Table 2 List of major placental characters and conditions in Hystricognathi
From: Growth and development of the placenta in the capybara (Hydrochaeris hydrochaeris)
Nr. | Character | Character condition(s) |
|---|---|---|
1 | Organization of main placenta | Moderate lobulation (1). Complex lobulation (2). |
2 | Capsule around placenta | Absent (1). Present until mid gestation (2). |
3 | Labyrinth I | Radial arrangement of the exchange areas around the maternal blood lacunas (1). |
4 | Labyrinth II | Countercurrent arrangement of the fetal and maternal blood flows (1). |
5 | Interhaemal barrier | Haemochorial placenta with cellular and syncytial trophoblast in early ontogeny and mostly syncytial barrier later on (1). |
6 | Interlobium | Substantial areas of interlobium associated with labyrinth (1). |
7 | Placental growth | Essentially the result of specialised growing zones at the outer margin, associated with internally directed projections on fetal mesenchyme (1). |
8 | Additional proliferation | Insignificant proliferation activity in trophoblast in the labyrinth (1). Remarkable proliferation in this trophoblast in early and mid gestation (2). |
9 | Presence of subplacenta | Distinct and specialised area, consisting of layers of cellular and syncytial trophoblast on fetal mesenchyme, occurring from early ontogeny to near term or term (1). |
10 | Blood supply of subplacenta | Associated with the maternal circulation in early ontogeny and supplemented by the fetal system later, without overlap between the two systems (1). Same composition, but some overlap between the systems during mid gestation (2). |
11 | Extraplacental trophoblast | Both cellular trophoblast and syncytial streamers in the decidua between the subplacenta and the materal arterial system, probably responsible for the replacement of the maternal arterial endothelium (1). |
12 | Visceral yolk sac | Inverted yolk sac with conspicuous villous areas (1). |
13 | Fibrovascular ring | Specialised arterial and capillary system within the yolk sac near the attachment to the main placenta (1). |
14 | Parietal yolk sac | Present, usually multi-layered from mid gestation on (1). |