Embryonic-Fetal Circulation

Question 1

4 heart regions @ week 4

Answer 1

• 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

Question 2

Process of cardiac chamber positioning

Answer 2

• 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

Question 3

xendocardial cushions bisect atrioventricular canals

Answer 3

xx

Question 4

Describe how and when the truncus arteriosus is subdivided into the pulmonary and aortic outflow tracts

Answer 4

• 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

Question 5

Describe the components of the embryonic heart that contribute to septation of the ventricles, and identify when this separation occurs

Answer 5

xx

Question 6

Describe how and when the left and right atria are separated.

Answer 6

xx

Question 7

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

Answer 7

xx

Question 8

Identify 2 components of fetal cardiac circulation which are no longer patent after birth

Answer 8

xx

Question 9

Location of precardial cells during week 3

Answer 9

-derive from mesoderm –> migrate cephalically = “cardiogenic area” -cardiogenic cells migrate ventrally –> form 2 endocardial tubes

Question 10

Anatomic development of embryonic structures (bulbus cordis, primitive ventricle, conus, primitive atria, truncus)

Answer 10

Question 11

Ductus venosis development

Answer 11

• 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.

Question 12

Ductus arteriosus development

Answer 12

• 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.

Question 13

Interatrial septum development

Answer 13

• 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).

Question 14

Interventricular septation development

Answer 14

• 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