Embryology of the Heart and Congenital Heart Defects

Question 1

At the stage for the 3 week old embryo, what is the job of the andiogenic clusters?

Answer 1

Gives rise to lining of blood vessels and lining of blood cells

Question 2

How many aortic arches are represent at the 3 week mark? How is the heart represented?

Answer 2

5. Note that the one present in the 3 week point will not be the final version. Hearts is represented as a heart tube. Shown as a cross section….a circle.

Question 3

Describe the flow of blood in the 3 week stage of the embryo.

Answer 3

Blood always flows from vein to heart to artery. In a 3 week tube, the path is from inferior to superior in direction, starting with the sinus venosus to atrium to ventricles to bulbis cordis to truncus arteriosus.

Question 4

Describe the changes that start to be made at the 3rd week of development.

Answer 4

Parts of the heart get larger, and the heart tube starts to bend. Specifically, ventricular side bends down (bulbis cordis moves downward) and the atrial side bends up

Question 5

How does the heart get larger, and what parts of the anatomy does the heart incorporate?

Answer 5

Heart gets larger by eradicating surrounding barriers from the sinus venosus and the bulbuis cordis. Sinus venosis becomes part of right atria, pulm, proximal pulm vein for left atrium, and bulbis cordis becomes part of ventricles.

Question 6

Where do all of the veins enter the heart?

Answer 6

They enter through the sinus venarum.

Question 7

How does the pulmonary vein develop in to the smooth portion of the left atrium?. Where does the smooth portion of the left atrial wall come from?

Answer 7

Literally, the trunk of the og (primitive…has a ROUGH wall) pulmonary vein gets incorporated into the left atrium, getting shorter and shorter. The two branches of the pulmonary vein get split off and this leads to the production of 4 pulmonary veins (slide 8). Smooth portion of the wall comes from the pulmonary veins.

Question 8

Describe most prominant period for birth defects.

Answer 8

Septal development during th e4th-7th week of development

Question 9

Why is the fossa ovalis thinner than the rest of the heart?

Answer 9

It’s only made from one septal layer.

Question 10

Tell the story of the development of the atrial septum.

Answer 10

1. Septum primum (THIN and relatively flimsy) decends from the top center of the atria to the bottom of the atrium. Stops partially during decend to create the foramen primum.
2. Endocardial cushion (Neural Crest Cells!!!!) migrate to for the A-V canal. A set migrates tot he left and right wings of the bottom of the atria. Another set migrates to the center and builds upwards to meet with the septum primum.
3. BEFORE the endocardial cushion makes contact with the septum primum, apoptosis occurds in the upper portion of the septum primum, creating the foramen secundum. Note that there is a point when 2 foramen are in the heart
4. Septum secundum, THICKER AND NOT MOVING AT ALL, forms on the RIGHT side of the heart, adjacent to the septum primum, to close off the foramen secundum.

Question 11

Why do we need the foramen during atrial development? Where does the limbus ovalis come from?

Answer 11

Allows for oxy blood to reach the left side of the heart so that it can enter the systemic circuit. Limbus ovalis come from the thicher portion being the septum primum and secundum and the fossa ovalis from the septum primum.

Question 12

Describe blood pressure and blood flow in the atria. Is there any blood coming into the left atria this point? Why/why not? What is the neame of the opening that the blood runs through into the left atria?

Answer 12

Because blood is coming from the umbilical vein to inferior vena cava directly into the right atrium, and blood is still coming from the superior vena cava, right atria is under high pressure, relative to the left atrium. This causes blood to flow from right to left, pushing through the FLIMSY septum primum. No blood is coming into the left atria since the lungs are not yet working (high pressure there since the alveoli are closed off, so none goes through the A-V septum from the right atrium). Blood goes from right atrium to left atrium through the foramen ovale.

Question 13

Describe the pressure shift of the right atrium after birth. What leads to the closure of the foramen ovale? Does the septum primum and secundum ever fuse?

Answer 13

After birth, umbilical vein is cut. So blood pressure in the right atrium is severely cut down. At the same time, baby starts to breathe, so pulmonary resistance drops and blood finally starts to flow through the lungs. Upon which, blood starts coming through the pulm vein into the left atrium. The pressure on the left atrium is finally higher than the pressure in the right atrium, and so, the septum primum (flimsy) is pushed against the septum secundum (STRONG AND STIFF), closing off the foramen ovale.

Question 14

Describe the atrial septal defect (ASD) (AFTER BIRTH) of the endocarial cushion not linking with septum primum. Which direction does blood flow? Why is the body not cyanotic? Are the AV valves suscueptible to birth effects? Why/Why not? What is a consequence of blood flowing back into the right atrium?

Answer 14

Neural crest cell migration is responsible for creating endocarial cushion. If the neural crest cells do not migrate properly/at all, there is now an opening between the two atria when there is not supposed to be (persistence of the foramen primum). Blood flows from left to right since the pressure of the blood is still higher on the left than the right after birth, so the body is not cyanotic. Body is not cyantoic because the blood gets to the left atrium already oxygenated, having already passed through the lungs. The AV valves are also susceptible to malfunctional growth because the the walls which make them are made from neural crest cells. Blood flowing back into the right atrium increases pressure int he right atrium (hypertrophy….)

