The Development Of The CVS

Question 1

What does cephalocaudal folding achieve?

Answer 1

Brings the heart tube into the thoracic region

Question 2

Where do the progenitor heart cells lie?

Answer 2

In the epiblast, immediately adjacent to the cranial end of the primitive streak

Question 3

Where do the progenitor heart cells migrate to when they have gone through the the streak?

Answer 3

Into the splanchnic layer of the lateral plate mesoderm, where some form a horseshoe shape cluster of cells called the primary heart field (PHF)

Question 4

Where is the PHF in relation to the neural folds?

Answer 4

Cranial to it

Question 5

What do the cells of the PHF form?

Answer 5

The atria, the left ventricles and part of the right ventricle

Question 6

Where do the secondary heart field cells reside?

Answer 6

In the splanchnic mesoderm ventral to the pharynx

Question 7

What do the cells of the SHF form?

Answer 7

The other part of the right ventricle, and the outflow tract (conus cordis and truncus arteriole)

Question 8

Initially, where is the central portion of the cardiogenic area?

Answer 8

Anterior to the oropharyngeal membrane and neural plate

Question 9

As the embryo grows and bends cephalocaudally, it also folds laterally. What happens to the caudal regions of the paired cardiac tube?

Answer 9

The causal regions of the paired cardiac tube merge except at their caudal most end.
At the same time, the central part of the horseshoe shaped tube expands to form the future outflow tract and ventricular regions.

The heart is now a continuous expanded tube

Question 10

Where does the cardiac tube receive blood from?

Answer 10

It receives venous drainage from its caudal pole and begins to pump blood out of the first aortic arch at its cranial pole.

Question 11

What is holding the heart tube in the pericardial cavity in place in chest at first?

Answer 11

A fold of mesodermal tissue, the dorsal mesocardium. Which eventually disappears further into development creating the transverse pericardial sinus.

Question 12

What does continued elongation result in?

Answer 12

At day 23 elongation causes the tube to bend

Question 13

What congenital outflow defects can occur if lengthening of the heart tube does not occur properly?

Answer 13

DORV, VSDs, tetralogy of fallot, pulmonary atresia, and pulmonary stenosis

Question 14

Explain the way cephalic and caudal part of the tube bends:

Answer 14

The cephalic part of the tube bends ventrally, caudally and to the right.

The caudal part bends dorsocranially, and to the left

This bending creates the cardiac loop.

Question 15

What day does cardiac looping complete on?

Answer 15

Day 28

Question 16

When looping occurs are the outflow tracts anterior or posterior to the inflow tracts?

Answer 16

Anterior

Question 17

What does looping achieve?

Answer 17

• Puts the primordium of the right ventricle closest to the outflow tract
• Puts the primordium of the left ventricle closest to the inflow tract
• Puts atrium dorsal to bulbus cordis e.g inflow dorsal to outflow

Question 18

After looping, how does the atrium connect with the ventricle?

Answer 18

Via the atrioventricular canal

Question 19

What does lateral folding achieve?

Answer 19

Creates the heart tube

Question 20

How does the sinuous venous us develop?

Answer 20

Initially the right and left sinus horns are equal in size, venous return then shifts to the right hand side and the left sinus horn recedes.

The right sinus horn then is absorbed by the enlarging right atrium.

Question 21

How does the right atria develop?

Answer 21

Forms from most of the primitive atrium, the sinus venosus goes into it, and it receives venous drainage from the body, the venae cava and the heart, the coronary sinus.

Question 22

How does the left atrium develop?

Answer 22

From a small part of the primitive atrium, absorbs proximal parts of the pulmonary veins and receives oxygenated blood from the lungs.

Question 23

How is the oblique pericardial sinus formed?

Answer 23

As the left atrium expands absorbing the pulmonary veins

Question 24

Where are the the 3 areas where a septum needs to be created?

Answer 24

An interatrial septa
An interventricular septum
Septation of the ventricular outflow tract between the aorta and the pulmonary trunk

Question 25

How does septation begin?

