1. © 2012 Pearson Education, Inc. Lecture by Edward J. Zalisko PowerPoint Lectures for Campbell Biology: Concepts & Connections, Seventh Edition Reece, Taylor, Simon, and Dickey Chapter 27 Reproduction and Embryonic Development

2. Introduction  Fertility drugs –increase the number of eggs that are ovulated and –have allowed thousands of infertile couples to have babies.  Ten percent of women taking fertility drugs become pregnant with more than one embryo. © 2012 Pearson Education, Inc.

3. Introduction  Newborns from multiple births are –more likely to be premature, –more likely to have lower birth weights, and –less likely to survive. © 2012 Pearson Education, Inc.

4. Figure 27.0_1 Chapter 27: Big Ideas Asexual and Sexual Reproduction Principles of Embryonic Development Human Reproduction Human Development

5. Figure 27.0_2

6. ASEXUAL AND SEXUAL REPRODUCTION © 2012 Pearson Education, Inc.

7. 27.1 Asexual reproduction results in the generation of genetically identical offspring  Asexual reproduction –is the creation of genetically identical offspring by one parent, –is a very rapid form of reproduction, and –can proceed via –budding, –fission, or –fragmentation/regeneration. © 2012 Pearson Education, Inc. Video: Hydra Budding

8. Figure 27.1A

9. Figure 27.1B

10. 27.2 Sexual reproduction results in the generation of genetically unique offspring  Sexual reproduction –is the creation of offspring by fertilization and –joins two haploid sex cells or gametes to form a diploid (2n) zygote. © 2012 Pearson Education, Inc.

11. 27.2 Sexual reproduction results in the generation of genetically unique offspring  The male gamete, the sperm, –is relatively small and –moves by means of a flagellum.  The female gamete, the egg, –is a much larger cell and –is not self-propelled. © 2012 Pearson Education, Inc.

12. 27.2 Sexual reproduction results in the generation of genetically unique offspring  Some organisms, such as sea anemones, can reproduce both –asexually and –sexually. © 2012 Pearson Education, Inc. Video: Hydra Releasing Sperm

13. Figure 27.2A Two offspring arising by fission Eggs

14. 27.2 Sexual reproduction results in the generation of genetically unique offspring  Some animals exhibit hermaphroditism in which an individual has both female and male reproductive systems.  Hermaphroditism makes it easier to find a mate for animals that are solitary or less mobile.  Hermaphrodites may –exchange gametes with other individuals or –fertilize their own eggs. © 2012 Pearson Education, Inc.

15. Figure 27.2B

16. 27.2 Sexual reproduction results in the generation of genetically unique offspring  External fertilization –occurs when eggs and sperm are discharged near each other and –is used by many fish and amphibian species.  Internal fertilization –occurs when sperm is deposited in or near the female reproductive tract and –is used by some fish and amphibian species and nearly all terrestrial animals. © 2012 Pearson Education, Inc.

17. Figure 27.2C Egg

18. HUMAN REPRODUCTION © 2012 Pearson Education, Inc.

19. 27.3 Reproductive anatomy of the human female  Both sexes in humans have –a set of gonads where gametes are produced, –ducts for gamete transport, and –structures for copulation. © 2012 Pearson Education, Inc.

20. 27.3 Reproductive anatomy of the human female  Ovaries contain follicles that –nurture eggs and –produce sex hormones.  An immature egg is ejected from the follicle in a process called ovulation. © 2012 Pearson Education, Inc. Animation: Female Reproductive Anatomy

21. 27.3 Reproductive anatomy of the human female  Oviducts convey eggs to the uterus where a fertilized egg develops.  The uterus opens into the vagina through the cervix.  The vagina –receives the penis during sexual intercourse and –forms the birth canal. © 2012 Pearson Education, Inc.

