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Chapter 27 Lecture Outline See PowerPoint Image Slides for all figures and tables pre-inserted into PowerPoint without notes. Sexuality from Different Points of View. Sexuality All of the factors that contribute to one’s female or male nature Structure and function of sex organs
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Chapter 27 Lecture Outline See PowerPoint Image Slides for all figures and tables pre-inserted into PowerPoint without notes.
Sexuality from Different Points of View • Sexuality • All of the factors that contribute to one’s female or male nature • Structure and function of sex organs • Sexual behavior • Cultural influences • Different approaches to sexuality • Behavioral • Cultural • Biological
A Spectrum of Human Sexuality • Ranges from heterosexual to homosexual • A complex trait; no one gene dictates where one falls on spectrum
Sexual Attraction, Sex and Sexual Response • Sexual attraction involves many factors, including sight and smell. • After initial attraction, the couple may engage in foreplay and sexual intercourse. • In heterosexual sex, the male achieves an erection of the penis, which allows it to be easily inserted into the female vagina. • Pelvic movements can result in ejaculation, which allows for release of sperm and other fluids (semen) from the penis, and is accompanied by a pleasurable sensation called orgasm. • Females often also experience orgasm. • Maintaining an active sex-life in a long-term relationship requires effort.
Moving Across the Spectrum • Pseudo-hermaphrodites • Humans born with partial development of both male and female genitalia • Due to a hormonal imbalance during embryonic development • Gender must be “chosen” and genitalia surgically altered to become completely female or completely male
Moving Across the Spectrum • Gender dysphoria • When one’s physical and psychological gender do not match • A male who “feels” like a woman, or vice versa • Frequently these individuals dress and act as members of the opposite sex (cross-dressers or transvestites). • Often leads to gender-reassignment surgery (sex-change)
Nature or Nurture? • Studies show that • A small region of the hypothalamus is of similar size in trans-gendered males as it is in women, and in trans-gendered females as it is in men. • Similar studies show differences in brain structure between homosexuals and heterosexuals. • Not confirmed • Complicated because homosexual brain donors were HIV+ and had been on antiviral drugs • Genes on chromosomes 7, 8 and 10 have been suggested to influence homosexuality. • Homosexuality is a complex behavioral pattern.
Chromosomal Determination of Sex and Early Development • 2 of the 46 human chromosomes are involved in gender determination • Called sex chromosomes • X and Y • Are not truly homologous because they contain different sets of information • X carries more information than just that needed for gender determination. • Blood-clotting, color vision, etc. • Y carries only information regarding maleness. • Contains SRY (Sex-determining Y) gene • SRY encodes for testes determining factor (TDF) • The presence of this gene leads to the development of a male; the absence leads to the development of a female.
Chromosomal Determination of Sex • Eggs carry 22 autosomes and an X. • Sperm carry 22 autosomes and either a Y or an X. • If an X sperm fertilizes an egg, a female is formed (XX). • If a Y sperm fertilizes an egg, a male is formed (XY). • Embryos become truly male or female during differentiation. • When embryonic gonads develop into ovaries or testes • The presence of SRY will lead to the development of testes.
Chromosomal Abnormalities and Sex • Turner’s syndrome (XO) • Results from a nondisjunction in one parent • Make egg or sperm that lack a sex chromosome. • When this gamete is used during fertilization, the individual ends up with only one sex chromosome, in this case, an X. • Symptoms • Abnormally short • Failure to complete sexual maturity • Thickened neck • Hearing impairment • Cardiovascular problems • Sterility
Chromosomal Gender Disorders • Klinefelter’s syndrome (XXY) • Also results from a nondisjunction in one parent • Leads to the development of gametes with two sex chromosomes • After fertilization, the individual has three sex chromosomes. • Symptoms • Sterility • Breast enlargement • Incomplete masculine development • Lack of facial hair • Minor learning problems
Fetal Development and Sex • Development of gonads begins about week 5. • Males • Between weeks 5-7 testes determining factor made from the SRY gene begins the differentiation of male gonads. • Week 8, testes begin making testosterone. • Testosterone leads to the differentiation of male sexual anatomy (penis, etc.). • In the 7th month, testes move through the inguinal canal to the external sac. • If this canal opens again later in life, an inguinal hernia can result. • Cryptorchidism • Failure of testes to descend • Can lead to sterility unless corrected
Fetal Development and Sex • Females • Ovaries develop about week 12 in the absence of TDF. • The absence of testosterone leads to the differentiation of female sexual anatomy (vagina, etc.).
