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In placental
mammal Mammals () are a group of vertebrate animals constituting the class Mammalia (), characterized by the presence of mammary glands which in females produce milk for feeding (nursing) their young, a neocortex (a region of the brain), fur ...
s, the umbilical cord (also called the navel string, birth cord or ''funiculus umbilicalis'') is a conduit between the developing
embryo An embryo is an initial stage of development of a multicellular organism. In organisms that reproduce sexually, embryonic development is the part of the life cycle that begins just after fertilization of the female egg cell by the male spe ...
or
fetus A fetus or foetus (; plural fetuses, feti, foetuses, or foeti) is the unborn offspring that develops from an animal embryo. Following embryonic development the fetal stage of development takes place. In human prenatal development, fetal dev ...
and the
placenta The placenta is a temporary embryonic and later fetal organ that begins developing from the blastocyst shortly after implantation. It plays critical roles in facilitating nutrient, gas and waste exchange between the physically separate mate ...
. During
prenatal development Prenatal development () includes the development of the embryo and of the fetus during a viviparous animal's gestation. Prenatal development starts with fertilization, in the germinal stage of embryonic development, and continues in fetal deve ...
, the umbilical cord is physiologically and genetically part of the fetus and (in humans) normally contains two arteries (the
umbilical arteries The umbilical artery is a paired artery (with one for each half of the body) that is found in the abdominal and pelvic regions. In the fetus, it extends into the umbilical cord. Structure Development The umbilical arteries supply deoxygenated ...
) and one
vein Veins are blood vessels in humans and most other animals that carry blood towards the heart. Most veins carry deoxygenated blood from the tissues back to the heart; exceptions are the pulmonary and umbilical veins, both of which carry oxygenated ...
(the umbilical vein), buried within Wharton's jelly. The umbilical vein supplies the fetus with
oxygen Oxygen is the chemical element with the symbol O and atomic number 8. It is a member of the chalcogen group in the periodic table, a highly reactive nonmetal, and an oxidizing agent that readily forms oxides with most elements ...
ated,
nutrient A nutrient is a substance used by an organism to survive, grow, and reproduce. The requirement for dietary nutrient intake applies to animals, plants, fungi, and protists. Nutrients can be incorporated into cells for metabolic purposes or excre ...
-rich
blood Blood is a body fluid in the circulatory system of humans and other vertebrates that delivers necessary substances such as nutrients and oxygen to the cells, and transports metabolic waste products away from those same cells. Blood in the cir ...
from the
placenta The placenta is a temporary embryonic and later fetal organ that begins developing from the blastocyst shortly after implantation. It plays critical roles in facilitating nutrient, gas and waste exchange between the physically separate mate ...
. Conversely, the fetal heart pumps low-oxygen, nutrient-depleted blood through the umbilical arteries back to the placenta.


