In
humans, aside from serving as the conduit for oxygen and nutrients for
fetus, the placenta secretes hormones that are secreted by syncytial
layer of chorionic villi) that are important during pregnancy.
Human Chorionic Gonadotropin (hCG):
The first placental hormone produced is hCG, which can be found in
maternal blood and urine as early as the first missed menstrual period
(shortly after implantation has occurred) through the 100th day of
pregnancy. This is the hormone analyzed by pregnancy test; a
false-negative result from a pregnancy test may be obtained before or
after this period. Women's blood serum will be completely negative for
hCG by one to two weeks after birth. hCG testing is proof that all
placental tissue is delivered. hCG is present only during pregnancy
because it is secreted by the placenta.
hCG also ensures that the corpus luteum continues to secrete
progesterone and estrogen. Progesterone is very important during
pregnancy because, when its secretion decreases, the endometrial
lining will slough off and pregnancy will be lost. hCG suppresses the
maternal immunologic response so that placenta is not rejected.
Human Placental Lactogen (hPL [Human Chorionic Somatomammotropin]):
This hormone is lactogenic and growth-promoting properties. It promotes
mammary gland growth in preparation for lactation in the mother. It
also regulates maternal glucose, protein, and fat levels so that this is
always available to the fetus.
Estrogen:
referred to as the "hormone of women" because it stimulates the
development of secondary female sex characteristics. It contributes to
the woman's mammary gland development in preparation for lactation and
stimulates uterine growth to accommodate growing fetus.
Progesterone:
necessary to maintain endometrial lining of the uterus during
pregnancy. This hormone prevents preterm labor by reducing myometrial
contraction. Levels of progesterone are high during pregnancy.
