Tj789
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#1
Report Thread starter 7 years ago
#1
Ok so I know the interatrial septum does not close until its born, and doctors slap it to trigger a pain receptor to close it. Is that right? But why is it not closed when its inside the womb? Is it because the blood of baby and mother need to mix so she can exchange materials with it?? Also what would happen if it doesnt close?
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Asklepios
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#2
Report 7 years ago
#2
(Original post by Tj789)
Ok so I know the interatrial septum does not close until its born, and doctors slap it to trigger a pain receptor to close it. Is that right? But why is it not closed when its inside the womb? Is it because the blood of baby and mother need to mix so she can exchange materials with it?? Also what would happen if it doesnt close?
In a fetus, the lungs do not function. This means that the mother has to oxygenate the fetus' blood. This oxygenated blood passes into the fetus through the umbilical vein (in the umbilical cord) and ultimately flows into the right atrium through the inferior vena cava. As you know, the right side of the heart pumps blood to the lungs, but we want to bypass these in the fetus. Hence there is a passage through the interatrial septum, called the foramen ovale, for oxygenated blood to cross straight into the left side of the heart and then into the systemic circulation.

See this diagramName:  ImageUploadedByStudent Room1411821731.149267.jpg
Views: 173
Size:  125.6 KB

If this hole does not close we have a patent foramen ovale, http://en.m.wikipedia.org/wiki/Atria..._foramen_ovale



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Dynamo123
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#3
Report 7 years ago
#3
(Original post by Tj789)
Ok so I know the interatrial septum does not close until its born, and doctors slap it to trigger a pain receptor to close it. Is that right? But why is it not closed when its inside the womb? Is it because the blood of baby and mother need to mix so she can exchange materials with it?? Also what would happen if it doesnt close?
Well, in the fetus, the lungs are non-functional and the resistance to blood flow inside the pulmonary vasculature is great. This doesn't allow the blood to go to the lungs. Also, in the fetus oxygenated blood is supplied by the umbilical vein that brings the oxygenated blood from the placenta (in case you aren't sure how this happens, do ask!). This oxygenated blood will go to the right atrium (there is a lot of detail in it associated with fetal circulation, but for now, I'll skip it). And through the "hole" in the interatrial septum (called the formaen ovale) this blood goes from the right atrium to the left, thence to the left ventricle, the aorta and the whole body of the fetus.

In case the defect or the hole (foramen ovale) does not close, it leads to a condition called an atrial septal defect (ASD). Now an ASD may be casued by any defect in the formation of the interatrial septum or by failure of the foramen ovale to close. In the latter case, it is called a patent foramen ovale.

After birth, the lungs start functioning. Also, the pulmonary vessels start conducting blood. Now in this case, the blood must go from the right atrium to the right ventricle to the pulmonary artery and then to the lungs.

Also, after birth, the pressures in the left side of the heart are much greater than in the right side of the heart.

From these two inferences, you can say that after birth, if the foramen ovale does not close, then oxygenated blood will go from the left atrium under high pressure to the right atrium of the heart. This is known as a left-to-right shunt of blood (some of these terms might be new to you, so ignore them). Since now there is more blood in the right side of the heart than on the left side, the right side of the heart will "expand" or undergo hypertrophy (and increase in cardiac muscle mass). This, if unchecked, can lead to heart failure.

An ASD needs to be treated surgically in most cases, by accessing the heart and then "sewing" up the hole or the defect.

If you have any questions, ask away!
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Tj789
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#4
Report Thread starter 7 years ago
#4
(Original post by Asklepios)
In a fetus, the lungs do not function. This means that the mother has to oxygenate the fetus' blood. This oxygenated blood passes into the fetus through the umbilical vein (in the umbilical cord) and ultimately flows into the right atrium through the inferior vena cava. As you know, the right side of the heart pumps blood to the lungs, but we want to bypass these in the fetus. Hence there is a passage through the interatrial septum, called the foramen ovale, for oxygenated blood to cross straight into the left side of the heart and then into the systemic circulation.

See this diagramName:  ImageUploadedByStudent Room1411821731.149267.jpg
Views: 173
Size:  125.6 KB

If this hole does not close we have a patent foramen ovale, http://en.m.wikipedia.org/wiki/Atria..._foramen_ovale



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Hey, this post was sometime ago but im going over this stuff again- just wanted to ask in a fetus is the whole septum not closed or just the atrial one?
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Asklepios
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#5
Report 7 years ago
#5
(Original post by Tj789)
Hey, this post was sometime ago but im going over this stuff again- just wanted to ask in a fetus is the whole septum not closed or just the atrial one?
Only the atrial system develops with a hole (foramen ovale) in it, the ventricular septum just develops straight as the two ventricles expand. see picture (D, E, F)
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