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Chapter 46 Presentation

  1. 1. Chapter 46 Animal Reproduction
  2. 2. Overview: Pairing Up for Sexual Reproduction Each earthworm produces sperm and eggs; in a few weeks, new worms will hatch from fertilized eggs Animal reproduction takes many forms Aspects of animal form and function can be viewed broadly as adaptations contributing to reproductive success
  3. 3. Fig. 46-1
  4. 4. Concept 46.1: Both asexual and sexual reproduction occur in the animal kingdom Sexual reproduction is the creation of an offspring by fusion of a male gamete ( sperm ) and female gamete ( egg ) to form a zygote Asexual reproduction is creation of offspring without the fusion of egg and sperm
  5. 5. Mechanisms of Asexual Reproduction Many invertebrates reproduce asexually by fission , separation of a parent into two or more individuals of about the same size Video: Hydra Budding
  6. 6. Fig. 46-2
  7. 7. In budding , new individuals arise from outgrowths of existing ones Fragmentation is breaking of the body into pieces, some or all of which develop into adults Fragmentation must be accompanied by regeneration , regrowth of lost body parts Parthenogenesis is the development of a new individual from an unfertilized egg
  8. 8. Sexual Reproduction: An Evolutionary Enigma Sexual females have half as many daughters as asexual females; this is the “twofold cost” of sexual reproduction Despite this, almost all eukaryotic species reproduce sexually
  9. 9. Fig. 46-3 Asexual reproduction Female Sexual reproduction Female Generation 1 Male Generation 2 Generation 3 Generation 4
  10. 10. Sexual reproduction results in genetic recombination, which provides potential advantages: An increase in variation in offspring, providing an increase in the reproductive success of parents in changing environments An increase in the rate of adaptation A shuffling of genes and the elimination of harmful genes from a population
  11. 11. Reproductive Cycles and Patterns Ovulation is the release of mature eggs at the midpoint of a female cycle Most animals exhibit reproductive cycles related to changing seasons Reproductive cycles are controlled by hormones and environmental cues Animals may reproduce asexually or sexually, or they may alternate these methods
  12. 12. Several genera of fishes, amphibians, and lizards reproduce only by a complex form of parthenogenesis that involves the doubling of chromosomes after meiosis Asexual whiptail lizards are descended from a sexual species, and females still exhibit mating behaviors
  13. 13. Fig. 46-4 Ovary size Hormone level Behavior Estradiol Ovulation Ovulation Progesterone Time Female Male- like Female Male- like
  14. 14. Fig. 46-4a
  15. 15. Fig. 46-4b Ovary size Hormone level Behavior Estradiol Ovulation Ovulation Progesterone Time Female Male- like Female Male- like
  16. 16. Sexual reproduction is a special problem for organisms that seldom encounter a mate One solution is hermaphroditism , in which each individual has male and female reproductive systems Some hermaphrodites can self-fertilize
  17. 17. Individuals of some species undergo sex reversals Some species exhibit male to female reversal (for example, certain oysters), while others exhibit female to male reversal (for example, a coral reef fish)
  18. 18. Concept 46.2: Fertilization depends on mechanisms that bring together sperm and eggs of the same species The mechanisms of fertilization , the union of egg and sperm, play an important part in sexual reproduction In external fertilization , eggs shed by the female are fertilized by sperm in the external environment Video: Hydra Releasing Sperm
  19. 19. Fig. 46-5 Eggs
  20. 20. In internal fertilization , sperm are deposited in or near the female reproductive tract, and fertilization occurs within the tract Internal fertilization requires behavioral interactions and compatible copulatory organs All fertilization requires critical timing, often mediated by environmental cues, pheromones, and/or courtship behavior
