The Penis: internal anatomy
• Consists of nerves,
blood vessels, fibrous
tissue & spongy tissue;
no bones!
• Interior portion of the
penis is the root
• Head of the penis is
called the glans
• Remainder of penis is
the shaft
The penis: external anatomy
• The glans of the penis is
covered by a loose layer of
skin called the foreskin
• The corona is a ridge of
tissue around the glans of
the penis; it along with the
frenulum, a strip of skin
that attaches the glans to
the shaft on the underside
of the penis, are among the
most sensitive areas
• urethral opening is site of
urine and semen exit
The scrotum
• Scrotum: pouch with two
chambers for each of two
testicles or testes
• Has two layers:
– skin layer: skin is darker
than on rest of body and
becomes covered with hair
at puberty; analogous to
labia majora in women
– tunica dartos: muscle layer
• Pulls sac closer to body
in cold temperatures or
with sexual stimulation
• Spermatic cord: suspends
testes in scrotum
• Vas deferens: transports
sperm
The testes: function
• Seminiferous tubules:
site of sperm
production
• Sperm travel from there
to the epididymis,
where they are stored
• Interstitial cells
between seminiferous
tubules make most of
the body’s testosterone
Function of the Male Anatomy: Erection
• Coordinated by the nervous system; ultimately
controlled by the brain
– Arteries leading to the three erectile layers of the penis
expand
– Bloodflow rapidly increases
• Capacity for erection is present at birth
– Common and natural for infant boys to have erections
during sleep, diaper changes, or stimulation from clothing
• Common to undergo erection during sleep—not
necessarily linked to sexual dreams!
• Erections may be psychogenic (from the mind) or
physiogenic (from the body)
Ejaculation
• Spinal reflex happens in
two phases:
– Emission: fluid from the
prostate, seminal
vesicles and vas
deferens enters the
urethral bulb; urethral
sphincters
simultaneously close;
“point of no return”
– Expulsion: semen
expelled when muscles
around urethral bulb & in
the root of the penis
contract
Ejaculatory problems
• Retrograde ejaculation:
if internal urethral
sphincter fails to contract,
semen can enter the
bladder
– Sometimes happens after
prostate surgery
– Some medications can
also cause
– Not harmful but impairs
fertility
• Nocturnal emissions:
“wet dreams,”
mechanism not
understood
Semen
• Seminal Vesicle
– Secretes 70% of seminal
fluid
• Prostate Gland
– Secretes 30% of seminal
fluid
• Cowper’s Glands
– Secretes fluid before
ejaculations
– May contain active,
healthy sperm
• Semen (seminal fluid)
– Volume is about 1
teaspoon
– 200 to 500 million sperm
Kegels for men
• Muscles at the base of the penis that help
control the expulsion phase of ejaculation are
similar to the pelvic floor muscles in women
• Kegel exercises can help improve strength and
have been associated with stronger and more
pleasurable orgasms, better ejaculatory
control and increased pelvic sensation during
sexual arousal
• YMMV
Concerns about Sexual Functioning:
Penis Size
• Penis size is seen as
a symbol of virility
• Erect penises show
less variation than
flaccid
• Does size matter?
Penile augmentation
• Phalloplasty: surgery to increase the length or girth of
the penis
• Length can be increased by making an incision at the
base of the penis, severing ligaments that attach root
to the pelvic bone, causing the root to be on the
outside
• Width can be increased by injecting fat or other tissue
into the penis
• Can be dangerous and disfiguring (scars, lumps)
• No evidence that creams and pills advertised online
work; they may enhance erection by increasing blood
flow to the penis
Genital Retraction Syndrome (Koro)
• Belief that one’s genitals
are shrinking or
disappearing
• Psychological not medical
disorder!
• “Outbreak” in Singapore in
1967 caused thousands of
men to visit the hospital,
many with clamps and
weights on their penises
• Sometimes associated with
accusations of witchcraft
or sorcery
Other Concerns about Sexual Functioning
• Phimosis: extremely tight foreskin, prevents
glans from being fully exposed during sex
• Without phimosis, circumcision makes no
difference in contact during intercourse
Sexual functioning
Sexual functioning
Male Genital Health
Penis Health-Care Issues
• Cleanliness
– Smegma: can serve as a breeding ground for infections
and have an unpleasant odor
• Reaction to vaginal secretions
– Can sometimes develop eczema-like reaction; can be
avoided with condom use
• Penile cancer
– Rare: only 1300 men develop per year, but deadly
– Early detection is key
– Risk factors include: old age, history of multiple sexually
transmitted diseases, especially genital warts, poor
hygiene, being uncircumcised, phimosis, and smoking
Penis injuries
• Cock rings can sustain
erection, but can also
damage or even destroy
penile tissue by cutting
off blood supply!
• Penis “fracture” can
occur when cavernous
bodies are ruptured
while erect, frequently
during intercourse
Prostate cancer
• Second most common cancer in American
males (after skin cancer)
• Risk factors are: old age, family history, highfat diet, African-American race
• 218,000 U.S. men are diagnosed each year
and 28,000 U.S. men die from it each year
• Can be detected with a blood test (somewhat
controversial) or with a physical examination
(digital rectal examination)
PSA test
• Prostate-specific antigen test is a blood test
that detects a chemical often elevated in
prostate cancer
• Many false positive results
• For many who actually do have prostate
cancer, a “watch and wait” approach is
recommended
Anonymous question box
• Write down any questions about male or
female sexual anatomy you may have
ANONYMOUSLY
• If you don’t want to answer a question, write
“No questions” on your card
• I will answer these in class next time