THE INFANT AT BIRTH
Immediately after delivery, the umbilical cord is clamped and cut, and the infant’s nose and mouth are aspirated to remove any fluid that might interfere with breathing. Now the infant is independent of the mother, and the most rapid changes occur in the respiratory and circulatory systems.
As the level of CO2 in the baby’s blood increases, the respiratory center in the medulla is stimulated and brings about inhalation to expand and inflate the lungs. Full expansion of the lungs may take up to 7 days following birth, and the infant’s respiratory rate may be very rapid at this time, as high as 40 respira-tions per minute.
Breathing promotes greater pulmonary circula-tion, and the increased amount of blood returning to the left atrium closes the flap of the foramen ovale. The ductus arteriosus begins to constrict, apparently in response to the higher blood oxygen level. Full closure of the ductus arteriosus may take up to 3 months.
The ductus venosus no longer receives blood from the umbilical vein and begins to constrict within a few minutes after birth. Within a few weeks the duc-tus venosus becomes a non-functional ligament.
The infant’s liver is not fully mature at birth and may be unable to excrete bilirubin efficiently. This may result in jaundice, which may occur in as many as half of all newborns. Such jaundice is not considered serious unless there is another possible cause, such as Rh incompatibility.
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