Anatomy Of The Sex Organs In Women And Men
Testicles and Production of Sperm
The testicles are analogous to the female ovaries. In the advanced stage of development of the fetus the testicles descend from the abdominal cavity into the scrotum.
The left testicle descends and rests slightly beneath the right testicle which follows and completes the descent. It is easier to walk with the testicles in this position than in the side-by-side position.
Unlike the ovaries located within the abdominal cavity, the testicles lie outside the abdominal cavity to produce and preserve spermatozoa at a lower temperature, which is conducive to longer life by spermatozoa. Each testicle is crowned with an elongated mass called epididymis.
The tail of the epididymis extends below the testicle and continues into the vas deferens duct.
As the ovary is the factory producing ova and the organ secreting female sex hormones, so the testicles are the organ secreting male hormones and the factory producing spermatozoa.
In a newborn baby boy, thousands of sperm cells exist immature and immobile in the testicles. At puberty the spermatozoa nurtured in the testicles are sent gradually to the head of the epididymis through tiny ducts.
They mature as they descend to the tail of the epididymis. Upon reaching the vas deferens ducts they are weakly mobile but are not yet fully active.
The male produces spermatozoa constantly and steadily until a comparatively old age. A sperm, consisting of head, neck and tail, grows to a length of 50-60/1,000 of a millimeter.
The head is the only portion of the sperm that unites with the egg cell. The head, shaped like a flattened pear, slightly dented at its point, contains a tiny cell less than one tenth the length of the sperm.
Its long tail, split into two or three ends, provides the means of locomotion. Although the life span varies with the sperm, it generally does not take longer than three days for a sperm ejaculated into the vagina to unite with the ovum.
It is interesting to note that two kinds of sperm exist at all times namely, the kind that produces a male embryo when united with the ovum and the kind that produces a female embryo. The numerous somatic cells (which compose the human body) and the sex cells (sperm and egg) are both based fundamentally on a single but different cell.
The chromosomes, which determine heredity and sex, in the sex cells number one-half those in the somatic cells. In other words, the somatic cell splits into two parts to produce a sex cell.
The character and nature of the new-born life developed from the union of the sperm and the ovum is determined by the quality of the united genes in the chromosomes as well as by the manner of splitting of the chromosomes.
There are 46 chromosomes, or 23 pairs in each somatic cell. The chromosomes in the sex cells total 23 and each lacks the other half to form a complete pair as in the somatic cell. Among the 23 pairs of the chromosome group in a somatic cell only one pair bears the sex gene.
In the female, one chromosome is as large as the other of the pair and is called 'X' chromosome. In the male, one is called 'X' chromosome and the other slightly smaller than "X," is called "Y" chromosome.
The ovum, one-half the size of the female somatic cell has only one 'X' chromosome; whereas, the sperm, also one-half the size of the male somatic cell has either the female-bearing 'X' chromosome or the male-bearing "Y" chromosome.
Vas Deferens Ducts and Seminal Vesicle
The vas deferens ducts are two narrow tubes, approximately 45 centimeters (18 inches) long, extending upward from the right and left tails of the epididymis and to the rear downward to the lower peritoneum in the lower abdominal cavity.
The walls of the sperm ducts are lined with muscles in annular shape which contract in turns from the bottom upward and function as a suction pump.
The spermatozoa maturing in the tail of the epididymis mix with the fluid secreted in the walls of the epididymis and develop into a semen-like substance.
Actually this is not semen, and the sperm are not fully mobile. In response to the suction pump action the fluid of sperm steadily increases and rises through the deferent duct. The long duct itself functions as a storage duct for the fluid of sperm.
The deferent duct widens at a point three or four centimeters (1.2-1.6 inches) near its end and serves as a large repository for the sperm-bearing fluid. Upon filling this repository, the sperm fluid passes through an opening and into the seminal vesicle, where the sperm are destroyed and the fluid is absorbed.
The main function of the seminal vesicle is not as an auxiliary repository but rather to secrete a yellow, agglutinative mucus to increase the amount of semen.
This is ejected at ejaculation. The farthest ends (2 cm, 0.8 inch) of the deferent ducts, following their expanded parts, run through the prostate gland (located in front of the bladder and surrounding the urethra at its starting end) and open into the urethra there.
Prostate Gland and Semen
Shaped like a chestnut, the prostate gland surrounds the neck of the bladder at the point where this organ empties into the urethra. Like the testicles, the prostate gland secretes hormones. The secretion consists of a milky alkaline fluid called spermin and a chemical substance with a marked odor.