Structure and development

The umbilical cord develops from and contains remnants of the
yolk sac The yolk sac is a membranous wikt:sac, sac attached to an embryo, formed by cells of the hypoblast layer of the bilaminar embryonic disc. This is alternatively called the umbilical vesicle by the Terminologia Embryologica (TE), though ''yolk sac' ...
and
allantois The allantois (plural ''allantoides'' or ''allantoises'') is a hollow sac-like structure filled with clear fluid that forms part of a developing amniote's conceptus (which consists of all embryonic and extraembryonic tissues). It helps the embryo ...
. It forms by the fifth week of development, replacing the yolk sac as the source of nutrients for the embryo. The cord is not directly connected to the mother's circulatory system, but instead joins the
placenta The placenta is a temporary embryonic and later fetal organ that begins developing from the blastocyst shortly after implantation. It plays critical roles in facilitating nutrient, gas and waste exchange between the physically separate mate ...
, which transfers materials to and from the maternal blood without allowing direct mixing. The length of the umbilical cord is approximately equal to the crown-rump length of the fetus throughout
pregnancy Pregnancy is the time during which one or more offspring develops ( gestates) inside a woman's uterus (womb). A multiple pregnancy involves more than one offspring, such as with twins. Pregnancy usually occurs by sexual intercourse, but ...
. The umbilical cord in a full term neonate is usually about 50 centimeters (20 in) long and about 2 centimeters (0.75 in) in diameter. This diameter decreases rapidly within the placenta. The fully patent umbilical artery has two main layers: an outer layer consisting of circularly arranged smooth muscle cells and an inner layer which shows rather irregularly and loosely arranged cells embedded in abundant ground substance staining metachromatic. The smooth muscle cells of the layer are rather poorly differentiated, contain only a few tiny myofilaments and are thereby unlikely to contribute actively to the process of post-natal closure. Umbilical cord can be detected on ultrasound by 6 weeks of gestation and well-visualised by 8 to 9 weeks of gestation. The umbilical cord lining is a good source of mesenchymal and epithelial stem cells. Umbilical cord mesenchymal stem cells (UC-MSC) have been used clinically to treat osteoarthritis, autoimmune diseases, and multiple other conditions. Their advantages include a better harvesting, and multiplication, and immunosuppressive properties that define their potential for use in transplantations. Their use would also overcome the ethical objections raised by the use of embryonic stem cells. The umbilical cord contains Wharton's jelly, a gelatinous substance made largely from mucopolysaccharides that protects the blood vessels inside. It contains one vein, which carries oxygenated, nutrient-rich blood to the fetus, and two arteries that carry deoxygenated, nutrient-depleted blood away. Occasionally, only two vessels (one vein and one artery) are present in the umbilical cord. This is sometimes related to fetal abnormalities, but it may also occur without accompanying problems. It is unusual for a vein to carry oxygenated blood and for arteries to carry deoxygenated blood (the only other examples being the pulmonary veins and arteries, connecting the lungs to the heart). However, this naming convention reflects the fact that the umbilical vein carries blood towards the fetus's heart, while the umbilical arteries carry blood away. The blood flow through the umbilical cord is approximately 35 ml / min at 20 weeks, and 240 ml / min at 40 weeks of gestation. Adapted to the weight of the fetus, this corresponds to 115 ml / min / kg at 20 weeks and 64 ml / min / kg at 40 weeks. For terms of location, the ''proximal'' part of an umbilical cord refers to the segment closest to the embryo or fetus in embryology and fetal medicine, and closest to the placenta in placental pathology, and opposite for the ''distal'' part, respectively.


Function


Connection to fetal circulatory system

The umbilical cord enters the fetus via the
abdomen The abdomen (colloquially called the belly, tummy, midriff, tucky or stomach) is the part of the body between the thorax (chest) and pelvis, in humans and in other vertebrates. The abdomen is the front part of the abdominal segment of the to ...
, at the point which (after separation) will become the umbilicus (or navel). Within the fetus, the umbilical vein continues towards the transverse fissure of the
liver The liver is a major organ only found in vertebrates which performs many essential biological functions such as detoxification of the organism, and the synthesis of proteins and biochemicals necessary for digestion and growth. In humans, it i ...
, where it splits into two. One of these branches joins with the
hepatic portal vein The portal vein or hepatic portal vein (HPV) is a blood vessel that carries blood from the gastrointestinal tract, gallbladder, pancreas and spleen to the liver. This blood contains nutrients and toxins extracted from digested contents. Appr ...
(connecting to its left branch), which carries blood into the liver. The second branch (known as the ductus venosus) bypasses the liver and flows into the inferior vena cava, which carries blood towards the heart. The two umbilical arteries branch from the internal iliac arteries and pass on either side of the
urinary bladder The urinary bladder, or simply bladder, is a hollow organ in humans and other vertebrates that stores urine from the kidneys before disposal by urination. In humans the bladder is a distensible organ that sits on the pelvic floor. Urine ente ...
into the umbilical cord, completing the circuit back to the placenta.


