Chapter 5
Male Sexual
Anatomy & Physiology
The Penis
• Nerves, blood vessels, fibrous tissue, and three
parallel cylinders of spongy tissue.
• There is no bone and little muscular tissue
(although there are muscles at the base of the
penis)
• Terms:
– Root, shaft, glans, cavernous bodies, spongy body,
foreskin (defined on next slide)
The Penis
• Penis: consists of internal root, external shaft, & glans.
• Root: the portion of the penis that extends internally into
the pelvic cavity.
• Shaft: the length of the penis between the glans and
the body.
• Glans: the head of the penis; has many nerve endings.
• Cavernous bodies: the structures in the shaft of the
penis that engorge with blood during sexual arousal.
• Spongy body: a cylinder that forms a bulb at the base of
the penis, extends up into the penile shaft, and forms
the penile glans. Also engorge with blood during
arousal.
• Foreskin: a covering of skin over the penile glans.
Internal structure of the penis: top view
(between glans and the body)
(internal, in
pelvic cavity)
Male Sexual Anatomy (cont.)
(head of the
penis; lots of
nerve endings)
(expands
to form
the glans)
(engorge with blood
during arousal)
Fig 5.1a Interior structure of the penis: (a) view from above.
Internal structure of the penis:
cross-section
Fig 5.1b Interior structure of the penis: (b) cross section of the penis
External penile structures
• Corona: the rim of the penile
glans
• Frenulum: thin strip of skin
connecting the glans to the
shaft on the underside of the
penis
Both are highly sensitive
areas to the touch
Fig 5.2 This figure, a view of the underside of the penis, shows
the location of the corona and frenulum—two areas on the penis
that harbor a high concentration of sensitive nerve endings.
Scrotum and testes
• Scrotum (or scrotal sac):
– Pouch of skin that encloses the testes
• 2 chambers inside scrotum; each contains one testis
– Two layers: skin layer and muscle layer (tunica dartos)
– Normally hangs loosely from body wall
• cold temperatures and sexual stimulation will cause it to move
closer to the body.
• Testis
– Male gonad inside scrotum that produces sperm and sex
hormones
• Spermatic cord
– A cord attached to the testis inside the scrotum that
contains the vas deferens, blood vessels, nerves, and
muscle fibers
Scrotum and testes (external)
Spermatic cord
(inside)
Fig 5.3 The scrotum and the testes. The spermatic cord can be located by palpating
the scrotal sac above either testicle with thumb and forefinger.
Internal structures of the scrotum
(contains vas deferens,
blood vessels, nerves,
and cremasteric muscle)
(sperm-carrying tube)
(muscle fibers that control
the position of the testis
in the scrotal sac)
(where sperm mature and
are stored temporarily)
Fig 5.4 Internal structures of the scrotum. This illustration shows portions of the
scrotum cut away to reveal the cremasteric muscle, spermatic cord, vas deferens, and
a testis within the scrotal sac.
Internal structures: the Testes
• Two functions:
1) Secrete male hormones
2) Produce sperm: testes must hang below body for them to be at the
proper temperature for sperm production.
• Asymmetry is typical: More commonly, the left testis hangs lower
than the right testis b/c the left spermatic cord is usually longer than the
right.
• Development
testis
– Form inside the abdominal cavity and during fetal
development migrate to the scrotum.
– cryptorchidism: undescended testis
• Affects 3-4% of male infants and 30% of premature male infants.
• May resolve on its own or may require surgery.
Structures inside the testis
• Seminiferous tubules
– Thin, highly coiled structures where sperm production
occurs.
• Interstitial cells
– Major source of androgens
– Located between seminiferous tubules
• Epididymis
– Site of sperm maturation
– Runs along back of testis
• Vas deferens
– Sperm-carrying tube
– Begins at the testis and ends at the urethra.
