Embryology - Unit 2 Structure And Development

Front 1

What is the coelom and what does it divide into?

Back 1

Embryonic cavity that divides into four body cavities (pericardial, pleural x 2, and peritoneal)

Front 2

What forms the coelomic cavity in the embryo?

Back 2

The LPM separates into the splanchnic and somatic layer and the coelom lies in between

Front 3

How is the dorsal mesentary formed?

Back 3

When the left and right sides of the coelom are brought together, the dorsal mesentary is in the middle

Front 4

What serous membrane is formed by the somatic LPM?

Back 4

Parietal layer

Front 5

What serous membrane is formed by the splanchnic LPM?

Back 5

Visceral layer

Front 6

What happens to the septum transversum during cranial body folding?

Back 6

It moves from cranial to caudal relative to the pericardial coelom

Front 7

What does the septum transversum do?

Back 7

It incompletely separates the primitive pericardial and peritoneal cavities

Front 8

What are the pericardioperitoneal canals and what role do they play in development?

Back 8

Provides continuity between the primitive pericardial and peritoneal cavities - lung buds push their way into these canals

Front 9

How are the lungs formed?

Back 9

Lung buds push their way into the pericardioperitoneal canals

Front 10

Where does the visceral pleura of the lungs come from?

Back 10

The mesoderm covering the lung buds as they push into the pericardioperitoneal canals

Front 11

Where does the parietal pleura of the lungs come from?

Back 11

The remaining mesoderm of the pericardioperitoneal canals

Front 12

What is the result of the ingrowth of the pleuropericardial folds?

Back 12

It partitiones the primitive pericardial cavity from the pericardioperitoneal canal - the phrenic nerves are also contained within these folds

Front 13

What forms the fibrous pericardium around the heart?

Back 13

The fusion of the pleuropericardial folds as they partition the coelom with their ingrowth

Front 14

What four structures form the diaphragm?

Back 14

1) Septum transversum
2) Mesentery of esophagus
3) Pleuroperitoneal membranes
4) Myoblasts from the body wall and C3 - C5 somites

Front 15

What causes a congenital diaphragmatic hernia?

Back 15

Failure of pleuroperitoneal folds to close

Front 16

Where does a congenital diaphragmatic hernia typically develop and what are the complications?

Back 16

Usually occurs on the left (b/c pericardioperitoneal canal is larger) - can cause hypoplastic lung and/or pulmonary hypertension

Front 17

What are the differences between the pleuropericardial folds and the pleuroperitoneal membranes?

Back 17

1) Pleuropericardial folds - partition the pleural and pericardial cavities and produce the fibrous pericardium
2) Pleuroperitoneal membranes - partition the pleural and peritoneal cavities and contribute to the diaphragm

Front 18

What is vasculogenesis?

Back 18

New formation of vessels by aggregates of angioblasts coalescing into vessels - used by major vessels in embryo

Front 19

What is angiogenesis?

Back 19

Angioblasts dvide, extending and sprouting from existing vessels

Front 20

Where do blood islands come from?

Back 20

They form from hemangioblasts within the splanchnic mesoderm of the yolk sac

Front 21

What are the first blood vessels in the embryo and where do they come from?

Back 21

Vitelline arteries and veins - formed as blood islands coalesce - the formation of the heart is a continuation of this

Front 22

What is the role of dorsal aortae and cardinal veins in early vascular development?

Back 22

They run along the cranio-caudal axis and the dorsal aorta gives rise to the ambilical arteries

Front 23

How do the umbilical arteries form and what is their purpose?

Back 23

They branch from the dorsal aortae and travel to the developing placenta

Front 24

What is the purpose of the umbilical veins?

Back 24

Carry oxygenated blood from the placenta to the fetus

Front 25

What is the structure of the aortic sac?

Back 25

It leads out of the heart and has 5 aortic arches that branch from it, surround the pharynx, and empy into the left and right dorsal aortae (these merge to form a single aorta in the thorax)

Front 26

What forms the carotid arteries?

Back 26

Aortic arches 1 - 3

Front 27

What forms the aortic arch and what does it connect?

Back 27

Left 4th arch - connects the aortic sac to the left dorsal aorta

Front 28

What forms the right subclavian artery?