Changes after birth

After birth, the umbilical cord stump will dry up and drop away by the time the baby is three weeks old. If the stump still has not separated after three weeks, it might be a sign of an underlying problem, such as an infection or immune system disorder. In absence of external interventions, the umbilical cord occludes physiologically shortly after birth, explained both by a swelling and collapse of Wharton's jelly in response to a reduction in temperature and by
vasoconstriction Vasoconstriction is the narrowing of the blood vessels resulting from contraction of the muscular wall of the vessels, in particular the large arteries and small arterioles. The process is the opposite of vasodilation, the widening of blood vess ...
of the blood vessels by smooth muscle contraction. In effect, a natural clamp is created, halting the flow of blood. In air at 18 °C, this physiological clamping will take three minutes or less. In water birth, where the water temperature is close to body temperature, normal pulsation can be 5 minutes and longer. Closure of the umbilical artery by vasoconstriction consists of multiple constrictions which increase in number and degree with time. There are segments of dilatations with trapped uncoagulated blood between the constrictions before complete occlusion. Both the partial constrictions and the ultimate closure are mainly produced by muscle cells of the outer circular layer. In contrast, the inner layer seems to serve mainly as a plastic tissue which can easily be shifted in an
axial Axial may refer to: * one of the anatomical directions describing relationships in an animal body * In geometry: :* a geometric term of location :* an axis of rotation * In chemistry, referring to an axial bond * a type of modal frame, in music * ...
direction and then folded into the narrowing lumen to complete the closure. The vasoconstrictive occlusion appears to be mainly mediated by
serotonin Serotonin () or 5-hydroxytryptamine (5-HT) is a monoamine neurotransmitter. Its biological function is complex and multifaceted, modulating mood, cognition, reward, learning, memory, and numerous physiological processes such as vomiting and va ...
and thromboxane A2. The artery in cords of preterm infants contracts more to
angiotensin II Angiotensin is a peptide hormone that causes vasoconstriction and an increase in blood pressure. It is part of the renin–angiotensin system, which regulates blood pressure. Angiotensin also stimulates the release of aldosterone from the adr ...
and
arachidonic acid Arachidonic acid (AA, sometimes ARA) is a polyunsaturated omega-6 fatty acid 20:4(ω-6), or 20:4(5,8,11,14). It is structurally related to the saturated arachidic acid found in cupuaçu butter. Its name derives from the New Latin word ''ara ...
and is more sensitive to
oxytocin Oxytocin (Oxt or OT) is a peptide hormone and neuropeptide normally produced in the hypothalamus and released by the posterior pituitary. It plays a role in social bonding, reproduction, childbirth, and the period after childbirth. Oxytoc ...
than in term ones. In contrast to the contribution of Wharton's jelly, cooling causes only temporary vasoconstriction. Within the child, the umbilical vein and ductus venosus close up, and degenerate into fibrous remnants known as the
round ligament of the liver The round ligament of the liver (or ligamentum teres, or ligamentum teres hepatis) is a ligament that forms part of the free edge of the falciform ligament of the liver. It connects the liver to the umbilicus. It is the remnant of the left umbi ...
and the ligamentum venosum respectively. Part of each umbilical artery closes up (degenerating into what are known as the
medial umbilical ligament The medial umbilical ligament (or cord of umbilical artery, or obliterated umbilical artery) is a paired structure found in human anatomy. It is on the deep surface of the anterior abdominal wall In anatomy, the abdominal wall represents the bo ...
s), while the remaining sections are retained as part of the circulatory system.


Clinical significance


Problems and abnormalities

A number of abnormalities can affect the umbilical cord, which can cause problems that affect both mother and child: *
Umbilical cord compression Umbilical cord compression is the obstruction of blood flow through the umbilical cord secondary to pressure from an external object or misalignment of the cord itself. Cord compression happens in about one in 10 deliveries.
can result from, for example, entanglement of the cord, a knot in the cord, or a nuchal cord,P02.5 Fetus and newborn affected by other compression of umbilical cord
in
ICD-10 ICD-10 is the 10th revision of the International Statistical Classification of Diseases and Related Health Problems (ICD), a medical classification list by the World Health Organization (WHO). It contains codes for diseases, signs and symptoms ...
, the International Statistical Classification of Diseases
(which is the wrapping of the umbilical cord around the fetal neck) but these conditions do not always cause obstruction of fetal circulation. * Velamentous cord insertion *
Single umbilical artery Occasionally, there is only the one single umbilical artery (SUA) present in the umbilical cord. This is sometimes also called a two-vessel umbilical cord, or two-vessel cord. Approximately, this affects between 1 in 100 and 1 in 500 pregnancies, m ...
*
Umbilical cord prolapse Umbilical cord prolapse is when the umbilical cord comes out of the uterus with or before the presenting part of the baby. The concern with cord prolapse is that pressure on the cord from the baby will compromise blood flow to the baby. It usuall ...
* Vasa praevia


