**The Main Function of the Mammalian Corpus Luteum: Estrogen vs. Progesterone**

The mammalian corpus luteum is a temporary endocrine structure that forms in the ovary after ovulation. It plays a crucial role in the regulation of the female reproductive system. One of its main functions is to secrete hormones, including estrogen and progesterone, which are essential for the maintenance of pregnancy or preparation for a possible pregnancy.

**1. Estrogen**

Estrogen is a group of steroid hormones that are responsible for the development and maintenance of female reproductive structures and secondary sexual characteristics. It is primarily produced by the ovarian follicles before ovulation. However, after ovulation, the corpus luteum becomes the main source of estrogen production. Estrogen has several important functions, including:

- **Stimulating the thickening of the endometrium**: Estrogen promotes the growth and proliferation of the endometrial lining of the uterus, preparing it for implantation of a fertilized embryo.
- **Supporting the growth and development of the mammary glands**: Estrogen stimulates the growth of mammary gland ducts, which are necessary for milk production during lactation.
- **Regulating the menstrual cycle**: Estrogen plays a crucial role in regulating the menstrual cycle by stimulating the growth of the ovarian follicles and promoting ovulation.

**2. Progesterone**

Progesterone is another important steroid hormone that is predominantly produced by the corpus luteum. It is often referred to as the "pregnancy hormone" as its main function is to prepare and maintain the uterus for implantation and support of a fertilized embryo. Progesterone has several key functions, including:

- **Preparing the endometrium for implantation**: Progesterone promotes the growth and development of blood vessels in the endometrium, making it more receptive to the implantation of a fertilized embryo.
- **Maintaining the uterine lining during pregnancy**: Progesterone helps to maintain the thickened endometrium during early pregnancy, providing a favorable environment for the developing embryo.
- **Inhibiting uterine contractions**: Progesterone relaxes the smooth muscles of the uterus, preventing premature contractions that could potentially lead to miscarriage.

**Conclusion**

While both estrogen and progesterone are secreted by the mammalian corpus luteum, the main function of the corpus luteum is to produce progesterone. Progesterone is essential for the preparation and maintenance of the uterus during pregnancy. Estrogen, on the other hand, primarily supports the growth and development of reproductive structures and regulates the menstrual cycle. Both hormones work together in a coordinated manner to ensure successful implantation and maintenance of pregnancy.

The main function of mammalian corpus luteum is the secretion of progesterone which is essential for the maintenance of endometrium. Endometrium is necessary for implantation of the fertilised ovum and other events of Pregnancy.

  Corpus luteum also secretes some amount of estrogen to maintain Pregnancy.