Cross-section of seminiferous tubule
Interstitial cells: secrete androgens
Spermatogenic cells: produce sperm
Immature sperm
Vas deferens
• After the sperm mature in the epididymis, they drain
into the vas deferens
• Vas deferens travels up through scrotum inside
spermatic cord, along top of bladder, and deposits
sperm into urethra
• Vasectomy: male sterilization procedure that
involves removing a section from each vas
deferens
Va
defer
Overview: male sexual anatomy
Fig 5.6 Male sexual anatomy: A cross-section side view of male reproductive organs.
Seminal vesicles
• Small glands adjacent to
end of vas deferens
• Secrete an alkaline (basic)
fluid
– Has high sugar content that
helps sperm motility by giving
them a lot of energy
– This fluid is the greatest
portion of the volume of
semen released during
ejaculation
Seminal vesicle
Prostate gland
• Walnut-sized gland at the base of the bladder.
• Secrete milky, alkaline (basic) fluid that makes
up about 30% of volume of semen released during
ejaculation.
– Alkalinity helps counteract the acidity of the male urethra
and the female vaginal tract to help sperm survive.
Prostate gland
Cowper’s glands
• Pea-sized glands that attach to
urethra just below prostate gland
• Secrete an alkaline fluid during
sexual arousal.
• Not the same as semen;
released before ejaculation Cowper’s
(in slang, often called “pre-cum.”)
gland
• Thought to counteract acidity of male urethra and
help lubricate flow of semen through the urethra.
• May possibly contain a few active, healthy sperm
(a potential problem for the withdrawal method of birth control).
Semen
• Volume per ejaculation: about 1 teaspoon
– Depends on length of time since last ejaculation, duration
of arousal before ejaculation, and age.
• Fluids from:
– Seminal vesicles (almost 70%)
– Prostate gland (about 30%)
– (possibly) a tiny bit of fluid from Cowper’s glands
depending on time of secretion
• Sperm
– Between 200 - 500 million sperm per ejaculation
– Only about 1% of total volume.
Analagous structures in
male and female sexual anatomy
(more on this will be covered in Chp. 3)
Male
Female
Glans
Foreskin
Shaft
Scrotal sac
Testes
Clitoris
Clitoral hood
Labia minora
Labia majora
Ovaries
Group activity: male A & P flashcards
One side: name of term
Other side: definition, function, location
TERMS:
Penis
Testes
Glans
Seminiferous tubule
Foreskin
Epididymis
Cavernous bodies
Vas deferens
Spongy body
Seminal vesicles
Corona
Prostate gland
Frenulum
Cowper’s glands
Scrotum
Discussion question: (5-A)
• What are some slang terms for male
genitalia? Keep track of how many terms
your group knows.
• Are these terms positive or negative?
• Why do people tend to use “nicknames” for
parts of the male sexual anatomy?
•
What do the nicknames we use for male
genitalia say about our thoughts or opinions
about male genitalia?
Kegel exercises: Strengthen the pelvic
floor muscles in men and women (see p. 85, 114)
• Exercises originally developed to treat incontinence
• Enhance sexual enjoyment
– Women: increased sensitivity during intercourse, possibly,
stronger orgasms
– Men: stronger orgasms, better ejaculatory control,
increased pelvic sensation during arousal
• Locate the correct muscles by trying to stop the flow
of urine while urinating
• Kegel exercises include both short contractions/
relaxations as well as longer contractions held for
several seconds
– Exercises should be done 2-3 times a day
Male sexual function: Erection
• Brain sends message that causes relaxation of the
arteries that supply blood to the cavernous and
erect
spongy bodies in the penis. flaccid
• Veins that drain blood away
from cavernous and
spongy bodies can’t keep up
with blood inflow, producing
an erection.
• Erection is maintained by pressure of spongy and
cavernous bodies against the skin, partially closing
off the veins.
• Involves both psychological and physiological
factors
How blood inflow helps maintain erection
• Inside the penis: like a tube within a tube
– When the inner tube fills with blood and
expands, it fills the space between the tubes and
blocks the outflow of blood, helping to maintain
erection.
