2.2 + 3.1 Development of the CVS

Question 0

When does lateral folding begin?

Answer 0

25 days after fertilisation

Question 1

How does development of the CVS start?

Answer 1

Folding of the embryo to form the heart tube

Question 2

What does cephalocaudal folding achieve?

Answer 2

Moves the heart tube into the thoratic region

Question 3

What are the 6 areas of the primitive heart tube?

Answer 3

Aortic roots
Truncus arteriosus
Bulbus cordis
Ventricle
Atrium
Sinus venosus

Question 4

What occurs in cardiac looping?

Answer 4

The heart tube continues to elongate which results in bending.

Question 5

In cardiac looping, how does the cephalic portion move?

Answer 5

Ventrally, caudally and to the right

Question 6

In cardiac looping, how does the caudal portion move?

Answer 6

Dorsally, cranially and to the left

Question 7

After looping, how does the atrium communicate with the ventrical?

Answer 7

Through the atrioventricular canal

Question 8

Describe how the sinus venosus develops

Answer 8

The right and left sinus horns are initially the same size. Venous return shifts to the RHS and the left side recedes. The right sinus horn is absorbed by the enlarging right atrium.

Question 9

How does the right atrium develop?

Answer 9

It develops from most of the primitive atrium and the sinus venosus.

Question 10

How does the left atrium develop?

Answer 10

It develops from a small portion of the primitive atrium and absorbs proximal parts of the pulmonary veins.

Question 11

How is the oblique sinus formed?

Answer 11

Formed as the left atrium expands absorbing the pulmonary veins

Question 12

What is septation?

Answer 12

The formation of the interatrial and interventricular septum and the separation of the ventricular outflow tract to create 4 chambers.

Question 13

What is the first step in septation?

Answer 13

The formation of the endocardial cushions which divides the heart into left and right channels.

Question 14

Describe the first step in atrial septation. What is the hole called?

Answer 14

The septum primum grows down towards the endocardial cushions
The ostium primum is the hole present before the septum primum fuses with the cushions.

Question 15

Describe the second step of atrial septation

Answer 15

Before the ostium primum closes, another hole, the ostium secundum appears in the septum primum.

Question 16

Describe the third step of atrial septation

Answer 16

Finally, a crescent shaped septum, the septum secundum, grows from the roof of the heart downwards. The hole is called the foramen ovale.

Question 17

How does the muscular portion form in ventricular septation?

Answer 17

It grows upwards towards the endocardial cushions leaving a small gap called the primary interventricular foramen.

Question 18

How does the membranous portion of ventricular septation form?

Answer 18

It is formed by connective tissue derived by the endocardial cushions. It fills the gap of the primary interventricular foramen to complete the septum.

Question 19

What happens in outflow tract septation?

Answer 19

Endocardial cushions appear in the truncus arteriosus. They twist as they grow towards each other to form a spiral septum.

Question 20

Why fetal shunts necessary before birth?

Answer 20

The lungs are non-functional so blood is diverted around them and to the placenta instead to become oxygenated.

Question 21

Why does the foramen ovale close at birth?

Answer 21

It closes because the pressure in the left atrium is greater than the pressure in the right atrium. The septum primum is pushed against the septum secundum.