  21. 21. Ensuring the Survival of Offspring All species produce more offspring than the environment can handle, and the proportion that survives is quite small Species with external fertilization produce more gametes than species with internal fertilization
  22. 22. Species with internal fertilization provide greater protection of the embryos and more parental care The embryos of some terrestrial animals develop in amniote eggs with protective layers Some other animals retain the embryo, which develops inside the female In many animals, parental care helps ensure survival of offspring
  23. 23. Fig. 46-6
  24. 24. Gamete Production and Delivery To reproduce sexually, animals must have systems that produce gametes In most species individuals have gonads , organs that produce gametes Some simple systems do not have gonads, but gametes form from undifferentiated tissue The most complex systems contain many sets of accessory tubes and glands that carry, nourish, and protect gametes and developing embryos
  25. 25. Most insects have separate sexes with complex reproductive systems In many insects, the female has a spermatheca in which sperm is stored during copulation
  26. 26. Fig. 46-7 Accessory gland Ejaculatory duct Testis Vas deferens Seminal vesicle Penis Ovary Oviduct Spermatheca Vagina Accessory gland (a) Male honeybee (drone) (b) Female honeybee (queen)
  27. 27. Even animals with simple body plans can have complex reproductive systems, for example parasitic flatworms
  28. 28. Fig. 46-8 Genital pore (Digestive tract) Male organs: Seminal vesicle Sperm duct (vas deferens) Vas efferens Testis Female organs: Uterus Yolk gland Yolk duct Oviduct Ovary Seminal receptacle (Excretory pore) 4 3 2 1 3 2 1
  29. 29. A cloaca is a common opening between the external environment and the digestive, excretory, and reproductive systems A cloaca is common in nonmammalian vertebrates; mammals usually have a separate opening to the digestive tract
  30. 30. Monogamy is relatively rare among animals Males and/or females of some species have evolved mechanisms to decrease the chance of their mate mating with another individual
  31. 31. Fig. 46-9 RESULTS Control; not remated Remated to wild-type males Remated to “no-sperm” males Remated to “no-ejaculate” males Percentage of females lacking sperm in spermatheca 30 20 10 0
  32. 32. Concept 46.3: Reproductive organs produce and transport gametes The following section focuses on the human reproductive system
  33. 33. Female Reproductive Anatomy The female external reproductive structures include the clitoris and two sets of labia The internal organs are a pair of gonads and a system of ducts and chambers that carry gametes and house the embryo and fetus Animation: Female Reproductive Anatomy
  34. 34. Fig. 46-10 Oviduct Ovary Uterus (Urinary bladder) (Pubic bone) Urethra (Rectum) Cervix Vagina Shaft Glans Prepuce Clitoris Labia minora Labia majora Vaginal opening Ovaries Uterus Follicles Oviduct Cervix Corpus luteum Uterine wall Endometrium Vagina
  35. 35. Fig. 46-10a (Rectum) Cervix Vagina Vaginal opening Oviduct Ovary Uterus (Urinary bladder) (Pubic bone) Urethra Clitoris Shaft Glans Prepuce Labia minora Labia majora
  36. 36. Fig. 46-10b Ovaries Oviduct Follicles Corpus luteum Uterine wall Uterus Cervix Endometrium Vagina
  37. 37. Ovaries The female gonads, the ovaries, lie in the abdominal cavity Each ovary contains many follicles , which consist of a partially developed egg, called an oocyte , surrounded by support cells Once a month, an oocyte develops into an ovum (egg) by the process of oogenesis
  38. 38. Ovulation expels an egg cell from the follicle The remaining follicular tissue grows within the ovary, forming a mass called the corpus luteum The corpus luteum secretes hormones that help to maintain pregnancy If the egg is not fertilized, the corpus luteum degenerates
  39. 39. Oviducts and Uterus The egg cell travels from the ovary to the uterus via an oviduct , or fallopian tube Cilia in the oviduct convey the egg to the uterus , also called the womb The uterus lining, the endometrium , has many blood vessels The uterus narrows at the cervix , then opens into the vagina
