Internal Sex Organs

The internal sex organs of the male include the testes, epididymis, vas deferens, seminal vesicles, prostate gland, and Cowper’s glands. All of these organs play important roles in spermatogenesis, testosterone production, and the process of ejaculation.

 

The Testicles

 

The testicles (also referred to as the testes, TEST-eez) are egg­shaped glands that rest in the scro­tum, each about 2 inches long and 1 inch in diameter. The left testi­cle usually hangs lower than the right in most men (T. Hamilton, 2002), though this can be reversed in left-handed men. Having one testicle lower than the other helps one slide over the other instead of crushing together when com­pressed. The testicles serve two main functions: spermatogenesis and testosterone production (see Figures 5.4 and 5.5). Spermatogenesis Sperm are produced and stored in some 300 microscopic tubes located in the testes, known as seminiferous (sem — uh-NIF-uh-rus) tubules. Uncoiled, this network of tubes would extend

 

Spermatic cord

 

Blood vessels and nerves

 

Head of epididymis

 

Seminiferous tubule

 

Vas deferens

 

spermatogenesis The production of sperm in the testes.

 

Testis

 

Outer layer of testis

 

seminiferous tubules The tightly coiled ducts located in the testes where spermatozoa are produced.

 

Figure 5.4 Internal structure of the testicle.

 

Figure 5.5 (a) The testis is the site of spermatogenesis. (b) The testicles are responsible for both sperm and testos­terone production.

Mitosis

Immature sperm (haploid)

Late spermatids

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Sertoli Cell

Early spermatids

Tubule wall

Spermatogonium (diploid)

Primary spermatocyte Secondary spermatocyte

Meiosis

Meiosis I

flagellum The taillike end of a spermatozoon that propels it forward. The word "testify" originates from the word "testes," the Latin word for testicles. The practice of holding one’s testicles while testifying in a court of law was based on the belief that unborn generations would seek revenge if the truth weren’t told (T Hamilton, 2002). This is why during Greek and Roman times eunuchs (men whose testicles were removed) were not allowed to testify in court.

Question: I’ve heard people say that what a man eats can influ­ence the taste of his semen. Is this really true?

Yes. The flavor and taste of a male’s ejaculate varies from man to man and is strongly influenced by what a man eats (T. Hamilton, 2002). For example, the ejaculate of a man who smokes cigarettes or marijuana and drinks coffee or alcohol is often bitter. A man who eats red meat, certain vegetables (such as spinach, asparagus, or broccoli), chocolate, garlic, or greasy foods often has a very sharp flavor to his ejaculate. And a mild to sweet ejaculate is often due to a vegetarian diet or one high in fruits (especially pineapple) and herbs such as pep­permint, parsley, or spearmint. A little experimentation with various foods could never hurt!

(flah-GEL-lum), which propels the mature spermatozoon. Human sperm formation re­quires approximately 72 days, yet because sperm is in constant production, the human male produces about 300 million sperm per day.

Testosterone Production Testosterone is produced in the testicles in interstitial (interstitial cells

(in-ter-STIH-shul) or Leydig cells and is synthesized from cholesterol. Testosterone is Cells responsible for the production of testos­terone; also referred to as Leydig cells.

the most important male hormone; we will discuss its role when we examine male pu­berty, later in this chapter.

Leydig cells

The cells in the testes that produce testos-

The Epididymis Once formed, immature sperm enter the seminiferous tubule and terone; also referred to as interstitial cells. migrate to the epididymis (ep-uh-DID-uh-mus; see Figure 5.5), where they mature for about 10 to 14 days and where some faulty or old sperm are reabsorbed. The epididymis (epididymis

is a comma-shaped organ that sits atop the testicle and can be easily felt if the testicle is A comma-shaped organ that sits atop the testi

cle and holds sperm during maturation.

gently roiled between the fingers. If uncoiled, the epididymis would be about 20 feet in length. After sperm have matured, the epididymis pushes them into the vas deferens, where they can be stored for several months.

The Ejaculatory Pathway

The vas deferens (vass DEH-fuh-renz), or ductus deferens, is an 18-inch tube that car — vas deferens

ries the sperm from the testicles, mixes it with fluids from other glands, and propels the One of two long tubes that convey the sperm

from the testes and in which other fluids are

sperm toward the urethra during ejaculation (see Figure 5.6). Ejaculation is the physio — mixed to create semen logical process whereby the seminal fluid is forcefully ejected from the penis. During

I ejaculation

The reflex ejection or expulsion of semen from the penis.

Hypothalamus

► GnRH

Figure 5.6

ejaculation, sperm pass successively through the epididymis, the vas deferens, the ejacu­latory duct, and the urethra, picking up fluid along the way from three glands—the sem­inal vesicles, the prostate gland, and the bulbourethral gland.

The Seminal Vesicles The vas deferens hooks up over the ureter of the bladder and ends in an ampulla. Adjacent to the ampulla are the seminal vesicles. The seminal vesicles contribute rich secretions, which provide nutrition for the traveling sperm and make up about 60 to 70% of the volume of the ejaculate. The vas deferens and the duct from the seminal vesicles merge into a common ejaculatory duct, a short straight tube that passes into the prostate gland and opens into the urethra.

The Prostate Gland The prostate (PROSS-tayt) gland, a walnut-sized gland at the base of the bladder, produces several substances that are thought to aid sperm in their attempt to fertilize an ovum. The vagina maintains an acidic pH to protect against bac­teria, yet an acidic environment slows down and eventually kills sperm. Prostatic secre­tions, which comprise about 25 to 30% of the ejaculate, effectively neutralize vaginal acidity almost immediately following ejaculation.

