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Chapter 10

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Janelle Leboutillier

Chapter 10 PSYB64 Chapter 10 Sexual Behavior Introduction  Bruce Reimer was circumcised as a child  But his penis was damaged so badly, it was suggested that he be raised as a girl  He became Brenda and developed into a normal female  Even though he was having female hormone therapy, he had suspicions that he was a boy and found out his medical history  Chose to live as a man (named David) and married and women and adopted her kids  Took his own life  This story suggests that our biological sex may influence our ultimate sense of being a man or a woman more strongly than how we are raised Sexual Development  Aristotle – sex of a child was the result of the temp. of semen at the time of conception o Hot semen – males, cold semen – females  Today – individual’s genetic sex begins with sex chromosomes inherited from two parents o Mother provides X to all offspring o Father provide X for females, or Y for males (determines the sex)  X chromosome: one of two types of sex chromosomes; individuals with two X chromosomes will usually develop into females  Y chromosome: One of two types of sex chromosomes; individuals with a Y chromosome will usually develop into males  The fetus is initially undifferentiated in regard to sex o Without exposure to male hormone, all babies would be born with female physical appearance and behavior Sex Chromosome Abnormalities  In some cases, variations occur in the transmission of sex chromosomes from parent to child  There is no viable organism with a single Y chromosome  Turner Syndrome: A condition caused by an XO genotype, characterized by frequent abnormalities of the ovaries and infertility o Child only receives a single X chromosome o Described by Henry Turner o Occurs in about 1 out of 2500 live births o The single X chromosome has sufficient genetic material to produce an individual who is quite normal in many way o Lack of second sex chromosome impacts fertility, growth and hormone production o Higher risk of diabetes, osteoporosis, cardiovascular disease o Have normal female external genetilia, but ovaries develop abnormally o Unidentified regions of the X chromosome are responsible for ovary development o Missing X chromosome may have a part in this abnormality o Ovaries do not produce either ova or normal levels of female hormones, leading to infertility o Some women are usually shorter, more folds at the neck, normal intelligence but deficits in spatial relationships and memory may occur o Human growth hormone, female hormone replacement therapy and assisted reproductive technology can address these issues  Kleinfelter syndrome: A condition in males caused by an XXY genotype, characterized by frequent problems with fertility, secondary sex characteristics and verbal skills Chapter 10 PSYB64 o Male individuals but have reduced fertility and require hormone treatment at puberty to promote development of secondary male sex characteristics (deeper voice, facial hair, external genetilia development) and inhibit female characteristics (breast development) o Occur in 1.79 our of 1000 male births o X-inactivation process leads to other symptoms o Existence of XYY genotype o Occurs 1 in 1000 male births o Normal intelligence, mild cognitive difficulties, social awkwardness o Delayed and reduced verbal skills o Left-handedness is more common  Suggest the effect on brain lateralization or localization of specific functions o Taller and leaner, suffer from acne and higher risk for minor abnormalities of the eye, elbow and chest o Slightly lower IQ o More likely to produce sperm with sex chromosome abnormalities o A report suggested that extra Y chromosome would produce a violent “super male” o Have a higher rate of antisocial and criminal behavior than control participants o Studies show that is probably due to lower intelligence and no directly by genotype Three Stages of Prenatal Development  Three distinct process in male and female structural development o Development of gonads: the internal organ, ovaries in females and testes in males, that produce reproductive cells (eggs and sperm) and secrete sex hormones o Development of internal organs o Development of external genetilia: The external sexual organs, including the penis and scrotum in males and labia, clitoris and lower third of the vagina in females  Intersex: a condition in which elements of both male and female development occur in the same fetus The Development of the Gonads  Until sixth week after conception, both male and female fetuses have identical primordial gonads o Have the capacity to develop into either