Reproductive system

Male reproductive system contains the external genitals (the penis, testes and the

scrotum) and internal parts, including the prostate gland, vas deferens and urethra. A

man's fertility and sexual traits depend on the normal functioning of the male

reproductive system, as well as hormones released from the brain.

The penis is the male organ of copulation

(sexual intercourse). It is flaccid for non-

sexual actions, such as urination, and turgid

and rod-like with sexual arousal. When erect,

the stiffness of the organ allows it to

penetrate into the vagina and deposit semen

into the female reproductive tract. The shaft

of the penis surrounds the urethra. The shaft is composed of three column-like chambers

of erectile tissue that span the length of the shaft. Each of the two larger lateral chambers

is called a corpus cavernosum (plural = corpora cavernosa). Together, these make up the

bulk of the penis. The corpus spongiosum, which can be felt as a raised ridge on the erect

penis, is a smaller chamber that surrounds the spongy, or penile, urethra. The end of the

penis, called the glans penis, has a high concentration of nerve endings, resulting in very

sensitive skin that influences the likelihood of ejaculation. The skin from the shaft

extends down over the glans and forms a collar called the prepuce (or foreskin). The

foreskin also contains a dense concentration of nerve endings, and both lubricate and

protect the sensitive skin of the glans penis.

Testosterone

Testosterone, an androgen, is a steroid hormone produced by Leydig cells. The alternate

term for Leydig cells, interstitial cells, reflects their location between the seminiferous

tubules in the testes. In male embryos, testosterone is secreted by Leydig cells by the
seventh week of development, with peak concentrations reached in the second trimester.

This early release of testosterone results in the anatomical differentiation of the male

sexual organs. In childhood, testosterone concentrations are low. They increase during

puberty, activating characteristic physical changes and initiating spermatogenesis.

Scrotum

The testes are located in a skin-covered, highly pigmented, muscular sack called

the scrotum that extends from the body behind the penis. This location is important in

sperm production, which occurs within the testes, and proceeds more efficiently when the

testes are kept 2 to 4°C below core body temperature.

The dartos muscle makes up the subcutaneous muscle layer of the scrotum. It

continues internally to make up the scrotal septum, a wall that divides the scrotum into

two compartments, each housing one testis. Descending from the internal oblique muscle

of the abdominal wall are the two cremaster muscles, which cover each testis like a

muscular net. By contracting simultaneously, the dartos and cremaster muscles can
elevate the testes in cold weather (or water), moving the testes closer to the body and

decreasing the surface area of the scrotum to retain heat. Alternatively, as the

environmental temperature increases, the scrotum relaxes, moving the testes farther from

the body core and increasing scrotal surface area, which promotes heat loss. Externally,

the scrotum has a raised medial thickening on the surface called the raphae.

Testes

The testes (singular = testis) are the

male gonads—that is, the male

reproductive organs. They produce both

sperm and androgens, such as

testosterone, and are active throughout

the reproductive lifespan of the male.

Paired ovals, the testes are each

approximately 4 to 5 cm in length and

are housed within the scrotum. They are surrounded by two distinct layers of protective

connective tissue. The outer tunica vaginalis is a serous membrane that has both a parietal

and a thin visceral layer. Beneath the tunica vaginalis is the tunica albuginea, a tough,

white, dense connective tissue layer covering the testis itself. Not only does the tunica

albuginea cover the outside of the testis, it also invaginates to form septa that divide the

testis into 300 to 400 structures called lobules. Within the lobules, sperm develop in

structures called seminiferous tubules. During the seventh month of the developmental

period of a male fetus, each testis moves through the abdominal musculature to descend
into the scrotal cavity. This is called the “descent of the testis.” Cryptorchidism is the

clinical term used when one or both of the testes fail to descend into the scrotum prior to

birth. The tightly coiled seminiferous tubules form the bulk of each testis. They are

composed of developing sperm cells surrounding a lumen, the hollow center of the

tubule, where formed sperm are released into the duct system of the testis. Specifically,

from the lumens of the seminiferous tubules, sperm move into the straight tubules (or

tubuli recti), and from there into a fine meshwork of tubules called the rete testes. Sperm

leave the rete testes, and the testis itself, through the 15 to 20 efferent ductules that cross

the tunica albuginea.

Inside the seminiferous tubules are six different cell types. These include

supporting cells called sustentacular cells, as well as five types of developing sperm cells

called germ cells. Germ cell development progresses from the basement membrane—at

the perimeter of the tubule—toward the lumen. Let’s look more closely at these cell

types.

Epididymis

The epididymis is a

long, coiled tube that rests on

the backside of each testicle. It

carries and stores sperm cells

that are created in the testes.

It’s also the job of the

epididymis to bring the sperm

of fertilization. During sexual arousal, contractions force the sperm into 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. The vas deferens transports

mature sperm to the urethra in preparation for

ejaculation.

Urethra

The urethra is the tube that

carries urine from the bladder to

outside of your body. In males, it

has the additional function of

expelling (ejaculating) semen

when you reach orgasm. When

the penis is erect during sex, the

flow of urine is blocked from the

urethra, allowing only semen to be ejaculated at orgasm. a dynamic fibromuscular tube

which serves as the terminal region of both the male urinary and reproductive systems.
The average male urethra is 20 cm long and begins within the bladder wall and ends in

the distal glans of the penis.

Seminal vesicles

The seminal vesicles are sac-like pouches

that attach to the vas deferens near the

base of the bladder. The seminal vesicles

make a sugar-rich fluid (fructose) that

provides sperm with a source of energy

and helps with the sperms’ ability to move

(motility). The fluid of the seminal

vesicles makes up most of the volume of

your ejaculatory fluid, or ejaculate. The two seminal vesicles are glands that produce the

fluids that will turn into semen. The vesicles may also be called seminal glands or

vesicular glands.

Prostate gland

The prostate gland is a walnut-sized

structure that’s located below the

urinary bladder in front of the rectum.

The prostate gland contributes

additional fluid to the ejaculate.

Prostate fluids also help to nourish the

through the center of the prostate gland.

Bulbourethral glands

The bulbourethral glands, or Cowper’s

glands, are pea-sized structures located

on the sides of the urethra, just below the

prostate gland. These glands produce a

clear, slippery fluid that empties directly

into the urethra. This fluid serves to

lubricate the urethra and to neutralize

any acidity that may be present due to residual drops of urine in the urethra.