Ultrastructure of the placenta of the tammar wallaby, Macropus eugenii: comparison with the grey short‐tailed opossum, Monodelphis domestica

The ultrastructure of the tammar placenta was studied throughout pregnancy. The uterine epithelium grows from a columnar to an enlarged, undulating epithelium between early gestation and mid‐gestation when the shell coat that surrounds the marsupial conceptus ruptures. Trophectoderm and uterine epit...

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Bibliographic Details
Published in:Journal of anatomy 2002-08, Vol.201 (2), p.101-119
Main Authors: Freyer, Claudia, Zeller, Ulrich, Renfree, Marilyn B.
Format: Article
Language:English
Subjects:
Animals
Capillaries
endometrium
Endometrium - ultrastructure
Epithelium - metabolism
Female
Macropodidae - anatomy & histology
marsupials
Microscopy, Electron
Opossums - anatomy & histology
Original
Placenta - ultrastructure
Pregnancy
Pregnancy, Animal - physiology
stem species pattern
uterine secretion
Uterus - blood supply
Uterus - metabolism
Uterus - ultrastructure
Yolk Sac - ultrastructure
yolk sac placenta
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Summary:The ultrastructure of the tammar placenta was studied throughout pregnancy. The uterine epithelium grows from a columnar to an enlarged, undulating epithelium between early gestation and mid‐gestation when the shell coat that surrounds the marsupial conceptus ruptures. Trophectoderm and uterine epithelium do not form syncytia, nor does invasion of the endometrium occur at any stage of pregnancy. Uterine secretion is provided to both the bilaminar and the trilaminar side of the yolk sac placenta up to birth. Fenestrations, abundant vesicles and lumenal processes of maternal capillaries, as well as deep basal folds of the uterine epithelium, suggest that there is transfer of hemotrophes adjacent to both parts of the yolk sac. In contrast, in the grey short‐tailed opossum, these structures are lacking. The yolk sacs of adjacent embryos fuse to form a common yolk sac cavity, thus losing most of the bilaminar yolk sac. The bilaminar and trilaminar components of the yolk sac placenta of the tammar are less different in structure and function than those of the grey short‐tailed opossum, but both types are fully functional placentas. The extended secretory phase of the tammar uterus and the maternal recognition of early pregnancy appear to be derived characters of macropodid marsupials.
ISSN:0021-8782
1469-7580
DOI:10.1046/j.1469-7580.2002.00084.x