zonary

In zonary placentas (Figure 15-17), a band of microvilli encompasses the equatorial region of the allantochorion.

TABLE 15-1 Timing of several key events during early pregnancy in several species of mammals Blastocyst stage Arrival in uterus Implantation (days after (days after (days after Species ovulation) ovulation) ovulation) Cattle 8-9 3-4 17-20 Sheep 6-7 2-4 15-16 Horses 8-9 4-10 28-40 Swine 5-6 2-2.5 11-14 Dogs 5-6 8-15 17-21 Cats 5-6 4-8 13-14 Rodents 3-4 3-4 5-10 Humans 4-5 4-5 6.5-26 TABLE 15-2 Classification of placentae of several types of mammals based on two criteria Species Gross Morphology Maternal-Fetal Barrier Cattle Cotyledonary Epitheliochorial Sheep Cotyledonary Epitheliochorial Horses Diffuse Epitheliochorial Swine Diffuse Epitheliochorial Dogs Zonary Endotheliochorial Cats Zonary Endotheliochorial Rodents Discoidal Hemochorial Humans Discoidal Hemochorial

Intrahepatocytic accumulated lipid vacuoles showed a zonary pattern similar to that found in individuals exposed to toxic substances, which produce a characteristic periacinar injury due to the low oxygen gradient (hypoxia and high concentrations of, for example, cytochrome P450).

We found such a zonary appearance in hepatocytic accumulation in the polar bears in the present study.

The signs and type of chronic inflammation, and the zonary lipid accumulation in hepatocytes, may indicate chronic exposure to environmental levels of OHCs.