1. Prepared by Jeffrey W. Grimm Western Washington University
PowerPoint Presentation for Biopsychology, 8th Edition by John P.J. Pinel
Prepared by Jeffrey W. Grimm
Western Washington University
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2. What’s Wrong with the Mamawawa?
Chapter 13
Hormones and Sex
What’s Wrong with the Mamawawa?
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3. Developmental and Activational Effects of Sex Hormones
Developmental (or “organizational”) – influencing the development of anatomical, physiological, and behavioral characteristics that differentiate the sexes
Activational – triggering reproduction-related behavior in mature individuals
Adolescent surges have both developmental and activational effects
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4. Neuroendocrine System: Glands
Exocrine – release chemicals into ducts which carry them to their targets
Sweat glands, for example
Endocrine – ductless; release hormones directly into the circulatory system
Only organs whose primary function is hormone release are referred to as endocrine glands
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FIGURE 13.1 The endocrine glands.
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6. Neuroendocrine System: Glands
Male testes produce sperm cells
Female ovaries produce ova
Sperm and ova each have 23 chromosomes
Fertilization
Sperm cell + ovum = zygote
23 pairs of chromosomes
X and Y – sex chromosomes
XX = female, XY = male
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Classes of Hormones
Amino acid derivatives
Epinephrine, for example (adrenal medulla)
Peptides and proteins
Short and long chains of amino acids
Steroids
Synthesized from cholesterol (fat)
Fat-soluble – able to enter cells and bind to receptors in cytoplasm or nucleus
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Sex Steroids
Released by gonads
Androgens - e.g., testosterone
Estrogens - e.g., estradiol
Adult testes release more androgens and ovaries more estrogens
Progestins – also present in both sexes
Progesterone prepares uterus and breasts for pregnancy
Adrenal cortex – also releases sex steroids
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9. Hormones of the Pituitary
“Master gland”
Tropic hormones influence the release of hormones by other glands
Posterior pituitary – hormones synthesized in the hypothalamus
Anterior pituitary – tropic hormones
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FIGURE A midline view of the posterior and anterior pituitary and surrounding structures.
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11. Cyclic vs. Steady Gonadal Hormone Levels
Female hormones go through a 28-day cycle, the menstrual cycle
Male hormone levels are constant
Anterior pituitary activity is controlled by the hypothalamus
The hypothalamus determines whether hormone levels cycle
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12. Neural Control of the Pituitary
Bird research was first to implicate the control over pituitary function by the nervous system
Light/dark cycling and breeding changed hormone release
Lesion and stimulation experiments established the hypothalamus as the regulator of the anterior pituitary
Did not explain how the signal was mediated as the anterior pituitary is not “connected” to the hypothalamus by neurons
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13. Control of the Pituitary by the Hypothalamus
Posterior – neural input from hypothalamus
Vasopressin – antidiuretic hormone
Oxytocin – labor and lactation
Synthesized in hypothalamic paraventricular and supraoptic nuclei
These nuclei have terminals in the posterior pituitary
Anterior pituitary – hypothalamopituitary portal system carries hormones from the hypothalamus to the anterior pituitary
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FIGURE Control of the anterior and posterior pituitary by the hypothalamus.
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15. Discovery of Hypothalamic Releasing Hormones
Thyrotropin-releasing hormone first isolated from the hypothalamus of sheep and then pigs
Triggers the release of thyrotropin from the anterior pituitary
Thyrotropin then stimulates release of hormones from the thyroid gland
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16. Regulation of Hormone Levels
Neural
All endocrine glands (except the anterior pituitary) receive neural signals
From cerebral or autonomic neurons
Hormonal
Tropic hormones, negative feedback
Nonhormonal chemicals
Glucose, Ca2+, Na+
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17. Pulsatile Hormone Release
Hormones tend to be released in pulses
Leads to often large minute-to-minute fluctuations in levels of hormones
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FIGURE A summary model of the regulation of gonadal hormones.
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19. Hormones and Sexual Development of the Body
Humans are dimorphic – exist in two forms
Genetic information on the sex chromosomes normally determines male or female development
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20. Fetal Hormones and Development of Reproductive Organs: Gonads
Initially there is a primordial gonad
Cortex – potential to be an ovary
Medulla – potential to be a testis
If XY, The Sry gene on the Y chromosome triggers the synthesis of Sry protein
If no Sry protein present, cortex develops into ovary
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FIGURE The development of an ovary and a testis from the cortex and the medulla, respectively, of the primordial
gonadal structure that is present 6 weeks after conception.
