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Reproductive behavior: Sexuality and physiology

Reproductive behavior: Sexuality and physiology. Hormones Organs Hypothalamus. Hormones. Neurotransmitters Neuromodulators or autacoids Hormones act on receptors Amino acid-based hormones Peptides and polypeptide proteins Steroids, from cholesterol Pheromones. Sex hormones.

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Reproductive behavior: Sexuality and physiology

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  1. Reproductive behavior: Sexuality and physiology Hormones Organs Hypothalamus

  2. Hormones • Neurotransmitters • Neuromodulators or autacoids • Hormones act on receptors • Amino acid-based hormones • Peptides and polypeptide proteins • Steroids, from cholesterol • Pheromones

  3. Sex hormones • Sex hormones are steroids • In addition to acting on surface receptors, steroids are fat-soluble and can enter cells to bind with internal receptors, even in the nucleus • Secreted by gonads and adrenal cortex, triggered by hypothalamus via the pituitary

  4. Estrogens and androgens • Gonads and adrenal cortex of both genders secrete both: The difference is in the relative amounts • Testosterone and estradiol • Progestins: Progesterone • Anterior pituitary: Gonadotropins and ACTH • Posterior pituitary: ADH and oxytocin

  5. Hypothalamic control • Hypothalamus controls posterior pituitary through neurohormones released from axon terminals in PP • Hypothalamus controls anterior pituitary through releasing hormones secreted into a portal vein system.

  6. Sexual effects of hormones • Fetal development • Perinatal development • Puberty • Adulthood

  7. Hormones in sexual development • Primordial gonads or fetal gonadal anlage are hermaphroditic: Medulla becomes testes, cortex becomes ovaries. • SRY gene on Y chromosome causes H-Y antigen to be synthesized, leading to development of medulla.

  8. Reproductive tracts • Mullerian and Wolffian tissue develop under hormonal control • Testosterone triggers Wolffian development, MIS inhibits Mullerian development • Mullerian tissue develops by default unless MIS is present

  9. Other differentiation effects • The external genitals develop in two different pathways from the same tissue, influenced by testosterone • Some brain structures develop different sizes or activity levels • Hypothalamus, corpus callosum, anterior commissure, thalamus, planum temporale • Temporal lobe and limbic system (more active in men); cingulate gyrus (more active in women)

  10. Brain effects of hormones • During early development, testosterone affects the hypothalamus by turning off the cycling pattern of gonadotropin release. • Testosterone acts on brain cells only after it is aromatized inside cells to estradiol, which then masculinizes the cells.

  11. More on brain effects • Estradiol in the mother’s blood is kept from the rat fetus by being bound by alpha fetoprotein; in humans by the placental barrier. • Synthetic estrogens, like DES, can cross the placental barrier, causing some masculinization in female children.

  12. Sexual effects of hormones • Fetal development • Perinatal development • Puberty • Adulthood

  13. Behavioral effects of hormones • In females: • In animal studies, perinatal testosterone treatment and ovariectomy leads to masculine sexual patterns (mounting) when testosterone is added at maturity. • When injected with progesterone and estradiol, they showed less female sexual response (lordosis).

  14. Sexual effects of hormones • Fetal development • Perinatal development • Puberty • Adulthood

  15. Hormones and puberty • Timing by the hypothalamus SCN • Anterior pituitary and growth hormone • Gonadotropic and adrenocorticotropic hormones trigger greater increases in either androgens or estrogens, but both are secreted in increased amounts by both genders, eg. androstenedione

  16. Exceptional development • Hermaphroditism • Androgen Insensitivity Syndrome • No receptors for androgens • Adrenogenital Syndrome • Insufficient cortisol to inhibit adrenal androgen • Sex reassignment

  17. Sexual effects of hormones • Fetal development • Perinatal development • Puberty • Adulthood

  18. Hormones and adults • Male sexual capacity and behavior relate to testosterone levels • Castration reduces sex drive and potency • Replacement testosterone increases sex drive and potency in men with a testosterone deficiency: castrati and elderly • Healthy males are unaffected by additional testosterone. They already have plenty.

  19. Sexual hormones in adult females • Sexual hormones do control the estrus cycle, which is related to sexual activity, and the menstrual cycle, which is not. • Ovariectomy does not reduce sex drive, if the consequent lack of lubrication is compensated. • Sexual interest appears to be controlled by testosterone.

  20. Other hormone effects • Social-cognitive functioning (Macrae et al., 2002)

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