ovaries or testis  Ovaries: Female gonads; the source of ova and sex hormones  Testes: Male gonads; source of sperm and sex hormones  Sex – determining region of the Y chromosome (SRY): a gene located on the short arm of the Y chromosome that encodes for testis-determining factor o Activated at around six weeks after conception  Testis-determining factor: A protein encoded by the SRY gene on the Y chromosome that turns the primordial gonads into testes  Female embryos lack SRY gene and testis – determining factor o Have alternate genes that guide development of the primordial gonad into ovaries Differentiation of the Internal Organs  Differentiation of internal organs follows the development of the gonads  Until third month of development, both male and female fetuses possess male Wolffian system and female Müllerian system  Wolffian system: internal system that develops into seminal vesicles, vas deferens, and the prostate gland in males  Müllerian system: the internal system that develops into a uterus, fallopian tubes and the upper two thirds of the vagina in the absence of anti-Müllerian hormone.  Testosterone is an androgen that promotes the development of the Wolffian system  Androgen: a steroid hormone that develops and maintains masculine characteristics Chapter 10 PSYB64  Anti – Müllerian hormones initiate degeneration of the Müllerian system  Female fetus does not need any additional hormones for development  Ovaries are not active during fetal development like the testes are  Nonfunctional remnants of the Wolffian system remain throughout a woman’s life  Androgen insensitivity syndrome (AIS): A condition in which a genetic male fetus lacks androgen receptor, which leads to the development of female external genitalia and typically female gender identity and sexual behavior o Disrupts normal development of the Wolffian system in males o Defective gene produces abnormal androgen receptors o Males with AIS have an XY genotype and normal testes o Their testes release androgens and anti-Müllerian hormone in a normal manner o Lack of functional androgen lead to lack of development of Wolffian system but since anti – Müllerian hormones work, female system does not develop. o ^There will be a shallow vagina, no ovaries, fallopian tubes or uterus (only 1/3 of vagina) o Are infertile and typical appearance is quite female  Gender identity: the sense of being male or female, independent of genetic sex or physical appearance  Individuals with AIS are genetic males, but typically have female appearance and strong female gender identities o Engage in normal female sexual behavior  AIS occurs in 1 in 60 000 male births Development of the External Genitalia  Male external genitalia: penis and scrotum  Female external genitalia: labia, clitoris and outer part of the vagina  No hormonal activity is required to develop female external genitalia but males need hormonal stimulation for external genitalia  5-alpha-dihydrotestosterone: an androgen secreted by the testes that masculinizes the external genitalia o Has to be reorganized by receptor sites for male genitalia development o Made from testosterone reacting with enzyme 5-alpha-reductase  If females are exposed to excess androgen prenatally, their external genitalia become masculinized  Congenital adrenal hyperplasia (CAH): recessive heritable condition in which the fetus’s adrenal glands release elevated levels of androgens o Males with CAH show less effects than females o Females; clitoris is enlarged, labia look similar to a scrotum and in some cases, there is no vaginal opening o Females are usually tomboyish and more likely to engage in bisexual and lesbian behavior Development at Puberty  At puberty, additional hormonal events lead to maturation of genitals and secondary sex characteristics development  Age of puberty has dropped dramatically over the past century and half o May be because of increased rates of obesity  Accumulation of enough body fat to support reproduction might serve as a signal for puberty o When body fat is low (anorexia nervosa), puberty is delayed o Exposure to female hormones in meat and dairy products, shampoo, plastics, and insecticides might trigger early puberty  All edible tissue from animals contain a type estrogen called estradiol Chapter 10 PSYB64  Estrogen: A steroid hormone that develops and maintains typically female characteristics  Estradiol: an estrogen hormone synthesized primarily in the ovaries  Phthalates (compounds found in plastics and cosmetics) have been found to advance puberty in rats  Gonadotropin-releasing hormone (GnRH): a hormone released by the hypothalamus that stimulates the release of luteinizing hormone (LH) and follicle-stimulating