..........The Penis.........

Your Penis (dick or cock) isn't just a roll of flesh with a tube down the middle, although that is an important part of its structure, since it allows you to (urinate) pee. This tube, or urethra, opens as a hole or a slit on the tip of the glans - both types of opening are equally common. Often there are two little lips on the glans surrounding the end of the urethra. These are full of with nerve endings that protect the sensitive urethra by alerting its owner to any intrusion into the body - although during sex play this sensitivity can be very exciting. The glans is the most sensitive part of the penis, as you'd expect, since it leads the way in sex. The coronal ridge and frenulum, which is a band of skin between shaft and glans, often missing in circumcised men, seem to be crucial in stimulating ejaculation at the right point in the penetration of the anal canal or a vagina. All the way up the shaft, the urethra is surrounded by spongy tissue called the corpus spongiosum. This fills with blood from a network of small arteries during sexual arousal, and it is this increase in blood supply, together with a muscular constriction of the veins which drain blood from the penis, that causes and maintains an erection. In the light of this, it may not surprise you to learn that two common causes of impotence or erectile dysfunction - i.e. you can't get or stay hard - are, firstly, occlusion of the penile arteries by fatty deposits and, secondly, venous leakage. There are two other channels of spongy tissue, which you can see in the cross-section above, and they too fill with blood during an erection. It is an unfortunate fact that that as men age, the blood supply to the penis can decrease because of the increased amounts of fat which are deposited in the penile arteries - and it doesn't take much to block them, for they are only the diameter of the tines of a fork. The consequences are that the muscle fibers inside the penis, whose job is to regulate blood flowing through the blood vessels, begin to turn to connective tissue. The greater the amount of connective tissue, the greater the difficulty getting an erection - eventually it will be impossible to get hard at all. Even in a penis with clear arteries, it seems that normal blood flow may not be enough to keep the tissues healthy, and it has been suggested that the need to ensure good oxygenation of the penis through increased blood flow may be one reason why men get spontaneous erections during sleep; in any event, it seems that to keep getting erections, you need to keep the erectile mechanism in regular usage. Make of that what you will! The penis goes deep back inside the body, with its root reaching back underneath the prostate gland towards the anus. This is the sensitive tissue that some men find great pleasure in having stimulated through either their scrotum or their perineum (the area between scrotum and anus). It is this "hidden" part of the penis that allows some men, who show no penile shaft when their cock is soft, and just have the glans sticking out of their body, to achieve a sizeable erection. You might want to read the size page for an anecdote on one guy with this sort of physique. The penis develops as a tube of flesh which seals gradually along its length during development in the uterus. Normally, the only remaining sign of this process after birth is a thin ridge of skin along the underside of the penis known as the raphe. Strangely, the skin of the penis is infiltrated with muscle fibers that extend from the muscle of the scrotum. The strength or activity of this muscle in any individual male determines in large part whether he has a scrotum which hangs loosely or is held tighter against the body: the more active the muscle, the tighter and more crinkly the scrotum appears, although it is of course also stimulated into contraction by fear (as in the expression "that was a real scrotum tightener!") or cold. The muscle fibers are also largely responsible for the contraction of the penis in length and for the variation in size of the preputial sphincter - which is just a fancy name for the opening of the foreskin at the end of the penis. This opening is not always seen in its classic textbook form, located just beyond the end of the glans, because, like every other aspect of the penis, the length of the foreskin is highly variable, so that in some men there is only partial coverage of the glans, even when the penis is flaccid. The frenulum is one of the most sensitive parts of the penis head, but it is often removed during circumcision.