Anatomy and function of the placenta

2021-06-09 02:30 PM

The trophoblast cells protrude, becoming villi, where the capillaries of the placenta develop. Thus, the villi carry fetal blood, surrounded by the maternal blood-filled sinuses.

While the trophoblasts from the blastocyst attach to the uterus, the blood capillaries develop into wires from the newly formed embryo's vascular system. Around day 21 after fertilization, blood begins to be pumped by the embryo's heart. At the same time, pools of blood supply from the mother develop around the outside of the petiole.

The trophoblast cells protrude, becoming villi, where the capillaries of the placenta develop. Thus, the villi carry fetal blood, surrounded by the maternal blood-filled sinuses.

Figure. Upper, organization of the mature placenta. Bottom, the relation of fetal blood in villi capillaries with maternal blood in interstitial space.

The final structure of the placenta is shown in Figure - fetal blood flows through 2 umbilical arteries, then into the capillaries of the villi, then back through 1 umbilical vein. Simultaneously, maternal blood flows from the uterine artery into the sinuses surrounding the villi, and then back into the mother's uterine veins. The lower part of the figure shows the relationship between placental blood and maternal blood surrounding the placenta when the placenta is fully developed.