where is the umbilical cord attached to the mother
Umbilical cord The umbilical cord develops from and contains remnants of the yolk sac and allantois. It forms by the fifth week of development, replacing the yolk sac as the source of nutrients for the embryo.[2] The cord is not directly connected to the mother's circulatory system, but instead joins the placenta, 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. The umbilical cord in a full term neonate is usually about 50 centimeters (20 in) long and about 2 centimeters (0.75Â 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.[3] 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 postnatal closure.[3]
Adaptation to extrauterine life Perfusing its body by breathing independently instead of utilizing placental oxygen delivered via the umbilical cord is the first challenge of a newborn. At birth, the baby's lungs are filled with lung liquid, which is distinct from amniotic fluid.[1] When the newborn is expelled from the birth canal, its central nervous system reacts to the sudden change in temperature and environment.[2] This triggers it to take the first breath, within about 10 seconds after delivery.[2] With the first breaths, there is a fall in pulmonary vascular resistance, and an increase in the surface area available for gas exchange. Over the next 30 seconds the pulmonary blood flow increases and is oxygenated as it flows through the alveoli of the lungs. Oxygenated blood now reaches the left atrium and ventricle, and through the descending aorta reaches the umbilical arteries. Oxygenated blood now stimulates constriction of the umbilical arteries resulting in a reduction in placental blood flow. As the pulmonary circulation increases there is an equivalent reduction in the placental blood flow which normally ceases completely after about three minutes. These two changes result in a rapid redirection of blood flow into the pulmonary vascular bed, from approximately 4% to 100% of cardiac output. The increase in pulmonary venous return results in left atrial pressure being slightly higher than right atrial pressure, which closes the foramen ovale. The flow pattern changes results in a drop in blood flow across the ductus arteriosus and the higher blood oxygen content of blood within the aorta stimulates the constriction and ultimately the closure of this fetal circulatory shunt.