22. Figure 27.3A Follicles Oviduct Ovaries Corpus luteum Wall of uterus Endometrium (lining of uterus) Vagina Uterus Cervix (“neck” of uterus)

23. Figure 27.3B Ovary Egg cell

24. Figure 27.3C Oviduct Ovary Uterus Urinary bladder (excretory system) Pubic bone (skeletal system) Urethra (excretory system) Shaft Prepuce Glans Clitoris Vulva Labia minora Labia majora Vaginal opening Vagina Cervix Anus (digestive system) Rectum (digestive system)

25. Figure 27.3C_1 Vagina Cervix Anus (digestive system) Rectum (digestive system) Oviduct Ovary Uterus

26. Figure 27.3C_2 Oviduct Ovary Uterus Urinary bladder (excretory system) Pubic bone (skeletal system) Urethra (excretory system) Shaft Prepuce Glans Clitoris Vulva Labia minora Labia majora Vaginal opening

27. 27.4 Reproductive anatomy of the human male  Testes (singular, testis) produce –sperm and –male hormones.  The epididymis stores sperm as they develop further.  Several glands contribute to semen. These are the –seminal vesicles, –prostate gland, and –bulbourethral glands. © 2012 Pearson Education, Inc. Animation: Male Reproductive Anatomy

28. Figure 27.4A Seminal vesicle (behind bladder) Urethra Scrotum Glans of penis Testis Epididymis Vas deferens Erectile tissue of penis Bulbourethral gland Prostate gland Urinary bladder (excretory system)

29. Figure 27.4B Testicle Scrotum Testis Epididymis Vas deferens Bulbourethral gland Prostate gland Ejaculatory duct Vas deferens Seminal vesicle Rectum (digestive system) Anus (digestive system) Urinary bladder (excretory system) Pubic bone (skeletal system) Urethra (excretory system) Erectile tissue Penis Glans of penis Prepuce

30. Figure 27.4B_1 Bulbourethral gland Prostate gland Ejaculatory duct Vas deferens Seminal vesicle Rectum (digestive system) Anus (digestive system)

31. Figure 27.4B_2 Testicle Scrotum Testis Epididymis Vas deferens Urinary bladder (excretory system) Pubic bone (skeletal system) Urethra (excretory system) Erectile tissue Penis Glans of penis Prepuce

32. 27.4 Reproductive anatomy of the human male  During ejaculation –sperm is expelled from the epididymis, –the seminal vesicles, prostate, and bulbourethral glands secrete into the urethra, and –semen is formed and expelled from the penis. © 2012 Pearson Education, Inc.

33. Figure 27.4C 21 Contractions of vas deferens Contractions of seminal vesicle Contractions of prostate gland Sphincter contracts Urinary bladder Urethral region here expands and fills with semen Sphincter contracts Contractions of epididymis Sphincter remains contracted Semen expelled Contractions of muscles around base of penis Sphincter relaxes Contractions of urethra

34. 27.4 Reproductive anatomy of the human male  Sperm production –is regulated by a negative feedback system of hormones and –involves the –hypothalamus, –anterior pituitary, and –testes. © 2012 Pearson Education, Inc. Animation: Male Hormones

35. Figure 27.4D Stimuli from other areas in the brain Releasing hormone Anterior pituitary Androgen production Sperm production Hypothalamus FSH LH Testis Negative feedback

36. 27.5 The formation of sperm and egg cells requires meiosis  Spermatogenesis occurs in seminiferous tubules. –Primary spermatocytes –are formed by mitosis and –divide by meiosis I to produce secondary spermatocytes. –Secondary spermatocytes –divide by meiosis II to produce round spermatids, –spermatids differentiate into elongate sperm, and –mature sperm are released into seminiferous tubules. © 2012 Pearson Education, Inc.

37. Figure 27.5A Epididymis Penis Testis Scrotum Seminiferous tubule Testis Cross section of seminiferous tubule Diploid cell Primary spermatocyte Secondary spermatocyte (haploid) (diploid; in prophase of meiosis I ) Developing sperm cells Sperm cells Mature sperm released into center of seminiferous tubule Differentiation and onset of meiosis I Meiosis I completed Meiosis II Differentiation 2n2n 2n2n n n n n nn n nn n

38. Figure 27.5A_1 Epididymis Penis Testis Scrotum Seminiferous tubule Testis Cross section of seminiferous tubule

39. Figure 27.5A_2 Diploid cell Primary spermatocyte Secondary spermatocyte (haploid) (diploid; in prophase of meiosis I ) Developing sperm cells Sperm cells Mature sperm released into center of seminiferous tubule Differentiation and onset of meiosis I Meiosis I completed Meiosis II Differentiation 2n2n 2n2n n n n n nn n nn n

40. Figure 27.5A_3 Diploid cell Primary spermatocyte (diploid; in prophase of meiosis I ) Differentiation and onset of meiosis I Meiosis I completed 2n2n 2n2n Secondary spermatocyte (haploid) n n

41. Figure 27.5A_4 Secondary spermatocyte (haploid) Developing sperm cells Sperm cells Mature sperm released into center of seminiferous tubule Meiosis II Differentiation n n n n nn n nn n

42. 27.5 The formation of sperm and egg cells requires meiosis  Oogenesis begins before birth when a diploid cell in each developing follicle begins meiosis. –Each month about one primary oocyte resumes meiosis. –A secondary oocyte arrested at metaphase of meiosis II is ovulated. –Meiosis of the ovum is completed after fertilization. © 2012 Pearson Education, Inc.