  40. 40. Vagina and Vulva The vagina is a thin-walled chamber that is the repository for sperm during copulation and serves as the birth canal The vagina opens to the outside at the vulva , which consists of the labia majora , labia minora , hymen , and clitoris
  41. 41. The clitoris has a head called a glans covered by the prepuce The vagina, labia minora, and clitoris are rich with blood vessels; the clitoris also has many nerve endings
  42. 42. Mammary Glands The mammary glands are not part of the reproductive system but are important to mammalian reproduction Within the glands, small sacs of epithelial tissue secrete milk
  43. 43. Male Reproductive Anatomy The male’s external reproductive organs are the scrotum and penis Internal organs are the gonads, which produce sperm and hormones, and accessory glands Animation: Male Reproductive Anatomy
  44. 44. Fig. 46-11 Seminal vesicle (behind bladder) (Urinary bladder) Prostate gland Bulbourethral gland Erectile tissue of penis Urethra Scrotum Vas deferens Epididymis Testis Seminal vesicle (Urinary bladder) (Urinary duct) (Rectum) Vas deferens Ejaculatory duct Prostate gland Bulbourethral gland Vas deferens Epididymis Testis Scrotum (Pubic bone) Erectile tissue Urethra Glans Prepuce Penis
  45. 45. Fig. 46-11a Seminal vesicle (behind bladder) Urethra Scrotum (Urinary bladder) Prostate gland Bulbourethral gland Erectile tissue of penis Vas deferens Epididymis Testis
  46. 46. Fig. 46-11b Seminal vesicle (Rectum) Vas deferens Ejaculatory duct Prostate gland Bulbourethral gland Vas deferens Epididymis Testis Scrotum (Urinary bladder) (Urinary duct) (Pubic bone) Erectile tissue Urethra Glans Prepuce Penis
  47. 47. Testes The male gonads, or testes , consist of highly coiled tubes surrounded by connective tissue Sperm form in these seminiferous tubules Leydig cells produce hormones and are scattered between the tubules Production of normal sperm cannot occur at the body temperatures of most mammals
  48. 48. The testes of many mammals are held outside the abdominal cavity in the scrotum , where the temperature is lower than in the abdominal cavity
  49. 49. Ducts From the seminiferous tubules of a testis, sperm pass into the coiled tubules of the epididymis During ejaculation , sperm are propelled through the muscular vas deferens and the ejaculatory duct , and then exit the penis through the urethra
  50. 50. Accessory Glands Semen is composed of sperm plus secretions from three sets of accessory glands The two seminal vesicles contribute about 60% of the total volume of semen The prostate gland secretes its products directly into the urethra through several small ducts The bulbourethral glands secrete a clear mucus before ejaculation that neutralizes acidic urine remaining in the urethra
  51. 51. Penis The human penis is composed of three cylinders of spongy erectile tissue During sexual arousal, the erectile tissue fills with blood from the arteries, causing an erection The head of the penis has a thinner skin covering than the shaft, and is more sensitive to stimulation
  52. 52. Human Sexual Response Two reactions predominate in both sexes: Vasocongestion , the filling of tissue with blood Myotonia , increased muscle tension The sexual response cycle has four phases: excitement, plateau, orgasm, and resolution Excitement prepares the penis and vagina for coitus (sexual intercourse)
  53. 53. Direct stimulation of genitalia maintains the plateau phase and prepares the vagina for receipt of sperm Orgasm is characterized by rhythmic contractions of reproductive structures In males, semen is first released into the urethra and then ejaculated from the urethra In females, the uterus and outer vagina contract
  54. 54. During the resolution phase, organs return to their normal state and muscles relax
  55. 55. Concept 46.4: The timing and pattern of meiosis in mammals differ for males and females Gametogenesis , the production of gametes by meiosis, differs in females and males Sperm are small and motile and are produced throughout the life of a sexually mature male Spermatogenesis is production of mature sperm
