Foramen ovale (heart)
Encyclopedia
In the fetal heart
, the foramen ovale (icon), also ostium secundum of Born or falx septi, allows blood to enter the left atrium
from the right atrium. It is one of two fetal cardiac shunts, the other being the ductus arteriosus
(which allows blood that still escapes to the right ventricle to bypass the pulmonary circulation
). Another similar adaptation in the fetus is the ductus venosus
. In most individuals, the foramen ovale closes at birth. It later forms the fossa ovalis
.
. Initially the atria are separated from one another by the septum primum
except for a small opening in the septum, the ostium primum
. As the septum primum grows, the ostium primum narrows and eventually closes. Before it does so, bloodflow from the inferior vena cava
wears down a portion of the septum primum, forming the ostium secundum
. Some embryologists postulate that the ostium secundum may be formed through programmed cell death
.
The ostium secundum provides communication between the atria after the ostium primum closes completely. Subsequently, a second wall of tissue, the septum secundum
, grows over the ostium secundum in the right atrium. Bloodflow then only passes from the right to left atrium by way of a small passageway in the septum secundum and then through the ostium secundum. This passageway is called the foramen ovale.
.
.
PFO has long been studied because of its demonstrated role in some cases of paradoxical embolism. After exclusion of more common causes of stroke and TIA, transesophageal echocardiography should be considered in order to exclude cardiogenic foci of embolism. The presence of a patent foramen ovale should be considered as a possible cause of the cerebrovascular event, even though it may simply be an occasional finding in patients with cryptogenic stroke.
Heart
The heart is a myogenic muscular organ found in all animals with a circulatory system , that is responsible for pumping blood throughout the blood vessels by repeated, rhythmic contractions...
, the foramen ovale (icon), also ostium secundum of Born or falx septi, allows blood to enter the left atrium
Atrium (anatomy)
In anatomy, the atrium , sometimes called auricle , refers to a chamber or space. For example, the term is used for a portion of the lateral ventricle in the brain and the blood collection chamber of the heart...
from the right atrium. It is one of two fetal cardiac shunts, the other being the ductus arteriosus
Ductus arteriosus
In the developing fetus, the ductus arteriosus , also called the ductus Botalli, is a shunt connecting the pulmonary artery to the aortic arch. It allows most of the blood from the right ventricle to bypass the fetus's fluid-filled lungs. Upon closure at birth, it becomes the ligamentum arteriosum...
(which allows blood that still escapes to the right ventricle to bypass the pulmonary circulation
Pulmonary circulation
Pulmonary circulation is the half portion of the cardiovascular system which carries Oxygen-depleted Blood away from the heart, to the Lungs, and returns oxygenated blood back to the heart. Encyclopedic description and discovery of the pulmonary circulation is widely attributed to Doctor Ibn...
). Another similar adaptation in the fetus is the ductus venosus
Ductus venosus
In the fetus, the ductus venosus shunts approximately half of the blood flow of the umbilical vein directly to the inferior vena cava. Thus, it allows oxygenated blood from the placenta to bypass the liver. In conjunction with the other fetal shunts, the foramen ovale and ductus arteriosus, it...
. In most individuals, the foramen ovale closes at birth. It later forms the fossa ovalis
Fossa ovalis (heart)
Found in the right atrium of the heart, the fossa ovalis is an embryonic remnant of the foramen ovale, which normally closes shortly after birth.In a heart specimen of a neonate, the fossa ovalis is translucent, but later in life the membrane thickens...
.
Development
The foramen ovale forms in the late fourth week of gestationGestation
Gestation is the carrying of an embryo or fetus inside a female viviparous animal. Mammals during pregnancy can have one or more gestations at the same time ....
. Initially the atria are separated from one another by the septum primum
Septum primum
In the developing heart, the cavity of the primitive atrium becomes subdivided into right and left chambers by a septum, the septum primum, which grows downward into the cavity. The increasingly smaller gap below it is known as the ostium primum...
except for a small opening in the septum, the ostium primum
Ostium primum
In the developing heart, the atria initially communicate with each other by an opening between the free edge of the septum primum and the AV cushions, known as the primary interatrial foramen or ostium primum , below the free margin of the septum.-Closing of ostium primum:This opening is closed by...
. As the septum primum grows, the ostium primum narrows and eventually closes. Before it does so, bloodflow from the inferior vena cava
Inferior vena cava
The inferior vena cava , also known as the posterior vena cava, is the large vein that carries de-oxygenated blood from the lower half of the body into the right atrium of the heart....
wears down a portion of the septum primum, forming the ostium secundum
Ostium secundum
The ostium secundum is a foramen in the septum primum.It should not be confused with the foramen ovale, which is a foramen in the septum secundum.-Clinical significance:...
. Some embryologists postulate that the ostium secundum may be formed through programmed cell death
Programmed cell death
Programmed cell-death is death of a cell in any form, mediated by an intracellular program. PCD is carried out in a regulated process which generally confers advantage during an organism's life-cycle...
.
The ostium secundum provides communication between the atria after the ostium primum closes completely. Subsequently, a second wall of tissue, the septum secundum
Septum secundum
The septum secundum, semilunar in shape, grows downward from the upper wall of the atrium immediately to the right of the primary septum and ostium secundum....
, grows over the ostium secundum in the right atrium. Bloodflow then only passes from the right to left atrium by way of a small passageway in the septum secundum and then through the ostium secundum. This passageway is called the foramen ovale.
Closure
Normally this opening closes in the first three months following birth. When the lungs become functional at birth, the pulmonary pressure decreases and the left atrial pressure exceeds that of the right. This forces the septum primum against the septum secundum, functionally closing the foramen ovale. In time the septa eventually fuse, leaving a remnant of the foramen ovale, the fossa ovalisFossa ovalis (heart)
Found in the right atrium of the heart, the fossa ovalis is an embryonic remnant of the foramen ovale, which normally closes shortly after birth.In a heart specimen of a neonate, the fossa ovalis is translucent, but later in life the membrane thickens...
.
Clinical relevance
In about 30% of adults the foramen ovale does not close completely, but remains as a small patent foramen ovaleAtrial septal defect
Atrial septal defect is a form of congenital heart defect that enables blood flow between the left and right atria via the interatrial septum. The interatrial septum is the tissue that divides the right and left atria...
.
PFO has long been studied because of its demonstrated role in some cases of paradoxical embolism. After exclusion of more common causes of stroke and TIA, transesophageal echocardiography should be considered in order to exclude cardiogenic foci of embolism. The presence of a patent foramen ovale should be considered as a possible cause of the cerebrovascular event, even though it may simply be an occasional finding in patients with cryptogenic stroke.