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In placental mammals, the umbilical cord (also called the navel string, [1] birth cord or funiculus umbilicalis) is a conduit between the developing embryo or fetus and the placenta. During prenatal development , the umbilical cord is physiologically and genetically part of the fetus and (in humans) normally contains two arteries (the umbilical ...
Cord entanglement: The close proximity and absence of amniotic membrane separating the two umbilical cords makes it particularly easy for the twins to become entangled in each other's cords, hindering fetal movement and development. [4] Additionally, entanglement may cause one twin to become stuck in the birth canal during labor and expulsion. [1]
The amnion is the innermost layer and, therefore, contacts the amniotic fluid, the fetus and the umbilical cord. [5] The internal pressure of the amniotic fluid causes the amnion to be passively attached to the chorion. [4] The chorion functions to separate the amnion from the maternal decidua and uterus. [4]
If one twin dies in utero, blood accumulates in that twin's body, causing exsanguination of the remaining twin. [2] In the case of monoamniotic twins the risk of complications is substantially higher because of additional potential umbilical cord entanglement and compression. [3] However, the perinatal mortality of monochorionic twins is fairly ...
In cattle (and other bovines), the placentas of fraternal twins usually fuse and the twins share blood circulation, resulting in exchange of cell lines. If the twins are a male–female pair, then XX/XY microchimerism results, and male hormones partially masculinize the heifer (female), creating a martin heifer or freemartin.
In humans, the circulatory system is different before and after birth. The fetal circulation is composed of the placenta, umbilical blood vessels encapsulated by the umbilical cord, heart and systemic blood vessels. A major difference between the fetal circulation and postnatal circulation is that the lungs are not used during the fetal stage ...
The twin reversed arterial perfusion, or T.R.A.P. sequence, results in an 'acardiac twin', a parasitic twin that fails to develop a head, arms and a heart.The parasitic twin, little more than a torso with or without legs, receives its blood supply from the host twin by means of an umbilical cord-like structure, much like a fetus in fetu, except the acardiac twin is outside the autosite's body.
The amniotic sac and its filling provide a liquid that surrounds and cushions the fetus. It is a site of exchange of essential substances, such as oxygen, between the umbilical cord and the fetus. [9] It allows the fetus to move freely within the walls of the uterus. [citation needed] Buoyancy is also provided.