Anderson Kristie E, Blackburn Daniel G, Dunlap Kent D
Department of Biology and Electron Microscopy Facility, Trinity College, Hartford, Connecticut 06106, USA.
J Morphol. 2011 Apr;272(4):465-84. doi: 10.1002/jmor.10925. Epub 2011 Feb 2.
Placental membranes mediate maternal-fetal exchange in all viviparous reptilian sauropsids. We used scanning electron microscopy to examine the placental interface in the mountain spiny lizard, Sceloporus jarrovi (Phrynosomatidae). From the late limb bud stage until birth, the conceptus is surrounded by placental membranes formed from the chorioallantois and yolk sac omphalopleure. The chorioallantois lies directly apposed to the uterine lining with no intervening shell membrane. Both fetal and maternal sides of the chorioallantoic placenta are lined by continuous layers of flattened epithelial cells that overlie dense capillary networks. The chorioallantoic placenta shows specializations that enhance respiratory exchange, as well as ultrastructural evidence of maternal secretion and fetal absorption. The yolk sac placenta contains enlarged fetal and maternal epithelia with specializations for histotrophic nutrient transfer. This placenta lacks intrinsic vascularity, although the vascular allantois lies against its inner face, contributing to an omphallantoic placenta. In a specialized region at the abembryonic pole, uterine and fetal tissues are separated by a compact mass of shed shell membrane, yolk droplets, and cellular debris. The omphalopleure in this region develops elongate folds that may contribute to sequestration and absorption of this material. Fetal membrane morphogenesis and composition in S. jarrovi are consistent with those of typical squamates. However, this species exhibits unusual placental specializations characteristic of highly placentotrophic lizards.
胎盘膜在所有胎生的爬行类蜥形纲动物中介导母胎交换。我们使用扫描电子显微镜检查了山地多刺蜥蜴（Sceloporus jarrovi，角蜥科）的胎盘界面。从肢体芽晚期到出生，胚胎被由绒毛膜尿囊和卵黄囊脐卵黄膜形成的胎盘膜包围。绒毛膜尿囊直接贴附于子宫内膜，中间没有壳膜。绒毛膜尿囊胎盘的胎儿侧和母体侧均由连续的扁平上皮细胞层覆盖，这些细胞层覆盖着密集的毛细血管网络。绒毛膜尿囊胎盘表现出增强呼吸交换的特化结构，以及母体分泌和胎儿吸收的超微结构证据。卵黄囊胎盘包含扩大了的胎儿和母体上皮，具有组织营养性营养物质转运的特化结构。尽管血管尿囊贴靠其内表面，为脐尿囊胎盘做出贡献，但该胎盘缺乏内在血管。在胚胎极的一个特殊区域，子宫和胎儿组织被一团紧密的脱落壳膜、卵黄滴和细胞碎片分隔开。该区域的脐卵黄膜形成细长的褶皱，可能有助于隔离和吸收这些物质。山地多刺蜥蜴的胎膜形态发生和组成与典型有鳞目动物一致。然而，该物种表现出高度胎盘营养型蜥蜴特有的异常胎盘特化结构。
