Ovulation
Nearing the midpoint of the menstrual cycle, the graafian follicle expands and moves to the surface of the ovary, where its outer follicular wall is weakened by collagen degradation and the death of some of the overlying cells. The egg contained by the follicle completes the first meiotic division and releases the first polar body. It then proceeds into the second meiotic division where it arrestes in metaphase II. Ovulation results when the graafian follicle bursts and both antral fluid and the ovum are released from the ovary into the peritoneal cavity. (Carlson, 1999)

(http://www.ultranet.com/~jkimball/BiologyPages/.html)

Hormones
The hypothalamus first releases gonadotropin-releasing hormone (GnRH), which stimulates the secretion of pituitary hormones. In specific, the anterior pituitary releases polypeptide gonadotrophic hormones FSH (follicle stimulating hormone) and LH (leutinizing hormone).

Within the ovaries, the granulosa cells of the ovarian follicle convert androgens into estrogens. These androgens are produced by the theca cells, which coat the ovarian follicle.

After ovulation, progesterone is the primary secretory product released from the follicle after it has converted into the corpus luteum.

If pregnancy does not occur, estrogens alone are produced. If pregnancy does in fact occur, a combination of estrogens and progesterones are released.

Also during pregnancy, the placenta releases human chorionic gonadotropin (HCG) that acts on the ovary to maintain the activity of the corpus luteum.

(Carlson, 1999)

(http://www.ultranet.com/~jkimball/BiologyPages/E/Estrogen.html)

Estrogens: (also referred to as estradiols)
- Estrogens are steroids. Being responsible for female maturation, they induce the development of breasts, the development of the uterus and vagina, the broadening of the pelvis, the growth of pubic and axillary hair, and an increase in fat tissue. They regulate monthly preparation of the body for possible pregnancy and participate in pregnancy if it occurs. Estrogens also play a role in non-reproductive events. They minimize calcium loss in bones and promote blood clotting. (http://www.ultranet.com/~jkimball/BiologyPages/S/SexHormones.html)

Regulation of Estrogen and Progesterone

Estrogen is synthesized and secreted in response to stimulations from FSH, which are essentially controlled by the hypothalamic gonadotropin releasing hormone (GnRH). High levels of estrogen suppress the release of GnRH and provide a negative-feedback control of hormone levels.

Progesterone production is stimulated by LH, which is also stimulated by GnRH. (http://www.ultranet.com/~jkimball/BiologyPages/S/SexHormones.html)

For More on Estrogen and Progesterone...

For Delay of Ovulation to Prevent Pregnancy

Continue with Female Reproductive Cycle

The origins of ovulation begin when the hypothalamus releases hormones that trigger further hormone production by the anterior pituitary gland. Spread via the blood, these hormones act on the ovaries, which then initiate their own production of hormones.

(http://www.ultranet.com/~jkimball/BiologyPages/.html)

FSH: In the female, it stimulates follicle cells to produce estrogens.
In the male, it stimulates Sertoli cells to produce androgen binding protein.
LH: In the female, it stimulates follicle cells and the corpus luteum to produce progesterone.
In the male, it stimulates Leydig cells to secrete testosterone.
Granulosa cells:
· Comprise part of the ovarian follicle
· Recept FSH and LH
· Convert androgens to estrogens
Theca cells:
· Comprise coat of ovarian follicle
· Recept LH
· Produce androgens

(Carlson, 1999)

(http://www.ultranet.com/~jkimball/BiologyPages/P/Progesterone.html)

Progesterones: (analog to progestins)
- Progesterones are steroids. They are secreted by the corpus luteum in response to LH stimulation, and continue the preparation of the endometrium for a possible pregnancy. In addition, they inhibit the contraction of the uterus and the development of a new follicle. (http://www.ultranet.com/~jkimball/BiologyPages/S/SexHormones.html)

Hypothalamus --> GnRH --> Pituitary --> FSH --> Follicle --> Estrogens

Hypothalamus --> GnRH --> Pituitary --> LH --> Corpus luteum --> Progesterone

(http://www.ultranet.com/~jkimball/BiologyPages/S/SexHormones.html)