At ejaculation the prostate gland contracts and forces this fluid into the urethra. In front of the prostate gland alongside the right and left deferent duct openings, the efferent duct of the prostate gland, too, opens into the urethra.
First, in the male ejaculation the deferent duct, its enlarged area and the seminal vesicle repeatedly contract simultaneously and build pressure in the urethra to ejaculate the spermatozoa with the epididymis secretion and the seminal vesicle secretion, and by the contraction of the prostate gland.
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The ejaculation is mixed and emitted as perfected semen. Stimulated by the prostate secretion, the spermatozoa grow highly motile.
Of the approximately 3 cubic centimeters of semen the male emits at one ejaculation, four-fifths comprise the prostate secretion.
The ejaculated sperm total approximately 200 to 300 million. Secondly, in an ejaculation the prostate gland contracts and presses the urethra at the upper sperm duct opening, which swells and closes the urethra at this point.
This prevents retrograde ejaculation of the semen in the urethra or emission of the urine. The deferent duct opening swells at the moment of erection.
We now go on to discuss the stages of sexual arousal in men and women in the context of normal sexual experience.
Erection and Ejaculation
The main prerequisite for sexual intercourse for a man is erection of the penis.
The penis is covered with a skin called the foreskin. At the head of the penis is the glans, a mucous membrane which is covered with a layer of skin highly concentrated with nerves.
Under the surface, the penis consists of a spongy body of blood vessels through which the urethra runs.
In an erection the spongy body is filled with blood. Erection is caused by:
1. Physical stimulation applied to the meatus, glans or foreskin. The stimulation is transmitted to the cerebrum, where it is received as a pleasant sensation. By reflex, blood flows in the spongy body and causes erection.
2. Emotional and mental stimulation transmitted directly from the cerebrum.
With the erection in sexual excitation, the right and the left Cowper's glands, opening into the urethra, and the numerous little mucous glands secrete a small amount of transparent, alkaline mucus and moisten the meatus to facilitate entry of the penis into the vagina.
This alkaline secretion neutralizes the urethra, acidic from urine, and assures safe passage of spermatozoa, which have low resistance to acids. Although this secretion is accelerated by local, direct stimulation from touch during erection, it may be caused entirely by emotional and sexual excitation even prior to erection.
Erection and mucous secretion from sexual excitation prepare the penis for intromission in the vagina.
Following it, the stimulation accelerated by friction reaches its height, and ejaculation takes place by reflex. It is an involuntary reflex, and though he may try, he cannot stop it.
Women and men alike should not jump to the conclusion that erection of the penis alone signifies sexual desire.
For instance, a man, even though weak from exhaustion, may experience erection from local stimulation, but he will not have full sexual desire.
Female sex organs
The female sex organs are composed partly of internal organs - the uterus, ovaries, Fallopian tubes - which are protected within the abdominal cavity and kept away from direct contact with the male, and partly of external organs such as the vulva and the clitoris, which are exposed to sexual contact.
Ovaries and Production of Ova
The female ovaries lie on both sides of the uterus in the abdominal cavity. The female at birth stores thousands of immature ova in the ovaries. In their growth and maturity, ova differ vastly from the male spermatozoa.
As the male reaches puberty numerous spermatozoa are constantly produced and stored; whereas in the female, a single ovum matures and is discharged alternately from the two ovaries at an interval of 28 to 32 days.
The ovum is a cell with a diameter of approximately 0.2 millimeter (8/1,000 inch), or four times the length of a spermatozoon.
It is the largest of all cells in the human body. We can determine the existence of spermatozoa by examining the semen, but by a similar method it is almost impossible to determine the existence of the ovum in the female.
Upon reaching maturity the ovum is ejected from the inner lining of the ovary. This process is called ovulation. It is difficult to know accurately in advance the date of ovulation.
We can determine the end of ovulation by taking the basal temperature and note the change from low to high temperatures after ovulation (refer to section on birth control), but we run into difficulties in predicting the day of ovulation.
When the ovum is not fertilized following its discharge, menstruation occurs on the 12th through the 16th day. Since the ejected ovum, as explained previously, contains only the 'X' chromosome, the sex of the new life to be created from the fertilization depends solely on whether the male spermatozoon has an "X" or "Y" chromosome.
The ovary secretes two kinds of hormones: estrogen and progesterone. Estrogen, mainly secreted prior to ovulation, promotes the maturing and growth of the uterus and lacteal gland as well as the development of the mucous membrane lining the uterus.
