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  • Title: Ultrastructure of the maternal-fetal interface of the yolk sac placenta in sharks.
    Author: Hamlett WC.
    Journal: Ital J Anat Embryol; 2005; 110(2 Suppl 1):175-81. PubMed ID: 16101036.
    Abstract:
    The blacknose shark, Carcharhinus acronotus, is a viviparous anamniote that develops an epitheliochorial yolk sac placenta. The fetal portion of the uteroplacental complex consists of a proximal portion that forms saccular evaginations. The cells are bilayered stratified squamous with surface microvilli and a high concentration of cytoplasmic filaments. The tertiary egg envelope intervenes between the distal portion of the placenta and uterus. It has delaminations on the uterine surface and is compacted on the placental surface. The uterine epithelium is cuboidal to columnar and is characterized by prominent RER, Golgi, and secretion vesicles. The capillary endothelium is continuous. Nutrient and respiratory exchange is effected between the uterus and distal portion of the yolk sac. The distal portion of the placenta is a bilayer. An elaborate array, of microvilli forms an interface with the egg envelope. Dense non-membrane bound granules occur in the interspace between the egg envelope and the distal placenta. This material, presumably of uterine origin, is endocytosed in smooth-walled vesicles of the placental cells. The endothelium of the capillaries is fenestrated.
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