Placenta/Fetal Unit

The next subject to cover is:

• the placenta, it's hormones and their functions, and
• the hormones and functions of the "placenta/fetal" unit.

The placenta is an organ unique to pregnancy. Shortly after conception, the blastocyst (a hollow ball) differentiates it's outer cells from the small inner mass. The outer cells, or trophoblast, will become the placenta. The inner cell mass will become the embryo.

The placenta/fetal unit refers to the interaction between the two to develop hormonal balance. For example, the fetus contributes the precursors to some hormones, and the placenta finishes the hormone development.

The next 4-5 pages of the course will be devoted to the major hormones of the placenta and placenta/fetal unit.

• The trophoblasts produce large amounts of the protein hormones, human chorionic gonadotropin (hCG) and human placental lactogen (HPL). After implantation, protein hormones are produced mainly by the placenta, and disappear after the placenta separates.
• In the nonpregnant woman, the steroid hormones, estrogen and progesterone are produced by the ovaries. During pregnancy, they are produced in much larger quantities by the placenta.