Ejaculation
•
•
Ejaculation: the process by which semen is
expelled through the penis outside the body.
Ejaculation is a separate process from orgasm,
and the two may not always occur simultaneously.
– It is possible for men to experience multiple orgasms
w/o ejaculation.
•
2 phases (see next slides for details):
1) Emission phase: semen collects in the urethral bulb
•
This stage is usually sensed by the man as the
“point of no return”
2) Expulsion phase: semen is expelled
Emission phase of ejaculation
(phase 1)
• Contractions in the prostate, seminal vesicles, and vas
deferens force secretions into urethral bulb.
• Both the internal and external urethral sphincters close,
trapping semen in the urethral bulb
(like a balloon)
Expulsion phase of ejaculation
(phase 2)
• Collected semen is expelled out of the body by
rhythmic contractions of muscles surrounding the
urethral bulb and also on the urethra.
• External urethral sphincter relaxes to allow semen out;
internal urethral sphincter stays contracted to prevent
the escape of urine.
• Retrograde ejaculation: when semen is expelled
into the bladder instead of out of the penis
– Due to reversed function of the two urethral sphincters
(internal sphincter relaxes and external sphincter
contracts instead of the other way around).
– Can result from prostate surgery, illness, birth defect,
tranquilizers.
– Not harmful, but would cause sterility and could be a sign
of an underlying health problem.
• Nocturnal emission: involuntary ejaculation during
sleep
– Also known as a wet dream
– Mechanism not fully understood
Penis size
• More men are concerned about penis size than their
female partners are.
• Much more variation in flaccid penis size than in
erect penis size.
– Comparisons in the locker-room don’t mean much.
• “Bigger is better” isn’t always the case
– Most women achieve orgasm through clitoral, not vaginal,
stimulation
– Obsession w/penis size results from a “penis-centered”
idea of sex--great sex can happen w/no penis at all!
• What is “average” length anyway?
– 5.1 - 5.7 inches (much less than you see or hear about in adult
movies or erotic literature).
Penile Augmentation (phalloplasty)
• Penis lengthening: involves severing of ligaments that
attach penile root to pelvic bone
– Part of the penis normally inside the body drops down
• Penile girth enhancement: usually involves injecting fat
from other areas of the body.
• Possible dangers and warnings:
– Some loss of sensation, scarring, changed angle of erection
– Penis could actually end up being shorter due to scar tissue
causing penis to retract further into body
– Injected fat can be rejected by the body, causing a lumpy,
misshapen appearance
• Most men who elect to have phalloplasty in fact do not
have undersized penises.
Circumcision
• Circumcision: surgical removal of the foreskin
of the penis.
Rates of circumcision
• International
differences:
• Ethnic differences
Country
U.S.
Canada
% circumcised
55 - 60%
<15%
Australia
Europe
10 - 20%
5 - 15%
Ethnic group
% circumcised
Caucasian
81%
Latino
54%
African-American 65%
Circumcision: medical perspective
• Medical benefits
– Reduced rate of penile cancer (from about 6 in 100,000 to about 1
in 100,000)
– If not properly cleaned, the area under the foreskin can
harbor infection-causing organisms, contributing to
increased susceptiblity to UTIs (urinary tract infections) and
STDs
– Most of the medical benefits of circumcision can probably be
realized in uncircumcised men with proper hygeine
• Medical risks
– Effects on sexual functioning are unclear
– Possible surgical complications (bleeding, infection, etc.)
– Pain during circumcision
• Can’t use general or narcotic anesthesia on infants
• Correlation btwn. infants circumcised w/o anesthesia and a stronger
pain response to subsequent vaccination.
Circumcision: medical perspective
• American Academy of Pediatrics position:
–
–
–
–
There are potential benefits but also potential risks.
Procedure is not medically essential.
Decision is left up to parents.
If parents decide to circumcise, they should ask for
analgesia to be used.
