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An umbilical cord, also known as a funis, is a tube found in placental mammals linking the unborn animal to its placenta. The placenta acts as a barrier within the uterus that stops many harmful substances from entering, as well as a store of energy and blood transfer for the developing embryo or fetus.
The umbilical cord passes blood between the fetus and the placenta. This blood is highly charged with oxygen to keep the fetus alive and well without a direct air source. After birth, the umbilical cord is severed and either removed or falls off, leaving a small scar — properly known as the umbilicus, more commonly known as the navel or belly button.
Umbilical cords have become very important in recent years, as it has been discovered they are a rich source of stem cells. Many groups in favor of stem cell research have pointed to this as a ready source of stem cells that do not require aborted fetuses. Parents are often turning to freezing their child's umbilical cord blood stem cells, in case they need them later in life.
The word umbilical comes from the middle Latin umbilicalis, meaning "of the navel", and is first recorded in use during the mid-18th century. In a metaphorical sense the umbilical cord is used to denote a strong connection between a mother and her offspring — so "cutting the umbilical cord" becomes an expression for becoming more independent in the world.
A number of studies have linked umbilical cord length to high risks for fetal malformation and stillbirths. While these studies are as yet inconclusive, the body of evidence appears to be growing and indicating strongly for a correlation. At birth a human umbilical cord ranges in length from 40-60cm, though variations can be more extreme in rare cases.
A prolapsed (out of place) umbilical cord may result in a number of problems for an unborn fetus. Most commonly the fetus may become strangled by the umbilical cord and die in utero, or the umbilical cord may become knotted or twisted to such a degree that blood flow is severely limited — resulting in heavy brain damage or death. In cases of prolapsed umbilical cords, Cesarean sections are often the only realistic option to save the fetus' life.