Chapter40-2: The Female Reproductive System
Chapter40-2: The Female Reproductive System
Bellringer
Assuming the hormones from the brain are the same in males and females, predict differences in hormones (names and locations) produced by the female reproductive system.
Key Ideas
What are the functions of the ovaries?
How does the female body prepare for pregnancy?
What changes occur in the female’s body when an ovum is not fertilized?
Egg Production
The female reproductive system prepares for a possible pregnancy each month by producing a mature egg cell. If the egg cell is fertilized by a sperm cell and then implants in the uterus, a pregnancy will begin.
The two ovaries of the female reproductive system are located within the female’s abdomen.
The ovaries produce egg cells. Ovaries also secrete estrogen and progesterone, the female sex hormones.
Egg cells have 23 chromosomes (the haploid number) because eggs, like sperm, are formed through meiosis.
When a female reaches puberty, the levels of sex hormones rise, triggering an egg cell to mature each month inside one of the female’s ovaries.
The female reproductive system produces about one viable egg each month. Although a female is born with about 2 million eggs in her ovaries, only 300 - 400 egg cells will mature in her lifetime.
A mature egg cell is called an ovum.
After an ovum is released from an ovary, cilia sweep the ovum into a fallopian tube, a passageway through which the ovum moves from the ovary to the uterus.
It takes about three or four days for the ovum to move down the fallopian tube and reach the uterus.
If sperm are present in the fallopian tube during this time, the ovum may become fertilized.
Path of an Egg through the Female Body
The vagina is a muscular tube that leads from the vulva to the cervix, the entrance to the uterus. Sperm are deposited inside the vagina during sexual intercourse.
The uterus is a hollow, muscular organ in which a fertilized ovum embeds itself and develops into a fetus.
Preparation for Pregnancy
Throughout a female’s reproductive years, her body undergoes a hormonal cycle that causes periodic changes. These changes prepare the body in the event that an egg is fertilized.
Follicle-stimulating hormone (FSH), luteinizing hormone (LH), estrogen, and progesterone control the female hormonal cycle and help prepare the body for fertilization.
If fertilization occurs, some of these hormones continue to be released to keep the body from producing another egg while a fertilized egg is developing.
If fertilization does not occur, production of progesterone and estrogen eventually stops and the uterine lining is shed in preparation for another cycle.
The ovaries prepare and release an ovum in a series of events called the ovarian cycle. The three parts of the ovarian cycle are the follicular phase, ovulation, and the luteal phase.
The release of an ovum from an ovary is called ovulation. After ovulation, the ovum is drawn into the fallopian tube and begins to move toward the uterus.
Ovulation
When the pituitary releases FSH into the bloodstream, an egg cell begins to mature within a follicle in an ovary.
A follicle is a cluster of cells that surrounds an immature egg cell and provides the egg with nutrients.
This phase where the follicle and egg develop is called the follicular phase and is considered the first step in the ovarian cycle.
The developing follicle begins to produce estrogen.
As the follicle nears maturity, it secretes larger and larger amounts of estrogen. The pituitary responds to the increasing estrogen by secreting more LH. This phase is an example of positive feedback, where an increase in one hormone results in an increase in another hormone.
Large amounts of LH cause the follicle to burst. Ovulation occurs when the follicle bursts and the mature ovum is released.
After ovulation, LH causes the cells of the ruptured follicle to grow and fill the cavity of the follicle, creating a new structure called the corpus luteum. Hence this phase of the ovarian cycle is called the luteal phase.
The corpus luteum secretes estrogen and progesterone.
The estrogen and progesterone from the corpus luteum stop the release of more FSH and LH, thus preventing the formation of new follicles within a single cycle. This phase is an example of negative feedback, where an increase in one hormone results in a decrease in a hormone from an earlier step.
Progesterone and estrogen also stimulate the growth of new blood vessels and the storage of fluids and nutrients in the uterus, causing the lining of the uterus to thicken.
If an egg does not become fertilized and embedded in the lining of the uterus during the luteal phase, the lining will be shed in a process known as menstruation.
Ovarian and Menstrual Cycles
The series of changes that prepares the uterus for a possible pregnancy is called the menstrual cycle.
The menstrual cycle lasts about 28 days and is driven by the changing levels of estrogen and progesterone.
Before ovulation, increasing levels of estrogen cause the lining of the uterus to thicken with blood vessels, preparing the uterus for the possible implantation of a fertilized egg.
After ovulation, high levels of both estrogen and progesterone cause further development and maintenance of the uterine lining.
If pregnancy does not occur, the levels of estrogen and progesterone fall. This decrease causes the lining of the uterus to be shed called menstruation.
The ovarian and menstrual cycles eventually stop, usually when a woman is between the ages of 45 and 55.
The end of menstruation is called menopause.
Summary
The ovaries produce egg cells. Ovaries also secrete estrogen and progesterone, the female sex hormones.
Throughout a female’s reproductive years, her body undergoes a hormonal cycle that causes periodic changes. These changes prepare the body in the event that an egg is fertilized.
If pregnancy does not occur, the levels of estrogen and progesterone fall. This decrease causes the lining of the uterus to be shed.
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