43. Figure 27.5B Ovary Before birth Diploid cell Differentiation and onset of meiosis I Primary oocyte (arrested in prophase of meiosis I ; present at birth) Primary oocyte within follicle Growing follicle Mature follicle Completion of meiosis I and onset of meiosis II Ovulated secondary oocyte Corpus luteum Degenerating corpus luteum First polar body Secondary oocyte Entry of sperm triggers completion of meiosis II Second polar body Mature egg (ovum) (arrested at metaphase of meiosis II ; released from ovary) Ruptured follicle

44. Figure 27.5B_1 Ovary Before birth Diploid cell Differentiation and onset of meiosis I Primary oocyte (arrested in prophase of meiosis I ; present at birth) Primary oocyte within follicle

45. Figure 27.5B_2 Growing follicle Mature follicle Completion of meiosis I and onset of meiosis II Ovulated secondary oocyte First polar body Secondary oocyte (arrested at metaphase of meiosis II ; released from ovary) Ruptured follicle

46. Figure 27.5B_3 Ovulated secondary oocyte First polar body Secondary oocyte (arrested at metaphase of meiosis II ; released from ovary) Ruptured follicle Corpus luteum Degenerating corpus luteum Entry of sperm triggers completion of meiosis II Second polar body Mature egg (ovum)

47. 27.5 The formation of sperm and egg cells requires meiosis  Oogenesis and spermatogenesis are –alike in that both produce haploid gametes but –different in that –oogenesis produces only one mature egg and polar bodies that degenerate and –spermatogenesis produces four mature gametes. © 2012 Pearson Education, Inc.

48. 27.6 Hormones synchronize cyclic changes in the ovary and uterus  About every 28 days –the hypothalamus signals the anterior pituitary to secrete follicle-stimulating hormone (FSH) and luteinizing hormone (LH), –which trigger the growth of a follicle and ovulation, the release of an egg. © 2012 Pearson Education, Inc.

49. Table 27.6

50. 27.6 Hormones synchronize cyclic changes in the ovary and uterus  After ovulation, the ovarian follicle becomes the corpus luteum.  The corpus luteum secretes estrogen and progesterone, which –stimulate the endometrium to thicken, –prepare the uterus for implantation of the embryo, and –inhibit the hypothalamus, reducing FSH and LH secretion. © 2012 Pearson Education, Inc. Animation: Post Ovulation Animation: Ovulation

51. 27.6 Hormones synchronize cyclic changes in the ovary and uterus  If the egg is fertilized –the embryo releases hormones that maintain the uterine lining and –menstruation does not occur.  If the egg is not fertilized –the drop in LH shuts down the corpus luteum and its hormones, –menstruation is triggered, and –the hypothalamus and pituitary stimulate development of a new follicle. © 2012 Pearson Education, Inc.

52. Figure 27.6 Control by hypothalamus A Hypothalamus Anterior pituitary Releasing hormone Inhibited by combination of estrogen and progesterone Stimulated by high levels of estrogen FSH LH 14625378 B C FSH LH Pituitary hormones in blood LH peak triggers ovulation and corpus luteum formation FSH stimulates follicle to grow LH surge triggers ovulation Ovarian cycle Pre-ovulatory phasePost-ovulatory phase Ovulation Growing follicle Mature follicle Corpus luteum Degenerating corpus luteum D E Estrogen secreted by growing follicle Progesterone and estrogen secreted by remnant of follicle Ovarian hormones in blood Peak causes LH surge Estrogen Progesterone Low levels of estrogen trigger menstruation Progesterone and estrogen promote thickening of endometrium Menstrual cycle Endometrium Menstruation Days 05101415202528

53. Figure 27.6_1 Control by hypothalamus Hypothalamus Anterior pituitary Releasing hormone Inhibited by combination of estrogen and progesterone Stimulated by high levels of estrogen FSH LH

