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Chapter 10

PSYB64 chapter 10

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Pare, Dwayne

PSYB64 – Chapter 10: Sexual Behavior Sexual Development  The fetus is initially undifferentiated in regard to sex (without exposure to male hormones, all babies would be born with female physical appearance and behavior) Sex Chromosome Abnormalities  Turner Syndrome – a condition in which a child receives only a single X chromosome from the parent o From this we have learned that a single X chromosome carries enough genetic material to produce a person who is normal but because he/she lacks the second chromosome, the person faces difficulties in growth, fertility, hormone production, risk of diabetes, osteoporosis, and cardiovascular disease o Individuals with this disease have normal female genitalia but the ovaries develop abnormally  Unidentified regions on the X chromosome are responsible for development of ovaries but having only 1 X chromosome interferes in this process  In most cases, the ovaries don’t produce either the ova or normal levels of female hormones which leads to infertility but when the X chromosome is missing in some but not all cells, women may be fertile  Women with Turner syndrome are short and may have increased skin folds at the neck; intelligence is normal but specific deficits in spatial relationships and memory can occur  Klinefelter Syndrome – it is the most common genetic abnormality related to sex chromosomes and features an XXY genotype o These individuals are male but experience reduced fertility and require hormone treatment at puberty to promote the development of secondary make sex characteristics and to inhibit female characteristics o The process of X-inactivation is also disturbed, leading to other symptoms o It is associated with normal intelligence along with cognitive deficits and social awkwardness o Delayed, reduced verbal skills, left-handedness, brain lateralization is affected along with localization of specific functions  An XYY genotype has also been identified (1/1000 births) in which boys appear to be physically within typical limits although they tend to be somewhat taller and leaner, suffer from acne, and have a higher risk for minor injuries o IQ scores are lower than average o The men are fertile but they have a higher chance of producing sperm with sex chromosome abnormalities  A report has suggested that individuals with XYY genotype were overrepresented in prison Three Stages of Prenatal Development  3 distinct phases of development: o Development of gonads o Development of internal organs o Development of external genitalia  Normally, all 3 processes occur congruently to produce an unambiguous male or female but in a rare condition called intersex, elements of both male and female development occurs in the same fetus  The Development of the Gonads o Up until 6 weeks of conception, male and female fetuses have the same gonads with the capacity to either develop into ovaries or testes o After the 6 weeks, the sex determining region of the Y chromosome (SRY) is expressed in male embryos o SRY encodes the Testis-determining factor protein which causes the gonads to develop into testes o In female embryos, there is no SRY gene or testis-determining factor protein so alternate genes guide the formation of the ovaries  Differentiation of the Internal Organs o In about the 3 month of development, both males and females fetuses possess a male Wolffian system and a female Mullerian system o In males, the Wolffian system develops into seminal vesicles, vas deferens and the prostate o In females, the Mullerian system develops into the uterus, upper portion of vagina and fallopian trdes o During the 3 month, the male’s testes begin to secrete testosterone (promotes development of Wolffian system) and anti-Mullerian hormone (initiates degeneration of the Mullerian system) o In the female fetus, no additional hormones are required for development; the ovaries are not active during fetal development; the Mullerian system will just develop in the typical female direction but the nonfunctional remnants of the Wolffian system still remain throughout a woman’s life o Androgen insensitivity syndrome (AIS) is a defective gene that produces abnormal androgen receptors and disrupts the normal development of the Wolffian system in males o In AIS, the fetus’s tissues are blind to the presence of androgens o Fetuses with AIS have an XY genotype and normal testes and the testes release androgens and the anti-Mullerian hormone in a normal manner but the lack of functional androgen receptors prevents the development of the Wolffian system o The anti-Mullerian hormone still works normally, so the female Mullerian system also fails to develop o Adult individuals with AIS are infertile, their external appearance is quite typically female o Individuals with AIS are genetic males but typically have female appearance and strong female gender identities o AIS might be an advantage for women in sports  Development of the External Genitalia o Happens during the 6 week after conception o No hormonal activity is required in order to develop female external genitalia o 5-alpha-dihydrotestosterone must be recognized