Systems development III: Cardiac embryology

Question 1

What percentage of all congenital defects are cardiac?

Answer 1

20%

Question 2

Give a brief overview of the 7 main stages of cardiac development?

Answer 2

Folding brings heart tubes into ventral midline
Heart tubes fuse (day 22)
Heart tube begins to beat (32)
Heart looping occurs
Separation occurs
Aortic and pulmonary trunks divide
Valves develop

Question 3

Where does the heart start to develop?

Answer 3

In the cardiogenic area inferior to the notochord

Question 4

What do mesodermal and endothelial cells become?

Answer 4

Mesodermal- blood and vasculature

Endothelial- vessels at around week 3

Question 5

Why does the heart tube fold?

Answer 5

To develop the 4 chambers of the heart

Question 6

What do the ends of the heart tube divide to form at the anterior aspect?

Answer 6

The arterial trunks- then you have the ventricles followed by the atria. The venous channels or cardinal veins form at the inferior aspect

Question 7

What does the heart do after the arterial trunks and venous channels are formed?

Answer 7

The heart tubes turn on the side to make a c shaped bending

Question 8

What follows the c shaped bending?

Answer 8

S shaped bending to bring the atria and ventricles together

Question 9

What does the gap between the atria and ventricles form?

Answer 9

AV groove

Question 10

What is septation?

Answer 10

The process of the chambers being divided to form the atria and ventricles of the left and right sides of the heart

Question 11

What is septation facilitated by?

Answer 11

Endocardial cushions which develop as outgrowths of mesodermal tissues in atrioventricular canal

Question 12

What do the endocardial cushions eventually form?

Answer 12

The valves of the heart which separate the atria and ventricles

Question 13

What little holes are there in the heart?

Answer 13

Septum primum grows downwards first and then the septum secondum. The foramen oval is formed from the gap between the AV body and the septum secondum

Question 14

In the early embryo, what origin is all of the vasculature from?

Answer 14

Mesodermal

Question 15

What are the first veins called?

Answer 15

Cardinal veins (with anterior/posterior and common branches

Question 16

Where does aortic circulation come from?

Answer 16

Aortic arches

Question 17

What happens to the first and second branches of the aortic arches in most people?

Answer 17

They regress

Question 18

What does the third branch of aortic arches form?

Answer 18

Internal carotid arteries

Question 19

What does the 4th aortic arch form in left and right artery?

Answer 19

Left- Aortic arch

Right- Right subclavian

Question 20

What happens in terms of the 5th aortic arch in most people?

Answer 20

It may never develop

Question 21

What does the 6th aortic arch form in the left and right artery?

Answer 21

Left- Ductus arteriosus and left pulmonary artery

Right- Right pulmonary artery

Question 22

What has to happen prior to separation?

Answer 22

One tube needs to be partitioned into R or L outflow tracts

Question 23

What do the partitions grow from?

Answer 23

Bulbar ridges- same process as endocardial cushions

Question 24

What is the ultimate effect of the partitions forming?

Answer 24

There’s a 180 degree spiralling of vessels in the heart

Question 25

How does blood from the mother come to the baby?

Answer 25

By the umbilical vein

Question 26

How does the umbilical vein bypass the liver?

Answer 26

Via the ductus venous- it then enters the inferior vena cava

Question 27

What happens when the blood from the mother reaches the right atrium?

Answer 27

It can either go into the R ventricle or bypass the pulmonary circulation through the foramen ovale

Question 28

How does some of the blood that is being pumped through to pulmonary circulation from right ventricle get into systemic circulation?

Answer 28

Via the ductus arteriosus

Question 29

In embryological circulation, where does the descending aorta carry blood?

Answer 29

Into the umbilical arteries which carries the blood into the placenta

Question 30

What changes to circulation and heart occur at birth?

Answer 30

Clamping of umbilical cord causes closure of umbilical arteries- this then forms the median umbilical ligaments proximal portion, superior vesicle arteries Taking a deep breath causes closure of umbilical vein and ductus venous Closure of ductus arterioles Closure of foramen ovale

Question 31

What can go wrong at birth in terms of heart development?

Answer 31

The foramen oval remains patent- can be either idiopathic or iatrogenic

Question 32

Why is the foramen ovale selectively kept open?

Answer 32

It is kept open with prostaglandins in babies who are at high risk of cyanotic heart disease to keep them deoxygenated

Question 33

What is ventricular septal defect?

Answer 33

When there's a hole between the ventricles which allows for blood to flow. The separation has malfunction- failure of the endocardial cushions which were responsible for ensuring the division process occurred properly

Question 34

What is truncus arteriosus?

Answer 34

There is one common blood vessel leaving the heart, draining both R and L sides. In the majority, there's also interventricular septal defect

Question 35

What causes truncus arteriosus?

Answer 35

Defect in division of outflow tracts- bulbar ridges which form and separate the outflow tracts into 2 distinct vessels don't form correctly

Question 36

What is pulmonary stenosis?

Answer 36

Very serious condition where pulmonary vasculature doesn't develop properly- pulmonary valves and blood vessels leaving the right side of the heart to the pulmonary circulation are very stenosed- usually a problem with outflow tracts

Question 37

What is transposition?

Answer 37

Usually a looping defect where the incorrect folding of the tubes results in the right ventricle being connected to the aortic circulation and the left ventricle being connected to the pulmonary circulation

Question 38

What is tetralogy of Fallot?

Answer 38

Four things have gone wrong- Pulmonary stenosis, this then leads to muscles in wall of right ventricle thickening as have to pump harder and this high pressure system prevents endocardial cushions from functioning effectively which causes a ventricular septal defect to form. The aorta then has to override this septal defect due to the malformation in the rigght side of the heart- due to combination of developmental issues