Back 28

Right 4th arch

Front 29

What forms the pulmonary arteries?

Back 29

6th arches (actually 5th but called 6th)

Front 30

What forms the ductus arteriosis and what is its function?

Back 30

Remaining portion of the left side of 6th aortic arch - shunts blood from the pulmonary trunk to the aorta, bypassing the lungs

Front 31

What do the recurrent laryngeal nerves loop around as the heart descends?

Back 31

6th aortic arches
On left: loops around ductus arteriosus and arch of aorta
On right: loops around subclavian artery

Front 32

What is the vitelline arterial plexus remodeled into?

Back 32

The arteries that serve the gut within the abdomen (celiac trunk, superior mesenteric, and inferior mesenteric)

Front 33

What are the lateral branches of the aorta called?

Back 33

Intersegmental branches

Front 34

What forms the left subclavian artery?

Back 34

7th intersegmental branch of the aorta (on left)

Front 35

What are the intersegmental arteries called in different parts of the body?

Back 35

Thoracic: intercostal arteries
Lumbar: lumbar and lateral sacral arteries

Front 36

What veins enter the sinus venosus of the heart?

Back 36

Cardinal, vitelline, and umbilical (latter two travel through developing liver)

Front 37

What do the vitelline veins and (left) umbilical vein form through remodeling?

Back 37

Vitelline: anastomose around gut and form the hepatic portal vein
Left Umbilical: closes to become ligamentum teres

Front 38

What is the ductus venosus and what does it become at birth?

Back 38

A channel that form within liver to allow blood to bypass the liver and enter the IVC - closes to form ligamentum venosum

Front 39

What do the cardinal veins remodel to?

Back 39

The caval system (SVC, IVC)

Front 40

What major structures do the aortic arches become?

Back 40

Carotid arteries, aortic arch, pulmonary arteries, and ductus arteriosus

Front 41

What do the paired dorsal aortae form?

Back 41

They fuse to form a single thoracic and abdominal aorta

Front 42

Where does the cardiogenic field initially form and what does it become?

Back 42

Lateral and cranial to developing brain in cardiogenic (splanchnic mesoderm) - through vasculogenesis, it forms left and right endocardial tubes

Front 43

How do the endocardial tubes reposition?

Back 43

Through cranial body folding, they come to lie ventral to the forgut - through lateral body folding, they come together and fuse in a mid-ventral location

Front 44

How does the heart enter the pericardial cavity?

Back 44

It bulges into it as the heart lengthens, but remains attached at the dorsal wall by dorsal mesocardium which eventually breaks down freeing the heart in the cavity

Front 45

How is the myocardium formed?

Back 45

Formed by the endocardium external to it - then secretes cardiac jelly in between the two layers

Front 46

How is the epicardium formed?

Back 46

Come from the proepicardial organ which originates on the surface of the septum transversum

Front 47

What are the 4 main regions of the tubular heart in the direction of blood flow (caudal to cranial)?

Back 47

Sinus venosus, atrium, ventricle, bulbus cordis (conus arteriosis and truncus arteriosus)

Front 48

What is the truncus arteriosis?

Back 48

Cranial portion of bulbus cordis which becomes the great vessels

Front 49

What is the conus arteriosus?

Back 49

Caudal portion of bulbus cordis which becomes the outflow region of ventricles

Front 50

How is the cardiac loop formed?

Back 50

The cubular heart loops in a counter-clockwise direction (looking from ventral view) and creates the atrioventricular canal

Front 51

What do the left and right sinus horns become?

Back 51

Initially - enter into common atrium
Left - diminishes in size and becomes coronary sinus
Right - enlarges and receives blood from vena cavae, eventually becomes part of right atria and forms smooth walled sinus venarum

Front 52

How do the pulmonary veins develop?

Back 52

After right sinus horn descends , the left atrium grows the pulmonary veins and are incorporated into its wall

Front 53

How does the septum form between the atria?

Back 53

The septum primum grows from cranial wall and divides the two chambers - the foramen primum is progressively closed but a foramen secundum is formed - a septum secundum also appears

Front 54

Where does the foramen ovale come from?

Back 54

An opening in the septum secundum - the septum primum acts as a flap valve

Front 55

What can left-to-right shunting lead to?