  56. 56. Fig. 46-12a Epididymis Seminiferous tubule Testis Cross section of seminiferous tubule Sertoli cell nucleus Primordial germ cell in embryo Mitotic divisions Spermatogonial stem cell Mitotic divisions Mitotic divisions Spermatogonium Primary spermatocyte Meiosis I Meiosis II Secondary spermatocyte Lumen of seminiferous tubule Plasma membrane Tail Neck Midpiece Head Mitochondria Nucleus Acrosome Spermatids (at two stages of differentiation) Early spermatid Differentiation (Sertoli cells provide nutrients) Sperm 2 n 2 n 2 n n n n n n n n n n n
  57. 57. Fig. 46-12b Epididymis Seminiferous tubule Sertoli cell nucleus Testis Cross section of seminiferous tubule Spermatogonium Primary spermatocyte Secondary spermatocyte Spermatids (two stages) Sperm Lumen of seminiferous tubule
  58. 58. Fig. 46-12c Primordial germ cell in embryo Mitotic divisions Spermatogonial stem cell Mitotic divisions Spermatogonium Mitotic divisions Primary spermatocyte Meiosis I Secondary spermatocyte Meiosis II Early spermatid Differentiation (Sertoli cells provide nutrients) Sperm 2 n 2 n 2 n n n n n n n n n n n
  59. 59. Fig. 46-12d Plasma membrane Tail Neck Midpiece Head Mitochondria Nucleus Acrosome
  60. 60. Eggs contain stored nutrients and are much larger Oogenesis is development of mature oocytes (eggs) and can take many years
  61. 61. Fig. 46-12e Ovary In embryo Primordial germ cell Mitotic divisions Oogonium Mitotic divisions Primary oocyte (present at birth), arrested in prophase of meiosis I First polar body Completion of meiosis I and onset of meiosis II Secondary oocyte, arrested at metaphase of meiosis II Ovulation, sperm entry Completion of meiosis II Second polar body Fertilized egg Primary oocyte within follicle Growing follicle Mature follicle Ruptured follicle Ovulated secondary oocyte Corpus luteum Degenerating corpus luteum 2 n 2 n n n n n
  62. 62. Fig. 46-12f Ovary Primary oocyte within follicle Ruptured follicle Growing follicle Mature follicle Ovulated secondary oocyte Corpus luteum Degenerating corpus luteum
  63. 63. Fig. 46-12g Primordial germ cell Mitotic divisions Oogonium Mitotic divisions Primary oocyte (present at birth), arrested in prophase of meiosis I Completion of meiosis I and onset of meiosis II Secondary oocyte, arrested at metaphase of meiosis II First polar body Ovulation, sperm entry Completion of meiosis II Second polar body Fertilized egg 2 n 2 n n n n n In embryo
  64. 64. Spermatogenesis differs from oogenesis: In oogenesis, one egg forms from each cycle of meiosis; in spermatogenesis four sperm form from each cycle of meiosis Oogenesis ceases later in life in females; spermatogenesis continues throughout the adult life of males Oogenesis has long interruptions; spermatogenesis produces sperm from precursor cells in a continuous sequence
  65. 65. Concept 46.5: The interplay of tropic and sex hormones regulates mammalian reproduction Human reproduction is coordinated by hormones from the hypothalamus, anterior pituitary, and gonads Gonadotropin-releasing hormone (GnRH) is secreted by the hypothalamus and directs the release of FSH and LH from the anterior pituitary FSH and LH regulate processes in the gonads and the production of sex hormones
  66. 66. The sex hormones are androgens, estrogens, and progesterone Sex hormones regulate: The development of primary sex characteristics during embryogenesis The development of secondary sex characteristics at puberty Sexual behavior and sex drive
  67. 67. Hormonal Control of the Male Reproductive System FSH promotes the activity of Sertoli cells, which nourish developing sperm and are located within the seminiferous tubules LH regulates Leydig cells, which secrete testosterone and other androgen hormones, which in turn promote spermatogenesis Animation: Male Hormones
  68. 68. Fig. 46-13 Hypothalamus GnRH FSH Anterior pituitary Sertoli cells Leydig cells Inhibin Spermatogenesis Testosterone Testis LH Negative feedback Negative feedback – – –
  69. 69. Testosterone regulates the production of GnRH, FSH, and LH through negative feedback mechanisms Sertoli cells secrete the hormone inhibin , which reduces FSH secretion from the anterior pituitary