Clamping and cutting

The cord can be clamped at different times; however, delaying the clamping of the umbilical cord until at least one minute after birth improves outcomes as long as there is the ability to treat the small risk of
jaundice Jaundice, also known as icterus, is a yellowish or greenish pigmentation of the skin and sclera due to high bilirubin levels. Jaundice in adults is typically a sign indicating the presence of underlying diseases involving abnormal heme meta ...
if it occurs. Clamping is followed by cutting of the cord, which is painless due to the absence of
nerve A nerve is an enclosed, cable-like bundle of nerve fibers (called axons) in the peripheral nervous system. A nerve transmits electrical impulses. It is the basic unit of the peripheral nervous system. A nerve provides a common pathway for the ...
s. The cord is extremely tough, like thick
sinew A tendon or sinew is a tough, high-tensile-strength band of dense fibrous connective tissue that connects muscle to bone. It is able to transmit the mechanical forces of muscle contraction to the skeletal system without sacrificing its ability ...
, and so cutting it requires a suitably sharp instrument. While umbilical severance may be delayed until after the cord has stopped pulsing (1–3 minutes after birth), there is ordinarily no significant loss of either venous or arterial blood while cutting the cord. Current evidence neither supports, nor refutes, delayed cutting of the cord, according to the
American Congress of Obstetricians and Gynecologists The American College of Obstetricians and Gynecologists (ACOG) is a professional association of physicians specializing in obstetrics and gynecology in the United States. Several Latin American countries are also represented within Districts o ...
(ACOG) guidelines. There are umbilical cord clamps which incorporate a 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, the newborn wears a plastic clip on the navel area until the compressed region of the cord has dried and sealed sufficiently. The length of umbilical left attached to the newborn varies by practice; in most hospital settings the length of cord left attached after clamping and cutting is minimal. In the United States, however, where the birth occurred outside of the hospital and an
emergency medical technician An emergency medical technician (EMT), also known as an ambulance technician, is a health professional that provides emergency medical services. EMTs are most commonly found working in ambulances. In English-speaking countries, paramedics are ...
(EMT) clamps and cuts the cord, a longer segment up to in length is left attached to the newborn. The remaining umbilical stub remains for up to 10 days as it dries and then falls off.


