Abstract
Summary. The uterine and maternal placental vasculature of the rabbit has been studied by serial angiography after selective catheterization of the urogenital artery or the corresponding vein and in specimens injected with barium sulphate suspension and gelatin. The uterus is supplied with blood through long, spiral arteries. Some of these perfuse the myometrium whilst others enter the placentae, opening into large arterial sinuses which supply the labyrinth through wide efferent vessels. It is suggested that blood pressure is reduced and pulse pressure damped during passage of the blood through the spiral arteries and that the function of the sinuses is to raise the lateral pressure and reduce the linear velocity, so that a slow even perfusion of the placental labyrinth can be achieved. Cross connections between the spiral arteries and a plexus of finer arterial vessels beneath each placenta enable redistribution of blood flow between the myometrium and placentae. In addition, there are probably arteriovenous anastomoses in pregnant as well as non-pregnant uteri. A sphincter mechanism in the placental feeding arteries is postulated to prevent intrapartum haemorrhage after delivery of the placentae and possibly to regulate maternal placental blood flow during pregnancy. Total uterine blood flow was estimated to be about 30 ml/min. Circulation time through the myometrium was much less than that through the placenta.
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