FUNCTIONAL ASYMMETRY OF THE LIVER

The human liver consists of two completely fused and almost equal sized physiological units. These appear to differ functionally very little in the adult, but there is considerable evidence to suggest that the same does not apply in the fetus and newborn child.1,2 The liver develops amid the vitelline sinusoids around the gut. The early blood supply from the placenta does not go through this plexus, but later the right umbilical vein involutes and the left connects with the vitelline plexus of the left liver. By the time that the fetal blood circulation is established, the blood from the placenta enters the left liver by way of a single umbilical vein passing through it to the inferior vena cava. Some of the blood goes directly through the ductus venoms and this appears to be an extremely variable amount. The diameter of the ductus uenosus is on average, 1//7 of that of the umbilical vein,3 and, in our own material, the ductus is virtually closed in about 1 in 30 newborn infants. Lind4 and his colleagues have shown that blood from the placenta circulates through the left liver on its way to the heart. Thus the cells of the left liver are bathed in the most highly oxygenated blood of the foetus. The blood going through the right liver is largely from the portal veins. Following birth, the placental blood supply to the left liver is suddenly cut off, and the main circulation to the liver is taken over by the vessels previously supplying only the right liver. Thus the cells of the left liver, from being bathed in the blood of highest oxygen and nutrient content, now become more than relatively destitute. In about a third of stillborns or children dying within the neonatal period, these circulatory features are represented clinically by a naked eye difference between the left and right livers, the change being seen best as a “coast line” running over the anterior surface of the liver to the gall bladder (FIGURE 1 ) . In some cases it is so marked as to be clearly visible on the cut formalin fixed liver (FIGURE 2). We have studied only a few aspects of the asymmetry of the liver in detail ( summarized in TABLE 1 ) . Weights of the lobes. From the fifth to ninth intrauterine month, the ratio of the weight of the right to left liver is 0.89, i.e., the left liver is a little over one-tcnth larger than the right. Within 24 hours of birth, the lobes are of equal weight, and by the end of 5 days after birth, the intrauterine ratio (R/L) is reversed being now between 1.1 and 1.16 and this continues for at least 12 weeks.5 In older children we have found no significant diff erence in weights. Postnatal incolution of the left lohe. Accompanying the diminution of the weight of the left lobe there is a shrinkage of the liver cells6 with relative prominence of the blood sinuses (FIGURE 3 ) . This change is more