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* MYTH Your sexual response depends on your anatomy. For example, the size of your clitoris determines whether you will have orgasms.
FACT Your mind is more important than your body in determining your sexual response.
THIS chapter describes the basics of your reproductive anatomy, tells you how it works, and explains how to keep your body in good working order throughout your life.
THE FEMALE ANATOMY
The external female genital organs, collectively called the vulva, include the mons pubis, labia majora, labia minora, clitoris, urethral opening, hymen, vaginal opening, and perineum.
The mons pubis, or mons, is a fatty pad that covers the pubic bone. The labia are two pairs of skin folds, one inside the other, that cover and protect the vagina. The outer ones, the labia majora (large lips), are derived from the same embryological tissues that give rise to the scrotum in males. After puberty the mons and labia majora are covered with hair. The inner pair, the labia minora (small lips), are aps of soft skin. Like the lips of your mouth, they are covered with epithelium and are delicate and pink. At the top or front, the narrow labia minora come together to form the hood of the clitoris. The labia minora can vary quite a bit in size from one woman to another; they can be hidden by the labia majora or may extend beyond them. The clitoris is a small cylindrical organ made of erectile tissue located where the folds of the labia minora come together toward the front of the body. It is derived from the same embryological tissue as the penis and plays an important role in female sexual pleasure and orgasm.
The opening of the urethra (the tube that carries urine from the bladder to the outside of the body) is located inside the labia minora between the clitoris and the vaginal opening. The vaginal opening is also covered by the labia minora. In virgins it may be partly covered by the hymen, a delicate membrane that usually encircles the opening like a ring or ruffle. The hymeneal tissue narrows the opening but still allows menstrual blood to flow out. In rare instances the hymen is completely closed. Women who have not had sexual intercourse may or may not have an obvious hymen; it can be ruptured by exercise or tampon use. Many women do not have a show of blood on the occasion of their first intercourse.
The perineum is the area of less hairy skin and tissue that lies between the vaginal opening and the anus. It has very little fat, so the skin in this area lies close to the muscle beneath.
The most prominent of the inner organs is the vagina. The canal, usually 3.5-4 inches (9-10cm) long, connects the vulva with the uterus. It is lined with epithelium and surrounded by layers of muscle. The vagina is ridged and expands like the folds of an accordion during intercourse and childbirth. Its muscular walls contract during orgasm, which helps the sperm deposited there ascend to the uterus. (The sperm can readily do so without help; thus it is definitely possible to become pregnant without having an orgasm.)
The cervix, the lower neck of the uterus, extends down into the vagina. If you think of the uterus as a pear sitting, stem end down, on a drinking glass, the cervix is the part inside the glass. Made of elastic and connective tissue and some muscle fibers, it serves as a gateway to the organs above. Looked at from below (as your doctor sees it during a pelvic examination), the cervix looks like a tiny doughnut. If you have not had children, the opening is small and round; once you have had a child, the opening becomes wider and more horizontal.
After intercourse the sperm pass through the cervix and uterus and head upward to the fallopian tubes. Certain glands in the cervix secrete mucus that seems to nourish sperm and definitely kills bacteria, thereby helping to prevent infection. Except around the time of ovulation, this mucus is sticky and opaque, and there is little of it. At the time of ovulation, the glandular cells secrete more mucus. It becomes thin, slippery, and rich in carbohydrates and amino acids, a perfect medium for the upward migration of sperm. During labor and delivery, the cervix thins out and dilates, increasing in size by a factor of about fifty, so that the baby can leave the uterus and enter the birth canal.
The uterus, or womb, is a thick-walled, hollow, pear-shaped muscular organ, whose job is to protect and shelter the fetus as it grows. In women who have never been pregnant, the uterus is about the size of a pear: inches (9cm) long, 2.5 inches (6.5cm) wide and 1.4 inches (3.5 cm) thick. The main body of the uterus has three layers. The outer layer is a thin peritoneal covering. The myometrium, the middle and thickest layer, is made of muscle that responds to hormonal and other chemical signals. This layer contracts rhythmically at the onset of menstruation and during labor and delivery. The inner layer, the endometrium, is composed of glandular tissue. The endometrium (along with some other fluids and cells) is shed during menstruation.