The prostate is close to the rectum, so a doctor can feel the prostate during a rectal examination. The prostate gland can cause a number of physical problems in men, es­pecially older men, including prostate enlargement and the development of prostate cancer (see the section later in this chapter on “Male Reproductive and Sexual Health”). Annual prostate exams are recommended for men over 35 years of age.

Cowper’s Glands The bulbourethral or Cowper’s glands are two pea-sized glands that flank the urethra just beneath the prostate gland. The glands have ducts that open right into the urethra and produce a fluid that cleans and lubricates the urethra for the passage of sperm, neutralizing any acidic urine that may remain in the urethra. The drop or more of pre-ejaculatory fluid that many men experience during arousal is the fluid from the Cowper’s glands. Be aware, however, that the fluid may contain some live sperm, especially in a second act of intercourse if the male has not urinated in between.

Ejaculation Earlier in this chapter, we discussed erection as a spinal reflex. Ejaculation, like erection, also begins in the spinal column; however, unlike erection, there is seldom a “partial” ejaculation. Once the stimulation builds to the threshold, ejaculation usually con­tinues until its conclusion.

When the threshold is reached, the first stage of ejaculation begins: the epididymis, seminal vesicles, and prostate all empty their contents into the urethral bulb, which swells up to accommodate the semen. The bladder is closed off by an internal sphincter so that no urine is expelled with the semen. Once these stages begin, some men report feeling that ejaculation is imminent, that they are going to ejaculate and nothing can stop it; however, others report that this feeling of inevitability can be stopped by imme­diately ceasing all sensation.

If stimulation continues, strong, rhythmic contractions of the muscles at the base of the penis squeeze the urethral bulb, and the ejaculate is propelled from the body, usually accompanied by the pleasurable sensation of orgasm. Most men have between 5 and 15 contractions during orgasm, and many report enjoying strong pressure at the base of the penis during orgasm. This may be an evolutionary way of encouraging deep thrusting at the moment of ejaculation to deposit semen as deeply as possible within the woman’s vagina.

Once orgasm subsides, the arteries supplying the blood to the penis narrow, the veins taking the blood out enlarge, and the penis usually becomes limp. Depending on the level of excitement, the person’s age, the length of time since the previous ejacula­tion, and his individual physiology, a new erection can be achieved anywhere from im­mediately to an hour or so later.

Ejaculate The male ejaculate, or semen, averages about 2 to 5 milliliters—about 1 or 2 teaspoons. Semen normally contains secretions from the seminal vesicles and the prostate gland and about 50 to 150 million sperm per milliliter. If there are fewer than

Question: Can a male have an orgasm without an ejaculation?

Yes. Before puberty, boys are capable of orgasm without ejaculation. In adulthood, some men report feeling several small orgasms before a larger one that includes ejaculation, whereas other men report that if they have sex a second or third time, there is orgasm without ejacula­tory fluid. There are also some Eastern sexual disciplines, like Tantra, that try to teach men to achieve orgasm without ejaculation because they believe that re­taining semen is important for men.

20 million sperm per milliliter, the male is likely to be infertile—even though the ejac­ulate can have almost 100 million sperm altogether! Sperm is required in such large numbers because only a small fraction ever reach the ovum. Also, the sperm work to­gether to achieve fertilization; for example, many die to plug up the os of the cervix for the other sperm, and the combined enzyme production of all sperm are necessary for a single spermatozoon to fertilize the ovum.

During vaginal intercourse, after ejaculation the semen initially coagulates into a thick mucuslike liquid, probably to keep it from leaking back out of the vagina. After 5 to 20 minutes, the prostatic enzymes contained in the semen cause it to thin out and liquefy. If it does not liquefy normally, coagulated semen may be unable to complete its movement through the cervix and into the uterus.

Other Sex Organs

Like women, men have other erogenous zones, or areas of the body that may be re­sponsive to sexual touch. This is often an individual preference, but it can include the breasts and other erogenous zones, including the scrotum, testicles, and anus.

The Breasts

Men’s breasts are mostly muscle, and though they do have nipples and areolae, they seem to serve no functional purpose. Transsexual males, who want to change their sex (see Chapter 3), can enlarge their breasts to mimic the female breast by taking estrogen. Some men experience sexual pleasure from having their nipples stimulated, especially during periods of high excitement, whereas others do not.

There are some breast disorders that occur in men, including gynecomastia (guy — neck-oh-MAST-ee-uh), or breast enlargement. Gynecomastia is common both in pu­berty and old age and usually lasts anywhere from a few months to a few years. It is caused by drug therapy, excessive marijuana use, hormonal imbalance, and certain dis­eases. Generally gynecomastia disappears in time, and surgical removal is not necessary. However, some men choose to undergo a new surgical technique that removes the ex­cessive tissue through suction, which is usually followed by cosmetic surgery.

Breast cancer does affect men, although it is rare and accounts for less than 1% of all cases (Kahla et al., 2005). Because it is uncommon, it often progresses to an advanced stage prior to diagnosis (Frangou et al., 2005). Treatment for breast cancer involves radiation or chemotherapy, and, if the cancer has spread to other parts of the body, surgical removal of the testes may be necessary to eliminate the hormones that may support the growth of the cancer (we will talk about this more later in this chapter).

Other Erogenous Zones

Besides the penis, many men experience pleasure from stimulation of the scro­tum, testicles (usually through gentle squeezing), and anus. As with women’s erogenous zones, there is no part of the male body that is not erogenous if

caressed in the right way and at the right time during lovemaking. When the body is sex­ually stimulated, almost all moderate sensation can enhance excitement—which is why gentle pinching, scratching, and slapping can be exciting for some lovers.