PLACENTA

The Placenta arises out of trophoblast tissue. It serves as the fetal lungs, kidneys and gastrointestinal tract and as a separate endocrine organ throughout pregnancy. Its growth parallels that of the fetus, growing from a few identifiable cells at the beginning of pregnancy to an organ 15 to 20 cm in diameter and 2 to 3 cm in depth at term. It covers about half the surface area of the internal uterus.


Endocrine Function
Aside from serving as the source of oxygen and nutrients for the fetus, the outer layer of the chorionic villi develops into separate, important hormone-producing system.


Human Chorionic Gonadotropin
The first hormone produced, hCG, can be found in maternal blood and urine as early as the first missed menstrual period through about the 100th day of pregnancy. Testing for hCG after birth can be used as proof that all of the placental tissue has been delivered. The purpose of hCG is to act as a fail-safe measure to ensure the corpus luteum of the ovary continues to produce progesterone and estrogen. hCG also may play a role in suppressing the maternal immunologic response so that placental tissue is not rejected. Because the structure of hCG is similar to that of leutinizing hormone of the pituitary gland, if the fetus is male, it exerts an affect on the fetal testes to begin testosterone production.


Relaxin
In females, their body produces a hormone called relaxin, it is produced by the corpus luteum, which is responsible for the softening of the ligaments in the pelvic area and other joints. This hormone helps the baby to pass through the pelvis during birth. As a result, these joints move more during and just after pregnancy.It rises to a peak within approximately 14 days of ovulation and then declines in the absence of pregnancy resulting in menstruation. During the first trimester of pregnancy levels rise and additional relaxin is produced by the decidua. Relaxin's role in human pregnancy remains under investigation, as in humans its peak is reached during the 14 weeks of the first trimester and at delivery.


Human Placental Lactogen (Human Chorionic Somatomammotropin)
hPL is a hormone with both growth-promoting and lactogenic properties. It is produced by the placenta beginning as early as the 6th week of pregnancy, increasing to a peak level at term. It can be assayed in both maternal serum and urine. It also serves the important role of regulating maternal glucose, protein, and fat levels so that adequate amounts of these nutrients are always available to the fetus.



References:
http://www.marchofdimes.com/professionals/14332_1154.asp
http://en.wikipedia.org/wiki/Placenta
http://info.med.yale.edu/obgyn/kliman/placenta/articles/Plac%20Hormones.html
http://www.birthgreeter.com/images/Placenta_1.jpg