Chapter ElevenReproductive Behaviors

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.