Embryology of Heart and Vessels

Question 1

Outline the main stages of heart development.

Answer 1

. Formation of linear heart tube
. Formation of cardiac loop
. Septation of heart
. Cavitation of ventricle
. Formation of great vessels
. 4-chambered heart

Question 2

In the linear heart tube, what do the following parts eventually become?: truncus arteriosus, bulbus cordis, ventricle, atrium, right sinus venosus horn, left sinus venosus horn

Answer 2

. Truncus arteriosus- proximal parts of aorta and pulmonary trunk
. Bulbus cordis- right ventricle
. Ventricle- left ventricle
. Atrium- portions of left and right atria
. Right sinus venosus horn- smooth wall of right atrium
. Left sinus venosus horn- coronary sinus

Question 3

What is another term for the truncus arteriosus? What is another term for the left and right sinus venosus horns?

Answer 3

. Truncus arteriosus also known as outflow tract

. Left and right sinus venosus horns also known as inflow tract

Question 4

What happens to the position of the atrium during formation of the cardiac loop? Why does this positioning arise?

Answer 4

. Atrial chamber becomes more dorsal and cranial to ventricle
. Happens because ventricle and bulbus cordis grow faster than other regions, so heart bends to the right and the atrium and sinus venosus (inflow tract) move cranially and dorsally

Question 5

Where are endocardial cushions found during the heart septation stage of development?

Answer 5

Found lining the atrioventricular region and outflow tract

Question 6

Why are endocardial cushions important?

Answer 6

They are important for the formation of heart valves and for heart septation

Question 7

How is the foramen ovale formed? How is the valve of the foramen ovale formed?

Answer 7

. Septum secundum forms next to septum primun and grows down to form the foramen ovale
. Valve of foramen ovale formed by septum primun

• This means blood can pass from the right atrium to the left atrium. At this stage, the pressure is higher in the right than in the left

Question 8

What is the importance of the foramen ovale?

Answer 8

Allows blood to flow from the right atrium to the left atrium during prenatal circulation

Question 9

When and how does ventricular septation occur?

Answer 9

. Ventricular septation occurs after atrial septation
. Interventricular septum (combination of septum primun which previously fused with endocardial cushion then was cleaved) grows up and interventricular foramen forms
. Membranous part of IV septum forms to fully close the left and right ventricles (which were already partly separated by muscle)

Question 10

What is the importance of the septum secundum?

Answer 10

Takes role of atrial septum (hangs down with valve of foramen ovale flapping upwards) as septum primun degrades

Question 11

Describe the process of cavitation.

Answer 11

. Myoblasts proliferate to form muscle bundles, which form the trabeculae carnae in the ventricles
. Papillary muscles attach to chordae tendinae, which attach to AV valve cusps
. Endocardial cushions form small protrusions, which form AV valves

Question 12

What could happen if endocardial cushions aren’t formed correctly?

Answer 12

Septal defects and valve defects can arise

Question 13

How are the great arteries formed?

Answer 13

. Ridges of the ECs spiral up the heart
. They expand and ultimately fuse
. Gives rise to aorta and pulmonary trunk (outflow region), which are twisted around each other
. ECs are continuous

Question 14

How are semilunar valves formed?

Answer 14

Derived from ECs in the outflow region quite late on

Question 15

How are the great veins formed?

Answer 15

. Vena cavae formed by other vessels fusing together, not really susceptible to defects
. Pulmonary veins formed from left atrium as it expands and new lumens are created

Question 16

Describe post-natal circulation.

Answer 16

3 shunts close: foramen ovale, ductus arteriosus, and ductus venosus
. Foramen ovale- lungs expand so resistance to blood flow decreases, which causes the foramen ovale to shut permanently (if it doesn’t close you get a atrial septal defect).

. Ductus arteriosus constricts and ligamentum arteriosum forms

. Ductus venosus constricts,
leading to closure and ultimately ligamentum
venosum (in liver) forms

Question 17

When is the peak time for congenital heart defects to arise?

Answer 17

At 5 weeks because this is when lots of complex processes are occurring

Question 18

What is an ostium secundum atrial septal defect (ASD)?

Answer 18

Hole in the foramen secundum, which results in enlarged chambers

Question 19

What does the foramen ovale become when it is closed up?

Answer 19

The fossa ovalis

Question 20

Draw and label a picture of the linear heart tube.

Answer 20

Check it yourself!