Female sex organs produce eggs receive sperm and nurture the embryo

When a mammalian egg matures, it is released from the ovary directly into the body cavity. But the egg does not go far. Each ovary is enveloped by the undulating, fringed opening of an oviduct (also known as a Fallopian tube), which sweeps the egg into that tube (Figure 43.11). Fertilization takes place in the oviduct. Whether or not the egg is fertilized, cilia lining the oviduct propel it slowly toward the uterus, a muscular, thick-walled cavity shaped in humans like an upside-down pear. The uterus is where the embryo develops if the egg is fertilized. At the bottom, the uterus narrows into a necklike region called the cervix, which leads into the vagina. Sperm are ejaculated into the vagina during copulation, and the fetus passes through the vagina during birth.

In humans, two sets of skin folds surround the opening of the vagina and the opening of the urethra, through which urine passes. The inner, more delicate folds are the labia minora (singular, labium minus); the outer, thicker folds are the labia majora (singular, labium majus). At the anterior tip of the labia minora is the clitoris, a small bulb of erectile tissue

| Eggs mature in and are released by the ovaries.

| Eggs mature in and are released by the ovaries.

2l Eggs are taken into the oviducts, where they travel to the uterus. Fertilization occurs in the upper regions of the oviduct, where development begins.

Vagina Sperm

The blastocyst implants in the endometrium of the uterus, where embryonic development continues.

Sperm are deposited in the vagina during copulation.The vagina is also the birth canal.

The neck of the uterus is the cervix which remains closed during pregnancy and dilates to allow childbirth.

that has the same developmental origins as the penis (see Figure 42.12). The clitoris is highly sensitive and plays an important role in sexual response. The labia minora and the clitoris become engorged with blood in response to sexual stimulation.

The external opening of a female human infant's vagina is partly covered by a thin membrane, the hymen. Eventually the hymen becomes ruptured by vigorous physical activity or first sexual intercourse; it can sometimes make first intercourse difficult or painful for the female.

To fertilize an egg, sperm deposited in the vagina swim, and are propelled by contractions of the female reproductive tract, through the cervical opening, the uterus, and most of the oviduct. The egg (actually a secondary oocyte) is fertilized in the upper region of the oviduct. Fertilization stimulates the completion of the second meiotic division, after which the haploid nuclei of the sperm and the egg can fuse to produce a diploid zygote nucleus. Still in the oviduct, the zygote undergoes its first few cell divisions to become a blas-tocyst. The blastocyst moves down the oviduct to the uterus, where it attaches itself to the epithelial lining of the uterus, the endometrium.

Once attached to the endometrium, the blastocyst burrows into it—a process called implantation—and interacts with it to form the placenta (see Figures 20.14 and 20.19). The placenta exchanges nutrients and waste products between the mother's blood and the embryo's blood. It also produces hormones that help sustain pregnancy.

As the egg matures in the ovary, the endometrium thickens. If a blastocyst does not arrive in the uterus, it regresses or is sloughed off. Thus the female reproductive cycle actu-

2l Eggs are taken into the oviducts, where they travel to the uterus. Fertilization occurs in the upper regions of the oviduct, where development begins.

43.11 The Reproductive Tract of the Human Female The female reproductive organs are shown in front and side views.

43.11 The Reproductive Tract of the Human Female The female reproductive organs are shown in front and side views.

The blastocyst implants in the endometrium of the uterus, where embryonic development continues.

Ovary

Oviduct

Body cavity

Urinary bladder

Urethra

Clitoris

Sperm are deposited in the vagina during copulation.The vagina is also the birth canal.

The neck of the uterus is the cervix which remains closed during pregnancy and dilates to allow childbirth.

Ovary

Oviduct

Body cavity

Urinary bladder

Urethra

Clitoris

Colon Uterus

Colon Uterus

Endometrium (lines uterus)

Cervix Rectum

Labia Labia Vagina majora minora

Colon Uterus

Endometrium (lines uterus)

Cervix Rectum

Labia Labia Vagina majora minora ally consists of two linked cycles: an ovarian cycle that produces eggs and hormones, and a uterine cycle that prepares the endometrium for the arrival of a blastocyst.

The ovarian cycle produces a mature egg

An ovarian cycle is about 28 days long in the human female,* but there is considerable variation among individuals. During the first half of each cycle, at least one primary oocyte matures into a secondary oocyte (egg) and is expelled from the ovary. During the second half of the cycle, cells in the ovary that were associated with the maturing oocyte develop endocrine functions and then regress if the egg is not fertilized. The progression of these events is shown diagrammatically in Figure 43.12.

At birth, a human female has about a million primary oocytes in each ovary. By the time she reaches puberty, she has only about 200,000 in each ovary; the rest have degenerated. During a woman's fertile years, her ovaries will go through about 450 ovarian cycles. During each cycle, a number of oocytes will begin to mature, but usually only one oocyte from one or the other ovary will mature completely and be released; the others will degenerate. At about 50 years of age, she

"Some mammals have ovarian cycles shorter than 28 days; others have longer ones. Rats and mice have ovarian cycles of about 4 days; many seasonally breeding mammals have only one ovarian cycle per year.

reaches menopause, the end of fertility, and may have only a few oocytes left in each ovary. Throughout a woman's life, oocytes are degenerating, and no new ones are produced.

Each primary oocyte in the ovary is surrounded by a layer of ovarian cells. An oocyte and its surrounding cells constitute the functional unit of the ovary, the follicle. Between puberty and menopause, six to twelve follicles begin to mature each month. In each follicle, the oocyte enlarges and the surrounding follicular cells proliferate. After about a week, one of these follicles is larger than the rest, and it continues to grow, while the others cease to develop and shrink. In the enlarged follicle, the follicular cells nurture the growing egg, supplying it with nutrients and with the macromolecules and proteins it will use in early stages of development if it is fertilized.

In humans, after 2 weeks of follicular growth, ovulation occurs: The follicle ruptures, and the egg is released. Following ovulation, the follicle cells continue to proliferate and form a mass of endocrine tissue about the size of a marble. This structure, which remains in the ovary, is the corpus lu-teum (plural, corpora lutea). It functions as an endocrine gland, producing estrogen and progesterone for about 2 weeks. It then degenerates unless a blastocyst implants in the endometrium.

From PMS To PPD

From PMS To PPD

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Responses

  • finley
    Are eggs in ovaries at birth?
    5 years ago
  • natalino
    Which organ produces sperm?
    5 years ago
  • callimaco
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    5 years ago
  • Michael Stoltz
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    5 years ago
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    5 years ago
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    5 years ago
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    5 years ago
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    5 years ago
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    5 years ago
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    5 years ago
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    5 years ago
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    5 years ago
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    5 years ago
  • mhret
    Where does the blastocyst implant in the uterus?
    5 years ago
  • Stephan
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    5 years ago
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    5 years ago
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    5 years ago
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    5 years ago
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    5 years ago
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    5 years ago
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    5 years ago
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    5 years ago
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    5 years ago
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    5 years ago
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    4 years ago
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    4 years ago
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    4 years ago
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    3 years ago
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    11 months ago
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    10 months ago
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    4 months ago
  • selamawit
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    4 months ago
  • Susanne Schroeder
    Where in the female organ do the sperm fertilize the ovum?
    3 months ago
  • Laura
    How can i nuture my fertilised egg?
    3 months ago
  • edilio toscani
    Can a single sperm swim from the clitoris to fertilize egg?
    22 days ago

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