Male Sexual Anatomy,
Physiology, and Response
Male Sex Organs
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Sex organs serve a reproductive function
Also serve other functions:
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Bringing pleasure to self
Giving pleasure to others
May serve to attract potential sexual partners
Sharing of genital sexuality can play a bonding role
in relationships
External Structures
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Penis, Scrotum
The Penis
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Penis: from Latin word for tail
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organ through which sperm and urine pass
Contains urethra for urine and semen
transport
Becomes erect to better penetrate the vagina
and deposit sperm near the os
No bone, little muscle
The Penis
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Myths about the penis abound
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Penis size not linked to body size or weight,
muscular structure, race or ethnicity or sexual
orientation. Determined by heredity.
No relationship between penis size and ability to
have sexual intercourse or satisfy a partner.
The Penis
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Three main sections:
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Root: attaches penis within the pelvic cavity
Shaft: body of the penis (hangs free)
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Contains 3 parallel columns of erectile tissue
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corpora cavernosa: 2 columns along the front surface
corpus spongiosum: runs beneath corpora cavernosa, also
forms the glans
The Root of the Penis
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Extends into the body below the pubic
bone
Attached to internal pelvic muscles and can
be felt in the perineum
Figure 6.1 The internal structure of the penis.
The Penis:
Cross-Section of the Shaft
The Penis
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Glans penis: head of penis; most sensitive
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Corona: rim at base of the glans
Frenulum: on underside of penis; triangle of
sensitive skin; attaches glans to foreskin.
The Penis
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Foreskin: sleeve-like covering of the glans
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Often surgically removed in infancy: circumcision
Crura (pl.): formed by the corpora cavernosa;
anchored by muscle to public bone
Urethra: a tube that transports urine & semen
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Runs from bladder through penis. Opens at tip of glans.
When penis erect, urinary duct is blocked
Figure 6.2 The male reproductive organs.
The Scrotum
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Scrotum: a pouch of skin that holds the two
testicles
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Scrotum skin more heavily pigmented
Sparsely covered with hair
Divided in the middle by a ridge of skin
During sexual arousal or cold conditions, scrotum
retracts to keep testicle temperature consistent
(about 93°F) Cremaster muscle moves the
scrotum closer to or farther from the body
(protects)
Internal Structures
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Testes:
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Two major functions: sperm and hormone production
Shaped like olives; 1.5” long and 1” diameter.
Size and weight decrease as men age
Not usually symmetrical in the way they hang
Suspended by spermatic cord
Within each testicle, there are about 1000 Seminiferous
tubules: tiny compressed tubes 1-3 feet long
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Production of sperm takes place in these tubes
Internal Structures: CrossSection of a Testis
Internal Structures
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Epididymis & Vas Deferens
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The ducts that carry sperm from testicles to
urethra for ejaculation
Sperm mature in epididymis, which joins with vas
deferens
Vas deferens joins the ejaculatory duct within
prostate gland
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Vas deferens can be felt within scrotal sac
Internal Structures
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Seminal vesicles
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Prostate gland
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Secrete fluid that makes up 60% of semen
Secretes fluid that makes up 30-35% of semen
Can be stimulated in anal play
Cowper’s (bulbourethral) glands
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Secrete thick clear mucus prior to ejaculation
Male Sexual Physiology
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Reproductive processes of the male body
include:
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production of hormones
production and delivery of sperm
Male Reproductive Hormones
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Testosterone
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Acts on seminiferous tubules to produce sperm
Regulates sex drive
Is responsible for development of secondary sex
characteristics in puberty
Influences growth of bones and muscle mass
May affect personality
Testosterone Production
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Testosterone is the most important male
hormone
Interstitial, or Leydig, cells in the testicles
produce testosterone out of cholesterol
Testosterone
Fluctuations in a Day
Spermatogenesis
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Ongoing process from puberty onward
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Sperm produced within seminiferous tubules of
testicles (64-72 days)
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20 days for sperm to travel through epididymis
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Several 100 million sperm produced daily
During this time they become fertile & motile
Upon ejaculation, sperm expelled through urethra
by muscular contractions
Spermatogenesis
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Seminiferous tubules produce and store
sperm
Sertoli cells (in the tubules) provide nutrition
for the development of sperm
This process begins with spermatogonium on
the outer wall of the tubules; they move
toward the center during development as
primary spermatocytes, then divide to form
secondary spermatocytes, and divide again
into spermatids
Spermatogenesis (Cont.)
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Spermatids form the compact head covered
by an acrosome that contains enzymes to
penetrate the egg
The midpiece is formed and serves as the
energy source
The flagellum propels the mature sperm
Sperm production takes 72 days, but is
constant and each male produces about 300
million sperm a day
Figure 6.5 Spermatogenesis is continually taking place with various levels of sperm development
throughout the testis.
Spermatogenesis
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Immature sperm travel from the tubules to
the epididymis; organ that rests atop the
testicle
Old and faulty sperm are reabsorbed here
They mature in 10-14 days in the
epididymis
Upon maturity they are transferred to the
vas deferens for storage
Male Sexual Response
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Erection
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Blood vessels expand and increase blood in penis
Veins that normally carry blood out are
compressed, leading to engorgement of penis
Secretions from Cowper’s glands appear at tip
The Ejaculatory Pathway
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Ejaculation – physiological process where
seminal fluid is powerfully expelled from
the penis
Pathway organs:
Vas deferens
 Seminal vesicles
 Prostate gland
 Cowper’s glands
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Ejaculation
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Begins in the spinal cord once a threshold is
reached, and proceeds until the conclusion
Ejaculation (Cont.)
