His Bits

His Bits
by Paul & Lori

Because they are easily seen, it may seem that the male sex organs are rather simple, but this is not the case. The penis, composed of many parts, contains an amazing and complex hydraulic system.

Penises are individual, coming in a wide range of shapes, sizes, and colorations. Some grow a great deal when they become erect, while others become hard without much change in size. When erect, some point straight out, others hang down, some curve, and still others become almost vertical.

the male genitals, external

external male genitals


The penis has three chambers running the length of the penis. Two cavernous bodies (corpora cavernosa) lie side by side on top of the penis and the spongy body (corpus spongiosum) is centered below the other two. The spongy body surrounds the urethra and extends out the end of the shaft to form the head of the penis (glans). All three chambers contain small hollow areas that fill with blood to produce an erection. Surrounding all three bodies is a semi-elastic membrane (tunica albuginea).

cross section of the penis

head (glans)

Also called the head of the penis, the glans contains a large number of nerve endings, making it the most sensitive part of the penis. The frenulum is the most sensitive area of the head, the corona the second most sensitive area. In most men, the glans is hypersensitive right after orgasm.

underside of penis


The corona is the ridge (rounded border) where the head ends at the shaft.


The frenulum is a small fold or ridge of tissue on the underside of the head.


The shaft of the penis contains neither bone nor any muscle other than those that control blood flow. The shaft is wider than it is high, and one side usually bulges out more than the other. The erect penis is very tough and can be squeezed quite firmly without causing pain or damage.


At birth, the head of the penis is covered by a retractable skin called the foreskin. Circumcision is the removal of this skin. Aside from religious reasons, circumcision has sometimes been performed out of concern for hygiene. Most men find that daily washing is effective in maintaining cleanliness. Circumcision is more common in America, and less so (other than for religious reasons) in Europe.


The scrotum is composed of skin and muscle. It is designed to pull the testicles (see internal genitals below) closer to the body for warmth and to hang away from the body for cooling. The scrotum also pulls the testicles toward the body during arousal. At orgasm, they are held tightly against the body. One side of the scrotum, usually the left, hangs slightly lower to keep the testicles from knocking together when a man walks or runs.

the male genitals, internal

internal male genitals

root of the penis

Only about half the penis shows externally: the rest is inside the body. The internal part of the penis also becomes erect. The cavernous bodies attach to the pelvic bone (this anchors the penis and allows it to stand away from the body when erect), while the spongy body continues back almost to the anus. During an erection, this internal part of the penis can be felt behind the scrotum.


Testicles (also called the testes or balls) are located in the scrotum. Both sperm (the male reproductive cell) and male sex hormones are produced by the testicles. Sperm production requires a temperature slightly below normal body temperature, and research suggests temperature also affects hormone production. The testicles are very sensitive to pressure. Even a slight bump can be painful.


Once produced in the testicles, sperm move into a long coiled tube called the epididymis to “ripen.” At this point the sperm are inactive and are being moved by the body, not by swimming.

vas deferens

The vas deferens are thin tubes that transport sperm from the epididymis up into the body.

seminal vesicles

The vas deferens end near the seminal vesicles, which produce part of the fluid ejaculated with the sperm. See Physiology of the Male Sex Drive for more information.


This gland produces a part of the seminal fluid, begins the ejaculation process, and keeps semen and urine from mixing. The prostate produces small amounts of fluid continually and greater amounts during sexual arousal. Since a man’s enjoyment of orgasm is affected by the quantity of his ejaculate, the extra fluid produced during prolonged arousal can lead to a stronger climax.

Prostatitis or congested prostate is a painful condition caused by repeated arousal without ejaculation, or by a “feast-or-famine” sex life (such as that of a traveling salesman). Mild cases can be easily remedied by climaxing. More serious cases require prescription medication and massaging of the prostate by a physician. As a man ages his prostate swells, often interfering with normal urination. Prostate cancer is very common in older men, although it is treatable if found early by routine screening.


Sphincters are small valves that control the flow of urine and semen in the prostate. The upper sphincter prevents semen from moving into the bladder during ejaculation. It also makes it more and more difficult for a man to urinate as he becomes erect. The lower sphincter helps pressurize the semen just before ejaculation.

ejaculatory duct

The sperm and various fluids mix in this area of the prostate as ejaculation begins. The closed sphincters and muscle contractions create the pressure needed for ejaculation. Once this happens, climax cannot be stopped.

cowper’s glands

These two pea-sized glands produce a slippery alkaline fluid when the man is aroused. This fluid prepares the urethra for ejaculation. During prolonged arousal, the fluid may form drops at the tip of the penis. Sperm are not usually present in this “pre-come” fluid.

Related Resources:

15 Minutes – Castings of male genitals as art showing the variety of appearances.

For more information on the physical changes that occur during sex, see The Anatomy of Male Arousal.


image credits
dripping faucet © David Hughes / Adobe Stock
male external genitals drawing © Lori Byerly / The Marriage Bed, Inc. All Rights Reserved
male internal genitals and penis cross-section diagrams © Lavreteva / Adobe Stock