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Chapter 10

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University of Toronto Scarborough
Janelle Leboutillier

10| SEXUAL BEHAVIOUR Sexual Development Sex Chromosome Abnormalities - turner syndrome: a condition caused by XO genotype, characterized by frequent abnormalities of the ovaries and infertility  has impact on fertility, growth, and hormone production and associated w/ higher risk of diabetes, osteoporosis, and cardiovascular disease  develop normal female external genitalia – ovaries develop abnormally (don’t produce either ova or normal lvls of female hormones) = infertility  if second X missing in some cells, or part of second X are missing = may be fertile  figure 10.3, p.287  normal intelligence  treatments: human growth hormone, female hormone replacement therapy, and assisted reproductive technologies - klinefelter syndrome: condition in males caused by XXY genotype, characterized by frequent problems w/ fertility, secondary sex characteristics, and verbal skills  exp. reduced fertility, require hormone treatment @ puberty = promote development of secondary male sex characteristics & inhibit female  other symptoms due to interference w/ process of x-inactivation  normal intelligence, mild cognitive difficulties and social awkwardness – usually take form of delayed and reduce verbal skills  left handedness common – might affect brain lateralization - XYY  physical and behavioural correlates typically subtle  boys appear physically w/in typical limits – tend to be taller and leaner, suffer from acne, and higher risk for minor physical abnormalities of eye, elbow, and chest  average IQ below avrg  fertile, but more likely to produce w/ sex chromosome abnormalities Three Stages of Prenatal Development - involve three distinct processes:  gonads: internal organs, ovaries in females and tests in males  internal organs  external genitalia: external sexual organs - intersex: condition in which elements of both male and female development occur in same fetus The Development of the Gonads - up until sixth week after conception, both male and female fetuses = identical primordial gonads  develop into either ovaries: source of ova and sex hormones, or testes: source of sperm and sex hormones - sex-determining region of the Y chromosome (SRY): gene located on short arm of Y chromosome that encodes for testis-determining factor: protein encoded by SRY gene on Y chromosome that turns primordial gonads into testes - female embryos lack SRY gene; alternate genes guide development of ovaries Differentiation of the Internal Organs - figure 10.4, p.289 - until about 3 month, both male and female possess male Wolffian system: internal system that develops into seminal vesicles, vas deferens, and prostate gland in males & Müllerian system: internal system that develops into uterus, fallopian tubes, and upper two thirds of vagina in absence of anti-Müllerian hormone  during third month  male’s new tests begin to secrete two hormones 1) testosterone: androgen produced primarily in testes 2) anti-Müllerian hormone: a hormone secreted by fetal testes that causes degeneration of Müllerian system  in female fetus, no additional hormones needed (ovaries not active during fetal development) – remnants of Wolffian system remain throughout woman’s life - androgen insensitivity syndrome (AIS): condition in which genetic male fetus lacks androgen receptors  development of female external genitalia and typically female gender identity and sexual behaviour  fetuses blind to presence of androgens  have XY genotype and normal testes  release androgens and anti-Müllerian hormone. Lack of androgen receptors prevents development of Wolffian system = shallow vagina and no varies, fallopian tubes, or uterus; infertile, external appearance typically female  figure 10.5, p.290  genetic males but have strong female gender identities Development of the External Genitalia - no hormonal activity required for female - male fetuses  5-alpha-dihydrotestosterone: androgen secreted by tests that masculinizes external genitalia  reacts w/ enzyme 5-alpha-reductase = 5-alpha-dihydrotestosterone - congenital adrenal hyperplasia (CAH): condition in which fetus is exposed to higher-than-normal androgens, resulting in masculinization of external genitalia and some cognitive behaviours in affected females  figure 10.6, p.291 Development at Puberty - secondary sex characteristics: appear at puberty; deepening voice and facial hair growth in males and widening hips and breast development in females - figure 10.7, p.291  could be due to increased rates of obesity  edible tissues from animals contain type of estrogen: steroid hormone