Development of the Heart and Great Arteries Flashcards
Learning outcomes
- Describe the normal development of the chambers and valves of the heart
- Describe the formation of the foramen ovale and the changes that occur at the time of birth that lead to the formation of the fossa ovalis
- Discuss how the complex development of the heart can lead to congenital abnormalities
- Describe what is meant by patent ductus arteriosus
- Describe what is meant by patent foramen ovale
- Describe the complex organisation of the aortic arches and how it relates to the position of the recurrent laryngeal nerves
- Discuss major congenital defects in the heart (ASD, Patent FO, VSD,) and major vessels (Tetralogy of Fallot, Transposition of the great vessels, Patent ductus arteriosus Coarctation of aorta)
What are the 7 main stages in the embryonic development of the heart?
When do these stages occur?
1) Formation of the heart (endocardial) tube
2) Folding and looping of the heart tube
3) Partitioning of the common AV canal
4) Formation of papillary muscles, chorda tendinea and AV valves
5) Formation of the interventricular septum
6) Formation of the interatrial septum
7) Spiral partitioning of the conus cordis and truncus arteriosus
- These stages occur concurrently (at the same time), not one after the other
How can early embryonic development be sustained?
When does the bilaminar disc become trilaminar?
What process is this?
What are the 3 layers?
How long is the embryo at this point?
- Early embryonic development can be sustained by diffusion of nutrients
- The bilaminar disc becomes trilaminar (gastrulation) in the early stages of development (only 2 weeks post conception)
- The 3 layers are ectoderm, endoderm, and mesoderm, which are formed during the 3rd week
- The embryo is 1.5mm long at this point
What becomes insufficient in the embryo?
What system if the first to develop?
- As the embryo grows diffusion is no longer sufficient to provide nutrients and development of both blood and vascular structures becomes necessary
- The vascular system is the first system to develop in the embryo
When does the heart begin to develop?
What are the 5 steps in the first stages of the development of the endocardial tube?
- Heart development starts at about day 18
- First stage of endocardial tube development (day 18):
1) Lateral plate mesoderm divides into visceral and parietal layers
2) in the visceral layer, there are clusters of angiogenic cells which can develop into organs and vessels
3) These clusters can join together to form blood islands
4) These blood islands can develop into vessels
5) Around the anterior and lateral portions of the neural plate, blood islands join together to form a horseshoe shape
what happens around day 17?
how are blood islands formed?
- splanchnic lateral plate mesoderm produces angiogenic cells
- they take the form of heamangioblasts
- they undergo vascularisation to make a cluster of cells called blood islands?
what are the causes of heart defects?
- genetic
- teratogenic
what cells will cause heart and facial defects?
neural crest cells (cardiac malformations)
What 7 steps occurs during the 2nd stage of endocardial tube development?
- 2nd stage of endocardial tube development:
1) Blood islands join and form the left and right endocardial tubes
2) There are also right and left dorsal aorta
3) Part of the mesoderm differentiates into myocardial cells
4) At around day 20, the visceral layers of the lateral plate mesoderm start to approach each other during lateral folding
5) When these layers approach each other, so do the endocardial tubes, which end up side by side
6) Cephalo-caudal folding also occurs simultaneously to lateral folding, and causes the heart tube to effectively migrate from the head end of the embryo, through the neck and in to the thorax
7) Cephalocaudal and lateral foldings fuse at the midline, enclose body walls, and form body cavities
what forms on day 20?
two sides of the horse shoe fuse to form single heart tube
- ventral to gut tube
- separated from somatic lateral plate mesoderm by pericardial cavity.
What 2 steps occurs during the 3rd stage of endocardial tube development?
- 2 steps occur during the 3rd stage of endocardial tube development (21 days):
1) Once the folds of the embryo fuse along the ventral midline, the space between the visceral and parietal lateral plate mesoderm is now enclosed, this space is called the intra-embryonic coelom
* The intraembryonic coelom will become the pericardium/pericardial cavity in week 5
2) There is a layer of myocardium deep to the visceral layer of lateral plate mesoderm
in what direction does the heart move during development?
- heart moves inferiorly from superior to oropharyngeal membrane into future thorax.
What 3 steps occurs during the 4th stage of endocardial tube development?
- 2 steps occur during the 4th stage of endocardial tube development?
