Cardiac Flashcards
What layer does Cardiovascular system develop from?
Mesoderm
What forms in yolk sac mesoderm, what do these structures contribute to?
Cardiac myoblasts and blood islands - form RBC and network of vessels
In what week does heart development begin?
Week 3
How is cardiac crescent formed?
Progenitor cells from epiblasts migrate through prim streak forming mesoderm
Migrate to left and right sides of embryonic discs joining up to form cardiac crescent
Signals from endoderm (e.g. BMP2) cause formation of cardiac mesoderm
Cardiac crescent divided into?
First and second heart field
What do 1st and 2nd heart field give rise to?
1st: give rise to left ventricle and atria
2nd: right ventricle, atria and outflow tract
When do progenitor heart cells from epiblast migrate through prim stream, what does it form?
Day 16
Mesoderm
How does an endocardial tube form?
Angiogenic clusters coalesce
Where do endocardial tubes develop relative to gastrulating embryo?
Rostrally in the cardiogenic crescent region
What type of mesoderm do paired endocardial tubes come from?
Splachnic mesoderm
When do endocardial tubes fuse?
Day 22
What direction do endocardial tubes fuse in
Cephalo-caudal direction
What sort of folding allows endocardial tubes to fuse
Rostral and lateral
When does contractile activity of heart begin
Before fusion of tubes, day 18
How are epicardium and myocardium formed
Mesodermal cells condense around inner endocardium of heart tube forming myocardium and surrounding epicardium
What do the two endocardial tubes do by day 22?
Fuse in the midline to form primitive heart tube
What secretes cardiac jelly?
Myocardium
What does cardiac jelly do?
Fills spaces between myocardium and endocardium
Which layer of heart is responsible for forming coronary arteries, including their endothelial layer?
Epicardium
Where is cardiac jelly prominent?
AV canal
Outflow tract
Which type of mesoderm is heart mostly derived from?
Splanchnic mesoderm
What does BMP do?
Induces mesoderm to become cardiogenic
What does heart tube consist of?
Primitive inflow tract (sinus venosus, 2 venous horns)
2 Prim Atrium
1 Prim Ventricle
Bulbus cordis
Truncus arteriosus
Which 3 pairs of veins drain blood to heart via sinus venosus?
Common cardinal
Vitelline veins
Umbilical veins
Initially heart tube is symmetrical but then…
Sinus venosus programmed to drain blood preferentially to right of heart so eventually all systemic venous blood drains to right side via SVC and IVC
What does each aortic arch artery link?
Link truncus arteriosus and dorsal aortae
What is the most distal part of the truncus arteriosus?
Aortic sac
What is the truncus arteriosus what does it form?
Distal part of the bulbus cordis, forms roots and proximal portion of aorta and pulmonary artery
What is the aortic sac?
Superior to truncus arteriosus- primordial vascular channel from which the aortic arches arise
What does the conus cordis form from?
Midportion of bulbus cordis
What does conus cordis form?
Outflow tracts of both ventricles
How does heart begin to devleop in thorax through change in position?
Cranial folding at rostral end sweeps cardiogenic region ventrally under developing heart
Describe blood flow through developing heart tube
Sinus venosus, atrium, ventricles, bulbus cordis, truncus arteriosus, aortic arch , dorsal aorta
When does looping of heart tube occur?
4.5 weeks
Is folding intrinsic to heart tubes?
Yes
Why is looping of heart tube important?
4 chambers of heart brought into correct spatial relationship
What is the first morphological sign of left/right asymmetry in embryo?
Looping of heart tube (4.5 weeks)
How are ventricle and outflow tract septation interlinked?
Both depend on haemodynamic forces as two spiralling bloodstreams act on cardiac jelly rich wall of outflow tract
What happens to ventricles in looping of heart tube?
Shift inferiorly and left
What happens to atria in looping?
Move behind the ventricles and come to lie superior to prim ventricle
What affects heart shape during septation?
Blood entering asymmetrical heart tube and creating differential haemodynamic forces acting on internal walls
What does breakdown of dorsal mesocardium allow?
