Page 86 - كتاب تمريض نسا الاكتروني

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The rest of the fetal blood entering the right atrium, including a large proportion of the

deoxygenated blood entering from the superior vena cava passes into the right ventricle

and out through the pulmonary trunk.

Only a small volume of blood enters the pulmonary circuit, because the lungs are

collapsed, and their blood vessels have a high resistance to flow.

Enough blood reaches the lung tissue to sustain them. Most of the blood in the pulmonary

trunk bypasses the lungs by entering a fetal vessel called the ductus arteriosus which

connects the pulmonary trunk to the descending portion of the aortic arch.

As a result of this connection, the blood with a relatively low O2 concentration which is

returning to the heart through the superior vena cava, bypasses the lungs.

At the same time, the blood is prevented from entering the portion of the aorta that

provides branches leading to the brain. The more highly oxygenated blood that enters the

left atrium through the foramen oval is mixed with a small amount of deoxygenated blood

returning from the pulmonary veins.

This mixture moves into the left ventricle and is pumped into the aorta. Some of it reaches

the myocardium through the coronary arteries and some reaches the brain through the

carotid arteries. The blood carried by the descending aorta is partially oxygenated and

partially deoxygenated. Some of it is carries into the branches of the aorta that lead to

various parts of the lower regions of the body. The rest passes into the umbilical arteries,

which branch from the internal iliac arteries and lead to the placenta. There the blood is

reoxygenated.

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