Wildman et al. 10.1073/pnas.0511344103. |
Definitions of Characters and Character States
Placental interface:
The number of maternal tissue layers penetrated by the fetal tissue. There are six types of placental interface (1):a. Epitheliochorial: the fetal chorion is in contact with the endometrium epithelium, and the blastocyst does not invade the maternal endometrium.
b. Syndesmochorial: the fetal chorion destroys the uterine epithelium; this character state was thought to exist in sheep and goats, but its existence has been refuted more recently (2).
c. Endotheliochorial: the fetal chorion erodes the endometrial epithelium and connective tissue, resulting in apposition to the uterine endothelium.
d. Hemochorial: the most deeply invasive form of placental interface. The trophoblast erodes all of the layers until the maternal vessels and the fetal trophoblast are directly in contact with the maternal circulation. This type of interface has been subdivided into three subtypes according to the number of layers of cytotrophoblast (3): (i) hemomonochorial, the outer trophoblast layer is constructed of syncytiotrophoblast only; (ii) hemodichorial, only one side of the trophoblast is covered by cytotrophoblast; (iii) hemotrichorial, both sides of the trophoblast are covered by cytotrophoblast.
Placental shape:
The shape and area of the maternal side of the placenta where it interfaces with maternal tissue. There are five types of placental shape (1):a. Diffuse: maternal--fetal interdigitation extends over the entire surface of the chorionic sac.
b. Cotyledonary: many spot-like areas of maternal--fetal interdigitation.
c. Zonary: ring-like area of maternal--fetal interdigitation.
d. Bidiscoid: two disk-like areas of maternal--fetal interdigitation.
e. Discoid: a single disk-like area of maternal--fetal interdigitation.
Maternofetal interdigitation:
The form of contact between maternal and fetal tissues and/or blood. There are five types of maternofetal interdigitation (1):a. Folded: ridge-like folds of the chorion that fit into grooves of the uterine mucosa.
b. Lamellar: ridge-like folds multiply in branch to form complicated column-like folds.
c. Trabecular: branching folds in which leaf-like and finger-like villi branch off.
d. Villous: tree-like branching of the chorion.
e. Labyrinthine: tissue block of trophoblast penetrated by web-like channels that are filled with either maternal blood or fetal capillaries.
1. Benirschke, K. & Kaufmann, P. (2000) Pathology of the Human Placenta (Springer, New York).
2. Ramsey, E. M. (1982) The Placenta: Human and Animal (Praeger, New York).
3. Enders, A. C. (1965) Am. J. Anat. 116, 29-67.