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Once the threshold is reached:
Epididymis, seminal vesicles, and prostate
empty their fluids into the urethral bulb
 A sphincter closes off the bladder
 5-15 contractions at the base of the penis
squeeze the urethral bulb
 Ejaculate is expelled
 Orgasm
 Return to flaccid state
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Ejaculation & Orgasm
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Emission stage
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Expulsion stage
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Sperm sent into vas deferens
Rhythmic contractions begin
Feeling of ejaculatory inevitability
Rapid contractions
Semen spurts from urethral opening
Orgasm
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Intensely pleasurable physical sensations that usually
accompany ejaculation
Followed by refractory period
Ejaculate/Semen
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2-5 milliliters of fluid
50-150 million sperm per milliliter
Few sperm reach the ovum
Sperm work together in order to fertilize the
egg
Semen coagulates upon ejaculation; this helps
it remain in the vagina and travel into the
uterus
5-20 minutes later it thins out
The Breasts and Anus
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Male anatomical structures that do not serve a
reproductive function but may be involved in
sexual activities include:
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Breasts
Urethra
Buttocks
Rectum
Anus
The Male Maturation Cycle
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Male puberty
Andropause
Male Puberty
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Around 10 years of age, the hypothalamus
starts to release gonadotropin releasing
hormone (GnRH) which signals the pituitary to
release FSH and LH
At the testes, LH stimulates testosterone
production; the two combine and FSH
stimulate sperm production (around 12 years)
Negative feedback loop
Figure 6.6 The cycle of male hormones.
Male Puberty (Cont.)
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Many organs and glands increase in size:
testicles, penis, epididymis, prostate, seminal
vesicles, Cowper’s glands
Growth spurt initiated by testosterone levels
Testosterone and DHT develop the secondary
sex characteristics: larger muscles and bones,
pubic hair, thick and tough skin, deep voice,
facial and chest hair, increased sex drive
Andropause
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Testosterone levels decrease about 1% per
year after 40 years of age
In the 70s and 80s, andropause occurs
Andropause symptoms: decreased
spermatogenesis, thinner ejaculate, less
ejaculatory force, libido decreases, fatigue,
mood disturbances, decreased strength
Controversy over hormone treatments
Male Reproductive and Sexual
Health
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Diseases of the male reproductive organs
Other conditions that affect the male
reproductive organs
Cancer of the male reproductive organs
Diseases of the Male Reproductive
Organs
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Cryptorchidism – testes do not descend
into the scrotum; surgery necessary to
correct
Male Reproductive and Sexual
Health
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Diseases of the male reproductive organs
Other conditions that affect the male
reproductive organs
Cancer of the male reproductive organs
Diseases of the Male Reproductive
Organs
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Cryptorchidism – testes do not descend
into the scrotum; surgery necessary to
correct
Figure 6.7 Although the testicles of a fetus begin high in the abdomen, they must descend into the
scrotum during fetal development. If they do not, the male may become infertile.
Diseases of the Male Reproductive
Organs
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Testicular torsion – testis is twisted on its
spermatic cord; many causes (sex, exercise,
sleep); symptoms are pain and swelling;
immediate surgery is required to maintain
the testicle
Figure 6.8 Testicular torsion can occur after exercise, sexual intercourse, and even while sleeping.
Diseases of the Male Reproductive
Organs
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Priapism – persistent, painful erection not
related to sexual excitement; blood is
trapped in erectile tissue; common causes
are drug use and unknown; treatment is
cessation of drug use and, possibly, surgery
Peyronie’s disease – painful curvature of
the penis making penetration impossible;
cause is unknown; may disappear within 2
years, or require drugs or surgery
Other Conditions that Affect the
Male Reproductive Organs
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Anabolic-androgenic steroid use – synthetic
testosterone can increase muscle mass and
endurance; there are also numerous
physical, psychological, and emotional side
effects, including erectile problems
Other Conditions that Affect the
Male Reproductive Organs (Cont.)
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Inguinal hernia – intestine goes through an
abdominal opening into the scrotum,
creating a bulge; can be due to heavy lifting
and straining; surgery may be required
Hydrocele – fluid accrues & forms a scrotal
mass
Cancer of the Male Reproductive
Organs
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Testicular
Penile
Prostate
Testicular Cancer
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Most common cancer in men 15-44 years
Few early symptoms, early detection
important; testicular self-exam
Symptoms: painless mass or hardness in
the testes; pain or increase in size of the
testes, lower back pain, gynecomastia,
shortness of breath, urethral obstruction
High cure rate: radiation, chemotherapy,
removal of testicle
Penile Cancer
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Lesions on the penis may be benign or
malignant and are usually treatable; may
also be a STI
Penile cancer is not common
Prostate Cancer
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Prostate glands enlarge with age and this is
typically unproblematic, other than interfering
with urination
Prostate cancer is one of the most common in
American men, typically in men over 50 years
Risk factors: age, high fat diet, race, genetics
Symptoms: pain in the lower back, pelvis, or
upper thigh, and urinary abnormalities
Detected through rectal exam and blood test
Prostate Cancer (Cont.)
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Treatments: “watchful waiting”, radical
prostatectomy, radiation, cryosurgery,
drugs that attack cancerous cells