Progesterone is a steroid and progestogen sex hormone involved in the menstrual cycle and pregnancy. It is mainly secreted in the ovaries during the second half of the menstrual cycle. It plays an important role in the menstrual cycle and to maintain the early stages of pregnancy.
During the menstrual cycle, when an egg is released from the ovary at ovulation(approximately day 14), the remnants of the ovarian follicle that enclosed the developing egg form a structure called the corpus luteum. This releases progesterone and, to a lesser extent, oestradial. The progesterone prepares the body for pregnancy in the event that the released egg is fertilised. If the egg is not fertilised, the corpus luteum breaks down, the production of progesterone falls and a new menstrual cycle begins.
If the egg is fertilised, progesterone stimulates the growth of blood vessels that supply the lining of the womb (endometrium) and stimulates glands in the endometrium to secrete nutrients that nourish the early embryo. Progesterone then prepares the tissue lining of the uterus to allow the fertilised egg to implant and helps to maintain the endometrium throughout pregnancy. During the early stages of pregnancy, progesterone is still produced by the corpus luteum and is essential for supporting the pregnancy and establishing the placenta. Once the placenta is established, it then takes over progesterone production at around week 12 of pregnancy. During pregnancy, progesterone plays an important role in the development of the foetus; stimulates the growth of maternal breast tissue; prevents lactation; and strengthens the pelvic wall muscles in preparation for labour. The level of progesterone in the body steadily rises throughout pregnancy until labour occurs and the baby is born.
If the egg is not fertilised and no embryo is conceived, the corpus luteum breaks down and the production of progesterone decreases. As the lining of the womb is no longer maintained by progesterone from the corpus luteum, it breaks away and menstrual bleeding occurs, marking the start of a new menstrual cycle.
Progesterone also affects brain function. It produces a sense of calmness, & its sedating, anti-anxiety effect helps promote rejuvenating sleep.
It is a very important hormone known as the mood hormone & keeping it in balance in Perimenopause is very crucial.
Courtesy of “You & your hormones”, January 14 2015 & The Wisdom of Menopause page 146 (Dr Christiane Northrup)