that develops and maintains typically female characteristics  estradiol: estrogen hormone synthesized primarily in ovaries  meat treated w/ sex hormones = increase exposure to estrogens by nearly 40% - at onset, gonadotropin-releasing hormone (GnRH): hormone released by hypothalamus that stimulates release of luteinizing hormone (LH): hormone released by anterior pituitary that signals male testes to produce testosterone and regulates menstrual cycle in females, and follicle- stimulating hormone (FSH): hormone released by anterior pituitary that stimulates development of eggs in ovaries and sperm in testes  tests produce additional testosterone (& small amounts of estrogens), ovaries produce estradiol (& small amounts of androgens)  males  muscular development, maturity of external genitalia, facial hair, and enlargement of larynx  females  breast growth, maturity of external genitalia, maturity of uterus, and changes in fat distribution and quantity  in both  estradiol slows skeletal growth - 5-alpha-reductase deficiency: rare condition in which child is born w/ ambiguous genitalia but develops male secondary sex characteristics at puberty Hormones and Sexual Behaviour - sex hormones classified as steroids (chemicals that are synthesized from cholesterol in gonads and in lesser amounts, in adrenal glands) – figure 10.9, p.294 Regulation of Sex Hormones by the Hypothalamus and Pituitary Gland - light sensed by retina increases GnRH through action of inhibiting melatonin (neurohormone implicated in regulation of sleep and produced by nearby pineal gland)  melatonin = inhibits release of GnRH  human beings show some evidence of seasonality in birth rates - figure 10.10, p.295 – GnRH travels to anterior pituitary gland = releases LH and FSH  LH signals testes to produce testosterone; LH and FSH control menstrual cycle in females Sex Hormones and Female Behaviour - estrus: regularly occurring period of sexual desire and fertility in some mammals  only humans and old world primates exp. menstrual cycles – different from seasonal mating patterns or estrus Sexual Interest in Human Females - little if any control of hormones involved w/ ovulation - show receptivity throughout menstrual cycle, some more around time of ovulation - menopause and surgical removal  little effect on sexual interest and activity - testosterone lvls = greatest impact Estrogens and Cognition - figure 10.12, p.298 – best scores when testosterone lvls were high, worst when estrogen lvls were high - verbal fluency and manual dexterity correlated w/ higher lvls of estrogens - males slight advantage in spatial tasks; females = verbal tasks - estrogens  protective effect on memory in generaly, verbal memory in postmenopausal women  estrogen replacement therapy (ERT) helped in few years following menopause for preventing later cognitive decline (but increases risk for cardiovascular disease and cancer) Sex Hormones and Male Behaviour - androgens activate male behaviour as well – male competitiveness, sexual frequency, and cognition Androgens and Competition - testosterone lvls shown to increase in anticipation of competition  following a competition – increase in winners, decrease in losers - observing competition = influences testosterone lvls Androgens and Sexual Interest - varies from culture to culture - subjective sexual well-being depends on # of factors: equality between sexes, mental and physical health, and importance of sex to individual - if young human male’s testosterone lvl falls w/in normal limit = doesn’t provide strong predictor of sexual frequency - in older men, sexual frequency more closely correlated w/ testosterone lvls - if dramatically reduced below normal lvls at any age = significant changes in sexual behaviour - men in stable, long-term marriages = lower testosterone lvls; single men/men w/in few years of divorce = higher lvls  two explanations 1) being partnered reduces testosterone – probably due to lower lvls of competition w/ other men for mates 2) men w/ lower lvls more successful in maintaining stable relationships  evidence: longitudinal study which partnering and unparterning didn’t impact men’s testosterone lvls  subsequent study: monogamous, committed relationship = lower testosterone lvls than single or involved in multiple committed relationships  women in multiple committed relationships = higher testosterone lvls Androgens and Cognitive Behaviour - slight advantage over women in tasks involving spatial relations  appears early in childhood  research: improved performance on spatial tasks by older men receiving testosterone supplements Anabolic Steroids - male steroid supplement w/ a variety of m
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