54. Figure 27.6_2 Days 0 5101415 20 25 28 FSH LH Pituitary hormones in blood LH peak triggers ovulation and corpus luteum formation FSH stimulates follicle to grow LH surge triggers ovulation

55. Figure 27.6_3 Days 05 10 14 15 20 25 28 Ovarian cycle Pre-ovulatory phasePost-ovulatory phase Ovulation Growing follicle Mature follicle Corpus luteum Degenerating corpus luteum Estrogen secreted by growing follicle Progesterone and estrogen secreted by remnant of follicle

56. Figure 27.6_4 Days 0 5101415 20 25 28 Ovarian hormones in blood Peak causes LH surge Estrogen Progesterone Low levels of estrogen trigger menstruation Progesterone and estrogen promote thickening of endometrium

57. Figure 27.6_5 Menstrual cycle Endometrium Menstruation Days 05101415202528

58. 27.7 CONNECTION: Sexual activity can transmit disease  Sexually transmitted diseases (STDs) caused by bacteria can often be cured.  Chlamydia –is the most common bacterial STD, –often produces no symptoms, and –can lead to pelvic inflammatory disease and infertility. © 2012 Pearson Education, Inc.

59. 27.7 CONNECTION: Sexual activity can transmit disease  Viral diseases –such as genital herpes and HIV, –can only be controlled.  The best way to avoid the spread of STDs is abstinence.  Latex condoms provide the best protection against disease transmission for “safer sex.” © 2012 Pearson Education, Inc.

60. Table 27.7

61. 27.8 CONNECTION: Contraception can prevent unwanted pregnancy  Contraception is the deliberate prevention of pregnancy.  Several forms of contraception can prevent pregnancy, with varying degrees of success. © 2012 Pearson Education, Inc.

62. Table 27.8

63. Figure 27.8 Skin patch

64. PRINCIPLES OF EMBRYONIC DEVELOPMENT © 2012 Pearson Education, Inc.

65. 27.9 Fertilization results in a zygote and triggers embryonic development  Embryonic development begins with fertilization, –the union of sperm and egg, –to form a diploid zygote. © 2012 Pearson Education, Inc.

66. Figure 27.9A

67. 27.9 Fertilization results in a zygote and triggers embryonic development  Sperm are adapted to reach and fertilize an egg. Sperm have –a streamlined shape, which moves easily through fluids, –many mitochondria, which provide ATP for tail movements, and –a head that contains a haploid nucleus and is tipped with an acrosome containing enzymes that help it penetrate the egg. © 2012 Pearson Education, Inc.

68. Figure 27.9B Tail Plasma membrane Mitochondria Nucleus Acrosome Head Middle piece

69. 27.9 Fertilization results in a zygote and triggers embryonic development  During fertilization, 1.sperm squeeze past follicle cells, 2.acrosomal enzymes digest the egg’s jelly coat, 3.a sperm binds to egg receptors, 4.sperm and egg plasma membranes fuse, 5.the sperm nucleus enters the egg cytoplasm, 6.The vitelline layer separates and becomes impenetrable, and 7.the egg and sperm nuclei fuse. © 2012 Pearson Education, Inc.

70. Figure 27.9C 123456 Sperm Nucleus Acrosome Plasma membrane A sperm touches the egg’s jelly coat, and its acrosome releases enzyme molecules. The sperm’s acrosomal enzymes digest the egg’s jelly coat. Acrosomal enzymes Proteins on the sperm head bind to egg receptors. The plasma membranes of sperm and egg fuse. The sperm nucleus enters the egg cytoplasm. The vitelline layer separates and becomes impenetrable. Sperm nucleus 7 Zygote nucleus The nuclei of sperm and egg fuse. Egg nucleus 2n2n n n n n Receptor protein molecules Cytoplasm Plasma membrane Vitelline layer Jelly coat Egg cell

71. Figure 27.9C_1 Sperm Nucleus Acrosome Plasma membrane A sperm touches the egg’s jelly coat, and its acrosome releases enzyme molecules. The sperm’s acrosomal enzymes digest the egg’s jelly coat. Acrosomal enzymes Proteins on the sperm head bind to egg receptors. Receptor protein molecules Plasma membrane Vitelline layer Jelly coat

72. Figure 27.9C_2 The plasma membranes of sperm and egg fuse. The sperm nucleus enters the egg cytoplasm. The vitelline layer separates and becomes impenetrable. Sperm nucleus n

