Session 3: Cardiovascular System - Embryology 1

Question 1

What kind of folding creates the heart tube?

Answer 1

The lateral folding of the embryo.

Question 2

What does cephalocaudal folding do?

Answer 2

It brings the heart tube into the thoracic region where it is supposed to be.

Question 3

Label the diagram.

Answer 3

Question 4

When does formation of primitive heart tube begin?

Answer 4

At around day 25

Question 5

Label the diagram. 7 labels required.

Answer 5

Question 6

What happens during looping?

Answer 6

The tube elongates

Pericardial space will start to get filled

It starts to twist and fold up

Question 7

Why is looping important?

Answer 7

Because it places the inflow and outflow in the correct orientation with respect to each other.

Question 8

What is the transverse pericardial sinus?

Answer 8

The space between the arteries which will become the aorta and the pulmonary trunk.

Question 9

Explain the development of the sinus venosus and its fate.

Answer 9

The sinus horns, both right and left are equal in size at the start. The venous return shifts to the right hand side and the left sinus horn will start to recede.

The right sinus horn is absorbed by the enlarging right atrium. THis means that some of the vessel will become the atrial wall.

Question 10

Where does the right atrium develop from?

Answer 10

Most of the primitive atrium and the sinus venosus. Right sinus horn is absorbed by the enlarging RA.

It receives venous drainage from the body VC and coronary sinus from the heart.

Question 11

Where does the left atrium develop from?

Answer 11

Only a small portion of the primitive atrium.

It absorbs proximal parts of the pulmonary veins which is smooth.

Question 12

What is the oblique pericardial sinus?

Answer 12

It is formed as left atrium expands absorbing the pulmonary veins.

You put your hand from the apex and have fingers pointing to top of the heart.

Question 13

How does circulation differ between mature and foetus?

Answer 13

Lungs don’t work so they are bypassed.

Question 14

Where does oxygenation and removal of CO2 occur in foetal circulation?

Answer 14

At the placenta.

Question 15

Explain foetal circulation with their shunts.

Answer 15

Oxygen-depleted blood goes from the body into placenta.

Here it is exchanged for oxygenated blood. The blood will now flow towards the liver but bypass the liver via ductus venosus so the liver doesn’t take up all the oxygen.

The blood enter the IVC via ductus venosus and flows into right atrium. We know have oxygenated blood in the right atrium. Most blood will no bypass the lungs by flowing directly into the left atrium via foramen ovale.

However some blood will go to right ventricle because if it doesn’t the right ventricle will atrophy and become underdeveloped. Blood will now flow from right ventricle and into pulmonary trunk. Well in the pulmonary trunk the blood from the RV will flow into the aorta via ductus arteriosus.

The blood which went via foramen ovale to left atrium will go to left ventricle and end up in the aorta as well.

All blood is now in the same place and can go out and be distributed in the body.

Question 16

So why are not these shunts which are present in foetal circulation found in mature circulation?

Answer 16

Because they close/contract once the baby takes its first breath.

Question 17

Explain how foramen ovale closes.

Answer 17

The increase in left atrial pressure once first breath has been taken by the baby causes the shunt to close. It will eventually grow to close.

Question 18

Explain how ductus arteriosus closes.

Answer 18

The ductus arteriosus contracts due to an increase in oxygen pressure after birth.

Question 19

Label

Answer 19

Question 20

Explain the importance and outcome of the aortic arches.

Answer 20

Early arterial system begins as a bilaterally symmetrical system of arched vessels. It will undergo extensive remodelling to create the major arteries leaving the heart.

Question 21

Two of the arches are of extreme important in the development of the major arteries.

Which?

Answer 21

4th arch and 6th arch.

Question 22

What does the 4th arch form?

Answer 22

The right part forms the proximal part of the right subclavian artery.

The left part forms the arch of the aorta.

Question 23

What does the 6th arch form?

Answer 23

It is also called the pulmonary arch.

Right part forms the right pulmonary artery.

Left part forms the left pulmonary artery and ductus arteriosus.

Question 25

Explain nerves associated with aortic arch formation.

Answer 25

As the heart descends, the nerves hook onto two arches.

One hooks around the 4th aortic arch (right)

The left recurrent laryngeal nerve hooks around ductus arteriosus and gets stuck there from the 6th left aortic arch. This is between the PT and aorta.

Question 26

What is PDA? (Patent ductus arteriosus)

Answer 26

A persistent communication between the descending aorta and the pulmonary artery. This means that ductus arteriosus never closed/contracted.

Question 27

In PDA, which direction will the blood flow through the shunt?

Answer 27

From left to right i.e. aorta to pulmonary artery.