Umbilical cord
The umbilical cord is a vital structure that connects a developing fetus to the placenta during pregnancy, facilitating the exchange of oxygen and nutrients while removing waste products. Typically measuring around 20 inches at term, it contains two umbilical arteries and one umbilical vein, all protected by a gelatinous substance. After birth, the umbilical cord dries and detaches naturally within seven to ten days; however, complications can arise if it persists beyond this period, necessitating evaluation for potential underlying issues.
In recent years, the umbilical cord has gained attention for its role in stem cell banking, offering a source of embryonic stem cells that can be cryopreserved for future medical use, particularly in treating various diseases. The practice of cord blood banking is debated due to its costs and the varying likelihood of needing such treatments. Additionally, research has suggested that delaying the clamping of the umbilical cord after birth can improve health outcomes for newborns, leading to recommendations from medical organizations to wait before cutting the cord. Overall, the umbilical cord plays a significant role in both fetal development and modern medical practices, garnering interest from healthcare professionals and parents alike.
Umbilical cord
Anatomy or system affected: Blood vessels, skin
Definition: The cord connecting the developing fetus to the placenta.
Structure and Functions
The umbilical cord is composed of a thickened fibrous covering over a gelatinous material that protects three blood vessels. Two umbilical arteries carry blood from the baby to the placenta and coil around the single umbilical vein. Blood containing oxygen and other essential nutrients returns from the placenta through the umbilical cord.
At term, the umbilical cord measures approximately 20 inches. The cord may be short if there is little amniotic fluid and if the baby has a muscular weakness, limiting movement inside the uterus. Umbilical cord lengths of less than 14 inches have a high incidence of traumatic separation and fetal blood loss at the time of a vaginal delivery.
Disorders and Diseases
Normally, the umbilical cord dries rapidly after birth, with most of its fluid content evaporating in two days. The base of the cord is then colonized by bacteria. An immune system response to the bacteria and chemicals released by white blood cells is required for the final shedding of the dried cord. The untreated umbilical cord is shed approximately seven to ten days after birth. Any treatment (such as alcohol) used to dry or delay cord bacterial colonization allows the cord to persist for nearly twice as long as in the untreated condition.
Persistence of an umbilical cord beyond three weeks after drying may be caused by a persistent blood supply and may require evaluation by a pediatricsurgeon. Conditions that are associated with a persistent cord blood supply include a hemangioma, a connection from an artery in the skin to the vein of the umbilical cord, a small outpouching of the lining of the abdominal cavity, or retained elements of tissue connected to the bladder.
Once the cord has been fully shed, a reactive overgrowth of tissue may occur at the base of the cord. This is termed an umbilical granuloma and is readily managed by the application of silver nitrate, which cauterizes the tissue. There should be no further drainage from the base of the umbilicus beyond six weeks after birth.
During normal embryonic development, the umbilical cord is associated with a portion of two extraembryonic membranes, the yolk sac and the allantois. In late embryonic stages, the umbilical region normally herniates out of the embryo’s body wall and is then fully retracted. If part of the herniated bowel is not returned to its normal position, then a connection between the base of the umbilical cord and the small intestine may occur. This is known as a Meckel’s diverticulum of the ileum. Similarly, if the allantois does not completely degenerate, then it can leave a connection between the umbilical cord and the top of the bladder, known as a patent urachus. Both conditions are usually easily corrected by surgery.
Perspective and Prospects
In the twenty-first century, the umbilical cord has taken on new significance as the source of embryonic stem cells. Blood from the umbilical cord taken immediately after the infant has been born can be isolated and cryoprotected for many years. Should the infant (or even individuals who are not perfectly matched immunologically) require new blood stem cells to repopulate the immune system after chemotherapy or radiation therapy, then the cord blood stem cells can be thawed and injected into the recipient. A host of diseases have been successfully treated using cord blood, including many genetic diseases, and thousands of parents have opted to bank their infant’s cord blood. The cost of harvesting and maintaining cord blood, however, is a source of controversy. Harvesting and storing cord blood is expensive, and the chances of an individual spontaneously acquiring a childhood neoplasm or serious genetic disease that would require cord cell therapy is not high. In addition, alternative therapies, such as bone marrow transplants, are sometimes available. On the other hand, parents in which such diseases run in the family may seriously consider cord blood banking.
The hope of stem cell technology in the future lies in the possibility that specific differentiated cell lineages can be stimulated to cure disease and not simply to reconstitute the immune system. For example, diabetic patients might have stem cells in cord blood engineered to produce insulin-secreting cells under appropriate control of circulating glucose concentration. Using the patient’s own cord blood to produce such differentiated stem cells would avoid the problem of host-graft rejection.
In July 2013, the New York Times reported on a study suggesting that doctors clamp umbilical cords too soon following birth. According to the study, waiting at least one minute before cutting the cord improves iron and hemoglobin levels in newborns. In the early 2020s, the American College of Obstetricians and Gynecologists recommended delayed cord clamping in vigorous term and preterm infants.
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