Oxygen umbilical arterial

Two umbilical arteries from the foetus carry blood to the placenta and a single umbilical vein returns blood from the placenta back to the foetus. The functions of the placenta in pregnancy are to supply oxygen and nutrients from the maternal circulation to the foetus and to remove waste materials, such as urea and carbon dioxide, from foetal blood. 

In the placenta a volume of oxygen sufficient for fetal needs must diffuse across the membranes from maternal to fetal blood during the short time the two circulations are in close contact. This oxygen transfer is a function of several factors which include uterine and umbilical arterial 02 partial pressures, maternal and fetal placental blood flow rates, the 02 capacity and 02 affinity of maternal and fetal hemoglobin, the diffusing capacity of the placenta, the amount of C02 exchanged, and the vascular arrangement of maternal to fetal vessels. 

It was recently proposed that kinin is responsible for the circulatory changes at birth which result in conversion of the foetal to the new-born circulation. Presumably, the decreased temperature of the umbilical cord, the increased partial tension of oxygen in the blood and the increased concentration of circulating granulocytes all activate the kininogenase and thus induce kinin release. Kinin then constricts the umbilical artery and vein and the ductus arteriosus and dilates the pulmonary vasculature. All these effects of kinin have been confirmed experimentally in the lamb. 

Later on, the importance of xanthine oxidase as the producer of reoxygenation injury was questioned at least in the cells with low or no xanthine oxidase activity. Thus, it has been shown that human and rabbit hearts, which possess extremely low xanthine oxidase activity, nonetheless, develop myocardial infractions and ischemia-reperfusion injury [9], However, recent studies supported the importance of the xanthine oxidase-catalyzed oxygen radical generation. It has been showed that xanthine oxidase is partly responsible for reoxygenation injury in bovine pulmonary artery endothelial cells [10], human umbilical vein and lymphoblastic leukemia cells [11], and cerebral endothelial cells [12], Zwang et al. [11] concluded that xanthine dehydrogenase may catalyze superoxide formation without conversion to xanthine oxidase using NADH instead of xanthine as a substrate. 

After it was determined that changing the linear velocity of the maternal or fetal blood stream did not affect the equilibration pressure, it was possible to determine the maternal to fetal volumetric flow rate ratio that would result in an equilibration pressure which matched experimentally determined values of umbilical vein and artery oxygen partial pressures (37). As the maternal to fetal volumetric flow rate ratio is increased, the partial pressure of oxygen at which equilibration... 

In late gestation, the fetal cardiovascular response to hypoxia is typified by a rapid, transient bradycardia and increased heart rate variability (21,22). The bradycardia reaches a nadir approximately 1-2 min after the onset of the hypoxic insult (15,23) and, presumably, economizes on myocardial oxygen consumption. Fetal hypoxic bradycardia occurs at the onset of hypoxic hypoxia (5), umbilical cord occlusion (24,25), and uterine artery occlusion (26)— the three most common experimental hypoxic challenges. 

Peeters L, Sheldon R, Jones M, Makowski E, Meschia G. Blood flow to fetal organs as a function of arterial oxygen content. Am J Obstet Gynecol 1979 135(5) 637-646. Johnson G, Palahniuk R, Tweed W, Jones M, Wade J. Regional cerebral blood flow changes during severe fetal asphyxia produced by slow partial umbilical cord compression. Am J Obstet Gynecol 1979 135(l) 48-52. 

Fig. P-66. The growing fetus depends on its mother for nutrients and removal of wastes. The mother s heart pumps blood through the uterine arteries into the placenta nutrients and oxygen diffuse through the placental membranes into the fetal bloodstream by way of the umbilical cord and wastes pass in the reverse direction to the maternal bloodstream through the uterine veins.

A special case of arterial /7O2 measurement is the monitoring of umbilical blood to prevent undue deficiency (hypoxaemia) or excess (hyperoxaemia) of oxygen. 

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