Chapter Eleven Reproductive Behaviors

Organizing Effects of Sex Hormones Defined-determine whether the brain and body will develop as male or female Sex Differences in the Gonads Chromosomal pattern is XX for females and XY for males Both fetuses have primordial gonads for both sexes Males 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 genitals The 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 Hypothalamus Sexually dimorphic nucleus-larger in males than females and is linked to male sexual behavior These changes are testosterone dependent Testosterone must be aromatized into estradiol to have effects on hypothalamus Alpha-fetoprotein protects females from seeing these changes in their hypothalamus due to exposure to their own estrogen Testosterone also encourages development of muscles around the penis Video

Sex Differences in Nonreproductive Characteristics Aggressiveness in males Dependent on prenatal testosterone Infant Care Estrogen-dependent Longevity Preference for sex-specific toys Females 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 behavior May 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 cycle Note 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 ovary FSH 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 Identity Physical Development Testicular Feminization/Androgen Insensitivity-a genetically male fetus develops as female Hermaphrodites-genitals do not match the genetic sex pseudohermaphrodites/intersexes-sexual development is ambiguous Prenatal Hormones-Ex: male children in the Dominican Republic raised as females Social Influences-Stereotypes

Possible Biological Bases of Sexual Orientation Hormones Stress during last week of pregnancy results in endorphins having an antitestosterone effect on the fetus (rats) Genetics Evidence for contribution but there also appear to be other factors involved Possibly 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 Structure Interstitial Nucleus connects to medial preoptic area and it is larger in men than women also smaller in homosexual men Suprachiasmatic Nucleus-unclear role anterior 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.