Atria to move rostrally and heart to bend laterally to right (dextral looping) forming S shape tube with atria above ventricle and bulbus cordis
What does dorsal mesocardium do?
Suspends heart from dorsal body wall
What factors lead to looping of prim heart tube?
Haemodynamic forces, different rates of cell proliferation, asymmetrical tissue
During initial heart tube folding, describe the outflow tract
Common outflow tract for pulmonary and systemic circulation (no septation yet)
When does septation of heart take place?
Weeks 4-7
What are the different forms of septation of the heart?
AV canal
Common atrium into left and right
Ventricle into left and right
Division of outflow tract into pulmonary and systemic
Cardiac jelly is originally non cellular but…
Mesenchymal cells migrate into it
What is AV canal cardiac jelly populated by?
Endocardial cells
What is outflow tract cardiac jelly (concus corids-truncus arteriosus) populated by?
Neural crest cells (remodel region and form septa)
What are endocardial cushions formed from?
Cardiac jelly and endocardial cells that migrate into it
What are endocardial cushions important for?
Formation of heart septa
When do you get division of AV canal?
Early 5th week
What do endocardial cushions in truncus arteriosus derive from?
Neural crest cells
How does AV canal separate?
Fusion between inferior and superior cushions
What do endocardial cushions forming AV septum also contribute to?
Mitral valve and tricuspid
Where does spiral septum form?
Truncus arteriosus
What does spiral septum do?
Separates future pulmonary artery and aorta (by splitting truncus artiosus and conus region)
How do semi lunar valves form?
At distal tips of ventricles (3 endocardial swellings)
What may be the cause of septation defects?
Abnormal blood flow through AV canal or truncus artierosus
4 signs of Fallot’s tetralogy
Overriding aorta
Pulmonary stenosis
RV hypertrophy
IV septal defect
What causes Fallot’s tetralogy?
Bulbar ridges (part of spiral septum) fail to divide aortic and pulmonary channels equally and fail to unite with endocardial cushions so ventricular defect
Or
Pulmonary stenosis leading to ventricular defect
When does atrial septation occur?
End of 4th week/5th week - 7th week
When does septum primum form?
Day 28
How does atrial septation begin (septum primum)?
Common atrium divided by septum primum growing down from roof
Fuses with endocardial cushions below
Cells in septum apoptose forming foramen/osteum secundum hole
How is atrial septation completed? (foramen secundum)
Septum secundum grows to right of septum primum, but doesn’t fuse with AV septum
Gap remaining foramen ovale
Creates one way interarterial valve (foramen ovale)
Why is the foramen ovale a one way valve, which direction?
R - L
One way as septum secundum stiffer than septum primum, high pressure in LA pushes septa together
What is the osteum primum?
Foramen lies beneath the edge of septum primum and the endocardial cushions (before fusion)
What forces two interatrial septa together?
Decrease in pulmonary resistance when lungs inflate
Increase in return to LA, higher pressure in LA, pushes septa together
Formanen ovale is a gap left by?
Septum secundum
Why is foramen ovale important?
Shunt as no breathing in development so allows blood flow from RA - LA - LV - systemic circulation
When does ventricular septation occur?
5th - 7th week
What happens in ventricular septation?
Muscular IV septum forms from base of heart to endocardial cushinon, leaving small IV gap
How does small IV gap close?
Fusion between membranous IV septum with base of spiral septum
What is the spiral septum made of?
Conotruncal ridges fusing
Fusion of truncus swellings/cushions and conus/bulbus swellings (in conus cordis region)
What finally separates ventricles?
Muscular IV septum fusing with conotruncal ridges forming the membranous part of IV septum
When do ventricles finally separate?
End of week 7/8th week
What part of septum does ventricular septation failure often affect?
Membranous part
When do AV valves form?
5th - 8th week
How is a valve leaflet formed?
Ventricular layer hollowed out and thinned by apoptosis to form leaflet
What is bulbar ridge also known as?
Conus ridge
Where are bulbar ridges found?
Junction between conus and truncus arteriosus