The Ejaculatory Ducts

Anatomy > Gray's Anatomy of the Human Body > XI. Splanchnology > 3c. 4. The Ejaculatory Ducts

Henry Gray (1821–1865). Anatomy of the Human Body. 1918.

The Ejaculatory Ducts

(Ductus Ejaculatorii)

The ejaculatory ducts (Fig. 1153) are two in number, one on either side of the middle line. Each is formed by the union of the duct from the vesicula seminalis with the ductus deferens, and is about 2 cm. long. They commence at the base of the prostate, and run forward and downward between its middle and lateral lobes, and along the sides of the prostatic utricle, to end by separate slit-like orifices close to or just within the margins of the utricle. The ducts diminish in size, and also converge, toward their terminations.

Structure

The coats of the ejaculatory ducts are extremely thin. They are: an outer fibrous layer which is almost entirely lost after the entrance of the ducts into the prostate; a layer of muscular fibers consisting of a thin outer circular, and an inner longitudinal, layer; and mucous membrane

http://www.wikimd.org/images/gray/large/image1153.gif

FIG. 1153– Vesiculae seminales and ampullae of ductus deferentes, seen from the front. The anterior walls of the left ampulla, left seminal vesicle, and prostatic urethra have been cut away. (Picture From the Classic Gray's Anatomy)

Function

Ejaculation

Main article: Ejaculation

Ejaculation occurs in two stages, the emission stage and the expulsion stage. The emission stage involves the workings of several structures of the ejaculatory duct; contractions of the prostate gland, the seminal vesicles, the bulbourethral gland and the vas deferens push fluids into the prostatic urethra. The semen is stored here until ejaculation occurs. Muscles at the base of the penis contract in order to propel the seminal fluid trapped in the prostatic urethra through the penile urethra and expel it through the urinary meatus. The ejaculate is expelled in spurts, due to the movement of the muscles propelling it. These muscle contractions are related to the sensations of orgasm for the male.

Sperm is produced in the testes and enters the ejaculatory ducts via the vas deferens. As it passes by the seminal vesicles, a fluid rich in fructose combines with sperm. This addition nourishes the sperm in order to keep it active and motile. Seminal fluid continues down the ejaculatory duct into the prostate gland, where an alkaline prostatic fluid is added. This addition provides the texture and odor associated with semen. The alkalinity of the prostatic fluid serves to neutralize the acidity of the female vaginal tract in order to prolong the survival of sperm in this harsh environment. Semen is now a fructose-rich, alkaline fluid containing sperm as it enters the bulbourethral glands below the prostate. The bulbourethral glands secrete a small amount of clear fluid into the urethra before the ejaculate is expelled. The functions of this fluid are not entirely known but are suggested to aid in lubricating the male urethra in preparation for the semen during ejaculation. The amount of semen produced and expelled during ejaculation corresponds to the length of time that the male is sexually aroused before ejaculation occurs. Generally, the longer the period of arousal, the larger the amount of seminal fluid.

Ejaculation and orgasm may occur simultaneously, however they are not coupled, in that one may occur without the other. For example, a man may have a dry orgasm (termed Retrograde ejaculation); there is no expulsion of ejaculate however the man still experiences orgasm. Also, paraplegics may ejaculate seminal fluid but not experience the sensation of orgasm.

Additional images

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  Lobes of prostate

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  Vertical section of bladder, penis and urethra.

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  Prostate with seminal vesicles and seminal ducts, viewed from in front and above.

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  Median sagittal section of male pelvis.

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  Dissection of prostate showing ejaculatory ducts opening into the prostatic urethra.

External links

• Anatomy figure: 44:03-15 at Human Anatomy Online, SUNY Downstate Medical Center - "Lateral (A) and posterior (B) views of the bladder and associated structures."
• figures/chapter_34/34-3.HTM: Basic Human Anatomy at Dartmouth Medical School

Gray's Anatomy

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