Progesterone, added following ovulation, restrains the oversensitive uterus and promotes the production of the mucous membrane in the uterus lining.
Therefore, during pregnancy - particularly until the placenta forms - a large amount of progesterone is secreted continuously as a natural means of preventing miscarriage.
Fallopian Tubes and Fertilization
The two Fallopian tubes are long, narrow ducts projecting from the upper ends of the uterus and embracing the two ovaries which lie under the tubes and on both sides of the ovary. When ovulation approaches, the Fallopian tube waits near the ovary and draws in the ejected ovum.
By means of the cilia lining the tube's inside wall and swaying toward the uterus the Fallopian tube sends the ovum to the uterus cavity. The ovum unites with the spermatozoon and fertilizes normally near the expanded area midway in the Fallopian tube.
The tube measures approximately 20 centimeters (7.8 inches) from its tip to the external orifice of the uterus. The spermatozoon advances on a flat surface, when seen under a microscope, at the average rate of approximately three millimeters (117/1,000 inch) per minute.
In the female body the ejaculated spermatozoa take at least eight hours to reach the swollen part of the Fallopian tube. The outer wall of the ovum is agglutinated with hyaluronic acid.
When the acid is dissolved by hyaluronidase contained in the sperm, the ovum is prepared to unite with a spermatozoon. The spermatozoon pierces a hole and enters into the ovum. The DNA in its head unites with the nucleus of the ovum.
The fertilized ovum continues its process of development called cell-division while passing through the Fallopian tube.
Approximately five days later it reaches the uterus and after another five days settles there.
Capable of remaining alive for not more than a day after ovulation without fertilization, the ovum passing beyond the tube's midpoint disintegrates and can no longer be fertilized. At this point a woman cannot normally get pregnant even if she has unprotected sex until her next ovulation.
Uterus and Menstruation
The uterus is a muscular structure shaped like an inverted pear with mucous membrane on the inside. The neck of the uterus at its lower end protrudes into the vagina.
The upper portion is, together with the ovaries and the Fallopian tubes, located in the abdominal cavity and is protected by the pelvis.
The mucous membrane in the uterus is characterized by a thin layer of tissue adhered to the muscular wall and overlaid with the functional zone.
Upon contact with estrogen and progesterone secreted from the ovaries, the functional zone starts growing immediately after menstruation.
By the time the fertilized ovum enters into the uterus, its mucous membrane has thickened and is ready to receive and nourish the ovum.
If there is no fertilized ovum to settle in the uterus, then all the preparation is shed in the monthly bleed.
After a while estrogen secretion decreases temporarily, causing excoriation of the layer.
This phenomenon is known as menstruation. At the end of menstruation the uterus lining repeats the cycle of growing and thickening, stimulated by estrogen and later by progesterone.
Labia Majora and Labia Minora
The female external sex organs are closed from the right and left by the labia majora (large lips) covered with a thick growth of pubic hair. The labia minora (lesser lips) and clitoris show large individual differences. During sex, the labia are stimulated by the penis. The smaller lips do not have hair on them and the left and right lips are not always the same size.
Vestibule and Clitoris
The clitoris is located at the upper meeting point of the right and left labia minora. Being the most sensitive of all female sex organs, it is responsible for orgasm. In response to pleasurable stimulus it rises and exposes its glans.
The clitoris is highly concentrated with nerves and normally more sensitive than the penis - and sensitive organs such as the labia majora, labia minora, vestibule and vagina give a woman subtle variations in sexual pleasure.
The urethral meatus opens directly below the clitoris and still lower lies the vaginal opening. Tiny openings on both sides of the urethral meatus secrete mucus from the glands called Skene's glands. Also secreting mucus and located on both sides of the vaginal opening are Bartholin's glands.
The Hymen and The Vaginal Opening
The hymen, known as the "maidenhead," is a thin fold of membrane partly closing the vaginal opening. It normally permits the entry of a finger but nothing larger.
In the initial sexual intercourse it may be ruptured with some bleeding and pain. It may be torn open naturally through other ways as in sports and masturbation.
The vagina is a canal measuring approximately 4 inches in length between the vaginal opening and the uterus.
The anterior and posterior walls of the vagina have folds, which in coital friction enhance the stimulation on the penis. This increases the sexual sensation in the woman as well.
The vagina secretes some lactic acid which increases or decreases in amount with the phase of the menstrual period.
The secretion contains a minimum amount of lactic acid during ovulation, helping promote the activity of spermatozoa.