Sexual Maturation in Young Adults • Puberty is the developmental period when: • The body changes to the adult form. • The body becomes sexually mature and able to produce offspring. • Usually occurs between 12-14 years old
The Maturation of Females • At 9-12 years of age • The hypothalamus, pituitary, ovaries and adrenal glands begin producing sex hormones. • Hypothalamus and pituitary gland • Hypothalamus releases gonadotropin-releasing hormone (GnRH) • GnRH stimulates the pituitary to release luteinizing hormone (LH) and follicle-stimulating hormone (FSH). • FSH stimulates the development of follicles in the ovary. • LH stimulates the ovary to produce more estrogen.
The Maturation of Females • Estrogen stimulates secondary sex characteristics. • Growth of breast tissue • Maturation of the uterus and vagina • Increased blood supply to the clitoris • The clitoris is a small, elongated erectile structure located at the head of the labia. It is equivalent to the penis. • Changes in pelvic bone structure • Production of androgens by adrenal gland • Leads to the growth of pubic hair • Influence female sex drive • Involved in the production of acne
The Maturation of Females • During puberty, females begin to experience the menstrual cycle. • LH from the pituitary causes the egg to be released from the follicle in the ovary (ovulation). • The ruptured follicle becomes the corpus luteum. • Begins releasing progesterone • Progesterone maintains the lining of the uterus. • When uterine lining breaks down, menstruation occurs.
The Maturation of Males • Between 11-14 years of age in males, the hypothalamus releases GnRH. • Like in females, GnRH stimulates the pituitary to release LH and FSH. • LH is also called interstial cell-stimulating hormone (ICSH) in males. • LH stimulates the production of testosterone by the testes. • FSH stimulates the production of sperm cells.
The Maturation of Males • Testosterone stimulates the development of male secondary sex characteristics. • Increased size of the penis • Growth of testes and scrotum • Growth of pubic hair • Facial and body hair • Larynx changes shape, leading to the deepening of the male voice • Increased height • Body shape changes (broad shoulders, more muscles)
The Maturation of Males • Semen production • Mixture of sperm and secretions released during ejaculation • Involves seminal vesicles, prostate gland, and bulbo-urethral gland • Seminal vesicles secrete an alkaline fluid that contains fructose and hormones. • Alkaline fluid neutralizes the acidic nature of the female reproductive tract. • Fructose is fuel for the sperm. • Prostate gland produces a thin milky fluid containing sperm-activating hormones. • Bulbo-urethral gland produces alkaline secretions.
Gametogenesis • The process of producing gametes • Spermatogenesis is the process of producing sperm, the male gamete. • Involves meiosis
Spermatogenesis • Takes place in the seminiferous tubules of the testes • The seminiforous tubules converge and become the epididymis. • Sperm are stored here and mature prior to ejaculation. • The epididymis leads into the vas deferens (sperm duct). • The vas deferens empties into the urethra. • Conducts sperm out of the body through the penis
Spermatogenesis • After puberty the cells in the seminiferous tubules begin to undergo meiosis. • Meiosis I produces two haploid cells. • Meiosis II produces four spermatids. • Spermatids lose most of their cytoplasm and develop long tails and mature into sperm.
Spermatogenesis • Sperm • Have only a small amount of food • Very active when released • Live about 72 hours • Can be deactivated and frozen for use in artificial insemination • Are produced throughout the life of a male • Normal males produce about 150 million sperm/ml.