Early versus delayed clamping

A
Cochrane review Cochrane (previously known as the Cochrane Collaboration) is a British international charitable organisation formed to organise medical research findings to facilitate evidence-based choices about health interventions involving health professi ...
in 2013 came to the conclusion that delayed cord clamping (between one and three minutes after birth) is "likely to be beneficial as long as access to treatment for jaundice requiring phototherapy is available". In this review delayed clamping, as contrasted to early, resulted in no difference in risk of severe maternal postpartum hemorrhage or neonatal mortality, and a low
Apgar score The Apgar score is a quick way for doctors to evaluate the health of all newborns at 1 and 5 minutes after birth and in response to resuscitation. It was originally developed in 1952 by an anesthesiologist at Columbia University, Virginia Apgar ...
. On the other hand, delayed clamping resulted in an increased birth weight of on average about 100 g, and an increased
hemoglobin Hemoglobin (haemoglobin BrE) (from the Greek word αἷμα, ''haîma'' 'blood' + Latin ''globus'' 'ball, sphere' + ''-in'') (), abbreviated Hb or Hgb, is the iron-containing oxygen-transport metalloprotein present in red blood cells (erythroc ...
concentration of on average 1.5 g/dL with half the risk of being iron deficient at three and six months, but an increased risk of jaundice requiring
phototherapy Light therapy, also called phototherapy or bright light therapy is intentional daily exposure to direct sunlight or similar-intensity artificial light in order to treat medical disorders, especially seasonal affective disorder (SAD) and circad ...
. In 2012, the American College of Obstetricians and Gynecologists officially endorsed delaying clamping of the umbilical cord for 30–60 seconds with the newborn held below the level of the placenta in all cases of preterm delivery based largely on evidence that it reduces the risk of intraventricular hemorrhage in these children by 50%. In the same committee statement, ACOG also recognize several other likely benefits for preterm infants, including "improved transitional circulation, better establishment of red blood cell volume, and decreased need for blood transfusion". In January 2017, a revised Committee Opinion extended the recommendation to term infants, citing data that term infants benefit from increased hemoglobin levels in the newborn period and improved iron stores in the first months of life, which may result in improved developmental outcomes. ACOG recognized a small increase in the incidence of jaundice in term infants with delayed cord clamping, and recommended policies be in place to monitor for and treat neonatal jaundice. ACOG also noted that delayed cord clamping is not associated with increased risk of postpartum hemorrhage. Several studies have shown benefits of delayed cord clamping: A meta-analysis showed that delaying clamping of the umbilical cord in full-term neonates for a minimum of 2 minutes following birth is beneficial to the newborn in giving improved hematocrit, iron status as measured by
ferritin Ferritin is a universal intracellular protein that stores iron and releases it in a controlled fashion. The protein is produced by almost all living organisms, including archaea, bacteria, algae, higher plants, and animals. It is the primary ...
concentration and stored iron, as well as a reduction in the risk of anemia (
relative risk The relative risk (RR) or risk ratio is the ratio of the probability of an outcome in an exposed group to the probability of an outcome in an unexposed group. Together with risk difference and odds ratio, relative risk measures the association be ...
, 0.53; 95% CI, 0.40–0.70). A decrease was also found in a study from 2008.Examination of the Newborn & Neonatal Health: A Multidimensional Approach, p. 116-117 Although there is higher hemoglobin level at 2 months, this effect did not persist beyond 6 months of age."Effect of timing of umbilical cord clamping of term infants on maternal and neonatal outcomes." ''Cochrane Database Syst Rev''. 2008; (2):CD004074 Not clamping the cord for three minutes following the birth of a baby improved outcomes at four years of age. A delay of three minutes or more in umbilical cord clamping after birth reduce the prevalence of anemia in infants. Negative effects of delayed cord clamping include an increased risk of
polycythemia Polycythemia (also known as polycythaemia) is a laboratory finding in which the hematocrit (the volume percentage of red blood cells in the blood) and/or hemoglobin concentration are increased in the blood. Polycythemia is sometimes called e ...
. Still, this condition appeared to be benign in studies. Infants whose cord clamping occurred later than 60 seconds after birth had a higher rate of
neonatal jaundice Neonatal jaundice is a yellowish discoloration of the white part of the eyes and skin in a newborn baby due to high bilirubin levels. Other symptoms may include excess sleepiness or poor feeding. Complications may include seizures, cerebral pal ...
requiring
phototherapy Light therapy, also called phototherapy or bright light therapy is intentional daily exposure to direct sunlight or similar-intensity artificial light in order to treat medical disorders, especially seasonal affective disorder (SAD) and circad ...
. Delayed clamping is not recommended as a response to cases where the newborn is not breathing well and needs resuscitation. Rather, the recommendation is instead to immediately clamp and cut the cord and perform
cardiopulmonary resuscitation Cardiopulmonary resuscitation (CPR) is an emergency procedure consisting of chest compressions often combined with artificial ventilation in an effort to manually preserve intact brain function until further measures are taken to restore spont ...
. The umbilical cord pulsating is not a guarantee that the baby is receiving enough oxygen.


Umbilical nonseverance

Some parents choose to omit cord severance entirely, a practice called "
lotus birth Lotus birth (or umbilical cord nonseverance - UCNS) is the practice of leaving the umbilical cord uncut after childbirth so that the baby is left attached to the placenta until the cord naturally separates at the umbilicus. This usually occur ...
" or umbilical nonseverance. The entire intact umbilical cord is allowed to dry and separates on its own (typically on the 3rd day after birth), falling off and leaving a healed umbilicus.


Umbilical cord catheterization

As the umbilical vein is directly connected to the central circulation, it can be used as a route for placement of a venous catheter for infusion and medication. The umbilical vein catheter is a reliable alternative to percutaneous peripheral or central venous catheters or intraosseous canulas and may be employed in resuscitation or intensive care of the newborn.


Blood sampling

From 24 to 34 weeks of gestation, when the fetus is typically viable, blood can be taken from the cord in order to test for abnormalities (particularly for
hereditary Heredity, also called inheritance or biological inheritance, is the passing on of traits from parents to their offspring; either through asexual reproduction or sexual reproduction, the offspring cells or organisms acquire the genetic informa ...
conditions). This diagnostic
genetic test Genetic testing, also known as DNA testing, is used to identify changes in DNA sequence or chromosome structure. Genetic testing can also include measuring the results of genetic changes, such as RNA analysis as an output of gene expression, ...
procedure is known as percutaneous umbilical cord blood sampling.


