The umbilical cord is a pretty amazing structure. In the developing
fetus, it goes from the
placenta (the
afterbirth) of the mother, through the baby's
navel and into the fetal
liver and
heart. This is how
oxygen and nutrients are conveyed into the growing fetus.
If the baby's
blood pressure gets too high, small blood vessles around the umbilical cord expand and cause the
abdominal wall to spread. This then allows two
arteries that run from the fetal
aorta by way of the
bladder to conduct excess blood back to the placenta. All of these blood vessels are usually still open at the time of birth and tubes may be inserted into them to reach the circulatory system or the heart for measuring blood pressure or obtaining blood samples.
Another passage leaves the bladder and goes out the navel, allowing the developing fetus to expel
urine. This eventually shrivels into a
ligament connecting the bladder to the abdominal wall after birth. In some cases, this passage may still be open at the time of birth, allowing the baby to expel urine through an open navel.
Even in adults, the
lumen of the umbilical
vein does not completely disappear and sometimes, it may be opened in order to inject
chemotherapeutic drugs.