Oogenesis • Oogenesis is the production of egg cells in females. • Occurs via meiosis in the ovary • Begins during prenatal development of the ovary • Special cells in the ovary stop dividing by mitosis and enlarge. • These are future eggs, called primary oocytes. • They go through the early stages of meiosis and stop until after puberty.
Oogenesis • At puberty (and every month after) • FSH stimulates a primary oocyte to complete meiosis. • Meiosis I generates two cells, but one receives most of the cytoplasm. • The smaller cell is called a polar body. • The larger cell will become the egg. • Prior to ovulation, the larger cell becomes encased in a follicle.
Oogenesis • When the follicle is mature, LH stimulates it to release the egg into the fallopian tube (oviduct). • Once ruptured, the follicle becomes the corpus luteum. • The corpus luteum releases progesterone that prevents the release of more eggs. • The egg travels through the fallopian tube to the uterus. • The egg completes meiosis in the uterus after it is fertilized.
Oogenesis • If it is not fertilized, it is released from the body through the vagina during menstruation. • Since eggs begin production during embryonic development, the older a woman is, the older her eggs are. • Contributes to abnormal births that are more common in older women.
Hormonal Control of Female Sexual Cycles • Estrogen and progesterone stimulate changes in the female body that will support a pregnancy. • Growth of uterine lining • Milk production in breasts • If fertilization does not occur, menstruation results. • Lining of uterus breaks down and is released (menses) • Once shed, the lining begins to build back up again. • This cycle happens about once a month.
Menstruation is Coordinated with Ovulation • FSH causes the follicle to grow. • At the same time, the follicle releases estrogen. • This causes the uterine lining to become thicker. • After ovulation, LH stimulates the ruptured follicle to become a corpus luteum. • The corpus luteum releases progesterone. • This increases blood flow to the uterine lining. • If the egg is not fertilized, the corpus luteum will break down. • This reduces the amount of progesterone released. • Without progesterone, the uterine lining breaks down and is shed.
Hormonal Control of Fertility • Fertility drugs • Hormones given to women to stimulate the release of eggs from the ovary (ovulation) • May increase the likelihood of achieving pregnancy • May be retrieved for use in in vitro fertilization • Will often result in the release and fertilization of more than one egg • Leads to multiple implantations
Hormonal Control of Fertility • Female contraception • Estrogen and progesterone inhibits ovulation. • Can help relieve the symptoms of PMS • Male contraception • Testosterone and progesterone can temporarily turn off the production of sperm. • Newly developed
Fertilization, Pregnancyand Birth • In most women, the egg is released on day 14 of the menstrual cycle. • About 2 weeks before the next menstruation • Once released, the egg is moved into the oviduct toward the uterus. • The egg must be fertilized in the oviduct. • Sperm swarm around the egg, but only one penetrates it. • The other sperm contribute an enzyme that digests away the mucus barrier around the egg.
Fertilization • Once fertilized, the egg can complete meiosis. • The second polar body is pinched off. • The true ovum is formed. • The chromosomes from the ovum and the sperm pair up, forming a diploid zygote. • The zygote begins to divide by mitosis. • This process is called cleavage. • Produces a ball of cells called a morula • The morula continues to divide to form a blastocyst.
Pregnancy • The blastocyst travels down the oviduct and enters the uterus. • In the uterus, the blastocyst implants into the uterine lining. • The blastocyst continues to divide and the cells migrate and differentiate to form an embryo. • The embryo is contained within the amnion. • A fluid-filled sac that keeps the embryo moist • The chorion and allantois fuse with the lining of the uterus to form the placenta. • Provides nutrients to the embryo • Stimulates the corpus luteum to continue releasing progesterone • Inhibits ovulation and menstruation during pregnancy
Embryonic Development • As the embryonic cells divide, they become differentiated into specialized cell types. • Molecules from the mother provide nourishment for this process. • Harmful substances that the mother may ingest can disrupt the development of the embryo. • Alcohol, drugs, medication, viruses, etc.