1) The 2 endocardial tubes, cardiac jelly, and the surrounding myocardium come together in the thoracic region to form the common endocardial tube in the midline
2) Around day 22, the myocardial cells start to generate electrical impulses and beat
on day 22, what happens in the primary heart tube?
- myocardial cells infiltrate cardiac jelly
- begin contraction and electrical activity
what is cardiac jelly?
extracellular matrix of loose connective tissue surrounded by myocytes
input veins into the developing heart?
- cardinal veins
- umbilical veins
- vitaline veins
(all branches of the sinus venosus)
what does the right and left ventricle develop from?
right = bulbs chordis (proximal part)
left = primitive ventricle
where will you find the bulboventricular flange?
in the ridge between primitive ventricle and bulbous chordis
- this starts to form a septum between the right and left ventricle
Describe the 7 steps of the changes in the endothelial tubes and dorsal aorta during development
- The changes in the endothelial tubes and dorsal aorta during development:
1) Diagram A – Angiogenic cells cluster and form blood islands
2) Diagram B – Blood islands join to form horseshoe shaped left and right endocardial tubes. The dorsal aorta is also formed from blood islands
3) Diagram C – During cephalo-caudal folding, the horseshoe is brough ventrally and the dorsal aorta approached the endothelial tubes
4) Diagram E – The dorsal aorta meets the endothelial tubes
5) Diagram F – The endothelial tubes join onto vitelline veins
6) Diagram G – when folding is done, the left and right endothelial tubes fuse to from the common endothelial tube (primary endocardial tube), and the left and right dorsal aorta fuse to form the common dorsal aorta
7) Diagram H – Common endothelial tube, Common dorsal aorta, and veins have joined together, and will eventually form the heart
What 2 ends does the common endocardial tube have?
- The common endocardial tube has a venous (inflow) and arterial (outflow) end
What do different parts of the endothelial tube experience?
Where does the endothelial tube initially stretch and grow?
When does the endothelial tube start to fold?
When does this process finish?
- Different parts of the endothelial tub experience different rates of growth
- Some will experience constriction/expansion
- The endothelial tube initially stretches
outwards as it grows it stretches anteriorly - On day 23, the endothelial tube begins to fold, and finishes folding on day 28
Describe the 3 parts of structure of the heart tube post folding.
How do these structures start to remodel?
What new structures do they start to form?
- Post-folding, the heart tube consists of:
1) Common AV canal – lumen of the heart
2) Dense mesenchymal tissue/Extracellular matrix surrounding AV canal called cardiac jelly (cardiac jelly will eventually undergo transformation and become myocardium)
3) Myocardium derived from mesoderm surrounding the cardiac jelly
* Remodelling of the ventricle myocardial walls leads to the formation of ventricular pockets where cardiac jelly has been scooped out
- New structures that appear:
1) Primordial atrium to primordial ventricle valve
2) Papillary muscle with chorda tendinea
3) Bulboventricular flange changes into interventricular septum
When is the AV canal partitioned?
Describe the steps in the partitioning of the AV canal
- The AV canal is partitioned from weeks 5-8
- Steps in the partitioning of the AV canal:
1) On the anterior and posterior wall of the heart tube, the dorsal and ventral endocardial cushions begin to form
* Endocardial cushions are cardiac neural crest cells
* They migrate from the neural crest and form endocardial cushions
2) Lateral endocardial cushions appear and go towards each other
3) When the ventral and dorsal endocardial cushions meet, they separate the AV canal into right and left AV canal / right and left AV orifices
* These will eventually be closed by AV valves
Describe the 4 steps in the separation of the Primordial ventricle and the Bulbus Cordis
- 4 Steps in the separation of the Primordial ventricle and the Bulbus Cordis:
1) While the AV canal is formed, the Interventricular septum grows towards the endocardial cushion between the right and left AV canals, but doesn’t get their yet
2) The gap between the top of the muscular IV septum and the endocardial cushion will be filled by an extension from the endocardial cushion later
3) This will separate the bulbus cordis from the primordial ventricle
4) The primordial ventricle will become the left ventricle and the proximal part of the Bulbus Cordis will become the right ventricle
Describe the 6 steps in the division the primordial atrium.
What forms the auricles of the heart?
What forms the atria of the heart?
What forms the SVC and IVC?