The fallopian tubes are the passageways through which eggs travel from the ovaries to the uterus. The tubes are attached to the uterus and reach out toward the ovaries without actually touching them. Each tube is just under 5 inches (10-12 cm) long and about 1 inch (2.5 cm) wide at the broad end near the ovary. As they join the uterus, the tubes narrow to the width of thin spaghetti. The ends near the ovaries are out like the bell of a trumpet and are surrounded by a fringe of specialized cells whose hairlike "fingers" (fimbriae, the Latin for "fringe") wave rhythmically, beckoning the egg into the tube. The fimbriae have quite a range of motion and can even drape themselves over the ovary like the tentacles of an octopus, making it easier for an egg to "find" its way into the tube.
The two ovaries, at the ends of the fallopian tubes, are the center of the action; they produce eggs. Each ovary is 1-2 inches (3-5 cm) long, 1 inch (2.5 cm) wide, and 0.75 inch (2 cm) thick, about the size of an almond in its shell, although the ovaries change in shape and size during the menstrual cycle. Each ovary produces, on average, one egg every other month, but if one ovary is lost through surgery or some other cause, the surviving ovary can usually manage double duty. The ovaries also produce hormones that serve the process of reproduction-mainly estrogen and progesterone, and a few others.
Many teenage girls and some women worry about whether their anatomy is "normal." If something about your reproductive anatomy worries you, don't hesitate to ask your caregiver, who will probably be able to set your concerns to rest. There is a wide range of what is normal in sex characteristics-patterns of hair growth and breast size and symmetry, for example-just as there are wide ranges of height and weight, hair color, and skin shade. The various parts of the female reproductive anatomy come in different sizes and shapes. Women can have short or long labia minora; sometimes the inner lips can be so long that they get in the way of underclothing, which is unusual but certainly normal.
Amy is a fine athlete. In high school she played soccer and in college she rows competitively, training every day on one of the local rivers. Amy has long labia that keep getting caught in her workout clothes. While this is not dangerous, it is annoying. Amy decides to have minor surgery, to trim back her labia and make her more comfortable when she works out.
Generally the clitoris is large enough to be seen externally between the folds of the labia minora, but sometimes it is not. In rare instances an abnormality that causes too much testosterone production (all women produce a little of this male hormone) may result in an enlarged clitoris.
There is also considerable normal variation in breast size and appearance. The colored area around the nipple (the areola) can be large or small, dark or light, ranging from pink to dark brown. Many women have one breast that is larger or slightly higher than the other.
Facial and body hair is another issue for some women. In general, your genes determine how much hair you have and where it grows. Almost a third of women between the ages of 15 and 44 have some upper-lip hair. Of this group maybe 6-9 percent have some hair on the sides of the face or the chin as well. If you are of Mediterranean descent, you may well have more facial hair than someone whose background is Scandinavian. If your hair is dark, it will be more noticeable. Only in rare cases-when a woman makes too much testosterone-can facial hair signal a problem.
Men and women have different distributions of pubic hair, though again there is a wide range of normal for each sex. Women's pubic hair is generally in a triangle with some spread to the inner thighs. Pubic hair also covers the outside of the labia majora between the legs and the area around the opening of the vagina. In men, pubic hair may extend up toward the belly button in the shape of a triangle or diamond. Some women too have a line of hair that reaches toward the belly button; others have hair that extends down inside the thighs. Some women have dark hairs around their nipples.
Chances are that your own pattern of pubic hair will resemble your mother's (though by the time you get around to checking, she may have gone through menopause and have less than she did as a young woman). Or your pattern will follow that of some other female relative, perhaps on your father's side of the family.
When one of my patients worries that she has some anatomical problem that interferes with her sex drive, I am able to reassure her about 99 percent of the time that nothing is physically wrong. There may be a psychological component to these persistent anxieties, and many women find counseling helpful.
If something should prove to be anatomically wrong, it probably will be a relief to know that nowadays gynecologists or surgeons can construct the external female anatomy quite easily. Years ago when I was a medical student, I did a routine checkup on a woman who had had a sex change operation, a total reconstruction of her anatomy. Of course she did not have a uterus or ovaries, and she took estrogen to make sure that she had breasts and the other female secondary sex characteristics, but outwardly-in terms of her genitals and her general appearance-she looked like a perfectly ordinary woman.
THE PHYSIOLOGY OF THE MENSTRUAL CYCLE
Although menstruation usually begins when a girl is between 10 and 16 years of age, the reproductive process actually starts before birth. It continues until menopause, which in this country generally occurs between the ages of 45 and 55.
