Lesson 1, Topic 1
In Progress

Accessory Glands

July 2, 2023

The term semen, or seminal fluid, is used to describe the mixture of sex cells or sperm produced by the testes and the secretions of the accessory or supportive sex glands. The accessory glands, which contribute more than 95% of the secretions to the gelatinous fluid part of the semen, include the two seminal vesicles, one prostate gland, and two bulbourethral (Cowper) glands. In addition to the production of sperm, the seminiferous tubules of the testes contribute somewhat less than 5% of the seminal fluid volume.

Usually 3 to 5 mL (about 1 teaspoon) of semen is ejaculated at one time, and each milliliter normally contains about 20 million to 100 million sperm. These numbers vary considerably in healthy men, even from day to day. Semen is slightly alkaline and protects sperm from the acidic environment of the female reproductive tract.

Seminal vesicles

The paired seminal vesicles (see Figure 23-1) are pouchlike glands that contribute about 60% of the seminal fluid volume. Their secretions are yellowish, thick, and rich in the sugar fructose. This fraction of the seminal fluid helps provide a source of energy for the highly motile sperm.

Prostate gland

The prostate gland lies just below the bladder and is shaped like a doughnut. The urethra passes through the center of the prostate before traversing the penis to end at the external urinary orifice.

The prostate secretes a thin, milk-colored fluid that constitutes about 30% of the total seminal fluid volume. This portion of the ejaculate helps to activate the sperm and maintain their motility.

Bulbourethral glands

Each of the two bulbourethral glands (also called Cowper glands) resembles a pea in size and shape. They are located just below the prostate gland and empty their secretions into the penile portion of the urethra. Because this fluid is often released just before the rest of the semen is ejaculated, it is called “pre-ejaculate.”

The mucuslike secretions of the bulbourethral glands serve several functions. They neutralize any residue of sperm—damaging acidic urine in the urethra. They also lubricate the urethra to protect sperm from friction damage and add to the external lubrication of the penis needed for intercourse.

The bulbourethral glands contribute less than 5% of the seminal fluid volume ejaculated from the urethra.

External genitals

The penis and scrotum constitute the external reproductive organs—sometimes called the genitals or genitalia.

The penis (Figure 23-7) is the organ that, when made stiff and erect by the filling of its spongy, or erectile, tissue components with blood during sexual arousal, can enter and deposit 624sperm in the vagina during intercourse. The penis has three separate columns of erectile tissue in its shaft: one corpus spongiosum, which surrounds the urethra, and two corpora cavernosa, which lie dorsally. The spongy nature of erectile tissue is apparent in Figure 23-7.

FIGURE 23-7​Penis. ​A, In this sagittal section of the penis viewed from above, the urethra is exposed throughout its length and can be seen exiting from the bladder and passing through the prostate gland before entering the penis to end at the external urinary meatus. B, Photograph of a cross section of the shaft of the penis showing the three columns of erectile or cavernous tissue. Note the urethra within the substance of the corpus spongiosum.

At the distal end of the shaft of the penis is the enlarged glans penis, or more simply glans. The glans is dense with sensory receptors that help stimulate the male sexual response. The external urinary meatus is the opening of the urethra at the tip of the glans.

The skin of the distal end of the penis is folded doubly to form a loose-fitting retractable, collar around the glans called the foreskin, or prepuce. Besides protecting the glans from abrasion, the foreskin is also dense with sensory receptors. Surgical removal of the foreskin is called circumcision (see Clinical Application box above).

The scrotum is a skin-covered pouch suspended from the groin. Internally, it is divided into two sacs by a septum; each sac contains a testis, epididymis, the lower part of the vas deferens, and the beginning of the spermatic cords.

CLINICAL APPLICATION

MALE CIRCUMCISION

In recent decades, there has been disagreement among medical professionals regarding whether routine circumcision is justified in all male infants. Certainly, circumcision may be required if the foreskin fits so tightly over the glans that it cannot be retracted, a condition called phimosis.

Also, if the foreskin cannot be replaced to its usual position after it has been retracted behind the glans, a condition called paraphimosis, circumcision may be required.

After a few years of withholding the recommendation, most health experts are again recommending routine circumcision to reduce the spread of human immunodeficiency virus (HIV) and other sexually transmitted infections (STIs) based on extensive research findings. However, there are risks to circumcision, including loss of its normal protective and sensory role, and many question the ethics of a surgery in which the patient cannot give informed consent.