Heart Development

Question 0

At what week does the heart to begin to form?

Answer 0

The formation of the heart begins in week 3. First contraction occurs in day 22.

Question 1

What three layers is the heart composed of?

Answer 1

Endocardium - heart tube.
Myocardium - derived from visceral mesoderm.
Epicardium - visceral layer of the pericardium.

Question 2

What does the endoderm do during day 17 and 18?

Answer 2

The endoderm induces some cells of the overlying visceral/splanchnic mesoderm to differentiate into angioblasts.

Question 3

What do angioblasts differentiate into?

Answer 3

Angioblasts differentiate into endothelial cells and form tubes (vasculogenesis) - endocardial tubes.

Question 4

When the endocardial tubes fuse, what do they form?

Answer 4

Endocardial tubes fuse during lateral folding to form the primitive heart tube.

Question 5

What does craniocaudal folding do to the developing heart tube?

Answer 5

Craniocaudal folding brings the developing heart tube into the thorax.

Question 6

What folding to the heart begins to happen on day 23?

Answer 6

On day 23 the heart tubes starts to fold in preparation for dividing into 4 chambers.

Question 7

What happens to the bulbus cordis and the primitive ventricle and atrium on day 23?

Answer 7

Bulbus cordis moves caudally, ventrally and to the right.
Primitive ventricle is displaced to the left.
Primitive atrium displaces craniallly and dorsally.

Question 8

When does the sinus venosus degenerate?

Answer 8

The sinus venosus largely degenerates by week 5. It remains part of the wall of the right atrium and the left horn forms the oblique vein of left atrium and coronary sinus.

Question 9

What does the right horn of the sinus venosus form?

Answer 9

The right horn forms the smooth walled part of the right atrium - sinus venarum.

Question 10

Which part of the right atrial wall was derived from the primitive atrium?

Answer 10

The rough trabeculated part of the right atrium was formed from the primitive atrium.

Question 11

What does the conus arteriosus form in the ventricle?

Answer 11

Conus arteriosus forms the smooth walls of the left and right ventricles that lead into the aorta and pulmonary trunk respectively.

Question 12

What is the rough ventricular wall derived from?

Answer 12

The rough part of the ventricular wall is formed from the primitive ventricle. Trabeculae Carneae.

Question 13

How are the pulmonary veins formed?

Answer 13

An outgrowth of the left atrial wall forms a single pulmonary vein. This branches into left and right and then bifurcatess

Question 14

During which weeks are the 4 pulmonary veins incorporated into the wall of the left atrium?

Answer 14

In week 5, the 4 pulmonary veins are incorporated into the wall of the left atrium - intussusception.

Question 15

When does septation of the primitive atrium occur?

Answer 15

At the end of week 4, a crescent shaped outgrowth comes from the dorsal wall - septum primum. As the septum primum descends, the diminishing connection between the two atria is called foramen primum

Question 16

By which week has the septum primum fused with the atrioventricular septum?

Answer 16

By week 6, the septum primum has fused with the atrioventricular septum, obliterating the ostium primum.

Question 17

At what week does the septum Secundum form and what does it do?

Answer 17

During week 6, the septum Secundum forms from the dorsal wall of the atrium. But it doesn’t form a complete partition. The opening is called the foramen ovale.

Question 18

What is the first origin of the inter ventricular septum?

Answer 18

At the end of week 4, a muscular part projects from the floor of the primitive ventricle towards the endocardial cushions leaving an inter ventricular foramen.

Question 19

During what week is the inter ventricular foramen closed?

Answer 19

During week 7 a membranous part projects inferiorly from the endocardial cushion to close the interventricular foramen.

Question 20

How is the truncus areteriosus divided?

Answer 20

The truncus arteriosus is divided into 2 channels by endocardial swellings - conotruncal ridges.

Question 21

How do the conotruncal ridges (swellings) form the aorta and pulmonary trunk?

Answer 21

The conotruncal ridges fuse to form a septum (conotruncal) that separates the outflow of the left and right ventricles and fuses with the inter ventricular septum.

Question 22

How do the contruncal swellings fuse?

Answer 22

The contruncal swellings fuse by spiralling around each other. This is needed to allow the right ventricle to connect with the pulmonary trunk and the left ventricle to connect to the aorta.

Question 23

Which dilation make up pericardial cavity?

Answer 23

Primitive ventricle, bulbous cordis