The stimulating hormones, FSH and I.H, are produced in the brain (init complex interplay between the hypothalamus and the pituitary gland, two parts of the brain). FSH sends a message to the ovary. One of the ovaries (they usually take it in turn) responds by developing follicles, which make potential eggs.
There are several follicles each cycle which respond to the FSH. Usually one of these follicles grows faster, and will become the ‘Egg of the Month’, as it were.
The ovary produces more oestrogen, and then a surge of L.H from the pituitary gland acts to stimulate the release of the egg from the follicle it has been developing in. This is ovulation. After ovulation the ruptured follicle takes on a hormone-producing role, and is called the corpus luteum. It produces progesterone, as well as oestrogen, and the progesterone works on the lining of the uterus to make it ready in case the egg is fertilised, and needs a place to settle. The progesterone also affects the cervical mucus, making it friendlier to sperm, and it also tends to change the body temperature a little, making the resting ‘basal’ temperature rise by about 0.5°C.
The egg, meanwhile, has been grasped by the ‘fingers’ of the nearby fallopian tube, and is making its way along the tube towards the uterus. This trip takes a few days, and if there are any sperm in the area they will usually swim up the fallopian tube and meet the egg there. If the egg is fertilised by the sperm (in a process called conception), the newly formed conceptus travels along the fallopian rube towards the uterus, where it can find a suitable place to implant and grow.
The ovary has been churning out oestrogen and progesterone, and keeping the home fires burning, so to speak, in case conception takes place. If it does not, then the corpus luteum usually stops working after fourteen days, so there is a drop in the level of oestrogen and progesterone. This drop affects the lining of the uterus, which starts to disintegrate and come away. That is what a menstrual period is, and that is why it usually takes place fourteen days after ovulation. After the lining is shed, the FSH and oestrogen start up again, and the ovary repeats the whole cycle.
If a conception does occur, and the conceptus finds a place to settle and starts growing, it too can produce hormones. These hormones include human chorionic gonadotrophin (HCG), which is the hormone measured in pregnancy tests. This HCG tells the corpus luteum to keep working beyond its usual four-teen days, and it continues to produce progesterone to support the growing embryo until it can make its own, which it does after about eight weeks.