S3 - Embryology 1

Question 1

What effect does folding have on the development of the heart?

Answer 1

Lateral folding = creates the heart tube

Cephalocaudal folding = brings tube into the thoracic region.

Question 2

Describe the structure of the primitive heart tube

Answer 2

A simple contractile linear tube that is suspended within the pericardial cavity, a confined. Blood flows in through the caudal pole and out through the cranial end (aortic roots). No valves or chambers.

Question 3

Describe the 6 segments of the primitive heart tube

Answer 3

From top to bottom:

Aortic roots
Truncus arteriosus
Bulbus cordis
Ventricle
Atrium
Sinus venosus

Question 4

Why does cardiac looping occur?

Answer 4

As the primitive heart tube elongates, it runs out of room in the set pericardial space. It then begins to twist and fold between the bulbis cardio and the primitive ventricle. This places the inflow and outflow in the correct orientation, with both at the cranial end. Inflow is dorsal to outflow.

Question 5

What are endocardial tubes?

Answer 5

A pair of tubes that develop in the cardio genie field in the 3rd week of development. They fuse during embryonic folding to form the primitive heart tube.

Question 6

What is the shape is the primitive heart tube?

Answer 6

Linear, inflow occurs at the caudal end and outflow occurs at the cranial pole.

Question 7

What is the first step in rearranging the primitive heart tube?

Answer 7

Looping, placing both inflow and outflow cranially. Inflow is dorsal to the outflow.

Question 8

What does the primitive atrium contribute to?

Answer 8

Contributes a small component to each atrium.

Question 9

What does the bulbis cordis contribute to?

Answer 9

Gives rise to the right ventricle

Question 10

What is the left ventricle derived from?

Answer 10

The primitive ventricle

Question 11

What does the truncus arteriosus give rise to?

Answer 11

The roots and proximal portions of the pulmonary trunk and aorta

Question 12

What process begins in the heart after looping?

Answer 12

The process of septation, dividing the heart into chambers and separating the pulmonary trunk and aorta.

Question 13

What is the atrioventricular canal?

Answer 13

A narrow chamber formed by contraction between the atria and ventricles.

Question 14

What are endocardial cushions

Answer 14

Formed in the region of the atrioventricular canal. Provide a platform towards which the septa grow. Also contribute to the spiral septum in the truncus arteriosus to divid the outflow.

Question 15

During looping, where does the heart fold?

Answer 15

Between the bulbis cordis and the primitive ventricle

Question 16

Where is the transverse pericardial sinus located?

Answer 16

Behind the aorta and pulmonary trunk and in front of the superior vena cava

Question 17

what is the sinus venosus? How does it develop?

Answer 17

Initially located at the bottom of the primitive heart tube. It contributes to the right atrium. Initially the right and left sinus horns are equal, but as the heart develops the venous return shifts to the right hand side and the left sinus horn recedes. The right sinus horn is then absorbed by the enlarging RA.

Question 18

What does the right atrium develop from?

Answer 18

Most of the primitive atrium, the sinus venousus

Question 19

How does the right atrium receive blood?

Answer 19

Receives drainage from the body and the heart

Question 20

What does the left atrium develop from?

Answer 20

Small portion from the primitive atrium, absorbs proximal parts of the pulmonary veins which forms the smooth walled part of the left atrium.

Question 21

What is the oblique sinus?

Answer 21

The oblique pericardial sinus is the

Question 22

Why are shunts required in the fetal heart?

Answer 22

As oxygenation and removal occur at the placenta, not the lungs. Shunts must be in place to bypass the lungs.

Question 23

What are the three shunts present in a fetal heart?

Answer 23

1. Foramen ovale
2. Ductus arteriosus
3. Ductus venosus

Question 24

Why does the fetal blood system bypass the liver?

Answer 24

As the liver in the first organ for the oxygenated blood to travel through and the oxygen demand of the liver is great. It would use up too much oxygen before the blood reached the rest of the body.

Question 25

What is the function of the foramen ovale?

Answer 25

This shunt allows blood to move from the right atrium to the left atrium, bypassing the right ventricle and lungs.

Question 26

What is the function of the ductus arteriosus?

Answer 26

The blood that is pumped into the right ventricle from the right atrium enters the pulmonary trunk and then travels through the ductus arteriosus to enter the aorta. This allows the blood to bypass the lungs.

Question 27

Some blood does not travel through the foramen ovale and instead travels into the right ventricle. Why is this?

Answer 27

This is important to allow proper development of the right ventricle. This blood then passes through the ductus arteriosus.

Question 28

What is the function of the ductus venosus?

Answer 28

The ductus venosus runs within the liver and allows blood to travel from the placenta to the inferior vena cava, bypassing the liver.

Question 29

Where does gas exchange occur in the fetal circulation?

Answer 29

In the placenta

Question 30

How does the foramen ovale close?

Answer 30

After birth the pressure increases in the LA and blood will flow from the left atrium to the right atrium, pushing the septum primium against the septum secundum. This blocks the foramen ovale and osteum secundum.