Follicular Phase

The actions of estradiol in the female predominate during the follicular phase of the menstrual cycle. Estradiol has powerful effect within the ovarian follicle to amplify the growth promoting properties of FSH. It acts on the uterine endometrium to promote growth and cellular proliferation through increased protein synthesis, proliferation of glands and increased blood flow.

It increases progesterone receptor content in the endometrium in preparation for implantation. Estradiol increases the contractility of the myometrium and fallopian tubes due to the increased synthesis of contractoproteins. In the lower reproductive tract estradiol increases the quantity and decreases the viscosity of cervical mucus to render it thin and watery and it causes thickening or quantification of the vaginal epithelia mucosa.

 

Luteal Phase

Inhibin A which is low during the follicular phase of the cycle is produced in copious amounts by the corpus luteum peaking in the mid luteal phase. As the corpus luteum regresses inhibin levels decline and FSH levels rise with the beginning of the next menstrual cycle. In the luteal phase progesterone appears to act by decreasing GnRH pulse frequency resulting in decreased LH pulse frequency.

In the luteal phase of the female menstrual cycle, the LH pulse interval is approximately 2 to 3 hours. During the luteal phase, progesterone inhibits myometrium contractions by increasing the membrane potential and the liminal stimulus required to cause contractions. After the ovulatory period, progesterone causes cervical mucus to be thick and sparse.

Dry mucus at the time of ovulation exhibits a characteristic firming pattern when it dries while that obtained in the late luteal or early follicular phases does not exhibit firming.