Placental Morphology Features Placental shape (diffuse, cotyledonary, zonary, discoidal) Definitive type of placental interface (eg. epitheliochorial, endotheliochorial, hemochorial) Fetomaternal interdigitation (folded, villous, labyrinthe) Fetomaternal blood flow interrelations (concurrent, countercurrent, crosscurrent, multivillous) Placental nutrient transport Wildman D, et al., 2006

Placental structure is highly diverse among mammals Thornburg and Faber, 1983

hu ^ Thornburg and Faber, 1983

Placental Morphology Features Placental shape (diffuse, cotyledonary, zonary, discoidal) Definitive type of placental interface (e.g. epitheliochorial, endotheliochorial, hemochorial) Fetomaternal interdigitation (folded, villous, labyrinthe) Fetomaternal blood flow interrelations (concurrent, countercurrent, crosscurrent, multivillous) Placental nutrient transport Wildman D, et al., 2006

The functions of the placenta are to establish a dialogue with maternal physiology for the success of pregnancy, and to provide nutrients for fetal growth and development. Many variations on the interface can be found and terminologies have evolved as morphological tools became more sensitive. Stroma

Fetal and maternal blood are separated by 1 capillary and (a) fetal epithelium: Hemochorial placentation (trophoblasts are directly exposed to maternal blood; human, rat, mouse, monkey). Kaufmann and Burton, 1994 Moffett and Lake, 2006

Placental Morphology Features Placental shape (diffuse, cotyledonary, zonary, discoidal) Definitive type of placental interface (e.g. epitheliochorial, endotheliochorial, hemochorial) Fetomaternal interdigitation (folded, villous, labyrinthe) Fetomaternal blood flow interrelations (concurrent, countercurrent, crosscurrent, multivillous) Placental nutrient transport Wildman D, et al., 2006

Villous Week 1 of gestation: Trophoblast differentiation Syncytio-trophoblast differentiation Invasion and formation of the trophoblastic shell No villous organization Villous Benirschke and Kaufmann, 1999

Extravillous trophoblast differentiation Week 2 of gestation: Extravillous trophoblast differentiation Syncytio-trophoblast expansion Formation of fetal vasculature Initiation of villous organization Benirschke and Kaufmann, 1999

Villous placentation

Placentation in primates: spiral artery remodeling Rapid invasion of spiral arteries: endovascular invasion Limited interstitial trophoblast invasion Remodeling of vessel wall Invasion to endometrial-myometrial junction around 1/3 of gestation Enders, 2007 CTK IHC

Inappropriate remodelling may lead to hypoxic, nitrative or oxidative stress and is thought to have clinical significance in adverse pregnancy outcomes. Genbacev et. al, 2001

Placental Morphology Features Placental shape (diffuse, cotyledonary, zonary, discoidal) Definitive type of placental interface (e.g. epitheliochorial, endotheliochorial, hemochorial) Fetomaternal interdigitation (folded, villous, labyrinthe) Fetomaternal blood flow interrelations (concurrent, countercurrent, crosscurrent, multivillous) Placental nutrient transport Wildman D, et al., 2006

Chorionic plate Villus tree Basal plate Decidua Ramsey and Harris, 1966

Adamson et al, 2002 This shows mouse placenta, but the idea of placental layers in the same for humans and other primates

Placental Morphology Features Placental shape (diffuse, cotyledonary, zonary, discoidal) Definitive type of placental interface (e.g. epitheliochorial, endotheliochorial, hemochorial) Fetomaternal interdigitation (folded, villous, labyrinthe) Fetomaternal blood flow interrelations (concurrent, countercurrent, crosscurrent, multivillous) Placental nutrient transport Wildman D, et al., 2006

Blue, red, yellow: type I, II, III stem villi. Pale blue, violet: terminal villi. These villi are thought to be the primary sites of nutrient transit to the fetal vessels. Fuchs and Ellinger, 2004

During pregnancy, there is thinning of the syncytial layer and formation of close association between the basal syncytium and outer layer of the villous endothelium. This is thought to be a major transport zone. Fuchs and Ellinger, 2004

Oxygen, glucose, amino acids, vitamins, ions, minerals, lipids, water Fuchs and Ellinger, 2004 Needed nutrients: Oxygen, glucose, amino acids, vitamins, ions, minerals, lipids, water Potential mechanisms of transit: diffusion, carrier-mediated transport, vesicular transcytosis