Cardiac Development and Malformations Flashcards
What are the tissue origins of embryonic heart tube?
-Comes from 2 sets of mesodermal cells
1- FHF (first heart field) visceral lateral mesoderm- originally these are a pair of tubes that undergo cranial folding –> below neural tube and foregut –> fuse into 1 tube
2- SHF (second heart field) also mesoderm- migrate later from pharynx
When is heartbeat first heard?
-Heart tube forms and starts beating at 3 wks (at this point it has unidirectional flow)
Fates of FHF, SHF, cardiac crest and proepicardial cells
FHF- L ventricle
SHF-outflow tract, sinus venosus, atria and R ventricle
Cardiac crest (from neural crest) - aorticopulmonary septum (OUTFLOW) and parasympathetic neurons
Proepicadial cells- epicardium, heart fibroblasts, coronary vessels
How is embryonic circulation remodeled?
- Starts symmetrical w/ paired veins and paired aortic arch/dorsal aorta
- Remodeling –> asymmetric (R horn enlarges and veins remodeled to become SVC and IVC) blood now just enters R atrium
What do the right and left sinus horns become?
R sinus horn- expands and becomes incorporated into wall of R atrium - SMOOTH MUSC SINUS VENARUM
L sinus horn - remains small and ultimately becomes CORONARY SINUS
What does the bulbus cordis become?
R ventricle + outflow regions
Truncus Arteriosus
Originally it is the cranial/top outflow portion of heart tube
Later become aorta and pulmonary trunk
Septation of AV Canal
Second Month
- Fusing of dorsal and ventral endocardial cushions to sep L and R AV canals
- Tricuspid and mitral valves endocardial tissue too
Septation of Primitive Atrium (4 components)
1- formation of septum primum (it grows down to close off foramen primum)
2- DMP (dorsal mesenchymal protrusion) protrudes into heart from dorsal mesocardium
3- septum primum and DMP both fuse w/ endocardial cushions –> wall b/n R and L atria
**Meanwhile foramen ovale forms
4- septum secundum forms flap that overlaps septum primum (AT BIRTH THEY FUSE TO CLOSE FORAMEN OVALE)
Septation of Ventricles/Outflow Region
- Muscular interventricular septum, conal cushions and inf/sup endocardial cushions all grow towards ea other and fuse
- Trunchal cushions (NEURAL CREST CELLS) meet ea other in midline to divide outflow tract –> aortic and pulmonary trunks
**Trunchal and conal cushions form in spiral manner –> so aortic and pulmonary trunks twist around ea other
Outflow Tract Defects (4)
1- Persistent Truncus Arteriosus - aortic and pulm trunks do not sep- mixed blood
2- Transposition of Great Arteries - aortic and pulm trunks reversed -failure to spiral
3- Ventricular Septal Defects - most common
4- Tetralogy of Fallot - get big aorta and small pulm trunk
-Pulm stenosis, overriding aorta, VSD, hypertrophy of R ventricle b/c has to work extra hard to pump into small pulm trunk
Atrial Septal Defects (4)
1- Primum ASD - septum primum does not grow fully to endocardial cushion to foramen primum not fully closed (lower hole)
2- Secundum ASD - too much septum primum resorbed or septum secundum insufficient so large foramen ovale (higher hole)
3- Common/Persistent AV Canal - large hole in center heart b/c cushion doesn’t form properly
4- Common Atrium -complete absence of atrial septum
Fetal Circulation
- Goal = bypass pulmonary system
- R atrium –> L atrium –> L ventricle –> dorsal aorta
Tbx5 Heart Defects (3 types)
- atrial septum
- ventral septum
- conduction
**NOT OUTFLOW
Pitx2 Heart Defects
-Pitx2 involved in R/L asymmetry so mutations –> heart loops wrong –> asymmetry problem
**Includes tetralogy of Fallot