The ovaries along with the primitive egg cells are among the first structures formed during fetal life. Before a baby girl is born, her ovaries have produced all the eggs she will ever have. By the twentieth week of pregnancy, the future baby girl has some 4 million to 6 million egg cells, which then decrease in number throughout her life. At birth, the number has dwindled to somewhere between 1 million and 2 million. When she reaches puberty, about 300,000 remain. (These figures represent informed guesswork.) During her reproductive life span, fewer than 400 will mature completely and be released into the fallopian tubes to await fertilization. The others deteriorate and are reabsorbed by the body, so that by the time a woman reaches menopause, only a very few remain.
The fact that women do not produce new eggs during their lifetime has an important impact on reproduction. The egg with which a woman becomes pregnant was formed during her prenatal life and if she is in her mid-40s, that egg will be 40-plus years old. Since men do produce new sperm as they go through life, this 40-something egg will be fertilized with sperm that was made perhaps two months previously.
By the time a girl reaches puberty, she has lost more than half the eggs she had at birth. The remainder are at rest, enclosed in structures that will form the ovarian follicles. In their simplest state, each follicle consists of an egg cell surrounded by a single layer of cells called granulosa cells. When the ovaries become more active at puberty, the eggs begin to develop.
Like a car engine that sputters a little before the ignition catches and fires, the cycle does not work perfectly at the beginning. Young girls who are just starting to menstruate may have heavy periods, light periods, or irregular periods as their cycles adjust. Once normal cycles begin, they repeat themselves each month, generally without much variation unless pregnancy takes place. Stress, severe weight loss, and certain birth control methods can also disrupt the regular pattern.
Every month some of the follicles start growing. In each growing follicle, the granulosa cells divide and reproduce many times. Instead of a single layer, many layers of cells now surround the egg cell; these granulosa cells produce most of the estrogen in the body. The cells in the ovary surrounding this developing follicle cause the outer layer of the follicle to grow and stimulate its cells to differentiate.
About a week into the menstrual cycle, the biggest follicle of the group that is growing and differentiating is chosen to be "follicle of the month"-in scientific terminology, the dominant follicle. It continues to get bigger while the other follicles degenerate and die off. Occasionally more than one follicle continues to develop, creating the possibility of fraternal twins.
When the dominant follicle reaches a certain size, it ruptures. The egg cell and some of the surrounding granulosa cells burst through the wall of the ovary, an event known as ovulation. This happens on about day 14 of a twenty-eight-day menstrual cycle. If all goes well, the egg cell is swept into the fallopian tubes by the specialized fringed cells. Once in the tube, the egg may or may not be fertilized. This first part of the menstrual cycle, which deals with the development of the follicles, is called the follicular phase.
Back in the ovary, what is left of the ruptured follicle becomes active again. It changes into a yellowish glandlike structure called the corpus luteum (Latin for "yellow body"). If the egg cell in the fallopian tube does not meet any sperm and become fertilized, the corpus luteum grows for about ten days (until day 24 of the cycle), then in its turn begins to degenerate. During its short life span (in a nonpregnant woman), the corpus luteum secretes large amounts of the hormones progesterone and estrogen.
All this hormonal action stimulates changes in the uterine lining (endometrium). As the follicles develop in the ovaries, the lining of the uterus begins to thicken, responding to the estrogen produced in the ovaries. After ovulation takes place, the estrogen level surges again.
Excerpted from THE YALE GUIDE TO Women's Reproductive Health by Mary Jane Minkin Carol V. Wright Copyright © 2003 by Mary Jane Minkin and Carol von Pressentin Wright. Excerpted by permission.
All rights reserved. No part of this excerpt may be reproduced or reprinted without permission in writing from the publisher.
Excerpts are provided by Dial-A-Book Inc. solely for the personal use of visitors to this web site.
|List of Illustrations|
|1||Your Reproductive System and How It Works||1|
|2||You and Your Gynecologist||12|
|3||Menstruation: Problems and Possible Solutions||30|
|5||Contraceptive Choices and Responsibilities||71|
|6||Vaginitis and Urinary Tract Infections||139|
|7||Sexually Transmitted Diseases||154|
|8||Fibroids and Endometriosis||194|
|9||Cervical, Ovarian, and Endometrial Cancer||223|
|11||Planning for Pregnancy||279|
|12||Fertility and Infertility||298|
|13||Abortion, Miscarriage, and Ectopic Pregnancy||328|
|14||Sex and Society||361|