73. Figure 27.9C_3 Sperm nucleus Zygote nucleus The nuclei of sperm and egg fuse. Egg nucleus 2n2n n n n n

74. 27.10 Cleavage produces a ball of cells from the zygote  Cleavage is a rapid series of cell divisions that produces –more cells, –smaller cells, and –a fluid-filled embryo called a blastula. © 2012 Pearson Education, Inc. Video: Sea Urchin Embryonic Development

75. Figure 27.10_s1 Zygote 2 cells

76. Figure 27.10_s2 Zygote 2 cells 4 cells 8 cells

77. Figure 27.10_s3 Zygote 2 cells 4 cells 8 cells Many cells (solid ball)

78. Figure 27.10_s4 Zygote 2 cells 4 cells 8 cells Many cells (solid ball) Blastocoel Blastula (hollow ball) Cross section of blastula

79. 27.11 Gastrulation produces a three-layered embryo  During gastrulation –cells migrate to new locations, –a rudimentary digestive cavity forms, and –the basic body plan of three layers is established with –ectoderm outside—becomes skin and nervous systems, –endoderm inside—becomes digestive tract, –mesoderm in the middle—becomes muscle and bone. © 2012 Pearson Education, Inc.

80. Figure 27.11_s1 Blastula (end of cleavage) Animal pole Blastocoel Vegetal pole

81. Figure 27.11_s2 Blastula (end of cleavage) Animal pole Blastocoel Vegetal pole Gastrulation (cell migration) Formation of a simple digestive cavity Blastopore Blastocoel shrinking

82. Figure 27.11_s3 Blastula (end of cleavage) Animal pole Blastocoel Vegetal pole Gastrulation (cell migration) Formation of a simple digestive cavity Blastopore Blastocoel shrinking Gastrula (end of gastrulation) Simple digestive cavity Endoderm Mesoderm Ectoderm

83. Table 27.11

84. 27.12 Organs start to form after gastrulation  Organs develop from the three embryonic layers. –The stiff notochord forms the main axis of the body and is later replaced by the vertebral column in most chordates. –The neural tube develops above the notochord and will become the –brain and –spinal cord. © 2012 Pearson Education, Inc. Video: Frog Embryo Development

85. Figure 27.12A Neural folds Endoderm Mesoderm Ectoderm Notochord Neural fold Neural plate

86. Figure 27.12A_1 Neural folds

87. Figure 27.12B Neural fold Neural plate Neural tube Outer layer of ectoderm

88. 27.12 Organs start to form after gastrulation  As the embryo elongates, paired somites –form along the sides of the notochord, –hollow out to form a coelom, and –eventually contribute to muscles, bone, and other connective tissues.  Other systems develop at the same time. © 2012 Pearson Education, Inc.

89. Figure 27.12C Neural tube Notochord Coelom Digestive cavity Somite SomitesTail bud Eye

90. Figure 27.12C_1 SomitesTail bud Eye

91. Figure 27.12D

92. 27.13 Multiple processes give form to the developing animal  Tissues and organs develop by –changes in cell shape, –cell migration, and –programmed cell death (also called apoptosis). © 2012 Pearson Education, Inc.

93. Figure 27.13A

94. Figure 27.13A_1

95. Figure 27.13A_2

96. Figure 27.13B Apoptosis Dead cell engulfed and digested by adjacent cell

97. 27.13 Multiple processes give form to the developing animal  Through induction, adjacent cells and cell layers –influence each other’s differentiation –via chemical signals. © 2012 Pearson Education, Inc.

98. 27.14 EVOLUTION CONNECTION: Pattern formation during embryonic development is controlled by ancient genes  Pattern formation, –the emergence of the parts of a structure in their correct relative positions, –involves the response of genes to spatial variations of chemicals in the embryo, and –results in tissues and organs developing in their proper positions at the correct times. © 2012 Pearson Education, Inc.

99. Figure 27.14A Limb buds Limb bud Anterior Posterior Limb bud develops Anterior Posterior Proximal Dorsal Ventral Distal

100. 27.14 EVOLUTION CONNECTION: Pattern formation during embryonic development is controlled by ancient genes  Homeotic genes –contain common nucleotide sequences (homeoboxes), –guide pattern formation in embryos, and –occur in diverse groups such as –prokaryotes, –yeast, –plants, and –animals. –Homeotic genes reveal the shared evolutionary history of life. © 2012 Pearson Education, Inc.