  70. 70. The Reproductive Cycles of Females In females, the secretion of hormones and the reproductive events they regulate are cyclic Prior to ovulation, the endometrium thickens with blood vessels in preparation for embryo implantation If an embryo does not implant in the endometrium, the endometrium is shed in a process called menstruation
  71. 71. Hormones closely link the two cycles of female reproduction: Changes in the uterus define the menstrual cycle (also called the uterine cycle ) Changes in the ovaries define the ovarian cycle
  72. 72. Fig. 46-14 (a) Control by hypothalamus Hypothalamus GnRH Anterior pituitary 1 Inhibited by combination of estradiol and progesterone Stimulated by high levels of estradiol Inhibited by low levels of estradiol 2 FSH LH Pituitary gonadotropins in blood (b) 6 FSH LH FSH and LH stimulate follicle to grow LH surge triggers ovulation 3 Ovarian cycle 8 (c) 7 Growing follicle Maturing follicle Corpus luteum Degenerating corpus luteum Follicular phase Ovulation Luteal phase Estradiol secreted by growing follicle in increasing amounts Progesterone and estradiol secreted by corpus luteum 4 Ovarian hormones in blood Peak causes LH surge (d) 5 Estradiol Progesterone 9 10 Estradiol level very low Progesterone and estra- diol promote thickening of endometrium Uterine (menstrual) cycle Endometrium (e) Menstrual flow phase Proliferative phase Secretory phase Days 0 5 10 14 20 25 28 | | | 15 | | | | | – – +
  73. 73. Fig. 46-14a Control by hypothalamus Inhibited by combination of estradiol and progesterone Stimulated by high levels of estradiol Inhibited by low levels of estradiol Hypothalamus GnRH Anterior pituitary FSH LH Pituitary gonadotropins in blood LH FSH FSH and LH stimulate follicle to grow LH surge triggers ovulation Ovarian cycle Growing follicle Maturing follicle Corpus luteum Degenerating corpus luteum Follicular phase Ovulation Luteal phase (a) (b) (c) Days 0 5 10 14 15 20 25 28 | | | | | | | | – – +
  74. 74. Fig. 46-14b Ovarian hormones in blood Peak causes LH surge Estradiol level very low Estradiol Progesterone Ovulation Progesterone and estra- diol promote thickening of endometrium Uterine (menstrual) cycle Endometrium 0 5 10 14 20 25 28 | | | | | | | | Days 15 Menstrual flow phase Proliferative phase Secretory phase (d) (e)
  75. 75. The Ovarian Cycle The sequential release of GnRH then FSH and LH stimulates follicle growth Follicle growth and an increase in the hormone estradiol characterize the follicular phase of the ovarian cycle The follicular phase ends at ovulation, and the secondary oocyte is released Animation: Ovulation
  76. 76. Following ovulation, the follicular tissue left behind transforms into the corpus luteum; this is the luteal phase The corpus luteum disintegrates, and ovarian steroid hormones decrease Animation: Post Ovulation
  77. 77. The Uterine (Menstrual) Cycle Hormones coordinate the uterine cycle with the ovarian cycle Thickening of the endometrium during the proliferative phase coordinates with the follicular phase Secretion of nutrients during the secretory phase coordinates with the luteal phase Shedding of the endometrium during the menstrual flow phase coordinates with the growth of new ovarian follicles
  78. 78. A new cycle begins if no embryo implants in the endometrium Cells of the uterine lining can sometimes migrate to an abnormal, or ectopic , location Swelling of these cells in response to hormone stimulation results in a disorder called endometriosis
  79. 79. Menopause After about 500 cycles, human females undergo menopause , the cessation of ovulation and menstruation Menopause is very unusual among animals Menopause might have evolved to allow a mother to provide better care for her children and grandchildren
  80. 80. Menstrual Versus Estrous Cycles Menstrual cycles are characteristic of humans and some other primates: The endometrium is shed from the uterus in a bleeding called menstruation Sexual receptivity is not limited to a timeframe
  81. 81. Estrous cycles are characteristic of most mammals: The endometrium is reabsorbed by the uterus Sexual receptivity is limited to a “heat” period The length and frequency of estrus cycles varies from species to species
  82. 82. Concept 46.6: In placental mammals, an embryo develops fully within the mother’s uterus An egg develops into an embryo in a series of predictable events
