Embryology of the heart

Question 1

What is Gastrulation?

Answer 1

• Mass movement and invagination of the blastula to form three layers (ectoderm, mesoderm and endoderm)

Question 2

What structures form from the ectoderm?

Answer 2

(Outside layer)
- Skin
- Nervous system
- Neural crest (contributes to cardiac outflow, coronary arteries)

Question 3

What structures form from the mesoderm?

Answer 3

(middle layer)
- All muscle types
- Most systems
- Kidneys
- Blood bone

Question 4

What structures form from the endoderm?

Answer 4

• Gastrointestinal tract (inc… liver, pancreas, but not smooth muscle)
• Endocrine organs

Question 5

Where is most of the cardiovascular system derived from?

Answer 5

Were situated in the mesoderm (blood, heart, smooth muscle, endothelium)
- Some contribution from the cardiac neural crest cells from the ectoderm

Question 6

How does the heart calcify?

Answer 6

• Femoral arteries can calcify
• Smooth muscle can become bones
• calcium deposits in heart, becoming a common cause of death due to ageing population

Question 7

What happens on Day 15?

Answer 7

This is when the first heart field (oldest, left ventricle)
and the second heart field (right ventricle, outflow tract, atria) begin to develop

Question 8

What develops in Day 21?

Answer 8

The first heart field generates a scaffold which is added to by the second heart field and cardiac neural crest
- Single loop begins to develop

Question 9

What develops on Day 28?

Answer 9

The heart structure becomes more looped giving the 4 quadrant layout

Question 10

When is the heart a standard fully developed heart?

Answer 10

Day 50

Question 11

What is a transcription factor?

Answer 11

Type of protein which when expressed “turns on/off” many other gene(s) expression: master regulators of complex processes
E.g. Nkx2.5 and GATA and Hand

Question 12

How are transcription factors used in embryology?

Answer 12

Different transcription factors are turned on or off during development, to orchestrate how the process develops

Question 13

How does evolution help gene development?

Answer 13

• As organisms evolve, gene duplication occurs sporadically (from single gene to entire genome)
• Each copy of each gene can then evolve separately into different (but related) gene
• This accounts for increasing complexity of development

Question 14

What are the three stages of cardiac formation?

Answer 14

• Formation of the primitive heart tube
• Cardiac looping
• Cardiac septation

Question 15

How does the primitive tube form?

Answer 15

• During the third week, the heart is formed from cells that form a horseshoe shaped region called the cardiogenic region
• By Day 19, 2 endocardial tubes form, which will fuse to form a single, primitive heart tube during lateral folding

Question 16

What does the Bulbis Cordis of the primitive tube develop into?

Answer 16

• Forms most of the right ventricle and parts of the outflow tract for the aorta and pulmonary trunk

Question 17

What does the primitive ventricle form?

Answer 17

Forms most of the left ventricle

Question 18

What do the right and left horns form?

Answer 18

• Called Sinus Venosus
• Forms the superior vena cava and part of the right atrium

Question 19

What does the primitive atrium form?

Answer 19

Forms the anterior parts of the right and left atria

Question 20

What does the Aortic sac form?

Answer 20

aortic arches

Question 21

What does the Truncus arteriosus form?

Answer 21

aortic arches and arteries

Question 22

How does cardiac looping take place?

Answer 22

• Bulbis cordis moves inferiorly, anteriorly and to the embryos right
• Primitive ventricle moves to left side
• Primitive atrium and sinus venosus move superiorly, posteriorly

Question 23

How can structures know which way is left?

Answer 23

• All vertebrate hearts have a leftward ventricle
• During development, the node secretes nodal (protein), which circulates to the left due to ciliary movement
• Nodal binds to cell, turns on left transcriptase factors (e.g. lefty)
• Many mutations are associated with improper left-right positioning (e.g. Kartagener’s syndrome)

Question 24

How does cardiac septation take place?

Answer 24

• At this stage there is one common atrium and one common ventricle and they are connected by an internal opening called the atrioventricular canal
• Blood enters the atrium, passes through atrioventricular canal and into ventricle then exits through truncus arteriosus
• Then endocardial cushions grows from the AV canal down and septates the right and left side