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In placental mammals, the umbilical cord is a tube that connects a developing embryo or fetus to the placenta. It normally contains three vessels, two arteries (Umbilical artery) and one vein (Umbilical vein), buried within Wharton's jelly, for the exchange of nutrient- and oxygen-rich blood between the embryo and placenta. The presence of only two vessels in the cord is sometimes related to abnormalities in the fetus, but may occur without accompanying abnormalities.
Shortly after birth, upon exposure to temperature change, the gelatinous Wharton's Jelly substance undergoes a physiological change that collapses previous structure boundaries and in effect creates a natural clamp on the umbilical cord which halts placental blood return to the neonate, causing the cord to cease pulsation. Though generally occurring as soon as 5 minutes after human birth, if the neonate's cord is submerged in warm water (i.e., a birthing pool) the cord may continue pulsing an additional time, up to 15-20 minutes. General obstetric practice introduces artificial clamping as early as 1 minute after birth of the neonate, a routine protocol questioned by some parents and care providers.
The umbilical cord develops from the same sperm and ovum from which the placenta and fetus develop, and contains remnants of the yolk sac and allantois. It forms by the fifth week of fetal development, replacing the yolk sac as the source of nutrients for the fetus. In humans, the umbilical cord in a full term neonate is usually about 50 centimetres (19.7 in) long and about 2 centimetres (0.75 in) diameter, shrinking rapidly in diameter in the after birth.
In the third stage of labour, after the child is born, the uterus spontaneously expels the neonate's placenta along with the cord from the mother's body, 10–45 minutes after the birth. However, the umbilical cord is generally clamped during or within minutes of birth and severed shortly after, a practice of "active management of labor" which has become increasingly controversial due to the lower transfer of placental blood to the neonate and associated stressors.
Today there are umbilical cord clamps which combine the cord clamps with the knife. These clamps are safer and faster, allowing one to first apply the cord clamp and then cut the umbilical cord. After the cord is clamped and cut (Western obstetrical protocol) the newborn wears a plastic clip on the navel area until the compressed region of the cord has dried and sealed sufficiently. The remaining umbilical stub remains for up to 2–3 weeks as it dries and then falls off. In nonseverance scenarios, also called lotus birth, the umbilical cord is wrapped up to within an inch of the newborn's belly, and the entire intact cord is allowed to dry like a sinew, which then falls off.
Makeup and composition
The umbilical cord is made of Wharton's jelly, not ordinary skin and connective tissue. There are no nerves, so cutting it is not painful, but it is very strong, like thick sinew, and requires a sharp instrument if it is to be cut. Provided that umbilical severance occurs after the cord has stopped pulsing (5-20 minutes after birth), there is ordinarily no significant loss of either infant or maternal blood while cutting the cord. The cord contains one vein, which carries oxygenated blood (from the mother to the fetus) and two arteries that carry deoxygenated blood (from the fetus back to the mother).
Provided that the cord is not clamped for the first 5 minutes after birth, and kept level with the newborn, it allows baby to receive many maternal antibodies, critical stem cells, hormones, and vitamin K and provides the neonate with one-third to one-half of its entire blood volume.
Loss of this volume of blood through harvesting for blood banking can be the equivalent of subjecting an infant to a massive hemorrhage. This cord blood is a rich source of primitive, undifferentiated stem cells (i.e. CD34-positive and CD38-negative) which assist in neonatal adaptation. A cord blood bank is in the business of cord blood harvesting, and is NASDAQ listed. These companies promote very early cord clamping and cutting, to freeze for long-term cryo-storage at a cord blood bank should the child ever require the cord blood stem cells for rare diseases (for example, to replace bone marrow destroyed when treating leukemia). This practice is controversial: the RCOG (Royal College of Obstetricians and Gynaecologists, Great Britain) in its 2006 opinion states, "There is still insufficient evidence to recommend directed commercial cord blood collection and stem-cell storage in low-risk families." Child health advocates criticize the aggressive marketing campaigns of blood banks to pregnant parents-to-be as misleading, and assert that early cord blood withdrawal may actually increase the likelihood of childhood disease.
For-profit cord blood banks receive from 80 ml to 180 ml of blood on the average amount of blood taken for CBC (cord blood collection). 'Banking' cord blood involves immediate, very early cord clamping to take a significant amount of blood (100mL on average) from the newborn at a crucial neonatal time. The amount of blood taken from the newborn child by early cord clamping can be understood by the fact that a 9 pound baby only creates 10 ounces of blood (300 ml). Therefore 180 ml is actually more than half this baby's blood supply and taking half of one's blood supply will weaken any child, or any adult that loses blood.
The cord banking business markets the use of CBEs as a mechanism that would eliminate the ethical difficulties associated with embryonic stem cells, however cord blood harvesting itself is fraught with ethical difficulties. (ESCs).
The American Academy of Pediatrics 2007 Policy Statement on Cord Blood Banking title states that:
"Physicians should be aware of the unsubstantiated claims of private cord blood banks made to future parents that promise to insure infants or family members against serious illnesses in the future by use of the stem cells contained in cord blood;"
"Cord blood collection should not be performed in complicated deliveries. The cord blood stem cell–collection program should not alter routine practice for the timing of umbilical cord clamping;" and
"Private storage of cord blood as "biological insurance" should be discouraged, and that cord blood banks should comply with national accreditation standards developed by the Foundation for the Accreditation of Cellular Therapy (FACT), the US Food and Drug Administration (FDA), the Federal Trade Commission, and similar state agencies."
A number of abnormalities can affect the umbilical cord, which can cause problems that affect both mother and child:
In other mammals, the mother animal generally will gnaw the cord off separating the placenta from the baby. It is often consumed by the mother, which nourishes her, and reduces tissue that would attract scavengers or predators. In chimpanzees, the mother focuses no attention on umbilical severance, instead staying still and nursing and holding her baby (with cord, placenta, and all) until the cord dries and separates within a day of birth, at which time she leaves the cord and placenta on the forest floor where it is recycled by scavengers. This was first documented by zoologists in the wild in 1974.
Other uses for the term "umbilical cord"
The term "umbilical cord" or just "umbilical" has also come to be used for other cords with similar functions, such as the hose connecting a surface-supplied diver to his surface supply of air and/or heating, or a space-suited astronaut to his spacecraft.
The phrase "cutting the umbilical cord" is used symbolically to describe a child's breaking away from the parental home.
Ectoderm: Surface ectoderm - Neuroectoderm - Somatopleure - Neurulation - Neural crest
Endoderm: SplanchnopleureMesoderm: Chorda- - Paraxial (Somite/Somitomere/Sclerotome/Myotome/Dermatome) - Intermediate - Lateral plate (Intraembryonic coelom, Splanchnopleure/Somatopleure)
|Extraembryonic/uterus||Trophoblast (Cytotrophoblast, Syncytiotrophoblast)
Umbilical cord (Umbilical artery, Umbilical vein, Wharton's jelly) - AllantoisPlacenta - Decidua (Decidual cells) - Chorionic villi/Intervillous space - Gestational sac (Amnion/Amniotic sac/Amniotic cavity, Chorion)
|Histogenesis||Programmed cell death - Stem cells - Germ line development|
|Organogenesis||Limb development: Limb bud - Apical ectodermal ridge/AER - Eye development - Cutaneous structure development - Heart development - Development of the urinary and reproductive organs|