HUMAN REPRODUCTION BIOLOGY 269

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HUMAN REPRODUCTIONBIOLOGY 269
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Both male and female reproductive functions
controlled by hormones

• It all starts with the pituitary gland

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Pituitary gland secretes

• Estrogen
• Stimulates development of female sexual
  characteristics
• Stimulates contractions of oviduct
• Stimulates endometrium of uterus to proliferate
• Inhibits secretion of more FSH from pituitary

Seminiferous tubules dont secrete any other
hormones, so FSH secretion by pituitary remains
constant
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Pituitary gland secretes

• Testosterone
• Stimulates development of male sexual
  characteristics
• Does not inhibit LH secretion by pituitary, so LH
  remains constant

• Progesterone
• Continues to inhibit secretion of FSH from
  pituitary
• Keeps endometrium of uterus ready for embryo
  implantation
• Inhibits contraction of muscle (myometrium) of
  uterus

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If fertilization occurs
If fertilization does not occur
HCG stimulates corpus luteum of ovary to continue
secreting progesterone this inhibits
menstruation and inhibits the pituitary from
secreting FSH, so another follicle will not start
to develop
As levels of progesterone fall, menstruation
occurs as the myometrium (muscle) of the uterus
contracts and the functional layer of its
endometrium falls off. The pituitary is no longer
inhibited and begins to secrete FSH again
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The pituitary gland secretes two more hormones
involved in reproduction
During pregnancy, pituitary secretes
this causes the breast to
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During menstruation, pituitary secretes
, which causes During childbirth, pituitary
secretes which causes During
breastfeeding, sucking on nipple causes pituitary
to secrete which causes
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Increased levels of oxytocin also leads to
feelings of both emotional and sexual attraction
The hormone of love.
Oxytocin levels increase sharply during early
stages of attraction and sexual arousal. This
starts a positive feedback loop which increases
your receptivity even more and increases your
sensitivity to sexual signals from others and to
sexual stimulation.
Oxytocin continues to rise during sexual
activity, eventually triggering both the muscular
contractions and the positive emotional responses
of orgasm.
For the same reason, oxytocin has also been
called The hormone of masturbation since any
sexual stimulation starts the same positive
feedback loop, leading to increased sensitivity
and eventually orgasm.
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Oxytocin significant differences between men and
women
Women secrete more oxytocin in response to
emotional and verbal cues Men secrete more
oxytocin in response to physical and visual cues.

Women produce more oxytocin than men during
arousal and intercourse, but also require these
higher levels to get the same level of arousal
and to reach orgasm.
Oxytocin levels fall rapidly in men after
intercourse, but stay elevated much longer in
women. This has been linked to womens
increased desire for a continued connection with
her mate after intercourse, and to mens relative
lack of this desire.
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