In the fetal

heart The heart is a muscular organ in most animals. This organ pumps blood through the blood vessels of the circulatory system. The pumped blood carries oxygen and nutrients to the body, while carrying metabolic waste such as carbon dioxide t ...

, the foramen ovale (), also foramen Botalli, or the ostium secundum of Born, allows blood to enter the left

atrium Atrium may refer to: Anatomy * Atrium (heart), an anatomical structure of the heart * Atrium, the genital structure next to the genital aperture in the reproductive system of gastropods * Atrium of the ventricular system of the brain * Pulmona ...

from the right atrium. It is one of two fetal

cardiac shunt A cardiac shunt is a pattern of blood flow in the heart that deviates from the normal circuit of the circulatory system. It may be described as right-left, left-right or bidirectional, or as systemic-to-pulmonary or pulmonary-to-systemic. The dire ...

s, the other being the

ductus arteriosus The ''ductus arteriosus'', also called the ''ductus Botalli'', named after the Italian physiologist Leonardo Botallo, is a blood vessel in the developing fetus connecting the trunk of the pulmonary artery to the proximal descending aorta. It a ...

(which allows blood that still escapes to the right ventricle to bypass the

pulmonary circulation The pulmonary circulation is a division of the circulatory system in all vertebrates. The circuit begins with deoxygenated blood returned from the body to the right atrium of the heart where it is pumped out from the right ventricle to the lungs ...

). Another similar adaptation in the fetus is the

ductus venosus In the fetus, the ''ductus venosus'' (Arantius' duct after Julius Caesar Aranzi) shunts a portion of umbilical vein blood flow directly to the inferior vena cava. Thus, it allows oxygenated blood from the placenta to bypass the liver. Compared to ...

. In most individuals, the foramen ovale closes at birth. It later forms the fossa ovalis.

Development

The foramen ovale () forms in the late fourth week of

gestation Gestation is the period of development during the carrying of an embryo, and later fetus, inside viviparous animals (the embryo develops within the parent). It is typical for mammals, but also occurs for some non-mammals. Mammals during pregna ...

, as a small passageway between the septum secundum and the ostium secundum. Initially the atria are separated from one another by the

septum primum During heart development of a human embryo, the single primitive atrium becomes divided into right and left by a , the septum primum. The septum primum () grows downward into the single atrium. Development The gap below it is known as the ostiu ...

except for a small opening below the septum, the

ostium primum In the developing heart, the atria are initially open to each other, with the opening known as the primary interatrial foramen or ostium primum (or interatrial foramen primum). The foramen lies beneath the edge of septum primum and the endocardi ...

. As the septum primum grows, the ostium primum narrows and eventually closes. Before it does so, bloodflow from the

inferior vena cava The inferior vena cava is a large vein that carries the deoxygenated blood from the lower and middle body into the right atrium of the heart. It is formed by the joining of the right and the left common iliac veins, usually at the level of the ...

wears down a portion of the septum primum, forming the

ostium secundum The foramen secundum, or ostium secundum is a in the septum primum, a precursor to the interatrial septum of the human heart. It is not the same as the foramen ovale, which is an opening in the septum secundum. Development The foramen secund ...

. Some embryologists postulate that the ostium secundum may be formed through

programmed cell death Programmed cell death (PCD; sometimes referred to as cellular suicide) is the death of a cell as a result of events inside of a cell, such as apoptosis or autophagy. PCD is carried out in a biological process, which usually confers advantage durin ...

. The ostium secundum provides communication between the atria after the ostium primum closes completely. Subsequently, a second wall of tissue, the

septum secundum The septum secundum is a muscular flap that is important in heart development. It is semilunar in shape, and grows downward from the upper wall of the atrium immediately to the right of the septum primum and ostium secundum. It is important in the ...

, grows over the ostium secundum in the right atrium. Blood then passes from the right to left atrium only by way of a small passageway in the septum secundum and then through the ostium secundum. This passageway is called the foramen ovale''.

Closure

The foramen ovale normally closes at birth. At birth, when the lungs become functional, the pulmonary vascular pressure decreases and the left atrial pressure exceeds that of the right. This forces the

against the

, functionally closing the foramen ovale. In time the septa eventually fuse, leaving a remnant of the foramen ovale, the fossa ovalis.

Function

fetus A fetus or foetus (; plural fetuses, feti, foetuses, or foeti) is the unborn offspring that develops from an animal embryo. Following embryonic development the fetal stage of development takes place. In human prenatal development, fetal deve ...

receives oxygen not from its lungs, but from the mother's oxygen-rich blood via the

placenta The placenta is a temporary embryonic and later fetal organ that begins developing from the blastocyst shortly after implantation. It plays critical roles in facilitating nutrient, gas and waste exchange between the physically separate mater ...

. Oxygenated blood from the placenta travels through the umbilical cord to the right atrium of the fetal heart. As the fetal lungs are non-functional at this time, the blood bypasses them through two cardiac shunts. The first is the foramen ovale (the valve present between them called eustachian valve) which shunts blood from the right atrium to the left atrium. The second is the

which shunts blood from the pulmonary artery (which, after birth, carries blood from the right side of the heart to the lungs) to the descending aorta.

Clinical significance

In about 25% of adults the foramen ovale does not close completely, but remains as a small patent foramen ovale ("PFO"). In most of these individuals, the PFO causes no problems and remains undetected throughout life. PFO has long been studied because of its role in

paradoxical embolism An embolus, is described as a free-floating mass, located inside blood vessels that can travel from one site in the blood stream to another. An embolus can be made up of solid (like a blood clot), liquid (like amniotic fluid), or gas (like air). O ...

(an

embolism An embolism is the lodging of an embolus, a blockage-causing piece of material, inside a blood vessel. The embolus may be a blood clot (thrombus), a fat globule ( fat embolism), a bubble of air or other gas (gas embolism), amniotic fluid (amniot ...

that travels from the venous side to the arterial side). This may lead to a

stroke A stroke is a medical condition in which poor blood flow to the brain causes cell death. There are two main types of stroke: ischemic, due to lack of blood flow, and hemorrhagic, due to bleeding. Both cause parts of the brain to stop functionin ...

transient ischemic attack A transient ischemic attack (TIA), commonly known as a mini-stroke, is a minor stroke whose noticeable symptoms usually end in less than an hour. TIA causes the same Symptoms of stroke, symptoms associated with strokes, such as weakness or numbn ...

Transesophageal echocardiography A transesophageal echocardiogram, or TEE (TOE in the United Kingdom and other countries such as Australia and New Zealand, reflecting the British English spelling ''transoesophageal''), is an alternative way to perform an echocardiogram. A speci ...

is considered the most accurate investigation to demonstrate a patent foramen ovale. A patent foramen ovale may also be an incidental finding.

References

* * {{Authority control Cardiology Embryology of cardiovascular system Obstetrics Pediatrics

Development

Closure

Function

Clinical significance

See also

References