Hy Embryology 06

Front 1

Describe the formation of the pericardial cavity

Back 1

Lateral plate mesoderm (at the cephalic area of the embryo) will split into a somatic layer and a splanchinic layer, thus forming the pericardial cavity

Front 2

Describe Heart-forming regions

Back 2

Precardiac mesoderm is preferentially distributed to the splanchnic layer during the lateral plate mesoderm split that forms the pericardial cavity and is now called heart-forming regions

Front 3

Describe what occurs with lateral folding of the embryo

Back 3

As lateral folding of the embryo occurs, the HFRs will fuse in the midline to form a continuous sheet of mesoderm

Front 4

What secretes VEGF? What does it do?

Back 4

Hypertrophied foregut endoderm secretes vascular endothelial growth factor (VEGF), which induces the sheet of mesoderm to form a discontinuous vascular channels that eventually get remodels into a single endocardial tube (endocardium)

Front 5

What does the mesoderm around the endocardium form?

Back 5

Mesoderm around the endocardium forms the myocardium which secetes a layer of extracellular matrix proteins called cardiac jelly

Front 6

Describe the formation of the epicardium

Back 6

Mesoderm migrating into the cardiac region from the coelomic wall near the liver forms the epicardium

Front 7

Describe heart tube dilitations after its formation

Back 7

Five dilatations soon become apparent along the length of the tube:
-Truncus arteriosus
-Bulbus cordis
-Primitive ventricle
-Primitive atrium
-Sinus venosus

These five dilatations develop into the adults structures of the heart

Front 8

Describe the formation of the Aorticopulmonary Septum

Back 8

1. Neural crest cells migrate from the hindbrain region through pharyngeal arches 3, 4, and 6 and invade both the truncal ridges and the bulbar ridges. The truncal and bulbar ridges grow and twist aroudn each other in a spiral fashion and eventually fuse to form the AP septum
2. The AP septum divides the truncus arteriosus and bulbus cordis into the aorta and pulmonary trunk

Front 9

Describe persistent truncus arteriosus (PTA)

Back 9

1. Caused by abnormal neural crest cell migration such that there is only partial development of the AP septum
2. PTA results in a condition in which one large vessel leaves the heart and receives blood from both the right and left ventricles
3. PTA is usually accompanies by a membranous ventricular septal defect (VSD)
4. Is associated clinincally with marked cyanosis (right to left shunting of blood)

Front 10

Describe D-transposition of the great arteries (complete)

Back 10

1. Caused by abnormal neural crest cell migration such that there is nonspiral development of the AP septum
2. D-transposition results in a ncondition in which the aorta arises abnormally from the RV and the pulmonary trusk arises abnormally fromthe LV
3. The systemic and pulmonary circulations are completely seperate
4. Incompatible with life unless an accompanying shunt exists like a VSD, patent foramen ovale, or patent ductus arteriosus
5. Associated clinically with marked cyanosis (Right to Left shunt)

Front 11

Describe L-transposition of the great vessels (corrected)

Back 11

1. The aorta and pulmonary trunk are transposed and the ventricles are "inverted" such thta the anatomical RV lies on the left side and the anatomical LV lies on the right side.
2. These two major deviation offset one another such that blood flow pattern is normal

Front 12

Describe Tetralogy of Fallot

Back 12

1. Caused by an abnormal neural crest cell migration such that there is skewed development of the AP septum
2. TF results in a condition in which the pulmonary trunk obtais a small diameter while the aorta obtains a large diameter
3. TF is characterized by four classic malformations
a. Pulmonary stenosis
b. RV hypertrophy
c. Overriding aorta
d. Ventricular septal defect
(Mneumonic: PROVE)
4. TF is associated clinically with marked cyanosis (R to L shunting) in which the clinincal consequences depend primarily on the severity of the pulmonary stenosis

Front 13

What forms the roof of the primitive atrium?

Back 13

Septum primum

Front 14

Describe the formation of the foramen primum

Back 14

The foramen primum forms between the free edge of the septum primum and the AV cushions

Front 15

Describe the septum primum

Back 15

The crescent-shaped septum primum forms in hte roof of the primitive atrium and grows toward the atrioventricular (AV) cushins in the AV canal

Front 16

Describe the formation of the foramen secundum

Back 16

The foramen secundum forms in the center of the septum primum

Front 17

Describe the formation of the septum secundum

Back 17

The cresent shaped septum secundum forms to the right of the septum primum

Front 18

Describe the foramen ovale

Back 18

1. The foramen ovale is the opening between the upper and lower limbs of the septum secundum
2. During embryonic life, blood is shunted from the RA ot the LA via the foramen ovale
3. Immediatedly after birth, functional closure of the foramen ovale is facilitated both by a decrease in RA pressure from occlusion ofplacental circulation and by an increase in LA pressure due to increased pulmonary venous return

Front 19

Describe the last step in the formation of a complete atrial septum

Back 19

Later in life, the septum primum and septum secundum anatomically fuse to complete the formation of the atrial septum

Front 20

Describe the role of the foramen ovale during embryonic life

Back 20

During embryonic life, blood is shunted from the RA ot the LA via the foramen ovale

Front 21

Describe what occurs to the foramen ovale after birth

Back 21

Immediatedly after birth, functional closure of the foramen ovale is facilitated both by a decrease in RA pressure from occlusion ofplacental circulation and by an increase in LA pressure due to increased pulmonary venous return

Front 22

What adult structures result from the truncus arteriosus?

Back 22

-Aorta
-Pulmonary trunk

Front 23

What adult structures result from the bulbus cordis?

Back 23

-Smooth part of RV (conus arteriosus)
-Smooth part of LV (aortic vestibule)

Front 24

What adult structures result from the primitive ventricle?

Back 24

-Trabeculated part of RV
-Trabeculated part of LV

Front 25

What adult structures result from the primitive atrium?

Back 25

-Trabeculated part of RA
-Trabeculated part of LA

Front 26

What adult structures result from the sinus venosus?

Back 26

-Smooth part of RA (sinus venarum)
-Coronary sinus
-Oblique vein of LA

Front 27

How are atrial septal defects detected on physical exam?

Back 27

They are noted on auscultation with a loud S1 and a wide, fixed, split S2

Front 28

Describe atrial septal defects

Back 28

Characterized by L to R shunting of blood

Front 29

Describe foramen secundum defects

Back 29

1. Caused by excessive resorption of septum primum, septum secundum, or both
2. This results in a condition in which there is an opening between the RA and LA
3. Some defects can be tolerated for a long time, with clinical symptoms manifesting as late as 30yo
4. It is the most common clinincally significant ASD

Front 30

Describe common atrium (cor triloculare biventriculare)

Back 30

1. Caused by the complete failure of septum primum and septum secundum to develop
2. Results in a condition in which there is formation of only one atrium

Front 31

Describe probe patency of the formamen ovale

Back 31

1. Caused by incomplete anatomic fusion of septum primum and septum secundum
2. Present in approx 25% of the population
3. Usually of no clinical importance

Front 32

Describe premature closure of the foramen ovale

Back 32

1. Is closure of foramen ovale during prenatal life
2. Results in hypertrophy of the right side of the heart and under development of the left side of the heart