Cardiac Embryonic-Fetal Circulation

Question 1

Where are the precardiac cells originally located, and how do they become the intraembryonic mesoderm?

Answer 1

They start on either side of the primitive streak in the epiblast. They then move through the primitive streak down below to become the intraembryonic mesoderm.

Question 2

What are the 3 layers of the gastrula?

Where are the precardiac cells located in the gastrula, and where do they move?

Answer 2

1) Ectoderm
2) Mesoderm
3) Endoderm

The precardiac cells are located in the mesoderm. They then migrate cephalically (towards the head of the embryo)

Question 3

How do the precardiac cells get from being at the head of the embryo to the chest region?

Answer 3

The head part folds back towards the middle around day 19 so that the precardiac cells are now located ventral to the rest of the embryo.

At this point the heart cells form 2 different tubes.

Question 4

Around what day do the 2 cardiac tubes fuse?

When does the heart start to beat?

Answer 4

Day 21-22.

It starts to beat around day 22 as well

Question 5

What does the atrioventricular sulcus eventually become? What is its orientation in relation to the straight heart tube?

Answer 5

It becomes the interventricular septum. It is oriented perpendicular to the plane of the straight tube.

Question 6

What does the primitive ventricle become?

Answer 6

it’s the primordium of the trabecular portion of the LV

Question 7

What does the proximal portion of the bulbus cordis become?

Answer 7

It becomes the primordium of the trabecular portion of the Right ventricle.

Question 8

By what day is blood flowing in the fetal heart?

Answer 8

Day 22.

Question 9

What does the inner layer of the tube become?

What about the outer layer of the primitive tube?

Answer 9

The inner layer is an endothelial lining that becomes the endocardium.

The outer layer is mesoderm that becomes the myocardium and the epicardium

Question 10

Where is cardiac jelly and what is it involved in?

Answer 10

It’s what’s between the 2 layers of the tube and plays a key role in the folding of the heart.

Question 11

What are the 4 parts of the cardiac tube that are then involved in folding during the 4th week of development?

Where does the right folding occur?

Answer 11

1) Truncus (most superior)
2) Bulbus Cordis
3) Primitive ventricle
4) Primitive atria (most inferior)

*The right folding occurs between the bulbus cordis and the primitive ventricle

Question 12

Differentiate between the truncus and conus and what do they become?

Answer 12

Truncus is most superior, it becomes the aortic and pulmonary valves and proximal portion of the aorta

Conus: Inferior to the truncus, becomes the outflow tract of the ventricles.

Question 13

In which direction do the atria rotate, and in what direction does the heart tend to loop?

Answer 13

The atria rotate posteriorly, and the heart loops to the right of the embryo.

Question 14

Prior to folding, the direction of blood flow is cephalic to caudal. After looping, what direction is blood flow?

Answer 14

It’s anterior to posterior because the atria rotate posteriorly.

Question 15

T or F?

Directly after folding, the truncus is only connected to the bulbus cordis

Answer 15

True.

That’s why it’s possible for babies to be born with a defect where both their aorta and pulmonary artery come out of the right ventricle (since the bulbus cordis becomes the RV). This is called double outlet right ventricle.

Question 16

When does atrial and ventricular septation occur?

Answer 16

Day 28-42

Question 17

What 3 veins enter the sinus venosus?

Answer 17

1) Umbilical vein (oxygenated blood from placenta)
2) Vitelline Vein (from yolk sac)
3) Cardinal vein (drains the embryo)

Question 18

Where do the pulmonary veins originate from?

Answer 18

From part of the splanchnic plexus

Question 19

How and when does the truncus arteriosis get subdivided into pulmonary and aortic outflow tracts?

Answer 19

It occurs between days 35-56. The DSTS and SITS form as well as the right and left intercalated swellings. The SVCC fuses with the SITS of the conus and the DDCC fuses with the DSTS of the conus, forming a spiral pattern

Question 20

What do the right and left intercalated swellings become?

Answer 20

Right-noncoronary aortic cusp

Left-anterior pulmonary cusp

Question 21

T or F?

In a fully formed heart, the pulmonary infundibulum is anterior to the aortic infundibulum, but at the great artery level the pulmonary artery is posterior to the aorta

Answer 21

True.

That’s just to reinforce the spiraling concept that occurs during development.

Question 22

Which aortic arch vessels remain after 8 weeks gestation?

Answer 22

Stapedial artery (2nd arch), Carotid arteries (3rd arch), right brachiocephalic and right subclavian (4th arch), transverse aortic artery (4th arch), ductus arteriosus (connects pulmonary artery circulation to the systemic artery circulation, distal left 6th arch), proximal left and right pulmonary arteries (6th arch).

Question 23

Which aortic arch vessels disappear?

Answer 23

1st, 2nd, 5th

Question 24

Which arch is most important and what vessels come from it?

Answer 24

The 6th arch.

Right and left proximal pulmonary arteries and ductus arteriosus.

Question 25

What structure does blood pass through in the fetal liver to mix with deoxygenated blood and move towards the right atrium?

Answer 25

The ductus venosus

Question 26

How much blood passes straight from the right atrium to the left atrium in the fetus, and what is the name of the structure it passes through?

Answer 26

1/3 of the blood passes through the foramen ovale, it bypasses the lungs this way.

Question 27

What happens to the other 2/3 of blood that doesn’t pass through the foramen ovale?

Answer 27

It moves to the RV, then the pulmonary artery, then passes through the ductus arteriosus and bypasses the lungs (it does this b/c it’s the path of least resistance since the lungs are filled with fluid)

Question 28

How much blood goes to the lungs in the fetus?

Answer 28

6-8%. This makes sure the lungs get blood for development.

Question 29

Which 3 structures that are unique to fetal circulation are vital for fetal survival?

Answer 29

The ductus venosus, the foramen ovale, and the ductus arteriosus

Question 30

Which fetal structure is most likely to remain patent after birth?

Answer 30

The foramen ovale.

The ductus venosus and arteriosus are not patent.

Question 31

T or F?

Closure of the ductus arteriosus usually takes longer in California than it does in Colorado.

Answer 31

False.

There’s a delay in closure at elevation. Normally it takes 10-15 hours though

Question 32

Why is closure of the ductus arteriosus more likely to be faulty in premature babies?

Answer 32

Because they don’t have as developed of spiral muscular fibers in the wall of the ductus, so it doesn’t have as good of contraction.

Question 33

What does the ductus arteriosus become?

Answer 33

The ligamentum arteriosum

Question 34

“Potential Board Question”

What 2 factors contribute to a persistent ductus arteriosus?

Answer 34

Elevation (>9,000 feet) and a maternal rubella infection