Back 55

Cardiac hypertrophy and pulmonary hypertension as more blood is routed to the lungs

Front 56

How are the AV canals seperated into left and right?

Back 56

Endocardial cushions form and fuse together in the middle to make left and right canal

Front 57

What are endocardial cushions?

Back 57

Mesenchymal growths that constrict and partition the AV canal

Front 58

What is persistent common AV canal?

Back 58

Ventricular septal defect when endocardial cushions fail to come together completely leaving an common AV canal which causes left-to-right shunting

Front 59

What is tricuspid atresia?

Back 59

Agenesis of right AV valve, causes right-to-left shunting

Front 60

How does the ventricular septum form?

Back 60

The muscular ventricular septum grows from base of common ventricle toward AV canals - septum completes as conotruncal swellings (cushions) grow toward each other

Front 61

What are conotruncal cushions?

Back 61

Endocardial swellings that complete the ventricular septum and also separates the conus arteriosis (right and left ventricles) and truncus arteriosus (aorta and pulmonary trunk)

Front 62

What are the two events of ventricular septum formation and the direction they happen?

Back 62

1) Septum grows from base toward AV canals (bottom to top)
2) Conotruncal swellings grow toward each other (from top to bottom)

Front 63

Where are the conotruncal cushions derived?

Back 63

Cardiac neural crest cells that migrate from hindbrain

Front 64

What are disorders of conotruncal cushion development?

Back 64

1) Persistent truncus arteriosis
2) Transposition of great vessels (AP septum doesn't spiral)
3) Tetralogy of Fallot

Front 65

What are the cardinal signs of Tetralogy of Fallot?

Back 65

Most common cause of cyanotic heart disease:
1) Pulmonary stenosis
2) Overriding aorta
3) IV septal defect
4) Hypertrophy of right ventricle

Front 66

Where do the tissues of the respiratory system come from?

Back 66

Endoderm and splanchnic mesoderm

Front 67

What structure do the trachea and lungs come from?

Back 67

Foregut

Front 68

What structures are formed by the foregut?

Back 68

Parts of the digestive system, pharynx, and small intestines

Front 69

What is the respiratory diverticulum?

Back 69

A ventral outpocketing of the foregut that forms the lining of trachea, bronchus, and lungs - divides into two lung buds

Front 70

What is the function of the tracheoesophageal ridges?

Back 70

Separates the trachea and esophagus

Front 71

What are two disorders caused by problems separating esophagus and trachea?

Back 71

Esophageal atresia and esophageal fistula - tracheoesophageal septum fails to form in the proper location

Front 72

What is an esophageal atresia?

Back 72

When the esophahagus has an abnormal termination

Front 73

What is an esophageal fistula?

Back 73

An abnormal opening in the esophagus that leads into trachea

Front 74

What specific portions of the respiratory tree are formed by endoderm and splanchnic mesoderm?

Back 74

Endoderm: lining epithelium
Splanchnic Mesoderm: remaining tissue

Front 75

What are the terminal sacs in the lungs and how do they form?

Back 75

Primitive alveoli - formed by the flattening of cuboidal epithelium (continue to develop post-natally

Front 76

What are type II alveolar cells?

Back 76

Cells that secrete surfactant

Front 77

What transition do alveoli go through to allow efficient gas exchange?

Back 77

From cuboidal cells to thin, flat squamous cells

Front 78

How is the primitive gut formed?

Back 78

Cranial and caudal folding of trilaminar embryoblast

Front 79

Where does the foregut terminate in the early embryo?

Back 79

Oropharyngeal membrane

Front 80

Where does the hindgut terminate in the early embryo?

Back 80

Cloacal membrane

Front 81

What forms the tubular primitive gut?

Back 81

Lateral folding of endodermal layer

Front 82

How is the peritoneal cavity formed?

Back 82

The coelomic cavities unite ventrally, caudal to the diaphragm

Front 83

What forms the parietal peritoneum?

Back 83

Somatic LPM

Front 84

What forms the visceral peritoneum?

Back 84

Splanchnic LPM

Front 85

What are mesenteries?

Back 85

Double layers of serous membranes that attach gut to the dorsal wall - "ligaments" that provide pathways for vessels, nerves, and lymphatics to and from abdominal viscera

Front 86

What is the dorsal mesentary and where is it located?

