Placental accommodations for transport and metabolism during intra-uterine crowding in XXXX .

@entity1707 @entity948 @entity16369 @entity4823 @entity3470 @entity8686 @entity3689 @entity413
Litter size and birth weights are limited by uterine capacity, defined as the ability of the uterus to maintain the appropriate development of some number of conceptuses. Uterine capacity is the result of the combined effects of uterine, placental and embryo/fetal function. The number of living conceptuses that the uterus is capable of supporting is greater during early gestation compared to later gestation. Plots of log fetal weight versus log placental weight also indicate that fetal weights are less sensitive to reduced placental weight (and therefore reduced intrauterine space) in early gestation compared to late gestation. However, even in late gestation, mechanisms still exist that maintain fetal growth when the size of the placenta is reduced. One such mechanism is likely to be improved development of the folded placental-epithelial/maternal-epithelial bilayer. Fold depth, and therefore the maternal fetal interactive surface, increases as gestation advances and is greater in placenta from small fetuses. On the fetal side of the placenta, the epithelial bilayer is embedded in stromal tissue. Glycosaminoglycans are major components of stroma, including hyaluronan and heparan sulfate. Hyaluronidases and heparanases are present within placental tissues, and likely play roles in modification of stromal components to facilitate fold development. Glycosaminoglycans are polymers of forms of @entity413 ( @entity4823 , @entity8686 , @entity16369 ) suggesting that glycosaminoglycan synthesis may compete with the @entity413 needs of the developing fetus. @entity1707 conceptuses are fructogenic, such that a substantial portion of @entity413 transferred from mother to fetus is converted to @entity948 . @entity948 is an intermediate product in the synthesis of @entity4823 from @entity413 , and @entity4823 is linked to regulation of trophoblast cell proliferation through regulation of @entity3470 . These findings suggest a link between @entity413 , @entity948 , @entity4823 synthesis, GAG production, and placental morphogenesis, but the details of these interactions remain unclear. In addition, recent placental epithelial transcriptome analysis identified several @entity413 , @entity3689 , lipid, vitamin, mineral and hormone transporter mechanisms within the placenta. Further elucidation of mechanisms of placental morphogenesis and solute transport could provide clues to improving nutrient transport to the @entity1707 fetus, potentially increasing litter size and piglet birth weights.
