Embryology of the heart Flashcards
What is Gastrulation?
- Mass movement and invagination of the blastula to form three layers (ectoderm, mesoderm and endoderm)
What structures form from the ectoderm?
(Outside layer)
- Skin
- Nervous system
- Neural crest (contributes to cardiac outflow, coronary arteries)
What structures form from the mesoderm?
(middle layer)
- All muscle types
- Most systems
- Kidneys
- Blood bone
What structures form from the endoderm?
- Gastrointestinal tract (inc… liver, pancreas, but not smooth muscle)
- Endocrine organs
Where is most of the cardiovascular system derived from?
Were situated in the mesoderm (blood, heart, smooth muscle, endothelium)
- Some contribution from the cardiac neural crest cells from the ectoderm
How does the heart calcify?
- Femoral arteries can calcify
- Smooth muscle can become bones
- calcium deposits in heart, becoming a common cause of death due to ageing population
What happens on Day 15?
This is when the first heart field (oldest, left ventricle)
and the second heart field (right ventricle, outflow tract, atria) begin to develop
What develops in Day 21?
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
What develops on Day 28?
The heart structure becomes more looped giving the 4 quadrant layout
When is the heart a standard fully developed heart?
Day 50
What is a transcription factor?
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
How are transcription factors used in embryology?
Different transcription factors are turned on or off during development, to orchestrate how the process develops
How does evolution help gene development?
- 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
What are the three stages of cardiac formation?
- Formation of the primitive heart tube
- Cardiac looping
- Cardiac septation
How does the primitive tube form?
- 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
What does the Bulbis Cordis of the primitive tube develop into?
- Forms most of the right ventricle and parts of the outflow tract for the aorta and pulmonary trunk
What does the primitive ventricle form?
Forms most of the left ventricle
What do the right and left horns form?
- Called Sinus Venosus
- Forms the superior vena cava and part of the right atrium
What does the primitive atrium form?
Forms the anterior parts of the right and left atria
What does the Aortic sac form?
aortic arches
What does the Truncus arteriosus form?
aortic arches and arteries
How does cardiac looping take place?
- Bulbis cordis moves inferiorly, anteriorly and to the embryos right
- Primitive ventricle moves to left side
- Primitive atrium and sinus venosus move superiorly, posteriorly
How can structures know which way is left?
- 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)
How does cardiac septation take place?
- 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