  83. 83. Conception, Embryonic Development, and Birth Conception , fertilization of an egg by a sperm, occurs in the oviduct The resulting zygote begins to divide by mitosis in a process called cleavage Division of cells gives rise to a blastocyst , a ball of cells with a cavity
  84. 84. Fig. 46-15 Ovary Uterus Endometrium (a) From ovulation to implantation (b) Implantation of blastocyst Cleavage Fertilization Ovulation Cleavage continues The blastocyst implants Trophoblast Inner cell mass Cavity Blastocyst Endo- metrium 1 2 3 4 5
  85. 85. After blastocyst formation, the embryo implants into the endometrium The embryo releases human chorionic gonadotropin (hCG) , which prevents menstruation Pregnancy , or gestation , is the condition of carrying one or more embryos in the uterus Duration of pregnancy in other species correlates with body size and maturity of the young at birth
  86. 86. Pregnancies can terminate spontaneously due to chromosomal or developmental abnormalities An ectopic pregnancy occurs when a fertilized egg begins to develop in the fallopian tube
  87. 87. First Trimester Human gestation can be divided into three trimesters of about three months each The first trimester is the time of most radical change for both the mother and the embryo During implantation, the endometrium grows over the blastocyst
  88. 88. During its first 2 to 4 weeks, the embryo obtains nutrients directly from the endometrium Meanwhile, the outer layer of the blastocyst, called the trophoblast , mingles with the endometrium and eventually forms the placenta Blood from the embryo travels to the placenta through arteries of the umbilical cord and returns via the umbilical vein
  89. 89. Fig. 46-16 Placenta Uterus Umbilical cord Chorionic villus, containing fetal capillaries Maternal blood pools Maternal arteries Maternal veins Maternal portion of placenta Fetal arteriole Fetal venule Umbilical cord Fetal portion of placenta (chorion) Umbilical arteries Umbilical vein
  90. 90. Splitting of the embryo during the first month of development results in genetically identical twins Release and fertilization of two eggs results in fraternal and genetically distinct twins
  91. 91. The first trimester is the main period of organogenesis , development of the body organs All the major structures are present by 8 weeks, and the embryo is called a fetus
  92. 92. Changes occur in the mother Growth of the placenta Cessation of ovulation and the menstrual cycle Breast enlargement Nausea is also very common
  93. 93. Fig. 46-17 (a) 5 weeks (b) 14 weeks (c) 20 weeks
  94. 94. Fig. 46-17a (a) 5 weeks
  95. 95. Fig. 46-17b (b) 14 weeks
  96. 96. Fig. 46-17c (c) 20 weeks
  97. 97. Second Trimester During the second trimester The fetus grows and is very active The mother may feel fetal movements The uterus grows enough for the pregnancy to become obvious
  98. 98. Third Trimester During the third trimester, the fetus grows and fills the space within the embryonic membranes A complex interplay of local regulators and hormones induces and regulates labor , the process by which childbirth occurs
  99. 99. Fig. 46-18 Estradiol Oxytocin from ovaries Induces oxytocin receptors on uterus from fetus and mother’s posterior pituitary Stimulates uterus to contract Stimulates placenta to make Prostaglandins Stimulate more contractions of uterus Positive feedback + +
  100. 100. Fig. 46-19-1 Placenta Umbilical cord Uterus Cervix Dilation of the cervix 1
  101. 101. Fig. 46-19-2 Expulsion: delivery of the infant 2
  102. 102. Fig. 46-19-3 Delivery of the placenta Uterus Placenta (detaching) Umbilical cord 3
  103. 103. Fig. 46-19-4 3 2 1 Dilation of the cervix Placenta Umbilical cord Uterus Cervix Expulsion: delivery of the infant Uterus Placenta (detaching) Umbilical cord Delivery of the placenta
  104. 104. Birth, or parturition, is brought about by a series of strong, rhythmic uterine contractions First the baby is delivered, and then the placenta Lactation , the production of milk, is unique to mammals
