5Differentiation of mesenchyme The early heart is a simple tube which commences beating during the third week (Day 21-22).Cardiogenic mesenchyme differentiates into three distinct cell populations:Endocardium 心內膜Myocardium 心肌Epicardium 心外膜
6Cell Population Functions and Fates EndocardiumEndothelial liningConnective tissue precursor (Valves and fibrous skeleton) MyocardiumMyocytesConduction system (Purkinje fibres)Myoendocrine cells (Atrial Natriuretic Factor production)EpicardiumCoronary vessel precursorsVisceral pericardial lining
8Early heart chambers Sinus venosus (SV)靜脈竇This is the collecting compartment of the heart. Oxygenated blood from the placenta and deoxygenated blood from embryonic tissues are mixed in the sinus. Primitive atrium (PA)心房原基This is the compartment destined for further partition to the definitive atria. Primitive ventricle (PV)心室原基This is the compartment destined for further partition to the definitive ventricles. Bulbus cordis (BC)心球This will contribute to the pulmonary trunk and aorta, along with the truncus arteriosus. Truncus arteriosus (TA)動脈幹This will contribute to the aortic arches. Fibrous skeleton (FS)纖維骨架This is the area of connective tissue proliferation, site of future valves.
9Folding of the heart tube Apoptosis in the dorsal mesocardium will allow movement of the early heart tube within the pericardial cavity
10The folding of the heart tube brings the inflow and outflow trunks in an adjacent position at the superior aspect of the developing heart.
11The dorsal fold forms the two pericardial sinuses and places the fibrous skeleton in a single plane
12Inflow and outflow trunks are positioned posteriorly as a result of the dorsal fold
14Normal development of Heart Early EventsCritical ChangesEndocardial cushion（心內墊） growth and fusionBulboventricular loopingInteratrial septum（心房間隔） formationInterventricular septum（心室間隔） formationAortico-pulmonary septum（主肺動脈隔） formationVascular Changes
15Endocardial cushion fusion Endocardial cushions are areas of the fibrous skeleton forming between the atrium and ventricle.Endocardial cushions serve two important functions:form a partition in the heart tube between the atrium (PA) and ventricle (PV) (tricuspid and bicuspid valves)provide a "scaffold" of the interatrial septae and the interventricular septumDefects in endocardial cushion fusion are associated with trisomies 18 and 21 (Down's syndrome).
16Valvular atresiaValvular atresias arise from the uneven partition of the AV canal. Depending on the size and position of the narrowed channel, a tricuspid atresia or a biscuspid atresia results. Atresias arising from anomalous partition of the canal are referred to as congenital atresias
17Bulboventricular looping BV looping is a consequence of several changes:- Dorsal foldingThe first dorsal fold forms an expanded primitive ventricle, referred to as the bulboventricular loop.- Ventricular growthDifferential growth of the proximal ventricular tissue causes a counter-clockwise rotation of the folded heart tube. The site of ventricular growth marks the future left ventricle. Abnormal growth of the distal primitive ventricle causes clockwise rotation, an anomaly known as dextrocardia心偏右.- AV canal房室管 partitioningThe Atrio-Ventricular (AV) canal between the primitive atrium and ventricle has now been partitioned by the fusing endocardial cushions.- Shunting of venous returnThe development of the venous system causes an increase in right-sided venous return to the primitive atrium. Combined with the partitioning of the AV canal, the change in blood flow volume and directions assists in the outgrowth of the left ventricle.
27Atrial septal defects心房間隔缺損 (ASD) Atrial septal defects (ASD) are fairly common, present in 10-15% of patients with congenital cardiac anomalies. It is more commonly observed in females than males (2-3:1).
30Interventricular septum formation AP - aorticopulmonary;ECC - endocardial cushion; Blue arrow - direction of bulbar ridge growth; Red arrow - direction of ventricular growth IVS PartOriginmuscularventricular wallmembranousfused bulbar ridges 球狀脊fused endocardial cushions
35Aortico-pulmonary septum formation The aortico-pulmonary (AP) septum arises within the truncus arteriosus. The septum results from the downwards growth and fusion of bulbar ridges, induced by invasion of neural crest cells. The AP septum serves to divide the ventricular outflow between the pulmonary artery and the ascending aorta
39Tetralogy of FallotThe tetralogy of Fallot results from the asymmetric division of the AP septum. The result is a stenosed pulmonary artery and a VSD.Tetralogy of fallot:Pulmonary valve stenosisVentricular septal defectOverriding aortaHypertrophy of right ventricle
63Embryologic Structure Adult EquivalentLeft anterior cardinal veindisappears proximallydistal portion contributes to Left superior intercostal veinanastomoses with Right anterior cardinal vein distally to form Left brachiocephalic vein Left common cardinal veinoblique vein of left atrium Left posterior cardinal veindisappears Left horn of sinus venosuscoronary sinus Right anterior cardinal vein superior vena cavaRight common cardinal veinsuperior vena cavaRight posterior cardinal veinazygous veinPrimitive atriumright auricleForamen ovalefossa ovalis and limbus First aortic archmaxillary arterycontribution to external carotid artery Second aortic arch persists dorsally as stapedial artery Third aortic archproximal portions form common carotid arterydistal portions form internal carotid artery Fourth aortic archleft arch (with aortic sac) forms ascending aorta and archright arch contributes to right subclavian artery Fifth aortic arch does not persist Sixth aortic archproximal left arch - left pulmonary arterydistal left arch - ligamentum arteriosumproximal right arch - right pulmonary arterydistal right arch - does not persist Ductus venosusligamentum venosumLeft umbilical veinligamentum teres distallydegenerates proximallyportion within septum transversum contributes to hepatic portal systemRight umbilical veindegenerates proximally and distally Left vitelline veinfuses with right vitelline vein to form portal vein Right vitelline veinfuses with left vitelline vein to form portal vein