Progesterone hormone is secreted by the corpus luteum in the ovaries. The corpus luteum is a temporary endocrine structure that forms in the ovary after the release of an egg during ovulation.

The process of progesterone secretion can be explained in the following steps:

1. Formation of Corpus Luteum:
- The corpus luteum is formed from the remnants of the ruptured ovarian follicle, which released the egg.
- After ovulation, the empty follicle fills with blood and forms a yellowish structure called the corpus luteum.

2. Role of Corpus Luteum:
- The corpus luteum plays a crucial role in maintaining and preparing the uterus for pregnancy.
- It secretes both progesterone and estrogen hormones, but progesterone is the primary hormone secreted.

3. Secretion of Progesterone:
- Progesterone is secreted by the corpus luteum under the influence of luteinizing hormone (LH) released from the pituitary gland.
- LH stimulates the corpus luteum to continue producing progesterone.

4. Functions of Progesterone:
- Progesterone prepares the uterine lining (endometrium) for implantation of a fertilized egg.
- It helps to thicken the endometrium and increase blood flow to support embryo development.
- Progesterone also inhibits uterine contractions, preventing premature labor.
- It also plays a role in the development of mammary glands in preparation for breastfeeding.

5. Duration of Corpus Luteum:
- If fertilization occurs, the developing embryo begins to produce human chorionic gonadotropin (hCG) hormone.
- hCG maintains the corpus luteum, ensuring the continued production of progesterone to support pregnancy.
- The corpus luteum remains functional, and progesterone secretion continues until the placenta takes over hormone production.
- If fertilization does not occur, the corpus luteum degenerates after around 14 days, leading to a decrease in progesterone production. This triggers menstruation.

In conclusion, the corpus luteum in the ovaries secretes the progesterone hormone. Progesterone plays a crucial role in preparing the uterus for pregnancy and maintaining early pregnancy until the placenta takes over hormone production.