How much do you know about men's bodies?

This educational content is designed to help you get the most out of your intimate relationships. By "relationship" we mean the dating, mating, and sex game -- that fun activity we spend so much energy on!

Testosterone is a steroid hormone found in mammals, highest in males, although females also have it in smaller amounts than males. Testosterone is primarily secreted by the testes of males and by the ovaries of females, although small amounts are also secreted by the adrenal glands. It is the principal sex hormone responsible for sexual desire. Now you can see why women accuse men of always thinking of sex so much more than women: men have approximately 50 times more testosterone than women.

In both men and women, testosterone is important for good health and well-being as well as for good sexual functioning. Low testosterone results in decreased libido, low energy, fewer red blood cells, and increased cholesterol and osteoporosis.

Testosterone levels decline in the later decades of adult life. This results in reduced physical fitness, especially in these areas.

• Maintenance of muscle mass and strength.
• Maintenance of bone density and strength.
• Mental and physical energy.
• Libido and clitoral engorgement/penile erection frequency.

This term is often used as a subtle insult in some countries. An adult gorilla's erect penis is approximately 4 cm (1.5 in) in length.

Physicians of different nationalities worldwide report men's erect-penis size averages vary between 9.6 cm (3.7 in) and 16 cm (6.2 in). This difference is probably due to genetics and environmental factors such as culture, diet, and chemical or pollution exposure. The average erect length is approximately 12.9-15 cm (5.1-5.9 in). The longest officially documented human length was found by Doctor Robert L. Dickinson. It was 34.3 cm (13.5 inches) long and 15.9 cm (6.25 inches) around. Bigger is not better!

The testes work best for men at temperatures slightly less than the core body temperature of 36.6 °C or 98.6 °F. The sperm are less efficient at the wrong temperatures. There are a number of muscles that raise and lower the testes to maintain the optimum temperature.

The cremasteric muscle is part of the spermatic cord that contracts, to shortened and pull the testicle closer toward the body, which provides more warmth when the outside temperature is cool. When testicle cooling is necessary, the cremasteric muscle relaxes and the testicle is lowered away from the warm body to cool.

Blue balls is a slang term for a temporary fluid congestion in the testicles and prostate region caused by prolonged sexual arousal. Heavy petting for hours with an erection but without orgasm and ejaculation is the usual cause. It is often accompanied by a cramp-like ache of prostatic congestion and pain and tenderness in the testes.

During arousal in a human male, the parasympathetic nervous system increases blood flow to the testicles and prostate areas. If orgasm is not achieved, blood and lymphatic fluid tend to pool, and the blood becomes oxygen-deprived. This results in the blood not appearing as red as normally oxygen-rich blood, and therefore the term "blue balls".

When men deprive themselves of an orgasm purposely to prolong sexual activity they may get "blue balls". Their sexual partner may also request that they refrain from ejaculation for a longer period to increase their duration of sex. If this is the case, massaging the testicles during the prolonged sexual activity may prevent the blood from pooling and decrease the severity of blue balls.

A healthy man's semen (the liquid carrier of the sperm) comes from his prostate gland. The milky-looking prostate fluid normally contains at least 20 million sperm per milliliter (mL). A man's ejaculate (his "shot") is between 1.0 mL and 6.5 mL of semen and sperm. Therefore each "load" passed on to the female (or whatever) is around 50 to 100 million sperm in a few mL of semen. His body is continuously making sperm to the tune of about 200 million to 300 million a day.

Over 90% of semen is fructose, a simple sugar to give the swimming semen energy to reach the target: the female's egg (ovum). In the semen are also some salts and phospholipids, substances that make sperm swim faster. The semen also contains some alkaline components (pH 7.1 - 8) to neutralize the vaginal and urethral acidity, which has a pH between 4 and 4.5. This may explain why most men like beer so much: beer pH is 4 - 4.4, the same as the healthy vagina!