Spermatozoa are most active in a dilute lactic acid solution, while they die early when exposed to a higher concentration of acids.
A transparent or white mucus forms at the lower end of the uterus called the cervix. It normally seals the mouth of the uterus, and in sexual intercourse it facilitates entry of the ejaculated spermatozoa into the uterus.
During female orgasm, as much mucus as the male semen gathers at the vaginal opening, mainly from the increased secretion from the cervix as well as by the continuous flow of secretion from Bartholin's glands near the vaginal entrance.
Orgasm and Pelvic Muscles
As in the case of the male, female orgasm is a reflexive convulsion caused by increasing stimulation of the clitoris and/or vagina.
The secretion from the vaginal walls and Bartholin's glands flows in abundance at orgasm and gives the impression that female ejaculation, similar to the male ejaculation, occurs in the female. The amount of this secretion varies with the individual.
As mentioned earlier, male orgasm often derives from increasing local stimulation and at other times by the sexual excitement transmitted from the cerebrum. The same can be said of female orgasm.
Nearing the culmination of intercourse, the stimulation grows until the tension is suddenly released as a woman reaches her orgasm. (To make a woman orgasm in sexual intercourse a man generally needs to be able to control his orgasm and ejaculation.
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A man reaches orgasm with ejaculation, and usually experiences it only once at each episode of sexual intercourse.
The woman, on the other hand, can have as many orgasms as the man can offer through his skilled love play or as many as she chooses to experience through masturbation. In the course of sex women can experience several, continual orgasms.
A characteristic noticeable in female orgasms is the contraction of the pelvic muscles. When the muscles lining the vagina contract, they strongly stimulate the penis in the vagina, which in turn stimulates the vaginal walls.
Two of the muscles produce a powerful stimulative effect, and through practice a woman can voluntarily contract one or both muscles in coordination.
One of them is the annular muscle surrounding the vaginal opening and is called the musculusconstrictor cunni. As it is connected to the musculus sphincter ani, the two muscles form a figure eight.
The other is the horseshoe shaped muscle embracing the vagina from inside the pelvic bone to the rear walls of the vagina and rectum.
The medical term for it is musculus levator ani. The muscle embracing the vagina is called the musculus levator vaginae.
By skillful contraction of these muscles during sexual intercourse the woman can stimulate the penis and arouses the male to extreme sexual pleasure and also enhances her own pleasure in bed. He may easily attain orgasm from repeated contraction of these muscles.
On the other hand, to prevent the penis from becoming flaccid following a premature orgasm, which falls short of the stimulation she needs to be fulfilled, she may continuously or continually contract these muscles to prolong his erection and time his ejaculation with her gradually diminishing orgasm.
This set of muscles may cause strong, abnormal contraction and prevent the entry of the penis or the withdrawal of the inserted penis. This phenomenon, called vaginismus, is caused by emotional issues.
Anticipation Of Sexual Intercourse
The most important of preparation for sexual intercourse is conversation; the most important subject matter is love, and its effectiveness depends on self-suggestion and mutual suggestion. We tend to forget the importance of conversation on love with the passing of each day in long term relationships or marriage.
A husband may say with a sigh, "I've told her all I know about love." A wife may say with a puzzled look, "It's the man's job to tell the woman about it."
Both are wrong. Enjoying his caresses the woman anticipates soft whispers of love. She wants to be assured with words spoken now and then that he loves her. It does not mean that she longs to hear a string of breathtaking adjectives. She is satisfied with conversations liberally sprinkled with phrases like "I love you."
Although the man is less eager for expressions of affection, he should certainly not feel uncomfortable listening to words of love.
They can even arouse his sexual desire. Conversation about love inspires us not only to stronger emotional love but also to constantly refreshing sexual love.
In the enhancing atmosphere conducive to love play, the man and the woman involuntarily experience arousal in their sexual organs before advancing to touch, kissing, and caressing.
Caressing - foreplay
Caresses preceding sexual intercourse are necessary not only for the woman but for the man as well. Stimulation starts with kissing and is then given by embraces, and then by contact with various parts of the body, especially the penis, breasts, vulva, clitoris, and balls.
The man is often assumed to initiate the caresses but the woman should initiate as well.
Caressing further increases secretion of pre-ejaculatory fluid and feminine love juices, ready for intercourse. The male does not secrete as much as the female.
This poses no great problem, but lack of the woman's secretion may prove a hindrance to smooth sexual intercourse and post-intercourse activity.
