progesterone

a steroid HORMONE that is vital in PREGNANCY . It is produced by the CORPUS LUTEUM of the OVARY when the lining of the UTERUS is prepared for the implanting of an egg cell. Progesterone is secreted under the control of other hormones (prolactin from the anterior PITUITARY GLAND and luteinizing hormone also from the pituitary, which stimulates ovulation and formation of the corpus luteum) until the PLACENTA adopts this role later in the pregnancy. The function of progesterone is to maintain the uterus and ensure that no further eggs are produced. Small amounts of this hormone are also produced by the testes (see TESTICLE ).