The corpus luteum is essential for establishing and maintaining pregnancy in females. The corpus luteum secretes
progesterone, which is a
steroid hormone responsible for the
decidualization of the
endometrium (its development) and maintenance, respectively. It also produces
relaxin, a hormone responsible for softening of the
pubic symphysis which helps in parturition.
Unsuccessful fertilization If the egg is not fertilized, the corpus luteum stops secreting progesterone and decays (after approximately 10 days in humans). It then degenerates into a
corpus albicans, which is a mass of fibrous
scar tissue. With cessation of progesterone release, the uterine lining (functional, inner layer of the endometrium) is expelled through the vagina (in mammals that go through a
menstrual cycle). Across an
oestrous cycle, the functional layer regenerates to provide nourishing tissue for potential fertilisation and implantation.
Successful fertilization showing a corpus luteum in a pregnant woman, with a fluid-filled cavity in its center If the egg is fertilised and
implantation occurs, the syncytiotrophoblast (derived from
trophoblast) cells of the
blastocyst secrete the hormone
human chorionic gonadotropin (hCG, or a similar hormone in other species) by day 9 post-fertilisation. Human chorionic gonadotropin signals the corpus luteum to continue progesterone secretion, thereby maintaining the thick lining (endometrium) of the uterus and providing an area rich in
blood vessels in which the
zygote(s) can develop. From this point on, the corpus luteum is called the
corpus luteum graviditatis. The introduction of
prostaglandins at this point causes the degeneration of the corpus luteum and the
abortion of the
fetus. However, in certain placental animals such as humans, horses, and sheep, the
placenta eventually takes over progesterone production and the corpus luteum degrades into a
corpus albicans without embryo/fetus loss.
Luteal support refers to the administration of medication (generally
progestins) for the purpose of increasing the success of
implantation and early
embryogenesis, thereby complementing the function of the corpus luteum.
Content of carotenoids The yellow color and name of the corpus luteum, like that of the
macula lutea of the retina, is due to its concentration of certain
carotenoids, especially
lutein. In 1968, a report indicated that beta-carotene was synthesized in laboratory conditions in slices of corpus luteum from cows. However, attempts have been made to replicate these findings, but have not succeeded. The idea is not presently accepted by the scientific community. Rather, the corpus luteum concentrates carotenoids from the diet of the mammal. ==In animals==