A man’s sex organ (penis) is separate from his internal reproductive anatomy (testes and glands). The penis is made up of the glans, the shaft and the internal organ. The penis has three main functions.
Firstly men use their penis to urinate (but only when flaccid). The urethra is a tube that runs down the middle of the penis. When a man has an erection, the muscles at the base of the bladder contract and close off the urethra so it is impossible for urine to be released when the penis is erect.
Secondly the penis is the male sex organ. There are also two cylinder-shaped chambers called the corpora cavernosa that run the entire length of the penis. When a man is mentally aroused, the arteries relax and open up to let more blood to flow in. At the same time the veins close up, trapping blood within the corpora cavernosa and causing the penis to become stiff. When the erect penis is stimulated, in conjunction with a mental focus on erotic stimuli, a man can achieve orgasm. He experiences pelvic muscle contractions and highly pleasurable sensations in the brain.
Thirdly the penis is a reproductive organ. Male orgasm triggers the ejaculation of semen containing a man’s spermatozoa (sperm). The male reproductive organs include the penis, the testes and the various glands (including Cowper’s gland and the prostate). Intercourse is an activity that facilitates male ejaculation of semen. The penis functions both as a sex organ and a reproductive organ. When a man ejaculates from intercourse, his sperm (from the testes) pass from the penis (via the vagina) into the uterus to meet the egg (produced by the ovaries). When sperm and egg meet and fuse together, a new life is formed.
The penis is designed for penetration so it has a shaft. The corpora cavernosa are located in the shaft (one either side of the central ureter tube). When these chambers fill with blood, the penis becomes highly sensitised and pleasurable to touch. The penis becomes very firm and increases in size (both width and length). It juts out from the body at an angle of approximately 45 degrees.
The prostate lies at the base of the penis, just below the bladder. Before a man can ejaculate he must be aroused, which involves getting an erection. Thereafter he usually needs penile stimulation to ejaculate. Orgasm is the trigger for ejaculation. During male ejaculation, sperm is transmitted from the ductus deferens into the male urethra via the ejaculatory ducts, which lie within the prostate gland. It is possible for some men to achieve orgasm solely through stimulation of the prostate gland (via the rectum).
Some male prostitutes climax five, six or more times per day regularly over many years. Even with such high frequencies, although the quantity of ejaculate is lower than usual, a little semen is always produced. Around three quarters of men do not ejaculate with any force. Their semen is merely exuded from the glans. Other men may ejaculate semen over distances of a few inches or even a few feet (rarely up to a meter or more!).
Having an erection, gives a man to have a strong desire to release sexual tension though thrusting through intercourse. During intercourse a man inserts his erect penis into a woman’s vagina and thrusts until he ejaculates. The penis and the vagina act as reproductive conduits during intercourse. Male orgasm is a vital aspect of male reproductive function. The pleasure of being a penetrator provides male orgasm, which triggers ejaculation and starts the reproductive process.
A man may be inordinately proud of his penis as the source of his own pleasure and his hopes for arousing (or at least penetrating) a lover. Achieving penetration and ejaculation are key factors in men’s sense of well-being. It is quite common and perfectly normal for the penis to be curved (sometimes sideways). This has no detrimental effect on either reproduction or sexual pleasure.
The role of being a penetrator involves substantially more pleasure than that of being penetrated. So the only reason a person offers to be penetrated by a partner is because they are relatively unresponsive men or they are women who are incapable of penetrating anyone. This is, after all, how responsiveness has evolved.
Psychologically intercourse is erotic from a male perspective. Responsiveness is primarily about being motivated to be penetrate another person (at least conceptually). Otherwise there is no point. But only a person who is born male can reproduce by ejaculating into a woman’s body. So only men have a sex drive. The male reproductive role involves persuading a woman to offer him an opportunity for intercourse.
The relaxed penis can be any size, depending on ambient temperature. (Antony Mason 1998)