Storage of cord blood

The blood within the umbilical cord, known as cord blood, is a rich and readily available source of primitive, undifferentiated
stem cell In multicellular organisms, stem cells are undifferentiated or partially differentiated cells that can differentiate into various types of cells and proliferate indefinitely to produce more of the same stem cell. They are the earliest type of ...
s (of type CD34-positive and
CD38 CD38 (cluster of differentiation 38), also known as cyclic ADP ribose hydrolase is a glycoprotein found on the surface of many immune cells (white blood cells), including CD4+, CD8+, B lymphocytes and natural killer cells. CD38 also functions in ...
-negative). These cord blood cells can be used for bone marrow transplant. Some parents choose to have this blood diverted from the baby's umbilical blood transfer through early cord clamping and cutting, to freeze for long-term storage at a
cord blood bank A cord blood bank is a facility which stores umbilical cord blood for future use. Both private and public cord blood banks have developed in response to the potential for cord blood in treating diseases of the blood and immune systems. Public cord ...
should the child ever require the cord blood stem cells (for example, to replace
bone marrow Bone marrow is a semi-solid biological tissue, tissue found within the Spongy bone, spongy (also known as cancellous) portions of bones. In birds and mammals, bone marrow is the primary site of new blood cell production (or haematopoiesis). It i ...
destroyed when treating
leukemia Leukemia ( also spelled leukaemia and pronounced ) is a group of blood cancers that usually begin in the bone marrow and result in high numbers of abnormal blood cells. These blood cells are not fully developed and are called ''blasts'' or ...
). This practice is controversial, with critics asserting that early cord blood withdrawal at the time of birth actually increases the likelihood of childhood disease, due to the high volume of blood taken (an average of 108ml) in relation to the baby's total supply (typically 300ml). The
Royal College of Obstetricians and Gynaecologists The Royal College of Obstetricians and Gynaecologists (RCOG) is a professional association based in London, United Kingdom. Its members, including people with and without medical degrees, work in the field of obstetrics and gynaecology, that ...
stated in 2006 that "there is still insufficient evidence to recommend directed commercial cord blood collection and stem-cell storage in low-risk families". The
American Academy of Pediatrics The American Academy of Pediatrics (AAP) is an American professional association of pediatricians, headquartered in Itasca, Illinois. It maintains its Department of Federal Affairs office in Washington, D.C. Background The Academy was found ...
has stated that cord blood banking for self-use should be discouraged (as most conditions requiring the use of stem cells will already exist in the cord blood), while banking for general use should be encouraged. In the future, cord blood-derived embryonic-like stem cells (CBEs) may be banked and matched with other patients, much like blood and transplanted tissues. The use of CBEs could potentially eliminate the ethical difficulties associated with embryonic stem cells (ESCs). While the American Academy of Pediatrics discourages private banking except in the case of existing medical need, it also says that information about the potential benefits and limitations of cord blood banking and transplantation should be provided so that parents can make an informed decision. In the United States, cord blood education has been supported by legislators at the federal and state levels. In 2005, the National Academy of Sciences published a
Institute of Medicine (IoM) report
which recommended that expectant parents be given a balanced perspective on their options for cord blood banking. In response to their constituents, state legislators across the country are introducing legislation intended to help inform physicians and expectant parents on the options for donating, discarding or banking lifesaving newborn stem cells. Currently 17 states, representing two-thirds of U.S. births, have enacted legislation recommended by the IoM guidelines. The use of cord blood stem cells in treating conditions such as brain injury and Type 1 Diabetes is already being studied in humans, and earlier stage research is being conducted for treatments of stroke, and hearing loss. Cord blood stored with private banks is typically reserved for use of the donor child only. In contrast, cord blood stored in public banks is accessible to anyone with a closely matching tissue type and demonstrated need. The use of cord blood from public banks is increasing. Currently it is used in place of a bone marrow transplant in the treatment of blood disorders such as leukemia, with donations released for transplant through one registry, Netcord.org, passing 1,000,000 as of January 2013. Cord blood is used when the patient cannot find a matching bone marrow donor; this "extension" of the donor pool has driven the expansion of public banks.


