L19 Development of the Heart

Question 1

What are cardiogenic cords?

Answer 1

A pair of elongated strands that form from the mesoderm around day 18 or 19 of gestation. They will eventually become the heart.

Question 2

Shortly after their development, the cardiogenic cords hollow out and become __?__

Answer 2

endocardial tubes

Question 3

Around day 22 of gestation, what happens to the endocardial tubes?

Answer 3

Lateral folding of the embryo brings the two endocardial tubes together and they fuse into a single primitive heart tube. The heart tube begins to beat.

Question 4

What are the 5 regions of the primitive heart tube?

Answer 4

1. Sinus venosus
2. Primitive atrium
3. Primitive ventricle
4. Bulbus cordis
5. Truncus arteriosus

Question 5

Why does the heart tube form an S-shape as it elongates?

Answer 5

As the heart tube elongates, bulbus cordis and primitive ventricle grow more rapidly that the other part. This causes the tube to loop and fold.

Question 6

What is the name of the primitive structure that forms:

• posterior wall of right atrium
• sinoatrial node
• coronary sinus

Answer 6

Sinus venosus

Question 7

What is the name of the primitive structure that forms:

• anterior walls of left and right atria
• left and right auricles

Answer 7

Primitive atrium

Question 8

What is the name of the primitive structure that forms:

- Left ventricle

Answer 8

Primitive ventricle

Question 9

What is the name of the primitive structure that forms:

- Right ventricle

Answer 9

Bulbus cordis

Question 10

What is the name of the primitive structure that forms:

• Ascending aorta
• Pulmonary trunk

Answer 10

Truncus arteriosus

Question 11

What will the sinus venosus develop into?

Answer 11

Posterior wall of right atrium

Coronary sinus

SA node

Question 12

What will the primitive atrium develop into?

Answer 12

Anterior wall of left and right atria

Left and right auricle

Question 13

What will the primitive ventricle eventually develop into?

Answer 13

Left ventricle

Question 14

What will the bulbus cordis eventually develop into?

Answer 14

Right ventricle

Question 15

What will truncus arteriosus eventually develop into?

Answer 15

Ascending aorta

Pulmonary trunk

Question 16

Which structure receives blood from the left and right sinus horns?

Answer 16

Sinus venosus (embryology of the heart)

Question 17

What is the eventual fate of the left and right sinus horn?

Answer 17

Left: becomes redundant in week 5 of gestation, disappears by week 10.

Right: enlarges and, along with sinus venosus, becomes incorporated into the right atrium.

Question 18

What components help form the septum spurium?

Answer 18

The right and left venous valves (flanking the sinoatrial orifice on either side) fuse to form the septum spurium.

Question 19

Describe the division of the atria

Answer 19

Septum primum develops, growing across the atrial chamber towards the endocardial cushions. The ostium (or foramen) primum is the hole remaining between the septum primum and the endocardial cushions.

As the ostium primum closes, the ostium (or foramen) secundum opens, preventing complete separation of the atria. The formation of ostium secundum coincides with development of a second septum (septum secundum) that grows to partially cover ostium secundum - forming an interatrial valve: foramen ovalis.

Foramen ovalis remains patent until shortly after birth when ↑ pressure in the left atrium forces it closed and it becomes the fossa ovalis.

Question 20

What is the name of the opening between the developing endocardial cushions?

Answer 20

Atrioventricular canal

The endocardial cushions are muscular extensions that form between the primitive atrium and ventricle.

Question 21

What structure forms in the developing heart to divide the outflowing blood into two parts: the aortic arch and the pulmonary arch.

Answer 21

Aorticopulmonary septum.

The spiral-shaped septum of the truncus arteriosus forms and joins the interventricular septum.

Outflow from left ventricle is directed to the aortic arch, while that of the right ventricle flows into the pulmonary artery

Question 22

The cells of which structure(s) eventually become pacemaker cells and the bundle of His?

Answer 22

Cells of the sinus venosus (AV node forms on left wall)

Cells of atrioventricular canal

Question 23

Abnormalities with cardiac looping can result in which of the following:

A) Dextrocardia
B) Ventricular septal defect
C) Atrial septal defect
D) All of the above

Answer 23

A) Dextrocardia

Question 24

True or false: Heterotaxy is a condition in which specific organs are reversed orientation

Answer 24

True

Question 25

True or false: Individuals with heterotaxy usually have additional heart defects

Answer 25

True

Question 26

What is the most common atrial septum defect?

Answer 26

Patent ostium secundum - allows shunting of blood from the left to the right atria

Question 27

What is cor triloculare biventriculare?

Answer 27

Condition in which the individual has a total lack of interatrial septa. Results in a common atrium, meaning the heart has three chambers instead of four.

Cor triloculare biventriculare is always associated with other serious defects of the heart.

Question 28

Which atrial septum defect results in hypertrophy of the right atrium and right ventricle, and underdevelopment of the left side of the heart?

Answer 28

Premature closing of the foramen ovalis

Question 29

Which structure is associated with a persistent atrioventricular canal and/or incomplete closure of the ostium primum?

Answer 29

Endocardial cushions

Failure to fuse causes these conditions

Question 30

What is the most common type of cardiac defect?

Answer 30

Ventricular septal defects (VSD)

Question 31

VSDs result in a shunt in which direction?

Answer 31

From left ventricle to right ventricle.

More blood passes through the pulmonary artery