Question

Describe the ovarian cycle in a nonpregnant female and the hormones involved. (pages \(360-62\) )

Short answer

The ovarian cycle in a nonpregnant female consists of three main phases: the follicular phase, ovulation, and the luteal phase. The cycle prepares the uterus for a potential pregnancy. During the follicular phase, follicle-stimulating hormone (FSH) stimulates the growth and maturation of ovarian follicles, and estrogen production increases. Ovulation occurs around day 14, when a surge in luteinizing hormone (LH) triggers the release of the mature egg. The luteal phase involves the production of progesterone and estrogen by the corpus luteum, which maintains and thickens the endometrial lining. If fertilization does not occur, menstruation begins. The main hormones involved are FSH, LH, estrogen, and progesterone.

Step-by-step solution

1. Introduction to the Ovarian Cycle

The ovarian cycle is the series of events that occur in a woman's ovaries during her menstrual cycle. It has three main phases: the follicular phase, ovulation, and the luteal phase. The primary function of the ovarian cycle is to prepare the uterus for a possible pregnancy.

2. Follicular Phase

The follicular phase begins on the first day of menstruation and ends with ovulation. It typically lasts between 10 and 14 days. During this phase, the levels of follicle-stimulating hormone (FSH) increase, which stimulates the growth and maturation of several ovarian follicles. Each follicle contains one immature egg cell (oocyte). The increase in FSH levels also leads to an increase in estrogen production. Estrogen helps to further develop the ovarian follicles and thicken the lining of the uterus (endometrium).

3. Ovulation

Ovulation occurs around day 14 of a typical 28-day menstrual cycle. A surge in luteinizing hormone (LH) triggers the release of the most mature egg (oocyte) from its follicle into the fallopian tube. This is the point in the cycle where the egg is available to be fertilized by a sperm cell.

4. Luteal Phase

The luteal phase begins after ovulation and lasts until the onset of menstruation, typically about 14 days. The empty follicle left behind after the release of the egg (called the corpus luteum) begins to produce progesterone and estrogen. These hormones help to maintain and further thicken the endometrial lining, preparing the uterus for a possible embryo implantation. If fertilization does not occur, the corpus luteum will degenerate, leading to a decrease in progesterone and estrogen levels, and ultimately causing the endometrial lining to shed as menstruation.

5. Hormones Involved

The main hormones involved in the ovarian cycle are: - Follicle-stimulating hormone (FSH): stimulates the growth and maturation of ovarian follicles. - Luteinizing hormone (LH): triggers the release of the mature egg (ovulation) and the development of the corpus luteum. - Estrogen: produced by the developing ovarian follicles and the corpus luteum, it helps to develop the ovarian follicles, thicken the endometrial lining, and regulate FSH and LH levels. - Progesterone: produced by the corpus luteum, it helps to maintain and further thicken the endometrial lining, and prepare the uterus for a possible embryo implantation. In summary, the ovarian cycle is a series of events that occur in a nonpregnant female's ovaries to prepare the uterus for a possible pregnancy. The cycle has three main phases: the follicular phase, ovulation, and the luteal phase. Hormones involved in the process include follicle-stimulating hormone (FSH), luteinizing hormone (LH), estrogen, and progesterone.