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The unpaired umbilical vein carries oxygen and nutrient rich blood derived from fetal-maternal blood exchange at the chorionic villi.More than two-thirds of fetal hepatic circulation is via the main portal vein, while the remainder is shunted from the left portal vein via the ductus venosus to the inferior vena cava, eventually being delivered to the fetal right atrium.
Twin anemia-polycythemia sequence (TAPS) is a chronic type of unbalanced fetal transfusion in monochorionic twins that results in polycythemia in the TAPS recipient and anemia in the TAPS donor due to tiny placental anastomoses. [1]
Produces abdominal collateral veins to bypass the blocked inferior vena cava and permit venous return from the legs. Determine the direction of flow in the veins below the umbilicus. After pushing down on the prominent vein, blood will: flow toward the legs → caput medusae; flow toward the head → inferior vena cava obstruction.
In response to this, the proportion of umbilical venous blood diverted to fetal heart increases. [25] This eventually leads to elevation of pulmonary vascular resistance and increased right ventricular afterload. [26] [27] [28] This fetal cerebral redistribution of blood flow is an early
As the umbilical vessels are obliterated and the infant starts breathing at birth, the source of oxygen changes from the placenta to the lungs. This major trigger will facilitate the transformation from fetal to postnatal circulation in many ways. First, the ductus venosus was previously kept open by the blood flow from the umbilical vein.
Reversing flow patterns in arteries and/or veins can also have the same effect, although it is unclear whether this is due to differences in physical or chemical properties of venous vs. arterial flow (i.e. pressure profile and oxygen tension). [10] Another example of the fluidity of arterial-venous identity is that of the intersomitic vessel.
Twin-to-twin transfusion syndrome (TTTS), also known as feto-fetal transfusion syndrome (FFTS), twin oligohydramnios-polyhydramnios sequence (TOPS) and stuck twin syndrome, is a complication of monochorionic multiple pregnancies (the most common form of identical twin pregnancy) in which there is disproportionate blood supply between the fetuses.
The classic definition by MP Spencer and AB Denison of compliance is the change in arterial blood volume due to a given change in arterial blood pressure ().They wrote this in the "Handbook of Physiology" in 1963 in work entitled "Pulsatile Flow in the Vascular System".