  105. 105. Maternal Immune Tolerance of the Embryo and Fetus A woman’s acceptance of her “foreign” offspring is not fully understood It may be due to suppression of the immune response in her uterus
  106. 106. Contraception and Abortion Contraception , the deliberate prevention of pregnancy, can be achieved in a number of ways Contraceptive methods fall into three categories: Preventing release of eggs and sperm Keeping sperm and egg apart Preventing implantation of an embryo
  107. 107. A health-care provider should be consulted for complete information on the choice and risks of contraception methods
  108. 108. Fig. 46-20 Male Female Method Event Event Method Production of sperm Production of primary oocytes Vasectomy Combination birth control pill (or injection, patch, or vaginal ring) Sperm transport down male duct system Oocyte development and ovulation Abstinence Condom Coitus interruptus (very high failure rate) Abstinence Sperm deposited in vagina Capture of the oocyte by the oviduct Tubal ligation Female condom Sperm movement through female reproductive tract Transport of oocyte in oviduct Spermicides; diaphragm; cervical cap; progestin alone (as minipill, implant, or injection) Meeting of sperm and oocyte in oviduct Union of sperm and egg Morning-after pill; intrauterine device (IUD) Implantation of blastocyst in endometrium
  109. 109. The rhythm method , or natural family planning , is to refrain from intercourse when conception is most likely; it has a pregnancy rate of 10–20% Coitus interruptus, the withdrawal of the penis before ejaculation, is unreliable Barrier methods block fertilization with a pregnancy rate of less than 10% A condom fits over the penis A diaphragm is inserted into the vagina before intercourse
  110. 110. Intrauterine devices are inserted into the uterus and interfere with fertilization and implantation; the pregnancy rate is less than 1% Female birth control pills are hormonal contraceptives with a pregnancy rate of less than 1%
  111. 111. Sterilization is permanent and prevents the release of gametes Tubal ligation ties off the oviducts Vasectomy ties off the vas deferens Abortion is the termination of a pregnancy Spontaneous abortion, or miscarriage, occurs in up to one-third of all pregnancies The drug RU486 results in an abortion within the first 7 weeks of a pregnancy
  112. 112. Modern Reproductive Technologies Recent advances are addressing reproductive problems
  113. 113. Detecting Disorders During Pregnancy Amniocentesis and chorionic villus sampling are invasive techniques in which amniotic fluid or fetal cells are obtained for genetic analysis Noninvasive procedures usually use ultrasound imaging to detect fetal condition Genetic testing of the fetus poses ethical questions and can present parents with difficult decisions
  114. 114. Treating Infertility Modern technology can provide infertile couples with assisted reproductive technologies In vitro fertilization (IVF) mixes eggs with sperm in culture dishes and returns the embryo to the uterus at the 8 cell stage Sperm are injected directly into an egg in a type of IVF called intracytoplasmic sperm injection (ICSI)
  115. 115. Video: Ultrasound of Human Fetus 1 Video: Ultrasound of Human Fetus 2
  116. 116. Fig. 46-UN1 Gametogenesis Spermatogenesis Oogenesis Primary spermatocyte Primary oocyte Polar body Secondary spermatocytes Secondary oocyte Spermatids Sperm Polar body Fertilized egg n 2 n 2 n n n n n n n n n n n n n n
  117. 117. Fig. 46-UN2
  118. 118. You should now be able to: Distinguish between asexual and sexual reproduction Explain how hermaphroditism may be advantageous to animals that have difficulty encountering a member of the opposite sex Describe various ways in which animals may protect developing embryos Using diagrams, identify and state the function of each component of the male and female reproductive systems
  119. 119. Describe oogenesis and spermatogenesis; describe three major differences between them Explain how the uterine and ovarian cycles are synchronized and describe the functions of the hormones involved List the various methods of contraception, how each works, and how effective each is Describe techniques that allow us to learn about the health and genetics of a fetus