When does the heart start developing? When does it start beating?
Week 3 Week 4
Is the right or left atrium higher pressure in utero? After birth?
RA higher pressure in utero, LA higher pressure after birth
Describe the development of the foramen ovale
1) septum primum grows down towards the ventricles. The gap ahead of it is called the foramen primum
2) around the same time the septum primum reaches the ventricles, a hole forms in the top from apoptosis of those cells, called foramen secundum
3) on the RA side another septum grows down past the lower border of the foramen secundum. Because the septum primum is floppy, blood can be pushed into the left atrium
What structures come together to form the membranous interventricular septum?
spiral (aorticopulmonary) septum
muscular interventricular septum
Fetal shunts, location and approximate percentage and/or composition of blood flowing through them
1) Foramen ovale: oxygenated blood from the placenta is preferentialy diverted from the RA to the LA. It is a one way valve.
2) Ductus arteriosis: 90% of blood from the pulmonary trunk is diverted into the aorta, just past the left subclavian artery.
3) Ductus vensosus: 50% of oxygenated blood returning from the placenta is directed straight into the IVC. The other 50% goes through the liver.
Closure of fetal shunts after birth: important events, and how they lead to closure of the shunts & timeline
1st breath expands the lungs and decreases pulmonary resistance --> blood that used to be pushed through the DA is redirected to the now lower pressure lungs
Clamping of the umbilical cord increases SVR--> left side of the heart has to pump harder. Pressure in the LA now exceeds pressure in RA, foramen ovale (one way valve) functionally closes
Oxygenation of the blood somehow makes COX (mostly in placenta) produce less prostaglandin, which causes the ductus arteriosis to constrict
The sphincter in ductus venosus closes, and eventually the DV atrophies into the ligamentum venosum of the liver
Foramen ovale <24hrs (remains probe-patent in 20%)
Ductus arteriosis <72 hrs
Differential oxgenation of the fetus based on shunts
The liver, head, and upper limbs get the most oxygenated blood due to the ductus venosus and ductus arteriosis, respectively.
Adult derivatives of:
-ligamentum venosum (of liver)
What does the sinus venosus become?
The right side is absorbed into the RA (the smooth walled portion) and the left side becomes the coronary sinus.
Describe fetal circulation
Differences between fetal and adult hemoglobin
Fetal hemoglobin has a higher oxygen affinity than adult hemoglobin so it takes the oxygen from maternal hemoglobin and unloads in at a lower pO2 in the fetus
What germ layer does the heart develop from?
mesoderm- the cardiogenic mesoderm sits right next to the septum transversum
Describe how the tubular heart folds
The bottom half (single atrium and sinus venosum) fold up and behind the ventricles
How to maintain a patent ductus arteriosis?
Administer prostaglandins at birth