Question 15

Describe the atrial septal defect resulting from the septum secundum not being able to cover up the foramen secundum because there was too much too much apoptosis of the septum primum. What is the direction of blood flow through the resulting hole? Is body cyanotic? Is this a neural crest migration issue?

Answer 15

High pressure on the left side pushes blood into the right side since the septum secundum is unable to cover the foramen secundum (left to right shunt). Body is not cyanotic. This is NOT a neural crest migration issue. this is one of the most common atrial septal defects.

Question 16

What is the job of the aorticopulmonary septum? What is the aorticoventricular septum and the embryonic ventricular septum made of? Which division (aorticoventricular septum or embryonic ventricular septum) is made of neural crest cells?

Answer 16

The aorticopulmonary septum is meant to EQUALLY divide the pulmonary trunk from the ascending aorta by descending and meeting with the embryonic ventricular septum (EVS). Aorticoventricular septum is made of MEMBRANE (tissue) and he embryonic ventricular septum is made of CARDIAC MUSCLE. Neural crest cells make up the aorticoventricular septum.

Question 17

What leads to the development of the Tetrology of Fallot? What are the 4 issues caused by the one major defect (and what is the one major defect?)

Answer 17

Aorticoventricular septum forms on the right side, not meeting with the embryonic ventricular septum and creating 2 uneven sides (pulmonary trunk and aortic arch.) The 4 issues associated with it are (1) Pulmonary stenosis since the pulmonary trunk is too small, (2) right ventricular hypertrophy since the heart is working harder to push blood through the pulmonary trunk, (3) the actual ventricular septal defect having been places to the right (dextraposition), creating an opening between the right and left ventricles, and (4) the overriding aorta since the aorta is taking up more space than the pulmonary trunk.

Question 18

Why are babies with tetrology of fallot cyanotic?

Answer 18

Deoxy blood is flowing from the right ventricle to the left ventricle because the aorticoventricular septum is shift too far to the right. This cause a right to left shift. This is the most common cyanotic birth defect.

Question 19

What is the birth defect of truncus arteriosus?

Answer 19

The aorticoventricular septum simply never forms. Blood from both ventricals flow together into the pulm trunk and the aortic arch. This still counts as a right to left shift, so the baby is still cyanotic.

Question 20

Describe what happens if the aorticopulmonary spetum does not spiral during embryological development.

Answer 20

You get a transposition of the the great arteries, leading to aorta pumping out deoxy blood to the rest of the body through the aortic arch and oxy blood being pumped to the lungs through the pulm trunk. Essentially, aorta arises from the right ventricle and the pulm trunk arises from the left ventricle.

Question 21

Describe the blood pathway to the right atrium before birth.

Answer 21

Blood from inferior vena cava is oxy since it comes straight from the umbilical cord (blood comes from inferior vena cava, but this is deoxy). Flows directly into the right atrium and past the deoxy blood from the superior vena cava to the foramen ovale into the right atrium. Blood flow is normal from the inferior side. Blood coming from the superior vena cava, however, runs straight into the right A then runs to the tricuspid valve and then the pulm trunk which leads to the pulm arteries. Since the pulm arteries are closed off (too much resistance since the baby is not breathing), the blood runs through the DUCTUS ARTERIOSUS directly into the aortic arch. The aortic arch is the first place bloo fromt he IVC and SVC truly link up.

Question 22

Describe the name changes after birth.

Answer 22

Ductus arteriosus becumes ligamentum arteriosum. Ductus venosus becomes ligamentum venosum (THER EIS NO LONGER A DIRECT SHUNT INTO THE AORTA FROM THE SUPERIOR VENACAVA-RA-RV pathway. From RV the blood goes straight to the right and left lungs). Umbilical vein becomes ligamentum teres. Right and left umbilical arteries becomes medial umbilical ligaments.

Question 23

What happens ot the ductus arteriosus after birth (What fosters the ductus arteriosus closing?)?

Answer 23

O2 increases and so does bradykinin. In addition, prostaglandin (inhibitor to the closing of ductus arteriosus closing) decreases. As in, what prostaglandin is present, the ductus arteriosus CANNOT close.

Question 24

What happens if ductus arteriosus does not close? How do you promote closure in preterm babies?

Answer 24

This is a NON cyanotic defect (blood still flows from right to left),. The only reason blood still flows from right to left is because high pressure blood coming from the aorta is able to enter the path of the ductus arteriosus back into the right ventrical. To help close it in preturm babies, bump up their O2 supply and provided drugs which inhibit prostaglandin.

Question 25

What is coarctation of the aorta? What is the difference between preductal and postductal coarctation of the aorta

Answer 25

It is the narrowing of the aorta. Preductal: issue seen immediately after birth (cyanotic) since blood cannot get to the rest of the body at all and ductus arteriosus is th eonly thing providing blood, but it came form the superior vena cava, which has nothing but deoxy blood and never got oxy yet. The amount of bloodflow did not drop yet, so there is no collateral circulation formed. In the case of postductal coarctation fo the aorta, the amount of bloodflo to the rest of the body did decrease. Body tries to solve this by creating an advances collateral circulation setup. Sympatematic in adults since the collaterals buy the kiddies time until the O2 demand increases as they get older.