Back 86

Partitions the dorsal portion of the coelomic cavity - extends from lower esophagus to the hindgut

Front 87

Where is the ventral mesentery derived from?

Back 87

Cuada part of septum transversum - the liver grows into the mesenchyme of septum transversum

Front 88

What are the two divisions of the ventral mesentery and how is it developed?

Back 88

Lesser omentum and falciform ligament - formed when liver grows into the mesenchyme of septum transversum

Front 89

What forms the muscular wall of the esophagus?

Back 89

Splanching LPM

Front 90

How does the stomach rotate?

Back 90

- 90 degrees clockwise (longitudinal axis from cranial perspective - left side becomes ventral)
- < 90 degrees along dorso-ventral axis (caudal part moves right and upward)

Front 91

What structures are associated with the dorsal mesentery of the stomach?

Back 91

Omental bursa, spleen, dorsal pancreas

Front 92

What holds the spleen in place?

Back 92

Lienorenal ligament: to the body wall
Gastrolienal ligament: to the stomach

Both of these are divisions of dorsal mesentery

Front 93

What is the greater omentum formed by?

Back 93

Dorsal mesogastrium

Front 94

What is unique about the formation of the pancreas?

Back 94

Formed by a dorsal bud and a vetral bud - ventral bud eventually comes to lie below and behind dorsal bud with rotation of duodenum to right.

Front 95

What does the ventral bud of pancreas form?

Back 95

Uncinate process and inferior part of head

Front 96

What does the dorsal bud of pancreas form?

Back 96

Tail and superior part of head

Front 97

What is annular pancreas?

Back 97

When the ventral pancreatic bud bifurcates and moves in opposite directions - causes duodenum to be surrounded by pancreatic tissue and can obstruct the duodenum

Front 98

What is the hepatic divericulum?

Back 98

"Limb Bud" - originates from the ventral foregut and penetrates septum transversum (gives rise to hepatocytes and cells of the biliary ducts)

Front 99

How is the bile duct formed and what else forms from this structure?

Back 99

From the narrowing of the connection between the hepatic diverticulum and duodenum - gallbladder and cystic duct are formed as small ventral outgrowths

Front 100

What happens on the surface of the liver?

Back 100

Splanchnic mesoderm surrounding liver differentiates to visceral peritoneum except on its cranial surface (bare area) - remains in contact with the septum transversum at central tendon of diaphragm

Front 101

What is recanalization of the duodenum?

Back 101

The lumen of the duodenum is obliterated by proliferation of cells in its wall, but is later recanalized to form hollow tube (duodenum derived by foregut and midgut)

Front 102

What is atresia and stenosis and what causes it?

Back 102

Complete blockage or narrowing - occurs from failure of recanalization or hypertrophy of th epyloric sphincter

Front 103

What compose the midgut?

Back 103

Lower duoden to first 2/3 of transverse colo (jejunem, ilium, cecum, appendix, ascending colong)

Front 104

What is physiological umbilical herniation?

Back 104

Elongation of cranial limb produces intestinal loops that enter extraembryonic cavity (umbilicus) - the intestines rotate -- 270 degrees around the superior mesentaric artery - intestines retract as space becomes available

Front 105

What is an omphocele?

Back 105

When midgut loop fails to retract - viscera protrude from body and are covered by umbilical cord

Front 106

What is gastroschisis and what distinguishes it from omphocele?

Back 106

Gastroschisis results from failur of ventral fusion following lateral body folding - has exterjal intestines not covered by umbilical cord

Front 107

What compose the hindgut?

Back 107

Distal 1/3 of transverse colon - rectum (also upper part of anal canal and internal lining of the bladder and urethra)

Front 108

What is the cloaca?

Back 108

Where the hindgut and allantois converge in the embryo

Front 109

What does the urorectal septum do?

Back 109

Separates the hindgut and allantois into the urogenital sinus and ano rectal canal

Front 110

What is Hirschsprung disease?

Back 110

Congenital megacolon due to an absence of parasympathetic ganglia in the bowel wall

Front 111

What compose the foregut?

Back 111

Pharynx - duodenum (liver, pancreas, and gall bladder form as buds from foregut)