Describe the changes in fetal circulation at birth and the possible associated congenital anomalies

Introduction: changes occurring in the vascular system at birth are caused by the cessation of the placental blood flow and the beginning of lung respiration. The following occur at birth:
1. Closure of the umbilical arteries.
2. Closure of the umbilical vein and ductus venous.
3. Closure of the doctus arteriosus.
4. Closure of the oval foramen.
1. Closure of the umbilical arteries: this is done by contraction of the smooth musculature in the walls of the arteries. They may be closed a few minutes after birth functionally but the actual obliteration by fibrous proliferation may take up to 2 or 3 month. The distal parts of the umbilical arteries then form the medial umbilical ligaments while the proximal portion remains open as the vesical arteries.
2. Closure of the umbilical vein and ductus venosus: this occurs shortly after that of the umbilical arteries. After obliteration the umbilical vein forms the ligamentum trees hepatis in the lower part of the falciform ligament, while the ductus venosis  is also obliterated to form the ligamengum venosum.
3. Closure of the ductus arteriosus: this is done by the contraction of the muscular wall. It occurs immediately after birth and is mediated by bradykinin released by the lungs during initial inflation. The obliterated ductus arteriosus then form the ligamentum arteriosum.
4. Closure of the foramen ovale: this is caused by an increase pressure in the left atrium combined with a decrease in pressure on the right side. With the first breath the septum primum presses against the septum secundum.
Clinical abnormalities:
1. Patent ductus arteriosus: a condition in which the ductus arteriosus is not properly closed. This means deoxygenated blood will be mixing with oxygenated blood at the aortic arch. This can result in cyanosis.
2. Patent foramen ovale: failure of the oval foramen to close causes this

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