by receptor sites for the male external genitalia to develop normally o The absence of 5-alpha-dihydrotestosterone leads the immature genitalia to develop in the female pattern o If genetic females are exposed to excess androgens prenatally, their external genitalia become masculinized (congenital adrenal hyperplasia CAH) o CAH is a recessive heritable condition in which the fetus’s adrenal glands release high levels of androgens o Males with CAH don’t show observable effects since they are already exposed to high levels of androgens but for females it is obvious because the clitoris is enlarged, the labia resemble the scrotum and sometimes there is no vaginal opening. They describe themselves as tomboys, engage in more male-interest play and are more likely to engage in bisexual and lesbian behavior o However, the majority of women with CAH are heterosexual and the majority of bisexual and lesbian women DO NOT have CAH or any similar condition Development at Puberty  At puberty, additional hormonal events lead to maturation of the genitals and the development of secondary sex characteristics  The average age of puberty has dropped from age 16 to 12 possibly because of increased rates of obesity (accumulation of enough body fat to support reproduction might serve as a signal for puberty)  All edible tissues from animals contain a type of estrogen called estradiol which can also trigger early puberty  Consumption of treated meat can also increase exposure to estrogens by 40%  At the onset of puberty, gonadotropin-releasing hormone (GnRH  ) is released by the hypothalamus which causes the release of follicle-stimulating hormone (FSH) and luteinizing hormone (LH)  Both males and females release the same hormones but with different effects  In response to FSH and LH, the testes produce more testosterone and the ovaries produce estradiol  The testes also small amounts of estrogen and the ovaries produce a small amount of testosterone  In males, the burst of androgens stimulates muscular development, maturity of external genitalia, facial hair and a deeper voice (enlarged larynx)  Testosterone regulates the production of sperm and affects a male’s hairline and can result in baldness later in adulthood  In both sexes, estradiol slows down skeletal growth  5-alpha-reductase deficiency is a condition that affects the maturation of external genitalia and affects the male’s ability to produce 5-alpha-reductase which converts testosterone into 5- alpha-dihydrotestosterone o 5-alpha-dihydrotestosterone is responsible for the masculinization of the external genitalia in the fetus o Without sufficient 5-alpha-reductase, these individuals are born with ambiguous external genitalia and are raised as females o Development of male internal sexual structures is not affected because this process is governed by unconverted testosterone Hormones and Sexual Behavior  Sex hormones organize circuits in the brain that differ according to sex and these circuits are activated by the sex hormones at the onset of puberty  Sex hormones are classified as steroids  Males and females both produce androgens and estrogens but in different amounts Regulation of Sex Hormones by the Hypothalamus and Pituitary Gland  Hypothalamus exerts control over release of sex hormones through secretion of GnRH  Light sensed by the retina increases GnRH secretion through its action on melatonin which normally inhibits the release of GnRH, and light in turn inhibits melatonin which is secreted at night  Light increases GnRH release by reducing the inhibition normally produced by melatonin  In non-human species, the response of the hypothalamus to light provides means for producing offspring at the right time of year (humans also show some evidence of seasonality in birth rates)  GnRH secreted by the hypothalamus travels to the anterior pituitary gland which in turn releases FSH and LH  The initial release of these hormones is associated with the onset of puberty and from puberty on, the gonadotropins continue to play a major role in fertility  In males, LH signals the testes to produce testosterone  Both testosterone and FSH are required for the maturation of sperm  In females, LH and FSH control the menstrual cycle The Menstrual Cycle and Female Fertility  On the first day of menstruation, the anterior pituitary gland increases secretion of FSH and when this circulates around the ovaries, they develop follicles (cluster of cells each with an egg cell, ovum)  One follicle develops more rapidly than the others and it releases estrogens that inhibit the growth of the other follicles but if more than one follicle is matured, the ova will fertilize and produce fraternal twins  Estrogens give feedback to the hypothalamus and pituitary gland which respond by increasing release of LH which in turn causes ovulation (release of the ovum)  Estradiol is released by the ovaries signals the uterus to thicken in anticipation of fertilized embryo  After the release of the ovum, the ruptured follicle is called the corpus luteum and that releases estradiol and progesterone  Progesterone promotes pregnancy by preventing the development of additional follicles and by further developing the lining of the uterus  When the levels of these hormones