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Fetal Hormones and Development of Reproductive Organs: Internal Reproductive Ducts
Both sexes begin with two sets of reproductive ducts
Wolffian system – male – seminal vesicles, vas deferens
Müllerian system – female – uterus, vagina, fallopian tubes
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23. Internal Reproductive Ducts Continued
Third prenatal month: differentiation of ducts
Testes produce testosterone and Müllerian-inhibiting substance
Wolffian system develops, Müllerian degenerates, testes descend
No testes – no testicular hormones
Müllerian system develops, Wolffian degenerates
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FIGURE The development of the internal ducts of the male and female reproductive systems from the Wolffian and Müllerian systems, respectively.
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25. External Reproductive Organs
External reproductive structures – genitalia – develop from one bipotential precursor
Differentiation occurs in second month
Testosterone produces male structures
Without testosterone, female structures develop
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26. Puberty: Hormones and the Development of Secondary Sex Characteristics
Fertility achieved
Secondary sex characteristics develop
Features unrelated to reproduction that distinguish sexually mature men and women
Increase in release of anterior pituitary hormones
Growth hormone – acts on bone and muscle
Gonadotropic hormone
Adrenocorticotropic hormone
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Puberty Continued
Relative levels of androgens and estrogens determine whether male or female features develop
Androstenedione – androgen necessary for the growth of axillary (underarm) and pubic hair in females (more evidence against mamawawa)
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28. Sex Differences in the Brain
Pfeiffer first discovered a sex difference in mammalian brain function
Pfeiffer (1936) – gonadectomized and implanted gonads in neonatal rats
Gonadectomy causes cyclic (female) gonadotropin release pattern
Transplant of testes to males or females causes steady (male) gonadotropin release pattern
Perinatal androgens lead to male pattern
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29. Aromatization Hypothesis
Sex steroids are all derived from cholesterol and are readily converted from one to the other
Aromatized testosterone becomes estradiol
Evidence suggests that estradiol masculinizes the brain, at least in rodents
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30. Evidence that Estradiol Masculinizes the Neonatal Brain
Neonatal injections of estradiol masculinize
Dihydrotestosterone can’t be converted to estradiol – doesn’t masculinize
Alpha fetoprotein deactivates circulating estradiol but does not cross the blood-brain-barrier
Blocking aromatization or estradiol receptors interferes with masculinizing effects of testosterone
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31. Mother’s Estradiol Doesn’t Masculinize Female Brains
In female rodents, Alpha fetoprotein in blood during perinatal period …
Protects the female brain from estradiol
Binds to circulating estradiol, so none gets to the brain
In male rodents, testosterone enters the brain and then is converted to estradiol
In humans, aromatization is apparently not necessary for testosterone to masculinize brain
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32. Modern Perspectives on Sexual Differentiation of the Mammalian Brain
No single mechanism can account for the development of sexual dimorphisms of mammalian brains:
Aromatase is only required for testosterone effects on masculinization in some areas of the brain
Female brain development may not automatically occur in absence of estrogens
Various dimorphisms emerge at different stages under different influences
Sex chromosomes influence brain development independent of their effect on hormones
Studies with gene knockout mice indicate that estradiol plays an active role in the female program of brain development
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33. Perinatal Hormones and Behavioral Development
Masculinize – promoting male behavior (i.e., mounting)
Defeminize – preventing female behavior (i.e., lordosis)
Perinatal testosterone masculinizes and defeminizes
Neonatal castration of male rats – feminizes and demasculinizes
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34. Three Cases of Exceptional Human Sexual Development
Anne S.
Elaine
John
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Anne S.
Knowing how normal development occurs, you should be able to understand what could cause abnormal sexual development
Why might a woman not cycle and not have pubic or axillary hair?
What determines whether male or female hormone patterns develop?
What causes the growth of pubic and axillary hair?
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Anne S. Continued
Anne is chromosomally male, XY
Internalized testes, but no ovaries
Hormone levels are those of a man
Androgenic insensitivity syndrome
Normal male androgen levels, but no response to them
She does respond to estrogens, so she effectively has more estrogens than androgens – leading to the development of female secondary sex characteristics
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Elaine
Born with somewhat ambiguous genitals but raised as a girl
Developed male secondary sex characteristics in puberty
Eventually diagnosed with adrenogenital syndrome
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38. Andrenogenital Syndrome
Andrenogenital syndrome is caused by congenital adrenal hyperplasia
Too little cortisol leads to compensatory excessive release of adrenal androgens in XX females
May masculinize female genitalia and behavior – surgical and hormonal treatments needed at birth.
