Reproductive behavior: Sexuality and physiology

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Reproductive behavior Sexuality and physiology

• Hormones
• Organs
• Hypothalamus

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Hormones

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

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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

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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

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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.

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Sexual effects of hormones

• Fetal development
• Perinatal development
• Puberty
• Adulthood

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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.

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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

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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)

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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.

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More on brain effects

• Estradiol in the mothers 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.

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Sexual effects of hormones

• Fetal development
• Perinatal development
• Puberty
• Adulthood

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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).

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Sexual effects of hormones

• Fetal development
• Perinatal development
• Puberty
• Adulthood

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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

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Exceptional development

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

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Sexual effects of hormones

• Fetal development
• Perinatal development
• Puberty
• Adulthood

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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.

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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.

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Other hormone effects

• Social-cognitive functioning (Macrae et al., 2002)