Final answer:
Progesterone is a hormone produced primarily by the ovaries to support conception and pregnancy. It thickens the uterine lining, regulates reproductive organs, and maintains the menstrual cycle. From the third trimester, progesterone is produced by the placenta and it plays a role in suppressing further ovulation and protecting the fetus through early pregnancy.
Step-by-step explanation:
Progesterone is a female sex hormone primarily secreted by the ovaries and is pivotal in preparing the body for conception and maintaining a successful pregnancy. Before pregnancy, progesterone prepares the uterus for the potential of pregnancy by thickening the endometrial lining. Once pregnancy occurs, the hormone continues to be essential in regulating the menstrual cycle and supporting the maturation and maintenance of reproductive organs. Interestingly, during the third trimester of pregnancy, progesterone production shifts as the placenta takes over the role of secretion from the corpus luteum, which originally produces it following ovulation.
Progesterone also plays a vital role in suppressing the pituitary hormones FSH and LH to prevent further egg development while the hormone levels remain high. Furthermore, it helps to inhibit uterine contractions early in the pregnancy, protecting the fetus from preterm birth. As the pregnancy advances to late gestation, progesterone levels start to decrease which allows for uterine contractions to intensify and progress toward labor.