Anatomie et physiologie : recherches en cours
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Conceptual Orientation: A Unique Phenomenon of the Equine Pregnancy

Derar Refaat Derar* and Ahmed Ali

There is a clear fact that the reproductive system of the domestic animals is subjected to rhythmic changes throughout the life of the animal and that make them unique among other body systems. The intimate relationship between the fetal membranes and the conceptus represent the cornerstone for the dynamic changes during the gestation period. Estrogen, progesterone and other ovarian steroids exerts a strict control over the function of the hypothalamus and the pituitary gland. Orientation occurs between the time of fixation and the appearance of the irregular shapes. Factors are believed to interact during orientation are thick (three-layered) and thin (two-layered) portions of the yolk-sac wall; asymmetrical encroachment from thickening of the upper turgid uterine wall on each side of the mesometrial attachment; and the massaging action of uterine contractions. The interaction of these factors results in the thickest portion of the yolk sac wall (embryonic pole) rotating to a ventral position (antimesometrial). It can be suggested that orientation is a unique phenomenon of the equine conceptus. Much speculation has been suggested about its significance but the fact that it is still unclear what is the exact role of this phenomenon during the early life of the equine fetus.