The evolutionary wisdom in this huge amount of sperm delivered each time can be understood when the sperm are viewed under a microscope. Normally less than half the sperm have acceptable forward movement and normal shape. It appears the many obstacles in the race to the female egg are there to sort out all but the strongest single sperm. Often there are no winners due to insurmountable odds against the sperm. It appears that the complex female body has developed a physical test course to insure she gets only the best-of-the-best sperm the man has to offer. Wimp sperm don't have a chance for success.

Recent studies in the U.S. found that average erect penis length varied by race, at least a sample of less than 1000 men in these three races, ages 20 to 30:
African-American: 7 inches/17.78 cm
Caucasians and Hispanic: 5.5 to 6.5 inches/13.75 - 16.25 cm
Orientals (Chinese, Japanese, Korean, or Vietnamese descent): 5 inches/12.5 cm

The flaccid penis does not necessarily correspond to the erect length. Some smaller flaccid tools-of-love can grow much larger, but some larger flaccid ones cannot grow much larger. Outside temperature, especially cold water, can also affect the flaccid size greatly. There is evidence of a very slight correlation with body height. The human penis is both longer and thicker than that of any other primate both in absolute terms and in relative size compared with the rest of the body.

Some interesting facts:

• Smallest natural penis recorded: 5/8 of an inch/ .98 cm
• Largest natural one recorded: 11 inches
• Largest in the animal kingdom: 11 feet (blue whale)
• All male primates (gorillas, chimpanzees etc.), except human males, have a bone in their penis to keep it erect. The females of these speciesis, except humans, have a bone in their clitoris. Many mammals (rabbits, bears, dogs etc.) also have a penile bone in males and a clitoral bone in females. (Many men regret this bone was lost through evolution.)

The average amount of semen per ejaculation is 1 - 2 teaspoons. It is estimated that men will ejaculate approximately 14 gallons of semen over their life time. Much of that will be by masturbation.

The actual amount is determined by a man's age. Younger men usually make more semen. Also affecting the amount is when he last ejaculated, and how long he is aroused before ejaculating.

Researchers on male sexuality have broken down men's climax into three different events: emission, ejaculation, and orgasm. The emission phase is when there are some muscular contractions and the semen is pushed to the base of the urethra (the tube that both urine and ejaculate come out of at the tip of the penis). The second stage is ejaculation, when the semen is propelled out of the penis by different muscles. These first two stages can come (chuckle) at the same time or one after the other in seconds or minutes. The third stage, orgasm, may come (chuckle) at the same time as ejaculation or may come (chuckle) before ejaculation.

Some men practice (and it takes a lot of practice) having multiple orgasms over time in extended sex and never ejaculating. This practice of having orgasms without ejaculation was born in India more than 6,000 years ago. It is called Tantra Sex and now is practiced by many people worldwide. There is no goal in Tantra Sex, only the present moment of exquisite union. Therefore sex is meditative, expressive and more intimate. Tantra teaches lovers how to extend the peak of their sexual ecstasy so that women and men can experience several orgasms in a single sexual encounter. (First and highest priority on your list of "Things to Do": Find Tantra Sex teacher.)

There is no "penis bone" in men, but a hard erect penis can break. Such an unfortunate accident is called a penile fracture, and it's not a subtle injury. When it happens, there's an audible pop or snap and it really hurts! Shortly afterward it turns black and blue and the terrible pain continues. (Guys, put this at the top of your list of "Things Not to Do"!)

Penile fracture is rare, and it typically happens to younger men because their erections tend to be quite rigid. (At least there is one advantage to getting older.) A penile fracture happens when a man is thrusting too hard and fast during sex, and slams into his partner's pubic bone. Guys, tell your woman to be careful while she is on top.

The ears and nose continue to grow constantly as we age but the eye size remains nearly the same throughout life. Women can use this comparison of a man's ears compared to the size of his eyes with great accuracy. So men, don't try to lie about your age!

