Placenta consists of structures called cotyledons. Each of these units consists of two or more placental villi, their branches and the fibrovascular meshwork that supports these structures. The maternal blood passes through the fetal-placental and maternal-placental circulation. During this circulation, the maternal blood passes through the intervillous spaces that originate from the spiral arteries of endometrium. The blood ultimately enters the villi where active transport of nutrients and waste products occurs. The umbilical arteries carry poorly oxygenated blood (blue) to the placenta. Once oxygenated in the placenta, the blood is transferred by the umbilical veins (red) to the fetus. This is in sharp contrast to the oxygenation of blood after birth with arteries containing the oxygenated blood and the veins containing the poorly oxygenated blood.
Maternal surface of the placenta
The maternal side of the mature placenta exhibits about 15-20 cotyledons. The deep grooves separate cotyledons from each other. Some of the decidua basalis may remain associated with the maternal side of the placenta.
Fetal surface of the placenta
The umbilical cord is attached to the placenta on the fetal surface. Usually, the cord attaches to the placenta eccentrically. Each umbilical cord consists of arteries and a vein and are covered with a gelatinous substance which in its outer layer is covered by the amnion.
Fetal surface of the placenta
In some placenta such as that shown in this figure, the umbilical cord is attached close to the margin of the placenta (battledore placenta).
Maternal surface of the placenta
Placenta consists of structures called cotyledons. Each of these units consists of two or more placental villi, their branches and the fibrovascular meshwork that supports these structures. The maternal blood passes through the fetal-placental and maternal-placental circulation. During this circulation, the maternal blood passes through the intervillous spaces that originate from the spiral arteries of endometrium. The blood ultimately enters the villi where active transport of nutrients and waste products occurs. The umbilical arteries carry poorly oxygenated blood (blue) to the placenta. Once oxygenated in the placenta, the blood is transferred by the umbilical veins (red) to the fetus. This is in sharp contrast to the oxygenation of blood after birth with arteries containing the oxygenated blood and the veins containing the poorly oxygenated blood.