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Chapter 10

Chapter 10 Textbook Notes - Sexual Behaviour

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Ayesha Khan

Notes From Reading C HAPTER 10: SEXUAL BEHAVIOUR (P GS. 284-311) Sexual Development - Individual’s genetic sex begins with sex chromosomes inherited from two parents - Mothers provide X chromosome to all offspring, fathers determine the sex by providing either another X (female) or a Y (male) Sex Chromosome Abnormalities - Turner Syndrome: only one X chromosome (XO) - lack of second sex chromosome impacts fetility, growth, hormone production and is associated with higher risk of diabetes, osteoporosis, and cardiovascular disease - Normal female genitalia but ovaries develop abnormally - Klinefelter syndrome: XXY genotype - individuals are male but they usually experience reduced fertility and require hormone treatment at puberty to promote the development of secondary male sex characteristics - Associated with normal intelligence, perhaps marked by mild cognitive difficulties and social awkwardness - XYY genotype: boys appear to be physically within typical limits but tend to be taller and leaner, suffer from acne, higher risk for minor physical abnormalities - Men with this genotype are fertile, but slightly more likely to produce sperm with sex chromosome abnormalities Three Stages of Prenatal Development - Structural development has 3 processes: gonads, internal organs, external genitalia - Intersex: a condition where elements of both male and female development occur in the same fetus Development of the Gonads - Until 6 week after conception, both M and F fetuses have identical gonads that can develop into ovaries or testes - Sex-determining region of the Y chromosome (SRY): gene located on short arm of Y chromosome that encodes for testis-determining factor - Females don’t have SRY gene so alternate genes guide the development of gonads into ovaries Differentiation of the Internal Organs - Until 3 month of development, both M and F have a male Wolffian system (will develop into the seinal vesicles, vas deferens and prostate) and a female Mullerian system (will develop into the uterus, upper portion of the vagina and fallopian tubes) - During 3 month, male’s testes secrete two hormones: testosterone and anti-Mullerian hormone - Testosterone or androgen, promotes development of Wolffian system - Anti-Mullerian hormones initiates degeneration of Mullerian system - Ovaries not active during fetal development - Females don’t need additional hormones for development - Without androgens or anti-Mullerian hormone, the Mullerian system will develop in the typical female direction - Androgen insensitivity syndrome (AIS): disrupts the normal development of the Wolffian system in males - In AIS, a defective gene produces abnormal androgen receptors - Since the male fetus lacks androgen receptors, the development of female external genitalia and typically female gender identity and sexual behaviour occur Development of the External Genitalia - Male external genitalia includes the penis and scrotum Chapter Ten: Sexual Behaviour - Female external genitalia include the labia, clitoris, and outer part of the vagina - No hormonal activity for development of external genitalia in females - 5-alpha-dihydrotestosterone must be recognized by receptor sites for the male external genitalia to develop normally - If females are exposed prenatally to excess androgens, their external genitalia become masculinized - Congenital adrenal hyperplasia (CAH): a recessive heritable condition in which the fetus’s adrenal glands release elevated levels of androgens - Exposure to this in women causes an enlarged clitoris, labia look similar to scrotum, in some cases also no vaginal opening Development at Puberty - Additional hormonal events lead to maturation of the genitals and development of secondary sex characteristics - These characteristics include: - Males: facial hair and deeper voice - Females: wider hip and breast development - average age of puberty has dropped significantly over past century - When body fat is abnormally low puberty is delayed - At onset of puberty, gonadotropin-releasing hormone (GnRH) is released by hypothalamus and initiates release of two gonadotropic hormones by anterior pituitary gland: - Follicle-stimulating hormone (FSH) - Luteinizing hormone (LH) - In response to these hormones, tested begin to produce additional testosterone and ovaries produce estradiol - In males, burst of androgens stimulates: muscle development, maturity of external genitalia, facial hair, enlargement of larynx - Testosterone also regulates sperm production and affect hairline - In females, estradiol produces breast growth, maturity of external genitalia, maturity of uterus, changes in fat distribution and quantity - In both sexes, estradiol slows down skeletal growth - 5-alpha-reductase deficiency: affects males ability to to produce the enzyme 5-alpha-reductase which converts testosterone into 5-alpha-dihydrotestosterone (which is responsible for the masculinization of the external genitalia in the fetus) Hormones and Sexual Behaviour - Sex hormones are classified as steroids, chemicals that are synthesized from the cholesterol in the gonads and in lesser amount, in the adrenal glands 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 retina increases GnRH secretion through its action on melatonin - GnRH secreted by hypothalamus travels to anterior pituitary gland which releases gonadotropins, LH and FSH - In males, LH signals testes to produce testosterone - In females, LH and FSH control the menstrual cycle The Menstrual Cycle and Female Fertility - on first day of menstruation, anterior pituitary gland increases FSH secretion which in the ovaries, responds by developing follicles that contain an egg cell or ovum - One follicle develops more rapidly and releases estrogens to inhibit growth of other follicles - Estrogen from follicle provide feedback to hypothalamus and pituitary, which respond by increasing LH Notes From Reading C HAPTER 10: SEXUAL B EHAVIOUR (PGS . 284-311) - Increased LH initiates release of ovum, or ovulation, two weeks after first day of menstruation - Estradiol released by ovaries signals uterus to thicken in anticipation of a fertilized embryo - after ovum released, ruptured follicle is called corpus luteum which releases estradiol and progesterone (promotes pregnancy by preventing development of other follicles and developing lining of uterus) - If fertilization doesn’t occur, corpus luteum stops making estradiol and progesterone, hormone levels drop, uterine lining can’t be maintained, menstruation begins Correlations Between, Menstruation, and Childbirth - Premenstrual syndrome (PMS): physical symptoms of bloating, breast enlargement and tenderness, psychological symptoms of depression and irritability - Premenstrual dysphoric disorder (PMDD): more depression changes in appetite, impaired cognitive performance than women who do not suffer from PMDD - Postpartum depression: a condition in which mothers who have recently given birth experience feelings of depression due to their rapidly changing hormonal environment Female Contraception - Birth control pills work by providing hormones that interfere with normal ovulation - Combination pill: contain synthetic hormones, an estrogen and progestin, and prevents maturation of follicles and ovulation - Progestin only pill: prevents thinning of cervical mucus that typically ac
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