Whispers of love and words of encouragement and appreciation or pleasure will drive further the couple's physical arousal and libido, guiding them into a world of their own. Genital caresses should always be gentle and slow at the beginning and steadily strengthened with the increase of arousal.
Sudden, strong stimulation at the start may cause pain and inflammation. Hurried strong stimulation, particularly of the glans of the penis, should be avoided. Some use saliva to supplement the lack of female secretion; a good alternative is a high quality lube.
Vigorous contact is not the only means of powerful stimulation. Gentler motions, and gentle, rhythmical stimulation can be highly effective in arousing pleasure for a woman during sex.
All conceivable ways of caressing, including oral-genital stimulation, are natural and normal. To prevent inhibition about hygiene from intervening in whatever form of caress they seek, a couple should both keep their bodies clean.
The erogenous zones in the human body, the parts capable of erotic feeling, are briefly described below. But the whole body is sensitive to stimulation of one kind or another.
Of different parts of the penis, the most sensitive to the touch is the glans - notably its underside just below the frenulum. The part most insensitive to finger stimulation is the shaft, although rhythmical pressure, particularly on its underside near the base, can be very pleasurable.
The clitoris is analogous to the male penis. The outer skin normally covers the clitoris and protects the glans. This area is highly sensitive and responsive to touch and rhythmic pressure.
Steady, continuous stimulation of the clitoris is usually not desirable as it may give an unbearably intense sensation to the woman. The man should remember that he can stimulate around the clitoris without touching it directly.
The inner area of the labia minora, or the lesser lips, is extremely sensitive to the touch. A woman's sexual arousal is intensified when the stimulation is rotated from one inner labium, over the clitoris, to the other inner labium.
The zone including the urethral meatus and the vaginal opening, especially the lower end, is highly sensitive to stimulation.
The sphincter vagina ring at the vaginal opening contracts in response to pressure. Rhythmic, downward pressure in the vaginal opening applied with the finger produces powerful sexual arousal.
The vaginal wall is highly sensitive to the touch around the G spot, though sexual sensation from the intromission of the penis is enhanced by psychological pleasure, the pressure on the sphincter vaginae muscles, and the stimulation of the vaginal vestibule, labia minora and clitoris. The vaginal vestibule is sexually aroused when the clitoris is stimulated.
This zone is sensitive to the touch. The woman feels the cervix being stimulated because impact from the penis during deep penetration is transmitted to the surface of the uterus, and also because the deep insertion inevitably causes a chain reaction in stimulation.
It is not advisable for the man to try to arouse it with his fingers, as he may possibly injure it.
Analogous to the scrotum, the labia majora add much to the woman's sexual feelings, and also apply some pressure on the penis.
Some men are aroused when the testicles are held in the palm and the base stimulated with the fingers. Most men feel pain in the testicles if they are pressed too hard. But the scrotum has high sensitivity and during intercourse, as a man thrusts, it hits gently against the woman's body, giving a pleasant sensation to both partners.
This zone between the vagina or the penis base and the anus is sensitive to the touch. The middle region is especially sensitive to pressure.
The sexual sensation of the anus differs with the individual and the extent of psychological influences. As the anus and the sex organ share the same network of muscles, the male and female anus contracts when the sex organs are stimulated, and the sex organs contract when the anus is stimulated.
The nipples, especially, are as highly sensitive as the clitoris. The stimulation the female receives from the breast is instantly transmitted to the uterus and other sex organs. Some women prefer this sensation, particularly from the kiss or suction, to the arousal of the sex organs.
Compared with the female breast, the male breast appears much less sensitive to sexual arousal unless a couple have worked to awaken a man's awareness of its sensory potential.
The lips, tongue and inner part of the
mouth have almost as much sex sensation as the sex organs. It is strongly felt in
long, deep kissing of the breasts and sex organs.
Sexual arousal is increased when the muscles in the buttocks contract. This is why the male and the female voluntarily or involuntarily contract the muscles in the buttocks.
By doing so, the anus naturally contracts, stimulates the sex organs, contracts the muscles in the vagina, tightens the vaginal opening and stimulates the male erection.
The inner sides of the thighs respond sharply to stimulation.
Some individuals develop highly erogenous zones about the eyes and ears, neck, throat, armpits, navel, abdomen, waist, small of the back, groin, pubic mound, the sides of the chest, and other areas. Light brushing of the pubic hairs and running the fingers through the hair on the head also arouses sexual feelings.
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Updated 23 February 2020