Cartoonists know about this and use it to make their characters appear young and appealing by drawing them with large eyes and small nose and ears. For enough money, surgery can change a man's or woman's nose and ears to remove a decade or two. Older woman who wish to appear as young as possible may want to wear their hair long to cover their ears!

Each sperm takes between 60 and 72 days to develop and reach maturity. In order for sperm to mature they must be at about three to six degrees F. below normal body temperature. A higher temperature not only prevents sperm production, but kills sperm in storage. That is why men's scrotums hang outside the body. Is also acts like an amazing temperature controlled elevator, lowering the testes when the outside or body temperature heats up.

There are about 250 separate chambers in each testicle where sperm is produced. Men who wear loose fitting boxer shorts (or none) have fewer cases of infertility. When tight jeans were fashionable for men, many men were reporting infertility. It was discovered to be due to their tight jeans holding their testicles too close to their body and therefore resulting in the overheating of their sperm. Tight brief shorts also do not allow the testes to lower and cool when needed, so the sperm may die in the too high temperature.

Incidentally, 65% to 85% of men have their left testicle hanging lower than their right. Also the majority of men hang their pride and joy down the left trouser leg. Clothes designers normally allow for this with a slightly wider left trouser leg.

Usually when a man's penis is erect, so are his nipples, and vice versa. At least many men's do. Men's nipples are just leftover from the foetal stage before birth when both males and females are identical.

Nipples are made of erectile tissue, a sponge-like material that swells up when blood flows faster in than out. Nipples are made of the same tissue as a penis in a man or a clitoris in a woman.

Some men get stimulated from manipulation or sucking on their nipples and the area around them, called the areola. Some men are more sensitive there than others, although the nipples are on the same circuit as the sex organs.

This concentration of nerves in the head of his love-tool is one of the most sensitive parts of a man's body. The head (glans) of the circumcised penis is less sensitive to fine touch than the head (glans) of the uncircumcised penis. The nerves are especially sensitive to temperature (heat) and friction (rubbing). The interior of the the woman's warm vagina has ridges and folds that are especially stimulating during the man's thrusting in and out the full length of the vagina.

It is news to most men that their thrusting is not as stimulating to women as it is to men. This is because only the first one-third of the vagina has nerves that are stimulated by friction of his penis. This is one reason that length of the man does not matter to most women. Most women get their stimulation from several areas at once by pressure and friction on the clitoris and all around the vagina opening. Short and thick, or upward pressure on the clitoris, are important to get the job done for most women. This may explain why 3 out of 4 women fake an orgasm when the man has his.

The testis must be 3 to 6 degrees F. cooler than the body in order to make healthy and active sperm. That is why the testicles hang outside the body, and raise and lower as the temperature changes. Wearing tight underpants holds the testis close to the body and that often makes their temperature higher than desired for sperm development.

Additionally many habits also force the testis close to the body such as sitting at the computer, driving, and wearing tight outer clothes. Also some men work in jobs where the temperature is high during manufacturing processes.

A high fever during an illness can leave a man with a low sperm count for a couple of months until he makes a new supply, which takes approximately 70 days for each sperm to develop.

In a 2002 survey of 50 adult men who experienced sex uncircumcised for a number of years then had to be circumcised for various reasons reported less sensitivity and diminished erectile ability. The frequency of sex did not change after circumcision.

There is no evidence that circumcised males are more or less likely to acquire a sexually transmitted disease of any type nor get cancer. The American Medical Society has flatly stated, "Circumcision is not of value in preventing cancer of the penis."

The prostate fluid is the carrier for the sperm. Only about 1% of the fluid ejaculated is sperm, the rest is primarily prostate fluid. Prostate fluid is alkaline and neutralizes the acidic female vagina to protect the seaman. It also contains fructose that provides energy for the sperm swimming toward the female's egg. There is over 100 calories in a teaspoon of prostate fluid.

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