Chapter Eleven Reproductive Behaviors. Organizing Effects of Sex Hormones Defined-determine whether...
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Transcript of Chapter Eleven Reproductive Behaviors. Organizing Effects of Sex Hormones Defined-determine whether...
Organizing Effects of Sex Hormones
Defined-determine whether the brain and body will develop as male or female
Sex Differences in the GonadsChromosomal pattern is XX for females and XY for malesBoth fetuses have primordial gonads for both sexesMales SRY gene stimulates the release of Mullerian inhibiting
substance and androgens In the absence of androgens, females develop only the
Mullerian system into ovaries and uterus
Figure 11.1 Differentiation of human genitalsThe male’s SRY gene causes the gonad to become a testis, and the testis produces
testosterone, which masculinizes development. In the absence of testosterone, development follows the female pattern.
Organizing Effects of Hormones
Sex Differences in the HypothalamusSexually dimorphic nucleus-larger in males than females and is
linked to male sexual behaviorThese changes are testosterone dependentTestosterone must be aromatized into estradiol to have effects
on hypothalamusAlpha-fetoprotein protects females from seeing these changes
in their hypothalamus due to exposure to their own estrogenTestosterone also encourages development of muscles around
the penis
Video
Sex Differences in Nonreproductive Characteristics
Aggressiveness in malesDependent on prenatal testosterone
Infant CareEstrogen-dependent
LongevityEstrogen-dependent
Preference for sex-specific toysFemales exposed to high levels of testosterone show great
preference for male-typical toys and activities
Activating Effects of Sex Hormones
Activate Sexual Behavior
Testosterone results in male sexual behavior
Estrogen followed by progesterone results in female sexual behavior
Male-typical sex behavior
Erection and orgasm dependent on dopamine
Female-typical sex behavior
Lordosis and orgasm dependent on dopamine
Sexual Behavior in Humans-MEN
Sexual excitement is highest when testosterone is highest
Cyproterone blocks binding of testosterone and can be used to decrease male sexual behavior
Triptorelin-is a long-lasting testosterone blocking drug that has been beneficial in reducing deviant sexual fantasies and abnormal sexual behavior
Sexual Behavior in Humans-WOMEN
High estrogen levels increase sexual behaviorMay determine what women find attractive in men (women pick a
more feminized face when approaching menstruation)
Figure 11.3 Blood levels of four hormones during the human menstrual cycleNote that estrogen and progesterone are both at high levels during the midluteal
phase, but drop sharply at menstruation, a short time later.
Figure 11.4 Interactions between the pituitary and the ovaryFSH from the pituitary stimulates the ovary to release and develop a
follicle, which produces estradiol, triggering a release of a burst of FSH and LH from the pituitary.Those hormones cause the follicle to release its ovum
and become a corpus luteum. The corpus luteum releases progesterone while the ovary releases estradiol.
Nonsexual Behaviors
Estrogen
Stimulates growth of dendritic spines in hippocampus
Increase DA2 receptors and 5HT2A receptors-may increase mood
Improves memory and fine motor skills
Decrease spatial performance
Testosterone
Improve spatial tasks
Puberty
Defined-onset of sexual maturity
Onset occurs when the hypothalamus begins to release luteinizing hormone (LH) releasing hormone
LH and FSH stimulate the release of gender-specific hormones from the gonads
Sex Hormones stimulate growth and secondary sex characteristics
Parental Behavior
Maternal Behavior-stimulated by prolactin and oxytocin (these hormones act on the medial preoptic area)
Vomeronasal organ and response to pheromones from infants (maintains connection between mother and their young)
Paternal behavior-regulated by testosterone and prolactin
Variations in Sexual Development and Orientation
Definitions of Gender Identity
Gender Identity-how we identify sexually and what we call ourselves
Gender role-activities and dispositions that a particular society encourages for one sex or the other
Variations in Sexual Development
Determinants of Gender IdentityPhysical Development
Testicular Feminization/Androgen Insensitivity-a genetically male fetus develops as female
Hermaphrodites-genitals do not match the genetic sexpseudohermaphrodites/intersexes-sexual development is
ambiguousPrenatal Hormones-Ex: male children in the Dominican
Republic raised as femalesSocial Influences-Stereotypes
Possible Biological Bases of Sexual Orientation
HormonesStress during last week of pregnancy results in endorphins
having an antitestosterone effect on the fetus (rats)
GeneticsEvidence for contribution but there also appear to be other
factors involvedPossibly a gene carried on the X chromosome
Figure 11.11 Sexual orientations in adult relatives of a homosexual man or woman
Note that the probability of a homosexual orientation is highest among monozygotic twins of a homosexual individual, lower among dizygotic twins,
and still lower among adopted brothers or sisters. These data suggest a genetic contribution toward the development of sexual orientation.
Possible Biological Bases of Sexual Orientation
Brain StructureInterstitial Nucleus
connects to medial preoptic area and it is larger in men than women
also smaller in homosexual menSuprachiasmatic Nucleus-unclear roleanterior commissure-unclear role
The data indicating a role for the interstitial nucleus has been questioned. Future studies will need to be done to confirm or deny these results.