Overview of the Male Reproductive System

The male reproductive system includes the penisthe testes, and a host of internal organs that assist the evolutionary function of reproducing genetic material. Because the penis and testes are largely external organs, males are typically more familiar with their own reproductive systems than females are of the female reproductive system. The purpose of the male reproductive system is to produce, maintain, and transport sperm and semen as well as producing and secreting male sex hormones responsible for maintaining a healthy and functional reproductive system.1 Internal and external male genitalia serve a vital function in the act of human reproduction by ejaculating semen into the female reproductive tract during sexual intercourse.1

External Male Genitalia

The Penis: The penis is the most recognizable part of the male reproductive system. This structure is the male organ used in sexual intercourse. It is comprised of three parts. The first part is the root, which attaches to the wall of the abdomen inside the body. The next component is the shaft, the middle and longest portion of the penis, between the base and the glans. The last portion is the glans, the cone-shaped structure at the end of the penis. The glans, also called the head of the penis, is covered with a loose layer of skin called foreskin. This skin is sometimes removed in a procedure called circumcision.1 The photo shows an uncircumcised penis (left) and a circumcised penis (right).

FrenulumThe frenulum is an elastic piece of skin on the underside of the glans. Stimulation of the glans and frenulum during intercourse or masturbation is believed to be the primary trigger of sexual climax, also called orgasm, in males.2 These structures contain thousands of erotically sensitive nerve endings, so stimulation produces intense feelings of pleasure.

The shaft of the penis is cylindrical in shape and consists of three circular shaped internal chambers that are made up of sponge-like tissue. This tissue contains thousands of porous spaces that fill with blood when a male is sexually aroused. As the absorbant inner chambers of the penis fill with blood, this organ becomes rigid and erect, which allows for penetration during sexual intercourse.1

The diagram below shows a cross section of a penis. The three chambers that fill with blood during erection are called the corpus cavernosum (two large spongy bodies) and the corpus spongiosum (smaller spongy body that lies on the underside of the penis). The urethra runs through the corpus spongiosum.

The opening of the urethra, also called the urethra meatus, is located at the tip of the penis. Semen is ejaculated out of the urethra meatus when a male reaches orgasm. When the penis is erect, the flow of urine is blocked from the urethra so only semen is ejaculated at orgasm.

Urethra: The urethra is the tube that carries urine from the bladder outside of the body. In males, it has the additional function of ejaculating semen when the man reaches orgasm.1 The urethra starts in the bladder and passes through the prostate. Seminal ducts from the testes enter the urethra. This is how sperms and other seminal fluids get deposited into the urethra before a male ejaculates.13

The male urethra can be divided into three parts: the prostatic urethra, the membranous urethra, and the spongy urethra.13 The prostatic urethra is the uppermost segment within the prostate and is about 3cm long. The membranous urethra is the segment surrounded by the urethral sphincter. The urethral sphincter is the muscle that allows a male to start and stop urinating.14 The spongy urethra is the lowermost and longest segment of the urethra. 

Scrotum: The scrotum is the loose sac of skin that hangs behind and below the penis. The scrotum contains the testes, also called testicles. Muscles in the wall of the scrotum allow it to contract and relax, moving the testicles closer to the body for warmth or farther away from the body to cool the temperature of the testes.1 This movement helps regulate the overall temperature of the testes, which house the production site for male sperm. For optimal sperm production, the testes need to be a few degrees cooler than normal body temperature.

Testes: The testicles are oval organs, about the size of large olives, that lie in the scrotum and are secured at either end by a structure called the spermatic cord.1 Most males are born with two testes which sit next to each other in the scrotum; the testes tend to have mirror images and adjoining structures. The testes produce testosterone, the primary male sex hormone. The testes are also the site of spermatogenesis, or sperm production. Sperm cells start growing in coiled masses of tubes called seminiferous tubules. From there they move to the epididymis, where they mature. During ejaculation, sperm move through both of the vas deferens attached to each testicle and into the urethra, where they exit the body through the tip of the penis.3

Spermatogenesis does not begin until the male reaches puberty, the period of sexual maturation when the body develops the ability to reproduce. 

