Development of the heart

Question 1

Outline the five steps involved in the development of the heart

Answer 1

1) Formation of the 4 chambered heart tube
2) Cardiac looping
3) Division of atrioventricular canal into left and right channels
4) Formation of the atrial septa
5) Formation of the conotruncal cushions and division of the outflow heart

Question 2

What is the morula?

Answer 2

Solid ball of cells formed as the zygote undergoes cleavage

Question 3

What is a blastocyst?

Answer 3

A hollow ball of cells with a fluid filled cavity

Question 4

What is a Gastrula?

Answer 4

An embryo with three primary germ layers(ectoderm, mesoderm and endoderm)

Question 5

What does the ring of blood island towards?

Answer 5

Ring of blood islands towards the head in a horse shoe shape

Question 6

What does the primitive streak define?

Answer 6

Primitive streak define the left and right of the embryo

Question 7

What will the notochord form?

Answer 7

Notochord will form part of the backbone

Question 8

What do the blood islands start to do and form what?

Answer 8

Blood islands start to fuse together and form two kinds of basic tubes

Question 9

What are these basic tubes called?

Answer 9

These are called the cardiogenic chords

Question 10

What do these cardiogenic chords do?

Answer 10

Cardiogenic chords fuse down the middle to make one single tube

Question 11

What is there at the end of these tubes and what do these ends do?

Answer 11

There’s a little bit of branching at the end of the tubes and these ends attach to the rudimentary blood supply that is starting to circulate around the embryo

Question 12

What happens after 18 days in terms of the formation of the heart tube?

Answer 12

-Heart develops from the primitive streak via the blood islands in the splanchnic mesoderm

Question 13

What happens after 20 days in terms of the formation of the heart tube?

Answer 13

Blood islands slowly form together into 2 tubes called cardiogenic cords

Question 14

What happens after 21 days in terms of the formation of the heart tube?

Answer 14

The tube fuse down the middle to make one heart tube

Question 15

What happens after 22 days in terms of the formation of the heart tube?

Answer 15

Further development gives rise to a tube with asymmetric openings forming an arterial and venous end

The beginning of asymmetry in the bulge to the left

Question 16

What is situs inversus?

Answer 16

Some people are a complete mirror image
Asymmetry is defined and location is defined by the primitive streak
They’re perfectly healthy

Question 17

What is the cardiac looping like after 22 days?

Answer 17

Cells at each end of the heart proliferate making the tube longer
Entire structure is in a confined space so begins to fold up on itself

Question 18

What is the cardiac looping after 23 and 24 days?

Answer 18

The primitive atrium loops up above and behind the primitive ventricle
Looping process brings the primitive areas of the heart into the proper spatial relationship for development

Question 19

What is dextrochardia and whats it caused by?

Answer 19

All the organs are in the normal place apart from the heart which is on the right side
Caused by chance

Question 20

What is the cardiac looping after 24 days?

Answer 20

Primitive atrium we see from the front when viewed from the side is growing out of the back and become two atria

Question 21

What is the cardiac looping after 35 days?

Answer 21

Heart is beating by this stage and the foetal heart can be seen on an ultrasound
However the four interior chambers are not yet divided

Question 22

How many years after does the atrioventricular canal divide?

Answer 22

30 days after

Question 23

What is the septum primum?

Answer 23

Grows along the midsagittal plane separating the atria except for a temporary space called the foramen primum

Question 24

What does the left side of the atrium grow during the division of the atrioventricular canal?

Answer 24

Left side of the atrium grows pulmonary veins sending growing veins to the developing lungs

Question 25

What fuse together to divide the atria from the ventricles?

Answer 25

The posterior and anterior endocardial cushions fuse, dividing atria from the ventricles

Question 26

What will the ventricular septum eventually do?

Answer 26

Ventricular septum will eventually grow upwards to form a division between the two ventricles
-It will attach to the divisions between atria and ventricles

Question 27

What is once cause of ventricular septal defect?

Answer 27

It is the failure of the endocardial cushions to provide an anchor point for the developing ventricular septum

Question 28

What happens during ventricular contraction in a ventricular septal defect?

Answer 28

During ventricular contraction, some of the blood from the LV leaks into the RV

Question 29

What are the 2 main effects in ventricular septal defect?

Answer 29

1) Systemic circulation doesn’t receive all the blood being pumped by the left ventricle
2) Leakage of blood into the right ventricle elevates right ventricular pressure and volume, causing pulmonary hypertension

Question 30

When is the atrial septa formed?

Answer 30

40 days