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Hormonal Influences

Hormonal Influences. on Sex & Sexuality. Hormones, Sex, & Gender. Dr. discovers young married woman is male! Adolescent girl grows penis! Baby boy undergoes sex change!. Hormones. Chemical messengers Organizational development critical periods Activational

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Hormonal Influences

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  1. Hormonal Influences on Sex & Sexuality

  2. Hormones, Sex, & Gender • Dr. discovers young married woman is male! • Adolescent girl grows penis! • Baby boy undergoes sex change!

  3. Hormones • Chemical messengers • Organizational • development • critical periods • Activational • control behavior & physiological processes ~

  4. Sex Hormones • Steroids • derived from cholesterol • Estrogens • estradiol • Androgens • testosterone • dihydrotestosterone (DHT) ~

  5. Dihydro- testosterone 5- a- reductase Testosterone aromatase Estradiol

  6. Sexual Differentiation • Sexually dimorphic • Genotypic sex • sex genes • Phenotypic sex • expression of genes ~

  7. Sexual Differentiation • Single gene • Sex-Determining Region on the Y Chromosome • SRY • Testis Determining Factor (TDF) ~

  8. Development of Reproductive Organs

  9. Primordial Gonad • Indifferent gonad • first 6 weeks • No TDF --> ovaries • cortex • TDF --> testes • medulla ~

  10. Internal Reproductive Ducts • Mullerian system • female • Wolffian system • male ~

  11. Internal Reproductive Ducts • 3d month • 1 set withers • TDF ---> testes • testosterone • Mullerian Inhibiting Hormone - MIH ~

  12. External Genitalia • Dihydrotestosterone • M/F same primordial tissue ~

  13. Sexual Differentiation of the Brain

  14. Sexual Differentiation of the Brain • Rats • Hypothalamus • Sexually Dimorphic Nucleus (SDN) • Spinal Cord • Spinal Nucleus of the Bulbocavernosus (SNB) ~

  15. Masculinization • Gonadotropin release patterns • Female: cyclical • Male: steady • Brain masculinized by... • testosterone? NO!--->ESTRADIOL ~

  16. Sexually Dimorphic Nucleus male female androgenized female

  17. Spinal Nucleus of the Bulbocavernosus F F + A M M - A

  18. Secondary sex characteristics • Puberty • Increased M/F sex hormone activity • Secondary characteristics • maturation of genitals • breasts • body shape • Pubic & axillary hair • females- androstenedione ~

  19. Sexual Development Syndromes

  20. Congenital Adrenal Hyperplasia • Prenatal adrenal cortex hyperactivity • high levels of androgens • partially masculinized external genitalia ~

  21. Congenital Adrenal Hyperplasia

  22. Androgen Insensitivity Syndrome • Genetically XY - • No androgen receptors • Genetic mutation - X chromosome • Female body, brain, & gender identity • functional testes ~

  23. 5- a - Reductase Syndrome • Genetically XY • Fetal 5 - a - reductase deficiency • no dihydrotestosterone • genitalia not masculinized ~

  24. At puberty • Undescended testes functional • Functioning penis develops • Normal male development ~

  25. Hormones &Sexual Behavior

  26. Sexual Behavior: Rats • Controlled by sex hormones • Female • Proceptive • ear wiggling, darting, hopping • Receptive - lordosis • Male • mounts • copulates ~

  27. Organizational Effects of Hormones • SDN & SNB • Critical periods • Humans - prenatal • Rats - Perinatal • easily manipulated ~

  28. Hormones: Sexual Behavior • Gonadectomy • at birth • Adult males • testosterone ---> no male behavior • estrogen ---> lordosis • Adult females • estrogens ---> no female behavior • testosterone ---> male behavior ~

  29. Human Sexual Behavior • No stereotypical M & F behaviors • Men are like rats • Testosterone: activational role • Women • Estrogens no activational effects • Testosterone levels correlated with frequency of intercourse ~

  30. Homosexuality • Sex hormones role? • rats - yes • Humans? • no difference in circulating hormones • Learning experiences? • or biologically determined?

  31. Homosexuality • Simon LeVay • Brains of male AIDS victims • Anterior Hypothalamus • Anterior Commissure • SDN (rats) • Humans: 3rd interstitial nucleus of the Anterior Hypothalamus • INAH-3 ~

  32. INAH-3 Male Female SDN

  33. INAH-3

  34. INAH-3 • Anterior Commissure similar relationship

  35. Suprachiasmatic Nucleus Swaab & Hoffman (1990)

  36. Homosexuality: 2 Hypotheses • 1. Androgen levels • low in XY fetuses that---> gay • high in XX fetuses ---> lesbian ~

  37. Homosexuality 2 Hypotheses 2. Inherited Genes • MZ twin concordance approx. 50% • DZ twins approx. 20% • Xq28- tip of the X chromosome • 33 of 40 pairs of gay brothers • fetal brain response to androgens ~

  38. Nature vs. Nurture • John/Joan • penis destroyed during circumcision • 1960s - Gender deemed neutral at birth • constructed female genitalia • hormone treatment • 12 yrs old: positive results reported ~

  39. Nature vs. Nurture • By 14 yrs old: living as male • reconstructive surgery • male hormone treatment • married by 25 • Reassessment in 1996 • rejected female role much earlier • Pendulum swings back toward nature • sex/gender not so malleable ~

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