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Observations on the morphogenesis and histochemistry of the bovine preattachment placenta between 16 and 33 days of gestation

Observations on the morphogenesis and histochemistry of the bovine preattachment placenta between 16 and 33 days of gestation

Anatomical Record 132(3): 321-341

Preliminary standards of daily development for the bovine placenta from 16 to 33 days of pregnancy are presented. Placental development is most advanced adjacent to the embryo and least at the extremities of the chorionic vesicle. The proliferating trophoblast is distinctly cellular and is composed originally of undifferentiated "stem cells" which give rise, independently, to 2 distinct cell types characteristic of later stages of pregnancy, the ordinary trophoblastic columnar cells, and the giant cells. The fetal origin of the bovine giant cell is confirmed. The giant cells are recognizable at 16-17 days, the stage at which the estrual corpus luteum would undergo regression. Their histochemistry suggests that they may play a role in the maintenance of the corpus luteum of pregnancy. Giant cells increase in number by direct transformation and growth of "stem cells" and undergo mitotic division to become binucleate or polynucleate. They are considered to be incapable of proliferation due to the absence of cytokinesis. The trophoblast accumulates considerable amounts of acetone-soluble lipids confined mostly to the ordinary columnar cells. The morphological attributes of these cells suggest both a nutritive and a secretory function. Glycogen is not an important histochemical feature of the developing placenta, this material being localized in the allantoic entoderm, mesenchyme and blood vessels. Diastase resistant, PAS-positive material indicative of a carbohydrate-protein complex is concentrated in the giant cell cytoplasm. The development of the giant cells, the elaboration of the yolk sac and vitelline circulation, and the transfer of the yolk sac function to the allantois are all concomitant with the period of high embryonic death between 16 and 33 days. Each of these processes can be considered to be critical for embryo survival.

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Accession: 025128594

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PMID: 13637407

DOI: 10.1002/ar.1091320308

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