(1999; reaffirmed in 2005)
Circumcision and sexual functioning
• Difficult subject to research
– Circumcision most commonly occurs at birth, so research
subjects rarely have experienced “before” vs. “after”
– Those men who are circumcised as adults often have a
medical problem that necessitates circumcision.
• Some reports have indicated that the glans of the
penis may be less sensitive in circumcised men.
– May or may not influence rate of premature ejaculation.
• Two reports that surveyed women who had
intercourse with circumcised men and uncircumcised
men suggested that circumcision may exacerbate
vaginal dryness and reduce clitoral stimulation during
intercourse.
Discussion question: (5-B)
PART 1: Which of the research methods
described in Chapter 2 might be effective to
demonstrate whether or not being circumcised
affects sexual response and pleasure (male and
female)? What kind of research design would
you use in such a study?
PART 2: If you had a newborn son, would you
have him circumcised? Why or why not?
Male Genital Health Concerns
• Urology: the medical specialty focuses on male reproductive
health issues, and urinary tract health problems in both sexes.
• General health issues:
– Cleanliness can reduce infections and build-up of smegma
• Smegma: “cheesy” substance of glandular secretions and skin
cells that sometimes accumulates under the foreskin.
– Some men can develop a reaction to vaginal secretions.
– Injuries:
• use of “cock rings” for > 30 min. can cut off blood supply and injure
penile tissue
• Masturbation with vacuum devices can cause severe injuries
• Penile “fracture” can occur during intercourse--involves rupture of
the cavernous bodies when penis is erect.
– Condoms offer protection against STIs (more on this in Chp. 17)
Penile cancer
• Penile cancer:
– One of the rarest forms of cancer (approx. 1300 cases in
the U.S. each year)
– Survival rate is less than half unless it is caught early.
– Usually begins as a small, painless sore on the glans or
foreskin that eventually changes into a cauliflower-like
mass that is chronically inflamed and tender.
– Risk factors: age over 50, history of multiple partners and
STDs (especially herpes), poor genital hygiene, long
history of smoking.
– Left untreated, will eventually destroy the penis and
spread to lymph nodes and beyond.
Testicular cancer
• Testicular cancer:
– Only 1% of cancers that occur in males.
– One of the most common cancers that occur in young men
(age 15-34); half of cases are in men younger than 35.
– Early stage: small mass within the testis that feels hard and
irregular to fingertips; may be as small as a pea and may be
painless or tender to the touch.
– Some other symptoms reported include fever, dull ache in
groin, feeling of heaviness in testes, tender breasts and
nipples.
– Some types of testicular cancer grow more rapidly than
other cancers; therefore, very important to catch it early.
– If caught early, survival rate is >90%.
Prostate Health Care Issues
• Prostatitis: when prostate becomes enlarged
and inflamed, usually due to infection
– Usually treated w/antibiotics.
• Benign prostatic hyperplasia
– Increase in the size of the prostate gland
– Increasingly common as men age
– Enlarged gland can put pressure on urethra and
decrease urine flow; can be treated w/medication.
Prostate Cancer
• 200,000 men diagnosed and 30,000 die each year in
U.S.
• One of the most frequentlly diagnosed cancer in men,
and second leading cause of cancer death (after lung
cancer)
• Associated factors: old age, family history, prior history
of STDs, diet high in saturated fats.
• Incidence is 60% higher in African Amerian men than
white men, and survival rate is lower--reasons not
known.
• Compared with white Americans, mortality is 40%
lower among Asian American men and 35% lower in
Latino American men.
Prostate Cancer: Symptoms & diagnosis
• Symptoms are similar to prostatitis:
– Pelvic and lower back pain, urinary complications
– May be no symptoms in early stages
• Screening and diagnosis
– Physical examination: physician inserts finger into
rectum to feel for lumps in prostrate gland.
– Blood test: examines levels of PSA (prostate-specific
antigen)
• Normal PSA levels are <4 nanograms per ml of blood.
– Detection of prostate cancer is not precise, and there is
controversy about whether screening is even beneficial.