Chapter 11: Reproductive Behaviors
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The document discusses how sex hormones influence reproductive and sexual behavior. It describes the organizing effects of sex hormones during early development which determine the development of male or female anatomy. It also discusses the activating effects of sex hormones which can occur throughout life and influence sexual behavior and pleasure. The document also examines gender identity, sexual orientation and their biological basis.
Chapter 11: Reproductive Behaviors
- 2. The Effects of Sex Hormones Hormones Chemicals secreted by the glands & carried by the blood to other organs whose activity they influence Endocrine Glands Hormones coordinate long-lasting changes in many parts of the body
- 3. Classes of Hormones Protein & Peptide Hormones Composed of chains of amino acids Proteins are longer chains; peptides are shorter chains Attach to receptors on cell membranes where they activate 2 nd messengers within the cell Steroid Hormones Cortisol & corticosterone Bind to membrane receptors like protein or peptide hormones Enter cells & attach to receptors in the cytoplasm, which then move to the nucleus where they determine gene expression Sex Hormones Androgens : testosterone Estrogen : estradiol Anabolic steroids : testosterone & other androgens, & synthetic chemicals derived from them Sex-linked genes : genes activated by sex hormones Other Hormones Thyroid hormones : released by the thyroid gland containing iodine Monoamine hormones : norepinephrine & dopamine
- 4. Control of Hormone Release Pituitary Gland Called the “master gland” because its secretions influence other glands Posterior Pituitary Gland Releases oxytocin & vasopressin Anterior Pituitary Gland Synthesizes 6 hormones: Adrenocorticotropic hormone (ACTH) Thyroid-stimulating hormone (TSH) Prolactin Somatotropin or Growth hormone (GH) Follicle-stimulating hormone (FSH) Leutinizing hormone (LH)
- 5. Organizing Effects of Sex Hormones Organizing Effects Occurs mainly during a sensitive stage of development Determines whether the brain & body develop as a male or female Activating Effects Are temporary, happening only while a hormone is present Can occur at any time in life Sex Differences in the Gonads & Hypothalamus Differentiation begins with the chromosomes Female = XX & Male = XY Gonads are the reproductive organs In mammals, the gonads of males & females are identical early in prenatal development SRY Gene Gene on the Y chromosome responsible for causing the primitive gonads in males to become testes Testes Sperm-producing organs which also synthesize the androgens Wolffian Ducts Precursors of the male reproductive organs that develop into the seminal vesicles & the vas deferons after testosterone exposure during prenatal development
- 6. Organizing Effects of Sex Hormones M llerian Inhibiting Hormone (MIH) A peptide hormone that degenerates the M llerian ducts in males Testosterone also results in the development of the penis & scrotum In females, primitive gonads become ovaries and her M llerian ducts develop & mature as long as she’s not exposed to large amounts of testosterone M llerian Ducts Precursor of female reproductive organs that develop into the oviduct, uterus & upper vagina during prenatal development
- 7. Organizing Effects of Sex Hormones The Sexually Dimorphic Nucleus Part of the medial preoptic hypothalamus that is larger in males than in females This area is linked to male sexual behavior The female hypothalamus differs from the male hypothalamus It can generate a cyclic pattern of hormone release; the male cannot Sensitive Period In early prenatal development, when a particular event has a long-lasting effect A mammal with low levels of hormones in early development will develop female anatomy Male characteristics develop with the introduction of testosterone Alpha-fetoprotein A protein that binds with estrogen & keeps it from entering cells during the early sensitive period This process keeps females from becoming masculinized with their own estsrogen Sex Differences in Nonreproductive Characteristics If female fetuses are exposed to androgens, they tend toward masculine behaviors Male & female brains differ in regions unrelated to sexual behavior I.e. language areas of the left temporal lobe & the corpus callosum
- 8. Activating Effects of Sex Hormones Rat Research Sex hormones activate sexual behavior partly by enhancing sensations Medial preoptic area, ventromedial nucleus & anterior hypothalamus are principle areas affected by sex hormones Sex hormones prime the MPOA & other areas to release dopamine At low concentrations, dopamine stimulates D 1 and D 5 receptors which facilitate erections in male & sexually receptive postures in female rats Higher concentrations of dopamine stimulate D 2 receptors which lead to orgasm