drops, the uterine lining cannot be maintained and menstruation starts  Correlations between mood, menstruation, and childbirth o Premenstrual syndrome is characterized by physical symptoms of bloating and breast enlargement and tenderness as well as psychological symptoms of depression and irritability o Severe cases of premenstrual mood changes are diagnosed as premenstrual dysphoric disorder (PMDD) in which women experience more depression, changes in appetite, and impaired cognitive performance o Within 1 year of the delivery of a newborn, 10-15% of women experience postpartum depression in which hormones shift from the pregnant state back to normal monthly cycles o The risk of psychiatric admission was only slightly increased for the women who had recently given birth. Mothers at highest risk for postpartum depression are young, unmarried, less educated, and of lower socioeconomic status  Female Contraception o Breastfeeding suppresses GnRH which in turn interferes with the pulse of LH associated with follicle growth and ovulation o Oral contraceptives (birth control pills) work by providing hormones that interfere with normal ovulation o There are 2 types of commonly used contraceptives, combination pill (contains estrogen and progestin which prevents maturation of follicles and ovulation) and progestin-only pill (prevents thinning of cervical mucus that accompanies ovulation)  The passage of sperm into the uterus and fallopian tubes becomes less likely  Both pills act to prevent fertilized eggs from implanting in the lining of the uterus o All oral contraceptives reduce a woman’s testosterone levels o A woman’s sexual interest is influenced by her testosterone levels and a small number of women using oral contraceptives report reduced sexual drive o Emergency contraception is administered within 72 hours of intercourse o The “morning after” pill actually consists of a series of typical birth control pills taken at specified time intervals o The high hormone levels resulting from this procedure interfere with the implantation of an embryo in the uterine lining o Copper-bearing intrauterine wires are also used for emergency contraception purposes o Mifepristone (abortion pill) interrupts pregnancies up to 9 weeks following conception by blocking the action of progesterone o The risk of many reproductive cancers is reduced with each pregnancy but it’s not the pregnancy that provides the protective benefit, it’s the lack of ovulation, menstruation, and high estrogen levels associated with menstrual cycle Sex Hormones and Female Behavior  In the females of species that undergo estrus (period of time in which the female is receptive to males) hormones play an important role in determining the timing and frequency of sexual behavior  Estrus coincides with ovulation  During non-estrus periods, females will reject sexual overtures from males and also respond aggressively to any advances  Sexual interest in Human Females o Human females show receptivity throughout the menstrual cycle, although some women report feeling slight more interest in sex around time of ovulation o Menopause and surgical removal of ovaries both exert a dramatic influence on a woman’s hormone levels yet have little effect on her sexual interest and activity o A woman’s ovaries produce testosterone and estrogen and her testosterone levels have the greatest impact on her sexual activity o Women who receive standard estrogen replacement therapy following the removal of their ovaries report less satisfaction with their sex lives than before surgery (the estrogen therapy alone did not prevent negative changes in sexual interest) o After the women were given testosterone through a skin patch, they reported having sex more frequently and enjoying it more  Estrogens and Cognition o On tests of mental figure rotations, women received their best scores when testosterone levels were high and their worst scores when estrogen levels are high o Verbal fluency and manual dexterity in women appear to be correlated with higher levels of estrogens o Estrogens have a protective effect on memory in general, and verbal memory in particular, in postmenopausal women Sex Hormones and Male Behavior  Androgens and Competition o Among male collegiate athletes, testosterone levels appear to increase in anticipation of a competition o Following a competition, testosterone increases in the winners and decreases in the losers o Men cheering for the winning team show an increase in testosterone levels while men supporting the losing team experienced a decrease  Androgens and Sexual Interest o The sexual frequency of older men is more closely correlated with their testosterone levels o MPA or Depo-Provera is used as a contraceptive method for women but in larger and more frequent doses, as a form of chemical castration for male sex offenders o MPA reduces circulating testosterone levels in men to pre-puberty levels, generally eliminating any sexual activity o Men in stable, long-term marriages have lower testosterone levels than single men or men who are within a few years of divorce because there is lower levels of competition with other men for mates and also that these men are more suc
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