Answer 25

Tissue from the walls of the endocardium begin to grow from either side, these are known as endocardial cushions.
They protrude into the atria-ventricular canal, fuse and divide the tube into the left and right channels.

Question 26

Describe the process of atrial septation:

Answer 26

• A sickled shaped crest grows from the roof of the common atrium into the lumen, this crest is the first part of the septum primum.
• the two limbs of this septum extend towards the endocardial cushions in the atrioventricular canal. Blood can still move between left and right at this point.
• the Ostium primum is a hole present before the septum primum fuses with the cushions
• before the Ostium primum closes, perforations in the septum primum appear by programmed cell death, making a second hole.

-a second crest shaped septum appears, the septum secondum. A hole in this forms the foreman ovale.

Question 27

Where is the foramen ovale? And what direction does the blood flow through it?

Answer 27

A hole in the septum secondum, between the right and left atria. Blood flows from right to left.

Question 28

What does the left atrium sprout?

Answer 28

The pulmonary vein, and then it grows to absorb the first 4 branches.

Question 29

What is the fossa ovalis? What was it in fetal life?

Answer 29

It is where the oval foramen has been sealed off after birth, due to the increase in pressure of the left atrium when lung circulation begins. Allows the complete separation of the left and right atria.

Question 30

What are the two components of the ventricular septum?

Answer 30

• The muscular part

- The membranous part

Question 31

Describe the formation of the ventricular septum:

Answer 31

Muscular portions forms most of the septum and grows upwards towards the fused endocardial cushions.

It leaves a small gap, which is the primary interventricular foramen.

Later in development, complete closure of the interventricular foramen is completed by the membranous tissue derived from the endocardial cushions.

Question 32

Briefly describe the formation of the septum of the outflow tract (the conotruncal septum):

Answer 32

Endocardial cushions appear in the truncus arteriosus. As they grow towards each other they spiral around. This forms a spiral septum.

Question 33

Describe fetal circulation before birth including which shunts are used:

Answer 33

• Oxygenated blood enters the umbilical vein in the placenta and goes through the ductus venousus to the IVC
• The blood then enters the right atrium, where then most of it goes through the foramen ovalis into the left atrium.
• However, some blood from the right atrium goes into the right ventricle and through the pulmonary trunk to the aorta via the ductus arterios, as it doesn’t need to go to the lungs yet.
• The blood which goes through the foramen ovalis then goes into the left atrium, then left ventricle to the aorta where it is pumped around the body.

Question 34

What changes occur after birth to the circulation?

Answer 34

After birth respiration begins. The increase in pressure in the left atria closes the foramen ovale due to the septum primum pushing against the septum secondum.
- The ductus arteriosus contracts due to the increase in oxygen saturation, fibrosis then occurs in the DA which closes it permanently. - The DV also then closes.

Question 35

What is the fate of the foramen ovale after birth?

Answer 35

Becomes the fossa ovalis

Question 36

What is the fate of the ductus arteriosus after birth?

Answer 36

Becomes the ligamentum arteriosum

Question 37

What is the fate of the ductus venousus?

Answer 37

Becomes the ligamentum venosum

Question 38

What is the fate of the umbilical vein after birth?

Answer 38

Becomes the ligamentum teres (hepatis)

Question 39

What is the right atrium formed from?

Answer 39

The sinus venosus, by the right sinus horn being absorbed by the right atrium. The crista terminalis forms the dividing line between the original trabeculated part of the right atrium and the smooth walled part (sinus venarum), which originates from the right sinus horn.

Question 40

What does the bulboventricular sulcus become?

Answer 40

The primary interventricular foramen

Question 41

The proximal one third of the bulbus cordis becomes what?

Answer 41

Trabeculated part of the right ventricle

Question 42

The conus cordis of the heart tube becomes what in the developed heart?

Answer 42

The outflow tract of the right and left ventricles

Question 43

What are the roots and proximal aorta and the pulmonary trunk derived from in the heart tube?

Answer 43

The truncus arteriosus