Internal Male Reproductive System

Seminal Vesicles: The seminal vesicles are two small glands next to the end of the vas deferens. These sac-like pouches secrete an alkaline fluid rich in fructose sugar which provides sperm with the source of energy they need in order to move.1 The two seminal vesicles contribute approximately 60% of the ejaculatory fluids.4 The fluid produced in the seminal vesicles has clotting properties that make the semen sticky. Stickiness ensures that the semen clings inside the vagina long enough for the sperm to travel to the egg.5

Cowper's Glands (Bulbourethral Glands): The Cowper's glands are pea-sized structures located on the sides of the urethra just below the prostate gland.1 During sexual arousal, this gland secretes a slippery, alkaline fluid that helps lubricate the urethra and neutralize any acidity that may be present due to residual drops of urine.1 This pre-ejaculatory fluid appears as a small drop of clear liquid on the tip of the penis, which is often called "pre-cum." Different males produce different amounts of pre-cum. This pre-ejaculate can contain sperm and may cause pregnancy. Although sperm is not produced by the Cowper's glands, pre-cum may contain residual sperm if a male has not urinated after his last ejaculation.

Prostate: The prostate gland is about the size of a chestnut and is located at the base of the bladder in front of the rectum, with the urethra running through its center.1 The prostate gland secretes milky and alkaline fluids that create a favorable environment for the sperm. Fluids from the prostate comprise approximately 20-30% of the seminal fluid.6 The prostate gland also has muscles that help expel semen out of the urethra during ejaculation.6

As a male ages, his prostate grows larger. This may lead to complications such as prostate cancer or prostatitis. A routine prostate exam is often encouraged by doctors for males once they reach age 40-50. During this procedure, the doctor will place his or her finger into the rectum and examine the prostate for unusual swelling by pressing along the wall of the rectal lining the faces the front of the body. The doctor is feeling for prostate enlargement or any other abnormalities. This procedure is painless and only takes a minute or two.

Seminiferous Tubules: The testes are composed of numerous thin, tightly coiled tubules known as the seminiferous tubules.16 The seminiferous tubules are the site of the germination, maturation, and transportation of the sperm cells within the male testes. Spermatogenesis takes place within the thin seminiferous tubules, which loop tightly throughout the testes to a length as long as a mile between the two testes.15 The sperm cells are produced within the walls of the tubules. Within the walls of the tubules are many randomly scattered cells, called Sertoli cells, that function to support and nourish the immature sperm cells by giving them nutrients and blood products needed for healthy sperm cell development.16

Epididymis: The epididymis is a structure within the scrotum that is attached to the back side of the testes. The epididymis is a coiled segment of the spermatic ducts that stores sperm while they mature and then transports the sperm cells between the testes and into the vas deferens.17 Each epididymis is comprised of three parts: the head, body, and tail. The head is near the top of the testis and this is where sperm is stored until it is ready to mature. The body is a long twisted tube where the sperm matures. The maturation process takes about one week. The tail connects to the vas deferens. From the vas deferens, mature sperm is transported to the ejaculatory duct.18

The image shows the major parts of the epididymis. A. shows the head of the epididymis, B. shows the body of the epididymis, C. shows the tail of the epididymis, and D. shows the vas deferens. 

Vas Deferens: The vas deferens is a long, muscular tube that travels from the epididymis into the pelvic cavity, to just behind the bladder.1 The vas deferens transports mature sperm out of the epididymis to the ejaculatory ducts in preparation for ejaculation. There are two vas deferens tubes in the male body, one for each testicle.7 The vas deferens tubes are protected by smooth muscle mass that contracts reflexively during ejaculation. This process is called peristalsis and it allows sperm to travel through the vas deferens and ultimately to the urethra. On its way, the sperm collects secretions from the prostate gland, Cowper's glands, and seminal vesicles.7

Some men to choose to have a surgical incision made in each of the vas deferens as a form of male contraception. This procedure is called a vasectomy. A vasectomy is a form of male sterilization and is meant to be permanent. Although it is possible to have a vasectomy reversed, the reversal procedure is expensive and not always effective. 

