Transcript Reproductive Behaviors - Manhattanville College

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
Estrogen-dependent
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.