Embryonic-Fetal Circulation Flashcards
4 heart regions @ week 4
- straight heart tube
- AV sulcus –> intraventricular septum
- primitive ventricle –> trabeculated portion of LV
- proximal bulbus cordis –> trabeculated portion of RV
- blood flow begins @ this time
Process of cardiac chamber positioning
- Day 23-25: Looping stage
- cardiac tube grows longitdunially quickly –> looping to the right of the embryo
- primitive atria rotate posteriorly
- long axis of atrioventricular canal goes from cephallic-caudal –> posterior-anterior
xendocardial cushions bisect atrioventricular canals
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Describe how and when the truncus arteriosus is subdivided into the pulmonary and aortic outflow tracts
- occurs @ ~day 35-36
- 4 masses @ conus DDCC (dextrodorsal cornal crest) and SVSS (sinoventral)
- masses appear @ truncus:
- Destrosuperior & Sinistroinferior swellings (DSTS & SITS)
- Right intercalated swelling (RITS) –> noncoronary aortic cusp
- Left intercalated swelling (LITS) –> anterior pulmonary cusp
- aorticpulmonary septum originates at extracardiac septum –> SVCC connects to SITS & DDCC connects to DSTS
Describe the components of the embryonic heart that contribute to septation of the ventricles, and identify when this separation occurs
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Describe how and when the left and right atria are separated.
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Identify which aortic arch vessels are lost, and which are maintained by 8 weeks gestation, and what are the anatomical names of the remaining vessels
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Identify 2 components of fetal cardiac circulation which are no longer patent after birth
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Location of precardial cells during week 3
-derive from mesoderm –> migrate cephalically = “cardiogenic area” -cardiogenic cells migrate ventrally –> form 2 endocardial tubes
Anatomic development of embryonic structures (bulbus cordis, primitive ventricle, conus, primitive atria, truncus)
Ductus venosis development
- highly oxygenated blood leaves the placenta through the umbilical vein. 50% of this blood is shunted through the fetal ductus venosus (bypassing the hepatic vasculature and proceeding directly to the IVC)
- Open at the time of birth, but structurally closes during the 1st week of life.
- If ductus venosus doesn’t close properly, the person has intrahepatic portosystemic shunt. In a normal adult the remnant of the ductus venosus is the ligamentum venosum.
Ductus arteriosus development
- Distal portion of left 6th aortic arch forms ductus arteriosus
- RV blood flows into pulmonary artery and then into the ductus arteriosus –> descending aorta (88% of RV output) or through the pulmonary arties and into the lungs (12% of RV output).
- High levels of prostaglandins due to hypoxia, causes the SMC of the ductus arteriosus to relax, keeping it open.
- baby is born –> prostaglandin levels decline as O2 tension rises and ductus constricts (“fxnl closure) –> eventually vascular remodeling leads to complete anatomic closure (by ~1 yr.)
- If the ductus fails to close at birth there is a persistent connection between the L pulmonary artery and the descending aorta.
Interatrial septum development
- primary atrial septum (septum primum) begins as a ridge of tissue on the roof of the common atrium and grows downward into the atrial cavity
- Septum primum advances down, but leaves openings that allow R to L blood flow as it fuses (ostium primum–>ostium secondum–>foramen ovale)
- Septum primum regresses leaving a “flap=like” valve that allows only R to L flow through the foramen.
- During gestation blood flows RA to LA because pressure in the fetal RA is greater than LA. After birth, the pressure gradient changes (LA is higher) and the valve closes.
- malformation –> atrial septal defect where the L and R atria have a direct connect and blood flows from LA to RA (commonly @ foramen ovale).
Interventricular septation development
- end of 4th week (Day, primitive ventricles begin to grow, leaving a median muscular ridge (the primitive interventricular septum) –> grows towards base of heart.
- 4 endocardial cushions appear (superior, inferior, R, L)
- septum primum, endocardial cushions and primitive interventricular septum become continuous
- Superior and inferior endocardial cushions fuse –> form L & R ventricular canal
