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Heart
- mesenchyme aggregates to form cardiogenic cords
- tubes canalise
- tubes move to midline and fuse
- mesenchyme condenses around tube to form myocardium and pericardium
- aortic arches emerge from rostral end
- vitelline, cardinal and umbilical veins enter caudal end
- dilatations formed :
- truncus arteriosus
- bulbus cordis
- ventricle
- atrium
- sinus venosus
- becomes U- then S-shaped
- atrium and sinus venosus dorsal to ventricle, bulbus cordis and truncus arteriosus
- myocardial contractions begin at 22 days
- atrioventricular endocardial cushions divide canal from atrium to ventricle into left
and right atrioventricular canals
- septum primum grows from roof of atrium to fuse with cushions
- gap before fusion known as foramen primum
- after fusion foramen secundum forms
- blood flows from right atrium to left atrium
- ventricle partitioned by interventricular septum
- partially from growth upwards, partially by enlargement of ventricles on either side
- gao closed by end of 7th week
- bulbo-truncal ridges form in bulbus cordis and truncus arteriosus
- fuse to form aorticopulmonary septum
- misalignment leads to tetralogy of Fallot and cyanosis (blue baby)
- failure of septum to unite with endocardial cushions
- narrowing of pulmonary tract
- hypertrophy of right ventricle
- interventricular septal defect
Vasculature
- Forms paired aortic arches leading into dorsal aorta
- 1st and 2nd arches regress almost completely
- 3rd pair forms common carotid and internal carotid
- 4th arch on left forms arch of aorta
- 4th arch on right forms brachiocephalic trunk
- 5th arches never really form
- 6th arch forms left pulmonary artery and ductus arteriosus
- 6th arch on right forms part of right pulmonary artery
- vagus supplies 6th arch: on left, recurrent laryngeal hook under ductus arteriosus on
right nothing to hook under until subclavian artery
- At birth increased oxygenation of blood in ductus arteriosus and changes in
prostaglandin production cause closure of ductus arteriosus
- can be either patent: shunts blood from systemic to pulmonary circulation
- or causes coarction of aorta and blood redirected through long thoracic arteries.
- Umbilical arteries
- develop in connecting stalk of embryo
- connect to dorsal aortae
- shift origin to internal iliac arteries
- close at birth
- umbilical veins
- develop in connecting stalk of embryo
- connect to sinus venosus
- right umbilical vein regresses
- left umbilical vein becomes reconnected to ductus venosus
- ductus venosus constricts at birth
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