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The evolution of epitheliochorial placentation.

Authors
Type
Published Article
Journal
Annual Review of Animal Biosciences
2165-8102
Publisher
Annual Reviews
Publication Date
Volume
1
Pages
443–467
Identifiers
DOI: 10.1146/annurev-animal-031412-103653
PMID: 25387027
Source
Medline
Keywords
  • Glucose Transporters
  • Macrophages
  • Natural Killer Cells
  • Placental Hormones
  • Regulatory T Cells
  • Uteroferrin

Abstract

Epitheliochorial placentation is a derived condition and has evolved separately in strepsirrhine primates and laurasiatherians (pangolins, whales, and hoofed mammals). Usually it is associated with a long gestation period, small litters, and precocial young. Oxygen transfer is facilitated by indenting of the uterine and trophoblast epithelia by maternal and fetal capillaries, respectively. Histotrophic nutrition is important, and adaptations include areolas and hemophagous regions. In pigs and horses, for example, iron is transported as uteroferrin secreted from the uterine glands and taken up by areolas. In the horse, invasive trophoblast cells form cups within the endometrium that are the source of equine chorionic gonadotropin. In ruminants, binucleate trophoblast cells fuse with uterine epithelial cells to form trinucleate cells or plaques that secrete pregnancy hormones. There is evidence of immunosuppression in connection with these more invasive types of trophoblasts. The epitheliochorial condition may be advantageous for long pregnancies in large animals.

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