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Updated: Jun 28, 2026
06:54
Ex Vivo Perfusion of the Rodent Placenta
Published on: May 30, 2019
The mammalian yolk sac placenta
Claudia Freyer1, Marilyn B Renfree
1Department of Zoology, The University of Melbourne, Melbourne, Victoria, Australia. freyerc@unimelb.edu.au
Summary
The mammalian yolk sac, crucial for early embryonic development, functions as a placenta in humans and other viviparous mammals. It facilitates nutrient transfer and retains ancestral metabolic roles, ensuring embryonic survival.
Area of Science:
- Developmental Biology
- Comparative Embryology
- Reproductive Biology
Background:
- Mammals possess three fetal membranes: yolk sac, allantois, and amnion.
- The yolk sac and allantois contribute to placental formation.
- Nutrient transfer via the yolk sac varies across mammalian subclasses (Monotremata, Marsupialia, Eutheria).
Purpose of the Study:
- To elucidate the ontogenetic development and functional significance of the mammalian yolk sac.
- To compare yolk sac function across different mammalian groups, particularly Eutheria and humans.
- To investigate the role of the yolk sac in nutrient transfer, metabolism, and embryonic survival.
Main Methods:
- Comparative analysis of yolk sac development and function across mammalian subclasses.
- Review of literature on gene expression, protein factors, and imprinted genes in the yolk sac.
- Examination of the yolk sac's role in nutrient transport and metabolic processes.
Main Results:
- In most eutherians, the yolk sac detaches from the chorion, forming a free structure that transfers substances from the exocoelomic cavity.
- The human yolk sac functions similarly to this free yolk sac, receiving secretions from the exocoelomic cavity.
- The yolk sac expresses critical factors for differentiation, hematopoiesis, angiogenesis, and nutrient metabolism, including imprinted genes like insulin and IGF2.
Conclusions:
- The human yolk sac, like that of all viviparous mammals, is a vital placenta essential for early embryonic development and survival.
- Its functions, including metabolic and biosynthetic roles, and hematopoiesis, reflect those of ancestral therian and eutherian species.
- Imprinted genes in the yolk sac suggest ongoing selective pressure for regulated resource allocation to the embryo.
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