- 6 Steps in the division the primordial atrium:
1) The septum primum starts to grow inferiorly towards the endocardial cushion, but it doesn’t reach, leaving a gap called the ostium primum
* Blood is coming to the atria through the sinus venosus (left and right horn of sinus venosus) and the pulmonary vein, so this interatrial septum can’t close
* If the IA develops completely, the foetus cant live
2) Before the septum primum can completely build the IA septum, a second deficit appears high on the septum primum called the ostium secundum
3) The septum primum then grows towards and joints the endocardial cushion
4) A new septum then grows down from the roof on the right side of the septum primum called the septum secundum
* On the septum secundum, there is also a deficit called the foramen ovale
* The foraman ovale and the ostium secundum allows blood to pass from the right atrium to the left atrium
5) Once the IA septum is complete, the primordial atrium is divided into the right and left atrium
6) The sinus venosus is sucked into the right primordial atrium
* This results in the right primordial atrium receiving blood from the sinus venosus and the left primordial atrium receiving blood from the pulmonary veins (small amount)
* The primordial atria will form the auricles of the heart
* The smooth part of the atria develops from either the sinus venosus on the right and the pulmonary veins on the left
* This is the reason we have a trabeculated auricle (muscular ridges) and smooth surface atria
* The SVC is a derivative of cardinal veins, and the superior part of the IVC is a derivative of the right vitelline vein
What are the 3 parts of the Bulbus cordis?
- The Bulbus Cordis Has 3 parts:
1) Truncus arteriosus – distal outflow tract of the aorta, which becomes the pulmonary trunk and ascending aorta
2) Conus Cordis – middle part which is the proximal outflow tract of the aorta will form the outflow tract of the aorta and pulmonary trunk
3) The proximal part forms the trabeculated portion of the right ventricle - Since the CC and TA become different vessels, they have to be separated
- For this process, think of the conus cordis and truncus arteriosus like a chimney on the walls of the RV and LV
When do aortic arches form?
Describe the 3 steps in the first stage of development of the heart’s aortic branches
- Aortic arches form between day 26-29
- The steps in the first stage of development of the heart’s aortic branches:
1) From the aortic sac, 2 arches originate, named the 1st right and left aortic arch (1aa – 1st aortic arch)
* They meet and continue with the left and right dorsal aorta, which join and form the common dorsal aorta
2) As the embryo grows, the 1st aa move upwards, and the 2aas form from, which also join the dorsal aorta
* These will pinch the gut tube when developing, causing the formation of pharyngeal pouches/arches
3) Mechanical branches called intersegmental arteries from the left, right, and common dorsal aorta will spear in segmented fashion to supply surrounding tissues
Describe the 2 steps in the second stage of development of the heart’s aortic branches
- The 2 steps in the second stage of development of the heart’s aortic branches:
1) At some point, the 1aas and 2aas start to degenerate and disappear while the 3aas and 4aas start to form
2) An anastomosic vessel which goes towards the heart starts to spear among the first 7 intersegmental arteries
Describe 4 the steps in the third stage of development of the heart’s aortic branches
- The steps in the third stage of development of the heart’s aortic branches:
1) 1aas and 2aas have completely disappeared
2) The 6th aa appear and join to the dorsal aorta, but no 5aa in humans
3) The dorsal aorta between the 3rd and 4th aas starts to degenerate, but the 4th aa is still connect to the dorsal aorta
4) The anastomosic artery between the intersegmental arteries continues to grow towards the base of the skull, while the 7th intersegmental artery goes outwards to supplies the limbs
Describe the steps 7 in the fourth stage of development of the heart’s aortic branches
- The steps in the fourth stage of development of the heart’s aortic branches:
1) 3aa will form the common carotid arteries
2) 6 aa (still connected to dorsal aorta) sends a branch to the developing lung buds
* These branches become the pulmonary arteries
3) The first 6 intersegmental arteries start to degenerate
4) The 7th intersegmental artery becomes the subclavian artery
5) Branches of the subclavian go to the skull (vertebral artery)
* The left and right vertebral arteries join to form the basilar arteries
6) The right dorsal aorta starts to degenerate and loses connection with common dorsal aorta
7) Around this time, the heart starts to partition the great vessels – aorta and pulmonary trunk start to spear
Aortic arch development diagram
Aortic arch development diagram
End product of aortic arch development
End product of aortic arch development
What are these embryo structures in adults?
What are these embryo structures in adults?
What do these structures form on the right and left?
What do these structures form on the right and left?
Describe these conditions and their causes
Describe these conditions and their causes
