HUMAN REPRODUCTION BIOLOGY 269

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HUMAN REPRODUCTIONBIOLOGY 269
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Previous lectures discussed how anatomy
physiology of the human reproductive system are
evolutionarily adapted for specific reproductive
strategies.
Human sexual responses are also the product of
adaptation.

• Includes
• Emotions
• Behaviors
• Biochemical changes
• Physiological changes
• Feelings of pleasure / satisfaction
• (many others)

Clearly, human sexuality and sexual responses are
a lot more complex than simply getting a penis
into a vagina for the deposition of semen.
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Humans, like all animals, send and receive many
sexual signals indicating availability,
willingness, health, stage of arousal, etc.
These allow us to communicate before, during,
and after sexual intercourse and coordinate our
sexual responses. Some are conscious, others are
not
Visual signals Changes in Changes in Flushing
of Changes in
Physical signals Standing
Verbal signals Changes in Changes in Changes
in
Odors
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1960s Masters Johnson defined four stages of
human sexual response during sexual intercourse
for both men and women
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Both physiologic and cultural reasons men and
women tend to be sexually aroused in different
ways
Men tend to be quickly aroused by signals which
indicate They are not
particularly selective, and typically do not view
arousal within
Women tend to be aroused more slowly by signals
which indicate They are more selective and view
arousal more
? Female Equivalent ?
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The male paradigm is simple erection and
release. Womens satisfactions and drives are
more complex, organized as much around the health
of the relationship as the majesty that is
orgasm.
Dr. John Bancroft
Kinsey Institute
Newsweek,
2000
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Male Sexual Response 1. Soliciting (Minutes
to hours) Primarily visual and verbal
I am available I am healthy
I am interested in you I am
sexually aroused
Eyes and pupils get larger, direct eye contact
Masculine posture, stands closer, touches
Lowering of volume, pitch, and rhythm of
voice Conversation to convince woman of
masculinity, health, interest, availability, etc.
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Male Sexual Response 2. Excitement (Minutes
to hours) Usually during foreplay
Increased blood flow to skin flushing
Increased respiration and vocalization
Increased sweating Secretion of pheromones
from armpits, genitals, anal region
Erection of penis Elevation of testes
Increased secretion of fluids by
seminal vesicles and prostate Pituitary
increases oxytocin secretion, causing
feelings of pleasure and drive
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Male Sexual Response 3. Plateau (Minutes)
Intercourse begins Sweating, flushing,
increased respiration, vocalization continue
Heart rate and blood pressure rise
Swelling of glans of penis Full elevation
of testes Lubrication of urethra by
bulbourethral (Cowpers) glands Leakage of
sperm and fluid from seminal vesicles
prostate into ejaculatory duct Secretion of
oxytocin from pituitary increases, thus
increased pleasure and drive
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Male Sexual Response 4. Orgasm (Seconds to
a minute or two) Heart rate, blood
pressure, respiration very high Contraction
of sphincter (valves) between bladder and
urethra prevents urination
Contraction of sphincter in anus prevents
defecation Ejaculation occurs in two
phases Emission Contraction of ductus
deferens, seminal vesicles,
and prostate force semen into urethra
Expulsion Contraction of muscles surrounding
urethra eject semen
from urethra Secretion of oxytocin from
pituitary very high brain produces many
other pleasure chemicals thus strong
feelings of pleasure and satisfaction.
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Male Sexual Response 5. Resolution
(Minutes) Heart rate, blood pressure,
respiration return to normal Sweating and
flushing decrease but may not completely
disappear Testes descend to normal position
into scrotum Penis softens, eventually
becomes flacid Sphincters of bladder and
anus relax Oxytocin secretion from
pituitary decreases slowly (minutes/hours)
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Male Sexual Response 6. Refractory period
(Minutes to hours) General body
relaxation, drowsiness Lower parts of
ductus deferens move sperm toward ampulla
Seminal vesicles and prostate begin replacing
fluids Erection or ejaculation not possible
Can also enter refractory period from excitement
or plateau periods if orgasm does not occur
If proper stimuli still present, men typically
re-enter excitement phase after refractory period
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Female Sexual Response 1. Soliciting
(Minutes to hours) Primarily visual and
verbal, includes physical signals and odors
I am available I am healthy
I am interested in you I am
sexually aroused
Eyes and pupils get larger, direct eye contact
Feminine posture, exposes more of body, stands
closer, touches Lowering of volume, pitch, and
rhythm of voice Conversation to convince man of
femininity, health, interest, availability,
etc. Odors from pheromones and vaginal lubrication
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Female Sexual Response 2. Excitement
(Minutes to hours) Usually during foreplay
Increased blood flow to skin flushing
Increased respiration and vocalization
Increased sweating Secretion of pheromones
from armpits, genitals, anal region
Erection of clitoris and nipples Swelling
of vagina and of labia Elevation of uterus
begins Lubrication of vagina begins (mostly
distal part) Pituitary
increases oxytocin secretion, causing
feelings of pleasure and drive
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Female Sexual Response 3. Plateau (Minutes
to hour) Intercourse begins Sweating,
flushing, increased respiration, vocalization
continue Heart rate and blood pressure
rise Swelling of vagina and of labia
continue Erection of clitoris more
pronounced Elevation of uterus continues,
swelling of uterus Lubrication of
vagina and vestibule by vestibular
(Bartholins) glands Pituitary
increases oxytocin secretion, causing
feelings of pleasure and drive
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Female Sexual Response 4. Orgasm (Seconds
to a minute or two) Heart rate,
blood pressure, respiration very high
Contraction of sphincters (valves) between
bladder and urethra prevents urination
Contraction of sphincter in anus
prevents defecation Rhythmic contractions
of vagina Rhythmic contractions of uterus,
primarily cervix Contractions of
muscles surrounding vagina to grasp
penis Secretion of oxytocin by pituitary
very high (more than in men) while
brain produces many other pleasure
chemicals thus strong feelings of
pleasure and satisfaction.
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Female Sexual Response 5. Resolution
(Seconds to minutes) Heart rate, blood
pressure, respiration return to normal
Sweating and flushing decrease but may not
completely disappear Uterus returns to
normal position Swelling of uterus,
vagina, and labia decreases
Clitoris softens Sphincters of bladder and
anus relax Muscles surrounding vaginal
opening relax Oxytocin secretion
from pituitary decreases more slowly
than in men (minutes/hours), thus period
of pleasure/satisfaction lasts much
longer
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Female Sexual Response Refractory period
generally does not occur in women
If proper stimuli still present, woman may
re-enter at excitement, plateau, or orgasm
phases. Thus, multiple orgasms possible
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