title: Development and morphology of the inverted yolk sac in the guinea pig (Cavia porcellus).
abstract: Although the guinea pig is an important animal model for human placentation, aspects of fetal nutrition are not fully understood, especially in regard to the yolk sac that is regarded to be essential for early development of the embryo. We investigated differentiation by means of histology, histochemistry, immunohistochemistry, and transmission electron microscopy. Data suggest that the guinea pig's yolk sac was not sufficiently developed to facilitate substantial fetal nutrition in early pregnancy. On Day 12, it was a flat, inverted, but avascular structure. This was followed by differentiation to form the typical, highly villous and vascularized condition of advanced gestation. Finally, the yolk sac degenerated toward term. We suggest that the guinea pig and other caviomorphs rely predominantly on hemotrophic nutrition via the placenta even in very early pregnancy. In contrast to the general pattern of mammals, histiotrophic nutrition via yolk sac routes seems to be most essential during mid-gestation.
authors.affiliation: Department of Surgery, School of Veterinary Medicine and Animal Science, University of Sao Paulo, Sao Paulo, Brazil.
authors.forename: Bruno Gomes
authors.initials: BG
authors.lastname: Vasconcelos
authors.forename: Phelipe Oliveira
authors.initials: PO
authors.lastname: Favaron
authors.forename: Maria Angelica
authors.initials: MA
authors.lastname: Miglino
authors.forename: Andrea Maria
authors.initials: AM
authors.lastname: Mess
mesh_terms: D000818:Animals; D005260:Female; D005865:Gestational Age; D006168:Guinea Pigs / Q000033:anatomy & histology / Q000196:embryology; D010929:Placentation / Q000502:physiology; D011247:Pregnancy; D011270:Pregnancy, Animal; D015017:Yolk Sac / Q000033:anatomy & histology* / Q000254:growth & development*
keywords: Caviomorphs; Hemotrophic nutrition; Histiotrophic nutrition; Reichert's membrane; Yolk sac placentation