NURS 3112 Chapter Notes - Chapter 11: Radial Artery, Umbilical Cord, Spiral Artery
14 Sep 2017
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The placenta is the means of metabolic and nutrient exchange between the embryonic and maternal circulations. Placental development and circulation does not begin until the third week of embryonic development. The placenta develops at the site where the developing embryo attaches to the uterine wall. Expansion of the placenta continues until about 20 weeks, when it covers about half the inside of the uterus. After 20 weeks"gestation, the placenta becomes thicker but not wider. At 40 weeks" gestation, the placenta is about 15 to 20 cm (5. 9 to 7. 9 in. ) in diameter and 2. 5 to 3 cm (1 to 1. 2 in. ) in thickness. It weighs approximately 400 to 600 g (14 to 21 oz). The placenta has two parts: the maternal portion and the fetal portion. The maternal portion consists of the decidua basalis and its circulation. Its surface is red and fleshlike (often called dirty duncan). The fetal portion consists of the chorionic villi and their circulation.