The umbilical cord in other animals

The umbilical cord in some mammals, including cattle and sheep, contains two distinct umbilical veins. There is only one umbilical vein in the human umbilical cord.''Meat Hygiene''. J. F. Gracey, D. S. Collins, Robert J. Huey. p. 32. In some animals, the mother will gnaw through the cord, thus separating the placenta from the offspring. The cord along with the placenta is often eaten by the mother, to provide nourishment and to dispose of tissues that would otherwise attract scavengers or predators. In
chimpanzee The chimpanzee (''Pan troglodytes''), also known as simply the chimp, is a species of great ape native to the forest and savannah of tropical Africa. It has four confirmed subspecies and a fifth proposed subspecies. When its close relative t ...
s, the mother leaves the cord in place and nurses her young with the cord and placenta attached until the cord dries out and separates naturally, within a day of birth, at which time the cord is discarded. (This was first documented by zoologists in the wild in 1974.) Some species of
shark Sharks are a group of elasmobranch fish characterized by a cartilaginous skeleton, five to seven gill slits on the sides of the head, and pectoral fins that are not fused to the head. Modern sharks are classified within the clade Selachi ...
hammerheads, requiems and
smooth-hound ''Mustelus'', also known as the smooth-hounds, is a genus of sharks in the family Triakidae. The name of the genus comes from the Latin word ''mustela'', meaning weasel. It should not be confused with the genus name ''Mustela'', which is used ...
s—are
viviparous Among animals, viviparity is development of the embryo inside the body of the parent. This is opposed to oviparity which is a reproductive mode in which females lay developing eggs that complete their development and hatch externally from the ...
and have an umbilical cord attached to their placenta. Animals that lay eggs seem to have a false umbilical-cord that attaches the embryo and yolk together in much the same way.


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 surface-supplied divers to their surface supply of air and/or heating, or space-suited
astronaut An astronaut (from the Ancient Greek (), meaning 'star', and (), meaning 'sailor') is a person trained, equipped, and deployed by a human spaceflight program to serve as a commander or crew member aboard a spacecraft. Although generally r ...
s to their spacecraft. Engineers sometimes use the term to describe a complex or critical cable connecting a component, especially when composed of bundles of conductors of different colors, thickness and types, terminating in a single multi-contact disconnect.


Cancer-causing toxicants in human umbilical cords

In multiple American and international studies, cancer-causing chemicals have been found in the blood of umbilical cords. These originate from certain plastics, computer circuit boards, fumes and synthetic fragrances among others. Over 300 chemical toxicants have been found, including
bisphenol A Bisphenol A (BPA) is a chemical compound primarily used in the manufacturing of various plastics. It is a colourless solid which is soluble in most common organic solvents, but has very poor solubility in water. BPA is produced on an industrial ...
(BPA), tetrabromobisphenol A (TBBPA),
Teflon Polytetrafluoroethylene (PTFE) is a synthetic fluoropolymer of tetrafluoroethylene that has numerous applications. It is one of the best-known and widely applied PFAS. The commonly known brand name of PTFE-based composition is Teflon by Chemo ...
-related perfluorooctanoic acid,
galaxolide Galaxolide (trade name; also known as Abbalide, Pearlide, Astrolide, Musk 50, Polarlide; chemical name 1,3,4,6,7,8-hexahydro-4,6,6,7,8,8,-hexamethyl-cyclopenta 'g''enzopyran or HHCB, hexamethylindanopyran) is a synthetic musk with a clean sweet m ...
and
synthetic musk Synthetic musks are a class of synthetic aroma compounds to emulate the scent of deer musk and other animal musks (castoreum and civet). Synthetic musks have a clean, smooth and sweet scent lacking the fecal notes of animal musks. They are used ...
s among others. The studies in America showed higher levels in
African Americans African Americans (also referred to as Black Americans and Afro-Americans) are an ethnic group consisting of Americans with partial or total ancestry from sub-Saharan Africa. The term "African American" generally denotes descendants of ens ...
, Hispanic Americans and
Asian Americans Asian Americans are Americans of Asian ancestry (including naturalized Americans who are immigrants from specific regions in Asia and descendants of such immigrants). Although this term had historically been used for all the indigenous peopl ...
due, it is thought, to living in areas of higher pollution.


Additional images

File:Gray34.png, Sectional plan of the gravid uterus in the third and fourth month. File:Gray38.png, Fetus in utero, between fifth and sixth months. File:Newborn umbilical suction.jpg, A newborn at 45 seconds, with umbilical cord clamped. File:Slide2BLA.JPG, Umbilic. Deep dissection. Serial cross section. File:Umbcord.jpg, dried umbilical cord stump.


See also

*
Navel The navel (clinically known as the umbilicus, commonly known as the belly button or tummy button) is a protruding, flat, or hollowed area on the abdomen at the attachment site of the umbilical cord. All placental mammals have a navel, altho ...
* Umbilical line


References

*


External links

* {{Authority control Childbirth Cloning Embryology Stem cells Vertebrate developmental biology