Lesson 1, Topic 1
In Progress

Reproductive Ducts

July 2, 2023

Overview

The ducts through which sperm must pass after exiting from the testes until they reach the exterior of the body are important components of the accessory reproductive structures. The other two components included in the listing of accessory organs of reproduction in the male—the supportive sex glands and external genitals—are discussed separately here.

Sperm are formed within the walls of the seminiferous tubules of the testes. When they exit from these tubules within the testis, they enter and then pass, in sequence, through the epididymis, vas deferens (ductus deferens), ejaculatory duct, and the urethra on their journey out of the body.

Epididymis

Each epididymis consists of a single and very tightly coiled tube about 6 m (20 feet) in length. It is a comma-shaped structure (see Figure 23-2) that lies along the top and behind the testes inside the scrotum. Sperm mature and develop their ability to move, or swim, as they pass through the epididymis.

Cells lining the epididymis secrete nutrients for developing sperm and also remove substantial amounts of excess testicular fluid as the developing sex cells enter and eventually pass through the lumen of this highly coiled tube.

Epididymitis is a painful inflammation of the epididymis. (Recall that the suffix -itis signifies “inflammation of.”) Epididymitis often occurs in association with sexually transmitted diseases, or STDs (see Table 23-4). The onset of pain is coupled with redness and swelling of the overlying scrotum, fever, and the appearance of white blood cells (WBCs) in the urine.

Vas deferens

The vas deferens, or ductus deferens, is the tube that permits sperm to exit from the epididymis and pass from the scrotal sac upward into the pelvic cavity (see Figure 23-1). Each vas deferens is a thick, smooth, very muscular, and movable tube that can easily be felt or “palpated” through the thin skin of the scrotal wall. It passes through the inguinal canal into the 623pelvic cavity as part of the spermatic cord, a connective tissue sheath that also encloses blood vessels and nerves.

CLINICAL APPLICATION

VASECTOMY

Severing or clamping off the vas deferens—that is, a vasectomy, usually done through an incision in the scrotum—makes a man sterile. Why? Because it interrupts the route to the exterior from the epididymis. To leave the body, sperm must journey in succession through the epididymis, vas deferens, ejaculatory duct, and urethra.

Vasectomy is one of many types of reproductive planning called contraception. For more strategies, and how they help illustrate how reproduction functions, see the article Contraception at Connect It! at evolve.elsevier.com.

Ejaculatory duct and urethra

Once in the pelvic cavity, the vas deferens extends over the top and down the posterior surface of the bladder, where it joins the duct from the seminal vesicle to form the ejaculatory duct (Figure 23-6).

FIGURE 23-6 ​Male accessory glands. ​Dissection photo showing bladder, prostate, vas deferens, left ejaculatory duct, and seminal vesicles from behind.

Note in Figure 23-1 and Figure 23-6 that the ejaculatory duct passes through the substance of the prostate gland and permits sperm to empty into the urethra, which eventually passes through the penis and opens to the exterior at the external urinary meatus.