- 9. Sexual Behavior in Humans Effects on Men Sexual excitement is highest when testosterone levels are highest Sexual pleasure during orgasm is due to the secretion of large amounts of oxytocin Decreases in testosterone levels generally decrease sexual activity Impotence: the inability to have or maintain an erection Usually not caused by low testosterone levels Treated by increasing blood circulation in the penis & hypothalamus Decreasing testosterone activity is a method to treat sex offenders
- 10. Sexual Behavior in Humans Effects on Women Menstrual cycle: periodic variation in hormones & fertility over the course of about one month At the end of the period, the anterior pituitary releases Follicle-stimulating Hormone (FSH) that promotes the growth of a follicle in the ovary Toward the middle of the cycle the follicle produces increasing amounts of estradiol leading to an increase in release of FSH & LH from the anterior pituitary At the end of the cycle, levels of LH, FSH, esstradiol & progesterone all decline
- 11. Sexual Behavior in Humans Effects on Women Birth control pills containing estrogen & progesterone prevent a surge of FSH & LH that would release an ovum This makes it harder for the sperm to reach the egg & for the egg to be implanted Preovulatory period : the midpoint of the menstrual cycle when sexual interest increases Premenstrual syndrome (premenstrual dysmorphic syndrome): characterized by anxiety, irritability & depression during the days before the menstruation
- 12. Sexual Behavior in Humans Nonsexual Behavior Testosterone increases aggressive behavior in many species Estrogen stimulates growth of dendritic spines in the hippocampus & prevents neuronal death Estrogen increases the production of dopamine (D 2 ) & serotonin 5-HT 2A ) receptors in the nucleus accumbens, prefrontal cortex & several other cortical areas Estrogen is linked to the ability to perform motor & cognitive skills
- 13. Parental Behavior The Biochemistry of Parenthood Increase in oxytocin & prolactin by the day of delivery is necessary for maternal behavior in rats Damage to the medial preoptic area impairs parental behavior in rats Later stages of maternal behavior is not dependent on hormones In male rats, testosterone levels drop after the delivery of the pups & prolactin levels increase
- 14. Interpertations of Mating Behavior Interest in Multiple Mates Men are more likely to be interested in short-term sexual relationships with many partners Men’s mating strategies: One-mate strategy Multiple-mate strategy Evolutionarily, either strategy (or both) will be effective in spreading the man’s genes Women have less to gain in multiple-mate strategy They have a limited number of pregnancies
- 15. What Men & Women Prefer in a Mate Main Preferences Healthy, intelligent, honest & physical attractiveness Women’s Additional Preferences Acceptable odor, being a good provider Power is highly attractive Men’s Additional Preferences Physical appearance is important Men have a strong preference for a younger partner
- 16. Jealousy Differences in Jealousy Men tend to be more upset about wives’ sexual infidelities than women about their husbands’ infidelities Women tend to be more upset about emotional infidelity than sexual infidelity If a behavior has a clear advantage for survival or reproduction & is similar across cultures, it can’t be concluded it developed by evolution
- 17. Determinants of Gender Identity Gender Identity How you identify yourself sexually & whether you call yourself male or female Your sense of maleness or femaleness Intersexes If a female fetus is exposed to elevated androgen levels, than partial masculinization of her anatomy will occur Hermaphrodites : individual whose genitals do not match normal development for their genetic sex Intersexes (pseudohermaphrodite) : individuals whose development is intermediate between male & female (not androgynous)
- 18. Determinants of Gender Identity Androgen Insensitivity Males with genital appearance of females Cause: inability of androgens to bind to cells Cells are insensitive to androgens & the external genitals develop similar to those of a female 5 -Reductase Deficiency Genetic disorder in males where the penis does not develop until puberty & the child is usually identified as female
- 19. Biological Basis of Sexual Orientation Probability of Homosexuality Highest in monozygotic twins of the originally identified homosexual person Lowest in dizygotic twins Lowest in adopted brothers & sisters Genetic factors not only the determinant of sexual orientation Animal Studies Suggest low testosterone levels during pregnancy may cause male offspring to respond sexually to either male or female partner Prenatal Stress Prenatal stress decreases male sexual behaviors Diethylstilbestrol (DES) , a synthetic estrogen can exert a masculinizing effect similar to testosterone Brain Anatomy Anterior commisure & suprachiasmatic nucleus is larger in homosexual men than in heterosexual men Interstitial nucleus 3 of the anterior hypothalamus (INAH-3) in homosexual males & heterosexual females is similar in size, but smaller in heterosexual males