Development of the heart

Question 1

Describe day 17 of development

Answer 1

• Blood islands appear between the visceral plate mesoderm and the endoderm

Question 2

Describe what happens next

Answer 2

• Blood islands coalesce and give rise to the right and left endocardial tubes and aorta
• Part of the mesoderm differentiates into cardiomyocytes

Question 3

What happens on day 20 of development?

Answer 3

• Layers of visceral plate mesoderm approach each other

Question 4

After day 20

Answer 4

• Folds of the embryo fuse in the midline
• The space between the visceral and somatic mesoderm becomes the intraembryonic coelon which then becomes the pericardial cavity
• The two layers of lateral plate mesoderm become the pericardium

Question 5

What is the heart tube formed form?

Answer 5

• Right and left endocardial tubes which were formed by the blood islands in between the visceral plate mesoderm and the endoderm

Question 6

What is the pericardium formed from?

Answer 6

The two layers of lateral plate mesoderm

Question 7

What is the pericardial cavity formed from?

Answer 7

The space between the visceral and somatic mesoderm which becomes the intraembryonic coelon

Question 8

Describe the parts of the heart tube from cranial to caudal

Answer 8

• 1st aortic arch 
• Aortic sac
• bulbus cordis 
- Conus cordis and truncus arteriosus 
• primordial ventricle 
• primordial atrium 
• sinus venosus 
- vitelline veins 
- Umbilical veins 
- Cardinal veins

Question 9

Describe day 23

Answer 9

• heart looping starts
• The primordial ventricle and bulbus cordis bulges anteriorly and into the intaembryonic coelon which will become the pericardial cavity
• The primordial atrium and sinus venosus moves dorsally and cranially
• Primordial atrium moves behind the primordial ventricle
• SV moves behind and to the right of the primordial atrium

Question 10

What day does the heart start to beat?

Answer 10

Day 22

Question 11

On what day is looping complete?

Answer 11

Day 28

Question 12

What is the myocardium derived from?

Answer 12

Mass of splanchnic mesoderm

Question 13

What does the myocardium produce?

Answer 13

Cardiac jelly which surrounds the common AV canal

Question 14

Describe the ventricular remodelling

Answer 14

• Erosion and remodelling of the ventricular myocardial wall leads to the formation of ventricular out pockets
• Valves, papillary muscles and chorda tendinae are carved out of the cardiac jelly
• At this stage the IV septum starts to form

Question 15

Describe the partitioning of the common AV canal

Answer 15

• Ventral and dorsal endocardial cushions start to form and grow and approach each other
• Lateral endocardial cushions start to appear and grow
• The ventral and lateral endocardial cushions meet and separate the common AV canal into the right and left AV canals which become AV orifices closed by tricuspid and mitral valves

Question 16

What does the muscular part of the IV septum form from?

Answer 16

It is formed from the bulbus cordis and the primordial ventricle
• it grows toward the endocardial cushion between the right and left AV canals but it doesn’t get there