The male reproductive system primarily consists of the paired testes and the penis. In addition, accessory sex glands contribute to seminal fluid. The male reproductive system matures during adolescence and remains active for the remainder of the lifespan of the male.
Male Genital Organs and Glands
The following genital organs and glands comprise the male reproductive system (Figure 13-1A):
- Testes. The primary male sex organ. The testes produce sperm and sex hormones (e.g., testosterone) and are located within the scrotum.
- Epididymis. A convoluted duct that sits on the superior pole of each testis. Sperm are stored in the epididymis during the maturation process.
- Ductus deferens. A thick-walled tube in the spermatic cord that transports sperm from the epididymis to the ejaculatory ducts in the prostate gland. The ductus deferens traverses the superficial inguinal ring, coursing through the inguinal canal, and enters the pelvis through the deep inguinal ring lateral to the inferior epigastric artery. En route to the ejaculatory duct, the ductus deferens crosses the medial side of the umbilical artery and the obturator neurovascular structures. Sympathetic nerves from the inferior hypogastric plexus cause peristaltic contractions in the thick smooth muscle wall and propel sperm during ejaculation.
- Ejaculatory ducts. Formed by the union of the ductus deferens and ducts from the seminal vesicles. The ejaculatory ducts open into the prostatic urethra.
- Seminal vesicles. Lobular glands located on the base of the bladder. During emission and ejaculation, the seminal vesicles empty their secretions (e.g., fructose, citric acid, prostaglandins, and fibrinogen) into the ejaculatory duct, along with sperm from the ductus deferens. Seminal vesicle secretions add substantially to the volume of semen.
- Prostate gland. Composed of five lobes, all surrounding the prostatic urethra. The prostate gland is located superior to the pelvic diaphragm and anterior to the rectum. The prostate gland secretes a milky fluid that contributes to the bulk of the semen.
A. Male reproductive system. B. Cross-section of the penis. C. Erectile muscles and tissues. D. Coronal section of the male perineum.
The prostate gland may hypertrophy as men age. As a result of an enlarged prostate gland
, affected men may have difficulty urinating because the gland surrounds the urethra. Because of its proximal anterior location to the rectum, the prostate gland is relatively easy to palpate. A digital rectal examination
is performed to determine the size of the prostate gland. During a digital rectal examination, the physician may also palpate the seminal vesicles and the ductus deferens.
The deep perineal space (pouch) is the region within the urogenital diaphragm (Figure 13-1D). In males, this space contains the bulbourethral glands and the internal urethral sphincter. The bulbourethral glands secrete mucus that flows through the urethra during sexual intercourse to aid in lubrication. Parasympathetic nerves from the inferior hypogastric plexus innervate the bulbourethral glands.
- Membranous urethra. The portion of the urethra that courses through the deep perineal space.
Superficial Perineal Space
The superficial perineal space (pouch) is the region inferior to the urogenital diaphragm. It is enclosed by the superficial perineal (Colles') fascia. The superficial perineal space contains (Figure 13-1A–D):
- Deep (Buck's) fascia of the penis. Continuous with the external spermatic fascia and deep perineal fascia. The deep dorsal vein of the penis is inside this fascial layer.
Each crus of the penis is composed of erectile tissue that is continuous with the paired corpus cavernosa of the penis. Erectile tissue consists of large, cavernous venous sinusoids (spaces like those found in a sponge) that normally are somewhat void of blood. However, during sexual arousal, the corpus cavernosa fill with blood, causing the penis to become erect (Figure 13-1B and C).
- Corpus cavernosa. The crura of the penis are separate along the ischiopubic ramus. However, at the pubic symphysis, the corpora cavernosa course along the dorsum of the penis, adjacent to each other. The deep arteries of the penis (branches of the internal pudendal artery) course within the center of the corpus cavernosa, providing blood that is necessary for an erection.
- Ischiocavernosus muscle. The ischiocavernosus muscles are voluntary skeletal muscles that surround the crura of the penis. The ischiocavernosus muscle helps to stabilize an erect penis and compresses the crus of the penis to impede venous blood return to maintain an erection. This muscle is innervated by the perineal nerve (branch of the pudendal nerve).
The bulb of the penis is the origin of the corpus spongiosum. The bulb of the penis is composed of erectile tissue and is continuous with the corpus spongiosum of the penis.
- Corpus spongiosum. The ventrally located erectile tissue that surrounds the spongy urethra, which transports urine and semen.
- Glans penis. The terminal part of the corpus spongiosum. A fold of skin called the prepuce (foreskin) covers the glans penis. The frenulum of the prepuce is a median ventral fold passing from the deep surface of the prepuce.
is the surgical removal of the prepuce.
- Bulbospongiosus muscle. Contributes to erection and ejaculation. This muscle also helps expel the final drops of urine during micturition. The bulbospongiosus muscle is innervated by the perineal nerve (branch of the pudendal nerve).
- Tunica albuginea. A thin layer of connective tissue that surrounds the corpora cavernosa and corpus spongiosum. The tunica albuginea is denser around the corpora cavernosa and inhibits blood return during an erection. The tunica albuginea is more elastic around the corpus spongiosum and enables semen to pass through the urethra during ejaculation.
The outline of the superficial perineal space can be observed when the spongy urethra is ruptured
inferior to the urogenital diaphragm. Urine flows into the superficial perineal space (extravasated urine) by spreading into the scrotum, around the penis, and superiorly into the abdominal wall.