Ejaculatory Duct: There are two ejaculatory ducts that are formed by the fusion of the vas deferens and the seminal vesicles.1 These ducts pass through the inside of the prostate gland and empty into the urethra. Semen flows through each ejaculatory duct during ejaculation.8

Bladder: The urinary bladder is a sac within the abdominal region of the human body that stores the fluid waste called urine. Like the stomach, it is an expandable sac-shaped organ that contracts when it is empty. The bladder releases urine from the urethra so that it is purged from the body. In males, the end of the urethra is located at the tip of the penis.9

In rare cases, the bladder can become involved in an orgasmic condition called retrograde ejaculation. Retrograde ejaculation is the reverse entry of semen through the urethra and back into the bladder during male sexual climax and ejaculation. This condition is relatively uncommon and may occur either partially or completely, which means that a male might reach sexual climax but may ejaculate very little or no semen (this is sometimes called a "dry orgasm"). This condition could be a sign of an underlying health problem such as diabetes or nerve/muscle damage.12

Rectum: The rectum is located at the end of the digestive tract. It is the final part of the large intestine through which feces travels in order to be released from the body by the anus.10

Anus: The anus is the opening where the gastrointestinal tract ends and exits the body. The anus begins at the end of the rectum and is the last portion of the colon (large intestine).11 It contains many sensitive nerve endings, which can make anal sexual activity very pleasurable for males and females. In males, the prostate gland can be stimulated directly through the anus, which many males find extremely pleasurable. The prostate gland is often referred to as the male G-spot, and is believed to lead to or enhance orgasm when stimulated. Unlike a vagina, the anus does not expand during arousal so it is important to prepare before engaging in anal sexual activity to ensure the experience is safe and pleasurable. 

Finally, it is important to be familiar with your own anatomy so you can make informed decisions about healthcare and sexuality. Additionally, if you know how a healthy reproductive system should function, you will be more prepared to identify any potential health issues. 

References

1. "The Male Reproductive System." WebMD.com. WebMD, LLC. 27 Feb. 2016. Web. 2 Oct. 2016.

2. "Anatomy of the Penis, Mechanics of Intercourse." CIRP.org. Circumcision Information and Resource Pages. 5 Jan. 2005. Web. 2 Oct. 2016.

3. "Testicle." WebMD.com. WebMD, LLC. 9 Sept. 2014. Web. 2 Oct. 2016.

4. "Seminal Vesicle." Britannica.com. Encyclopedia Britannica. n.d. Web. 2 Oct. 2016.

5. "Seminal Gland." Healthline.com. Healthline Media. 2 April 2015. Web. 2 Oct. 2016.

6. "Prostate." Healthline.com. Healthline Media. 18 March 2015. Web. 2 Oct. 2016.

7. "Vas Deference." Healthline.com. Healthline Media. n.d. Web. 2 Oct. 2016.

8. "Ejaculatory Duct." Healthline.com. Healthline Media. 1 April 2015. Web. 2 Oct. 2016.

9. "Bladder." Healthline.com. Healthline Media. 10 March 2015. Web. 3 Oct. 2016.

10. "Rectum." Healthline.com. Healthline Media. 19 March 2015. Web. 3 Oct. 2016.

11. "Picture of the Anus." WebMD.com. WebMD, LLC. 2014. Web. 3 Oct. 2016.

12. "Retrograde Ejaculation." SenInfoOnline.com. SexInfoOnline. 15 Apr. 2014. Web. 21 Oct. 2016.

13. "Urethra." Britannica.com. Encyclopedia Britannica. 10 Apr. 2015. Web. 21 Oct. 2016.

14. "Anatomy of the Urethra." CenterforReconstructiveUrology.com. The Center for Reconstructive Urology. n.d. Web. 21 Oct. 2016.

15. "Seminiferous Tubules." InnerBody.com. Inner Body. n.d. Web. 23 Oct. 2016.

16. "Spermatogenesis." Britannica.com. Encyclopedia Britannica. n.d. Web. 23 Oct. 2016.

17. "Definition of Epididymis." MedicineNet.com. MedicineNet.com. 13 May 2015. Web. 23 Oct. 2015.

18. "Epididymis." Healthline.com. Healthline Media. 1 Apr. 2015. Web. 23 Oct. 2016

Last Updated: 23 October 2016