Embryology

Question 1

Where is the cardiogenic area found prefolding?

Answer 1

It is found in front of the buccophalangeal membrane.

Question 2

Describe what cephalocaudal folding does for the heart’s location.

Answer 2

This brings the heart down so that it is in the correct position, below the foregut

Question 3

What happens to the cardiogenic area during lateral folding?

Answer 3

In lateral folding, the two cardiogenic areas are brought together and there is formation of the heart tube.

Question 4

At what stage in development is there circulation in the embryo?

Answer 4

By the 4th week.

Question 5

What are the regions of the primitive heart tube?

Answer 5

Aortic roots, truncus cordis, bulbous arteriosus, ventricle, atrium, sinus venosum.

Question 6

What is the significance of the primative heart tube being tethered both cranially and caudally?

Answer 6

This means that as the tub groups is much remain with the same amount of space. This is what causes looping.

Question 7

In what direction does the caudal portion move during looping?

Answer 7

It moves dorsally, cranially and to the left.

Question 8

After looping, where are inflow and outflow in relation to each other?

Answer 8

They are both cranial. The inflow is Infront of the outflow.

Question 9

What can be said about the vessels around the transverse pericardial sinus?

Answer 9

All the vessels in front flow in, and all the vessels behind flow out.

Question 10

In the sinus venosum, in which direction does the venous return shift and what does this lead to?

Answer 10

Venous return shifts to the right. The left sinus recedes, becoming the coronary sinus and the right is engulfed by the right atria - enlarging it.

Question 11

What structures from the primative heart tube go on to be part of the right atria?

Answer 11

Majority of the primative atrium and also the engulfed part of the sinus venosum - recieves drainage of blood from the body.

Question 12

How does the left atria develop?

Answer 12

The left atria contains a small portion of primitive atrium. It sprouts a pulmonary vein and as it absorbs the proximal part of this, this leads to the pulmonary trunk and there being 4 holes into the atrium for blood to drain from the lungs

Question 13

What can be said about the tissue absorbed from the pulmonary veins into the left atria?

Answer 13

It is smooth.

Question 14

When does the oblique sinus form?

Answer 14

Is forms as the left atria enlarges and engulfs the pulmonary veins.

Question 15

What organs must be bypassed in the fetal circulation?

Answer 15

The lungs - as they are not sufficiently developed.

The liver - this would use up all the nutrients in the blood.

Question 16

In the fetus, where does oxygenated blood get delivered into in the heart?

Answer 16

The right atrium. It bypasses the right ventricle and lungs by moving into the left atrium.

Question 17

What is the ductus arteriosus?

Answer 17

This is a vessel which joins the aorta and pulmonary trunk. In adults a ligamentous reminant may be seen of this.

Question 18

What are they aortic arches in a fetus?

Answer 18

This is the initial, symmetrical, bilateral arrangements of 6 arches. Some regress and some go on to become important structures.

Question 19

From which aortic arch is the arch of aorta derived from?

Answer 19

4th (left side) the right side of this forms the right subclavian artery.

Question 20

Why is the 6th aortic arch also named the pulmonary arch?

Answer 20

The right side forms the right pulmonary artery and the left side forms the left pulmonary artery and the ductus arteriosus.

Question 21

Describe the influence of the developing heart on the recurrent laryngeal nerves.

Answer 21

As the heart develops, it descends caudally. These nerves are hooked around the 6th aortic arch and so the right becomes hooked around the right subclavian artery and the left around the ductus arteriosus.

Question 22

What is the name of the process which results in production of the 4 heart chambers?

Answer 22

Septation.

Question 23

What happens at the beginning of septation?

Answer 23

Endocardial cushions push out into the middle of the heart, dividing it into left and right channels.

Question 24

What is the septum primum?

Answer 24

This is the beginning of atrial septation and grows down onto the endocardial cushions. As it grows down the ostium primum is present but then before this closes the ostium secundum appears in the septum primum.

Question 25

What happens after completion of growth of the septum primum?

Answer 25

A septum secundum forms which has a hole in called the foramen ovale. This is not exactly in line with the ostium secundum.

Question 26

What is the clinical significance of the foramen ovale and the ostium secundum?

Answer 26

This acts as a shunt from RA to LA meaning that the oxygenated blood can enter the systemic circulation.

Question 27

What is the fossa ovalis?

Answer 27

This is a remnant seen in an adult of the foramen ovale which can be observed as a thumb print on the inter atrial septum.

Question 28

Comment on the structure of the ventricular septum.

Answer 28

It contains two parts. The muscular part forms first and grows up towards the septum, and the membranous part is at the top of this.

Question 29

What is the name of the gap between the muscular part of the septum and the endocardial cushions?

Answer 29

Primary interventricular foramen.

Question 30

Where does the membranous portion of the interventricular septum originate from?

Answer 30

The CT of the endocardial cushions.

Question 31

How does septation of the outflow tract occur?

Answer 31

Endocardial cushions grow in the truncus arteriosus and as this occurs they twist around each other which is why we get the position of the pulmonary artery and aorta as it is.

Question 32

What is the name of the shunt which bypasses the liver?

Answer 32

Ductus venosus

Question 33

What effect does the removal of placental support have on the fetus after birth?

Answer 33

The ductus venosus shuts as there is no longer blood flow through it.

Question 34

What causes the foramen ovale to close?

Answer 34

After birth, pulmonary circulation is established and this alters the pressures meaning that lA is now higher than RA and this pushes the two septums together preventing blood flow.

Question 35

From what embryonic germ layer does the CVS originate from?

Answer 35

Mesoderm.