Often tomboyish; late onset of menstruation
Prior to modern treatments of 1950s, changes in sexual identity at puberty was unpredictable and likely to be traumatic
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John/Joan
A surgeon’s error led one of a pair of male twins to be raised as a girl
Artificial vagina created
Estrogen administered at puberty
John/Joan never felt or acted like a girl – indicates that the key to one’s gender is in the brain
John/Joan chose to become John later in life, but never recovered from the ordeal
David Reimer (“John”) took his life in May, 2004
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40. Male Reproduction-Related Behavior and Testosterone
Effects of orchidectomy (Bremer, 1959)
Reduced sexual interest and behavior
Rate and degree of loss varies
Still have adrenal testosterone
Level of male sexuality is NOT correlated with testosterone levels in healthy men
Increasing male testosterone levels does NOT increase sex drive
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41. Female Reproduction-Related Behavior and Gonadal Hormones
Rats and guinea pigs – surges of estrogen and progesterone initiate estrus, a period of fertility and receptivity
Women – sexual motivation and behavior not tied to cycle
Sex drive may be under androgenic control
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42. Human Female Sexuality and Androgens
Testosterone increases the proceptivity of ovariectomized and adrenalectomized female rhesus monkeys
Correlations seen between sexual motivation and testosterone
Testosterone found to rekindle sexual motivation in ovariectomized and adrenalectomized women
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43. Anabolic Steroid Abuse
Anabolic – growth-promoting
No firm scientific evidence that muscularity and strength are increased
Sex-related side effects
High circulating hormones cause a reduction of natural release (negative feedback loop)
Men – testicular atrophy, sterility, gynecomastia (breast enlargement)
Women – amenorrhea (cessation of menstru-ation), sterility, hirsutism (excessive growth of body hair)
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44. Neuroprotective Effects of Estradiol
Reduces brain damage if given just before or after inducing cerebral hypoxia
Reduces inflammation, encourages axonal regeneration, promotes synaptogenesis
Increases adult neurogenesis
May account for sex difference in longevity and some diseases
Possible salutary cognitive effects
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45. Neural Mechanisms of Sexual Behavior
Sexually dimorphic nucleus (SDN)
Medial preoptic area of rat hypothalamus
Larger in males, due to estradiol shortly after birth
Size of male SDN correlated with testosterone levels and aspects of sexual activity
Nuclei in preoptic, suprachiasmatic, and anterior regions of the hypothalamus are larger in men than in women
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46. Medial Preoptic Area of the Hypothalamus
Contains the SDN
Destruction abolishes male sexual behavior of mammalian males and females studied, but does not affect female sexual behaviors in females
Stimulation elicits copulatory behaviors
Evidence favors a motivational role for male sexual behavior
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47. Ventromedial Nucleus (VMN) of the Hypothalamus
Contains circuits critical for female rat sexual behavior
Lesion eliminates lordosis
Microinjections of estrogen and progesterone induce estrus
Lesions of periaqueductal gray (PAG) or the tracts to it eliminate lordosis
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48. Sexual Orientation and Sexual Identity
Heterosexual – sexually attracted to members of the opposite sex
Homosexual – sexually attracted to members of the same sex
Bisexual – sexually attracted to members of both sexes
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49. Sexual Orientation and Genes
48% homosexual concordance rate for monozygotic twins; 16% for dizygotic twins
Limited evidence for a particular gene related to homosexuality
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50. Sexual Orientation and Early Hormones
Orchidectomy reduces sexual behavior of males, but does not redirect it
Non-human studies indicate that perinatal hormones can influence sexual “orientation”
Human research is less conclusive
No differences in adult hormone levels
Prenatal exposure to artificial estrogen has weak correlation with homo- or bisexuality in women
Fraternal birth order effect: younger brothers are increasingly more likely to be homosexual
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51. What Triggers the Development of Sexual Attraction?
May be due to adrenal cortex steroids
Adrenal maturation occurs at about the same time (age 10) as sexual interest
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52. Is There a Difference in the Brains of Homosexuals and Heterosexuals?
No reliable difference between the brains of heterosexuals and homosexuals has been discovered
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Sexual Identity
Sexual identity does not always coincide with a person’s anatomical sex
Transsexualism
Person believes that he or she is trapped in the body of the other sex
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54. Independence of Sexual Orientation and Sexual Identity
Sexual attraction, sexual identity, and body type are sometimes unrelated
Points to many possible differences in brain development, organization, and function between individuals
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