hormone (FSH) by the anterior pituitary gland  Follicle-stimulating hormone (FSH): a hormone released by the anterior pituitary that stimulates the development of eggs in the ovaries and sperm in the testes  Luteinizing hormone (LH): a hormone released by the anterior pituitary that signals the male testes to produce testosterone and that regulates the menstrual cycle in females  FSH and LH – testes produce additional testosterone and ovaries produce estradiol o Testes also produce a small amount of estradiol and ovaries produce some androgens (incl. testosterone)  Burst of additional androgen stimulates maturity of external genitalia, facial hair, enlargement of the larynx (deeper voice), muscular development o Along with LH and FSH, testosterone regulates production of sperm o Testosterone may also result in baldness later in adulthood  Estradiol in females, produces breast growth, maturity of external genitalia, maturity of uterus and changes in fat distribution and quantity  Estradiol in both sexes slows down skeletal growth o Earlier sexual maturation  stop growing at earlier ages  5-alpha-reductase deficiency: A rare condition in which a child is born with ambiguous genitalia but develops male secondary sex characteristics at puberty o Rare condition o Lack of 5-alpha-reductase leads to insufficient conversion of testosterone into 5-alspha- dihydrotestosterone (fetus masculinization) o 60% of individuals take on male gender after puberty even though they were raised as girls Hormones and Sexual Behavior  In prenatal and early postnatal development, sex hormones organize circuits in the brain that differ according to sex  Circuits are activated by the sex hormones at the onset of puberty  Sex hormones are steroids (chemicals synthesized form cholesterol in the gonads and in lesser amounts in the adrenal glands) Regulation of Sex Hormones by the Hypothalamus and Pituitary Gland  Hypothalamus controls release of sex hormones through the secretion of gonadotropin-releasing hormone (GnRH)  Example: Light sensed by the retina increases GnRH secretion through action on melatonin o Melatonin inhibits GnRH, light inhibits melatonin which is usually secreted at night o Light increases GnRH release by reducing the inhibition that melatonin produces  In non-human species, response of hypothalamus to light provides means for producing offspring at the right time of the year; fertility is timed  Happens in humans but exact relationship is unknown between light and sexual behavior  GnRH secreted by hypothalamus travels to anterior pituitary gland o Anterior pituitary releases gonadotropins, LH and FSH o After onset of puberty gonadotropins contribute to fertility o Males – LH signals testes to produce testosterone o Females – LH and FSH control menstrual cycle Chapter 10 PSYB64 The Menstrual Cycle and Female Fertility  Menstrual cycle represents a very stable and predictable fluctuation in events controlled by LH and FSH  1 Menstruation: anterior pituitary increases FSH secretion  FSH circulates to ovaries and ovaries develop follicles (One of several clusters of cells in the ovary each of which contain an egg cell (ovum))  One follicles will develop more rapidly than others and it releases estrogens which inhibit growth of the rest of the follicles  If more that one follicle matures and ovum are fertilized, fraternal twins will develop  Fertility drugs stimulate development of follicles and ova and subsequently promote multiple births  Estrogen provides feedback to hypothalamus and pituitary gland; respond by releasing sharp levels of LH o Increases LH initiate release of ovum (ovulation); happens about two weeks after first day of the last menstruation o Released estradiol from ovaries causes uterus wall to thick in anticipation of fertilized embryo  Corpus luteum/yellow body: a yellow mass of cells in the ovary formed by a ruptured follicle that has released an egg o Releases estradiol and progesterone  Progesterone: prevents development of additional follicles and promotes growth of uterine lining; this helps start pregnancy o If fertilization does not take places, corpus luteum stops producing estradiol and progesterone  When hormone levels drop, uterine lining cannot be maintained, menstruation will start and entire cycle will repeat Correlations Between Mood, Menstruation, and Childbirth  Premenstrual syndrome: A condition in which some women experience physical and psychological symptoms immediately prior to the onset of menstruation o In response to shifts in hormone that regulate menstrual cycle  Symptoms: bloating, breast enlargement and tenderness, depression, irritability  Premenstr
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