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Hormonal Influences

Explore the fascinating realm of hormones, sex, and gender. Learn how hormones such as estrogen and testosterone shape sexual development, behavior, and identity. Discover the complexities of sexual differentiation and the impact of hormones on sexual behavior. Unravel the mysteries of hormonal influences on sexuality, from developmental stages to adult behaviors. Delve into the pivotal role of hormones in shaping human sexual experiences and gender identity.

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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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