101. Figure 27.14B Fly chromosomeMouse chromosomes Fruit fly embryo (10 hours) Mouse embryo (12 days) Adult mouse Adult fruit fly

102. HUMAN DEVELOPMENT © 2012 Pearson Education, Inc.

103. 27.15 The embryo and placenta take shape during the first month of pregnancy  Pregnancy, or gestation, is the carrying of developing young within the female reproductive tract.  Human pregnancy –averages 266 days (38 weeks) from fertilization or –40 weeks (9 months) from the start of the last menstrual period. © 2012 Pearson Education, Inc.

104. 27.15 The embryo and placenta take shape during the first month of pregnancy  Human development begins with fertilization in the oviduct.  Cleavage produces a blastocyst whose –inner cell mass becomes the embryo and the –trophoblast, the outer cell layer, which –attaches to the uterine wall and –forms part of the placenta.  Gastrulation occurs and organs develop from the three embryonic layers. © 2012 Pearson Education, Inc.

105. Figure 27.15A–B Cleavage starts Fertilization of mature egg Secondary oocyte Oviduct Ovary Ovulation Blastocyst Blastocyst (implanted) Endometrium Uterus Uterine cavity TrophoblastUterine cavity Cavity Inner cell mass

106. Figure 27.15C Uterine cavity Endometrium Multiplying cells of trophoblast (contribute to future placenta) Trophoblast Embryo Future yolk sac Blood vessel (maternal)

107. 27.15 The embryo and placenta take shape during the first month of pregnancy  Four extraembryonic membranes develop. 1.The amnion –surrounds the embryo and –forms a fluid-filled amniotic cavity that protects the embryo. 2.The yolk sac, –in reptiles, stores yolk, –in humans, does not store yolk but is a source of the first germ cells and blood cells. © 2012 Pearson Education, Inc.

108. 27.15 The embryo and placenta take shape during the first month of pregnancy 3.The allantois –contributes to the umbilical cord, –forms part of the urinary bladder, and –in reptiles, stores embryonic waste. 4.The chorion –contributes to the placenta and –secretes human chorionic gonadotropin (HCG), which prevents menstruation in mammals. © 2012 Pearson Education, Inc.

109. Figure 27.15D Yolk sac Chorion Amnion Amniotic cavity Mesoderm cells

110. Figure 27.15E Embryo: Endoderm Mesoderm Ectoderm Chorionic villi Chorion Amnion Allantois Yolk sac

111. Figure 27.15F Amnion Placenta Amniotic cavity Embryo Chorion Chorionic villi Allantois Yolk sac Mother’s blood vessels

112. 27.15 The embryo and placenta take shape during the first month of pregnancy  The placenta is a –close association of –embryonic chorion and –mother’s blood vessels, and –site of –gas exchange—from mother to embryo, –nutrient exchange—from mother to embryo, and –waste exchange—from embryo to mother. © 2012 Pearson Education, Inc.

113. 27.16 Human development from conception to birth is divided into three trimesters  The first trimester is the period of greatest change. –The embryo forms, looking like other vertebrate embryos. –Extraembryonic membranes form. –All major organ systems are established. –After 9 weeks after fertilization, the embryo is called a fetus and –can move its arms and legs and –starts to look distinctly human. © 2012 Pearson Education, Inc. Video: Ultrasound of Human Fetus 2 Video: Ultrasound of Human Fetus 1

114. Figure 27.16A–C Conception 35 days63 days 98 days 0 JanuaryFebruaryMarch April

115. Figure 27.16A 5 weeks (35 days)

116. Figure 27.16B 9 weeks (63 days)

117. 27.16 Human development from conception to birth is divided into three trimesters  During the second trimester, –there is a great increase in the size of the fetus, and –human features are refined. –At 20 weeks, the fetus –is about 19 cm long (7.6 in.) and –weighs about 0.5 kg (1 lb.). © 2012 Pearson Education, Inc.

118. Figure 27.16C 14 weeks (98 days)

119. Figure 27.16D–E 140 days 280 days MayJuneJulyAugustSeptemberOctober

120. Figure 27.16D 20 weeks (140 days)

121. 27.16 Human development from conception to birth is divided into three trimesters  The third trimester is also a time of rapid growth. –The circulatory and respiratory systems mature. –Muscles thicken and the skeleton hardens. –The third trimester ends with birth. –Babies born as early as 24 weeks may survive only with extensive medical care. © 2012 Pearson Education, Inc.

