns of tissues that have specialized functions

Question 3

What is the intraembryonic coelom?

Answer 3

Empty U-shaped cavity that develops from spaces forming in the lateral plate and cardiogenic mesoderm

Question 4

The spaces in the lateral plate mesoderm forms what layers and what parts of the lateral mesoderm? What is each part continuous with?

Answer 4

Somatic (parietal) - amnion mesoderm

Splanchnic (visceral) = umbilical vesicle mesoderm

Question 5

What is the somatopleure and sphlanchopleure?

Answer 5

Somatic mesoderm + covering ectoderm

Splanchnic mesoderm + covering ectoderm

Question 6

Describe the nature of embryo folding in different planes (Cranial, caudal, lateral)

Answer 6

Embryo transforms from flat to cylindrical. All parts fold simultaneously, but cranial folding is fast and lateral sides lag behind.

Question 7

Describe the steps to cranial folding:

Answer 7

1. Elongation on both ends (4th week, Day 22)
2. Neural fold travels downward and backward and covers the oropharyngeal membrane
3. Neural fold growth causes movement of the septum transversum, intraembryonic coelom, primordial heart to correct positions
4. Foregut endoderm is incorporated

Question 8

After cranial folding, what happens to the intraembryonic coelom?
Pericardial cavity
Pericardioperitoneal canals

Answer 8

Forms the pericardial cavity (Ventral to foregut) which opens to 2 pericardioperitoneal canals (dorsal) on either side of the foregut

Question 9

Describe the process of caudal folding:

Answer 9

1. Caudal eminence grows over the cloacal membrane (future anus)
2. Part of the endoderm forms the hindgut and then end dilates to form the cloaca (rudiment of bladder/rectum)

Question 10

What happens after caudal folding?

Answer 10

1) Primitive Streak now caudal to cloacal membrane
2) Moves cloacal membrane (future anus) to correct position
3) Endoderm is incorporated into hindgut

Question 11

Describe how the lateral fold happens

Answer 11

Lateral edges wrap around the embryo and fuse
Umbilical vesicle is compressed and pinches off
Endoderm gut tube is now enclosed

Question 12

Gastroschisis

Answer 12

Protruding uncovered bowel, exposed to salty amniotic fluid. Usually located right of midline

Question 13

Congenital epigastric hernia

Answer 13

Herniation but bowel not exposed to amniotic fluid. Usually located on the midline.

Question 14

What cavities are formed from the division of the intraembryonic coelom?

Answer 14

Pericardial, pleural and peritoneal cavity

Question 15

What lines the cavities? What are the walls derived from? What layer of the peritoneum do these walls form?

Answer 15

Mesothelium
Parietal wall - somatic mesoderm, parietal layer
Visceral wall - splanchnic mesoderm, visceral layer

Question 16

What is the dorsal mesentery?

Answer 16

Suspends the caudal foregut, midgut and hindgut in the peritoneal cavity (basically holds the gut in place while the rest of the embryo moves)

Question 17

How are the peritoneal and pericardial cavities separated from each other?

How are the pleural and pericardial cavities separated from each other?

Answer 17

Pleuroperitoneal folds grow and cover the pericardioperitoneal canals

Primordial lungs from the respiratory diverticulum grows laterally. The pleural cavity expands with it and its growth pushes the pericardial cavity forward and allows it to fuse together. Pleuropericardial folds push medially and fuse, closing both cavities off.

Question 18

Pleuropericardial folds are located on which end and separates?
Pleuroperitoneal folds are located on which end and separates?

Answer 18

• cranial, heart and lungs

- caudal, lungs from GI

Question 19

Describe how the pleuropericardial folds develop:

Answer 19

They project inward to form membranes that grow into the canals and form separations between heart and lungs

Question 20

Briefly describe how the lungs develop

Answer 20

Bronchial buds grow into the canals ventrally and expands to form the pleural cavity, while pushing the pericardial cavity ventrally

Question 21

Bronchial bud growth splits the mesenchyme into…

Answer 21

Outer layer - thoracic wall

Inner layer - fibrous pericardium

Question 22

What happens to pleuroperitoneal membranes? When does this happen?

Answer 22

• Fuses with the dorsal mesentary and septum tranvsersum, separates the lungs and the GI
• Week 6

Question 23

What forms the diaphragm?

Answer 23

Septum transversum, dorsal mesentery and pleuroperitoneal membranes fuse to form the diaphragm

Question 24

What part of the diaphragm do each of these form?
Septum transversum
Dorsal mesentery
Myoblasts

Answer 24

central tendon
Median diaphragm
Crura of the diaphragm

Question 25

Why is the innervation of the diaphragm (phrenic n.) originate in the cervical region?

Answer 25

It forms at C1-3 initially but is repositioned during development when myoblasts pull the ventral rami downward

Question 26

Congenital diaphragmatic hernia (CDH)
Cause
Clinical

Answer 26

• (usually) L canal doesn’t close so pleural and peritoneal cavities are not separated
• viscera bulges up into the chest cavity and affect development of lungs. Polyhydramnios (excess amniotic fluid) may be present