122. Figure 27.16E At birth (280 days)

123. 27.17 Childbirth is induced by hormones and other chemical signals  Hormonal changes induce birth. –Estrogen makes the uterus more sensitive to oxytocin. –Oxytocin acts with prostaglandins to initiate labor. –The cervix dilates to about 10 cm. –The baby is expelled by strong uterine contractions. –The placenta dislodges and is expelled after the baby. © 2012 Pearson Education, Inc.

124. Figure 27.17A EstrogenOxytocin from ovaries Induces oxytocin receptors on uterus from fetus and mother’s pituitary Stimulates uterus to contract Stimulates placenta to make Prostaglandins Stimulate more contractions of uterus Positive feedback

125. 27.17 Childbirth is induced by hormones and other chemical signals  Labor occurs in three stages: 1.dilation of the cervix, 2.expulsion, delivery of the infant, 3.delivery of the placenta. © 2012 Pearson Education, Inc.

126. Figure 27.17B Placenta Umbilical cord Uterus Cervix Dilation of the cervix 123 Expulsion: delivery of the infant Delivery of the placenta Uterus Placenta (detaching) Umbilical cord

127. Figure 27.17B_1 1 Placenta Umbilical cord Uterus Cervix Dilation of the cervix

128. Figure 27.17B_2 2 Expulsion: delivery of the infant

129. Figure 27.17B_3 3 Delivery of the placenta Uterus Placenta (detaching) Umbilical cord

130.  New techniques can help many infertile couples. –About 15% of couples wanting children are infertile. –Drug therapies can help address problems of impotence (erectile dysfunction) and induce ovulation. –Assisted reproductive technologies (ART) require eggs to be harvested from the ovaries, fertilized, and returned to a woman’s body. –In vitro fertilization (IVF) is the most common assisted reproductive technology. Fertilization occurs in a culture dish and an early embryo is implanted in the uterus. 27.18 CONNECTION: Reproductive technologies increase our reproductive options © 2012 Pearson Education, Inc.

131. Figure 27.18 Collected egg Collected sperm Zygote In vitro fertilization Implantation 8-cell embryo

132. Figure 27.18_1

133. You should now be able to 1.Compare the types, advantages, and disadvantages of asexual and sexual reproduction. 2.Describe the structures and functions of the female and male human reproductive systems. 3.Describe and compare the processes and products of spermatogenesis and oogenesis. 4.Describe the events of and control of the menstrual cycle. © 2012 Pearson Education, Inc.

134. You should now be able to 5.Describe the nature of the most common sexually transmitted diseases. 6.Describe the most common forms of birth control and explain how each works. 7.Relate the structure of sperm to its role in fertilization. 8.Describe the process and results of cleavage. 9.Describe the process of gastrulation and the resulting arrangement of the embryo. © 2012 Pearson Education, Inc.

135. You should now be able to 10.Explain how organs form after the development of a gastrula. 11.Explain how changes in cell shape, induction, cell migration, and apoptosis contribute to development. 12.Explain how the one-dimensional information in DNA is used to direct the three-dimensional form of an embryo. 13.Describe the initial embryonic stages and the formation and functions of the extraembryonic membranes in humans. © 2012 Pearson Education, Inc.

136. You should now be able to 14.Describe the main changes that occur during each of the trimesters of human development. 15.Explain how labor begins and describe the main events of the three stages of labor. 16.Describe the common causes of human infertility and the technologies currently available to help couples conceive. © 2012 Pearson Education, Inc.

137. Figure 27.UN01 2n2n n n n n nn 2n2n n n n OogenesisSpermatogenesis Primary oocyte Primary spermatocyte 2n2n n n Once per month Secondary oocyte Secondary spermatocyte Polar body Continuously Sperm Developing sperm cells Fertilization Polar body Mature egg Zygote

138. Figure 27.UN02 CleavageGastrulation Ectoderm Mesoderm Endoderm Zygote2-cell embryo Many-celled solid ball Blastula (cross section) Gastrula (cross section)

139. Figure 27.UN03 Hormones (A–D) Events (P–S) Days Hormone level in blood (arbitrary units) 50 40 30 20 10 0 05 15202528 SR Q P A B C D