1. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings PowerPoint Lectures for Biology: Concepts and Connections, Fifth Edition – Campbell, Reece, Taylor, and Simon Lectures by Chris Romero Chapter 27 Reproduction and Embryonic Development

2. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Baby Bonanza The increased use of fertility drugs has caused an increase in the number of multiple births in the United States Infertility affects about one in seven couples in the United States Fertility drugs are an example of technology affecting the normal reproductive cycle

5. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings ASEXUAL AND SEXUAL REPRODUCTION 27.1 Sexual and asexual reproduction are both common among animals In asexual reproduction, one parent produces genetically identical offspring – Allows isolated animals to reproduce without having to find mates – Produces offspring quickly – Diminishes genetic diversity of offspring

6. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Asexual Reproduction Asexual reproduction does not involve the fusion of sperm and egg There major forms of asexual reproduction Budding Fission Fragmentation/regeneration Parthenogenesis

7. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Asexual Reproduction Budding A miniature version of adult grows off of the parent’s body Example: hydras and some sea anenomes

9. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings

10. Asexual Reproduction Fission/fragmentation When an animal divides in two/more Each piece grows into an adult by regeneration Example: some flatworms and annelids/starfish

11. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings

12. ASEXUAL REPRODUCTION VIA FISSION

13. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Asexual Reproduction Parthenogenesis When a female’s haploid egg develops into adult without fertilization Example: whiptail lizards and aphids

14. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings

16. Sexual reproduction involves the fusion of gametes from two parents – Two haploid gametes unite to produce a diploid zygote – Male sperm is small, flagellated – Female ovum is larger and not self- propelled – Increases genetic variability among offspring – May enhance reproductive success in changing environments

17. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Many animals can reproduce both sexually and asexually – Rotifer Asexual in good environmental conditions Sexual in more stressful conditions – Hermaphrodites Each individual has both female and male reproductive systems Most mate with another member of their species

18. LE 27-01c “Head” Intestine Ovary Eggs LM 210 

20. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings External Fertilization External fertilization: release of sperm and eggs into the water, where fertilization occurs (spawning) Mates synchronize their reproductive behaviors temporally and spatially Reproductive behaviors can be reliant on – Pheromone release – Courtship rituals – Environmental cues (example: coral spawning)

21. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings

22. External Fertilization Siamese fighting fish exhibit elaborate courtship dances

23. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings External Fertilization Seahorses also exhibit courtship behaviors that result in eggs being transferred to the male

24. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings External Fertilization Frogs and toads assume a specific mating position while spawning called amplexus

25. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Internal Fertilization Internal fertilization: transmission of male gametes into the female Copulation: male directly deposits sperm Spermatophore use: a sperm packet that is picked up by the female, or is deposited in female by the male In most mammals, mating coincides with ovulation

26. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings

27. Internal Fertilization Competition may occur between animals that copulate to reproduce Example: hundreds of male red-sided garter snakes compete to copulate with a single female, but only one succeeds

28. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings

29. HUMAN REPRODUCTION 27.2 Reproductive anatomy of the human female Humans have separate sexes, reproduce sexually, and make sex cells using paired gonads Males produce sperm continuously Females release an egg cell (ovulate) once per month

30. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Puberty The ability to reproduce begins at puberty Puberty Rapid growth and appearance of secondary sexual characteristics at the onset of sexual maturity Occurs between 8 and 15 years of age

31. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Puberty As the result of brain maturation The hypothalamus stimulates GnRH release – GnRH stimulates LH and FSH release from the pituitary gland – LH and FSH stimulate gamete, testosterone, and estrogen production

32. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Puberty In males The penis and testes enlarge Secondary sexual characteristics develop In females Menstruation and breast development begin Secondary sexual characteristics develop

33. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The Female Reproductive Tract Includes the ovaries and accessory structures

34. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings

38. Oogenesis occurs mostly in the ovaries – Before birth, a diploid cell in each developing follicle begins meiosis – At birth, each follicle contains a dormant diploid primary oocyte – After puberty, one primary oocyte is released each month Continues meiosis Unequal division of cytoplasm forms a single secondary oocyte If fertilized, oocyte completes meiosis and becomes a haploid ovum

39. LE 27-04b Diploid cell Primary oocyte (arrested in prophase of Meiosis  ) Secondary oocyte In embryo Differentiation and onset of Meiosis  Present at birth Completion of Meiosis  and onset of Meiosis  First polar body 2n n n (arrested at meta- phase of Meiosis  ; released from ovary) Entry of sperm triggers completion of Meiosis  Second polar body n n Ovum (haploid)

40. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings

41. Follicle Development A mature ovarian follicle develops every 28 days Occurs in response to LH and FSH secretion Secretes estrogen which stimulates uterine development

42. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Ovulation A single secondary oocyte ruptures from the follicle and leaves the ovary during ovulation The secondary oocyte enters the uterine tube The ruptured follicle turns into the corpus luteum – Secretes estrogen and progesterone for continued uterine development

43. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings

45. LE 27-04c Corpus luteum Degenerating corpus luteum Start: Primary oocyte within follicle Growing follicles Mature follicle Ovary Ruptured follicle Ovulation Secondary oocyte

46. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings

47. Female Accessory Structures Uterine tubes Fimbriae sweep up ovulated egg Site of fertilization Beating cilia sweep zygote toward uterus

48. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Female Accessory Structures Uterus Muscular site of fertilized egg (zygote) implantation and embryo development Has two functional tissue layers – Endometrium: inner uterine lining; supplied with blood vessels; form the mother’s contribution to the placenta – Myometrium: thick smooth muscle layer; contracts during childbirth

49. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Uterus (womb) – Actual site of pregnancy Embryo: from first division of zygote until body structures begin to appear Fetus: from about ninth week until birth

50. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings – In ectopic pregnancy, embryo implants somewhere other than uterus Other structures of the female reproductive system – Labia minora =slender skin folds at the opening – Labia majora =thick, fatty ridges used for protection – Clitoris= unit for sexual arousal – Bartholin's gland= secretes mucus for lubrication

51. LE 27-02a Follicles Oviduct Corpus luteum Wall of uterus Vagina Endometrium (lining of uterus) Ovaries Uterus Cervix (“neck” of uterus)

52. LE 27-02c Cervix Vagina Bartholin’s gland Rectum (digestive system) Anus (digestive system) Vaginal opening Labia majora Labia minora Prepuce Glans Shaft Clitoris Urethra (excretory system) Urinary bladder (excretory system) Pubic bone Uterus Ovary Oviduct

53. LE 27-02b Ovary Egg cell LM 200 

54. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 27.3 Reproductive anatomy of the human male Testes, housed outside the body in the scrotum, produce sperm Pathway of sperm from testis to outside – Epididymis – Vas deferens – Ejaculatory duct – Ejaculation through urethra in penis Connection between reproductive and excretory systems

55. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Several glands contribute to the formation of fluid that nourishes and protects sperm – Seminal vesicles – Prostate gland – Bulbourethral glands – Semen combines sperm and glandular secretions

56. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings

57. LE 27-03a Rectum (digestive system) Vas deferens Seminal vesicle Ejaculatory duct Bulbourethral gland Prostate gland Vas deferens Epididymis Testis Scrotum Urethra (excretory system) Prepuce Glans of penis Penis Erectile tissue of penis Pubic bone Urinary bladder (excretory system)

58. LE 27-03b Urinary bladder (excretory system) Prostate gland Bulbourethral gland Erectile tissue of penis Vas deferens Epididymis Testis Scrotum Glans of penis Urethra Seminal vesicle (behind bladder)

59. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The process of ejaculation involves coordinated contractions and expulsion of fluids Hormones control sperm production by the testes through a negative-feedback system

60. LE 27-03c First stage Contractions of prostate gland Contractions of seminal vesicle Contractions of vas deferens Sphincter contracts Sphincter contracts Urinary bladder Urethra region here expands and fills with semen Contractions of epididymis Sphincter remains contracted Contractions of muscles around base of penis Second stage Sphincter relaxes Contractions of urethra Semen expelled

61. LE 27-03d Stimuli from other areas in the brain Releasing hormone Anterior pituitary Hypothalamus Androgen production Testis FSHLH Sperm production Negative feedback

62. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 27.4 The formation of sperm and ova requires meiosis Gametogenesis: the formation of diploid gametes from haploid sperm and ova during meiosis Spermatogenesis: the formation of sperm cells – Diploid cells made continuously in seminiferous tubules of testes – Differentiated primary spermatocytes – Haploid secondary spermatocytes – Haploid sperm

63. LE 27-04a Testis Scrotum Diploid cell Differentiation and onset of Meiosis  Primary spermatocyte Secondary spermatocyte Meiosis  (in prophase of Meiosis   (haploid; double chromatids) (haploid; single chromatids) Developing sperm cells Differentiation Sperm cells Epididymis Penis Seminiferous tubule Cross section of seminiferous tubule Center of seminiferous tubule Testis (haploid) nn n n nn nn n n 2n completed Meiosis 

64. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The development of an ovarian follicle involves many different processes Comparison of oogenesis and spermatogenesis – Both produce haploid gametes – Only one ovum results from each diploid cell that undergoes meiosis – Cells from which gametes develop are thought not to divide throughout life in the female – Oogenesis has long resting periods; spermatogenesis is uninterrupted

65. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 27.5 Hormones synchronize cyclic changes in the ovary and uterus The reproductive cycle in females involves an integrated process between the ovaries and the uterus – Ovarian cycle: produces the oocyte – Menstrual cycle: involves the monthly changes in the uterus – Hormonal messages synchronize the two cycles through intricate feedback systems

66. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Events in the menstrual cycle are coordinated with the ovarian cycle – Events synchronized by five hormones – Menstrual cycle prepares uterus for implantation of embryo – Menstruation lasts 3-5 days, corresponding to pre-ovulatory phase of ovarian cycle – Continues through time of ovulation (20-25 days) – If no embryo is implanted, menstruation begins again

68. LE 27-05 Control by hypothalamus Hypothalamus Anterior pituitary Releasing hormone Inhibited by combination of estrogen and progesterone Stimulated by high levels of estrogen FSHLH Pituitary hormones in blood LH peak triggers ovulation and corpus luteum formation LH FSH Ovarian cycle Growing follicle Pre-ovulatory phase Post-ovulatory phase Ovulation Mature follicle Corpus luteum Degenerating corpus luteum Progesterone and estrogen Estrogen Ovarian hormones in blood Estrogen Progesterone Estrogen Progesterone and estrogen FSH stimulates growth of a follicle LH stimulates completion of meiosis and rupture of follicle Corpus luteum secretes estrogen and progesterone High levels of estrogen and progesterone exert negative feedback on hypothalamus and pituitary

69. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Control of the menstrual cycle – When levels of estrogen and progesterone drop, endometrium begins to slough off – Menstrual bleeding begins on day 1 of a new cycle

70. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings

71. 27.6 The human sexual response occurs in four phases Excitement phase: prepares the sexual organs for coitus Plateau phase: breathing and heart rate increase Orgasm: rhythmic contractions, pleasure for both partners, ejaculation Resolution phase: completes the cycle and reverses the previous responses

72. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings CONNECTION 27.7 Sexual activity can transmit disease Sexually transmitted diseases (STDs) are contagious diseases spread by sexual contact Viral diseases are not curable but can be controlled by medication Many STDs can cause long-term problems or even death if untreated STDs are most prevalent among teenagers and young adults

74. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings CONNECTION 27.8 Contraception can prevent unwanted pregnancy Contraception is the deliberate prevention of pregnancy Contraception must be used correctly to prevent failure "Safe sex" provided by condoms can prevent both unwanted pregnancy and sexually transmitted disease

75. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Common contraceptive methods – Abstinence – Tubal ligation or vasectomy – Rhythm method (natural family planning) – Withdrawal – Barrier methods: condom, diaphragm Most effective if used with spermicide – Oral contraceptives – Morning after pills

77. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings

80. LE 27-08 Diaphragm Spermicide Birth control pills Condom Skin patch

81. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings PRINCIPLES OF EMBRYONIC DEVELOPMENT 27.9 Fertilization results in a zygote and triggers embryonic development Embryonic development begins with fertilization – Many sperm reach an egg, but only one fertilizes it – Sperm and egg unite to form a diploid zygote

83. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The properties of sperm cells – Streamlined shape an adaptation for swimming – Thick head contains haploid nucleus – Acrosome at tip of head contains enzymes that help sperm penetrate the egg – High-energy nutrients absorbed from semen provide energy for propulsion and penetration

84. LE 27-09b Plasma membrane Tail Acrosome Nucleus Mitochondrion (spiral shape) Neck Head Middle piece A lysozyme containing enzymes to penetrate the egg produce energy for sperm movement

85. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The process of fertilization 1.Sperm approaches egg 2.Sperm's acrosomal enzymes digest egg's jelly coat 3.Proteins on sperm head bind to egg receptors 4.Plasma membranes of sperm and egg fuse 5.Sperm nucleus enters egg cytoplasm

86. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 6.Fertilization envelope forms, preventing other sperm from entering egg 7.Nuclei of sperm and egg fuse, producing diploid nucleus of zygote

87. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings

89. LE 27-09c The sperm approaches the egg The sperm’s acrosomal enzymes digest the egg’s jelly coat Sperm Nucleus Acrosome Plasma membrane Acrosomal enzymes Sperm head Proteins on the sperm head bind to egg receptors The plasma membranes of sperm and egg fuse A fertilization envelope forms Jelly coat Vitelline layer Plasma membrane Receptor protein molecules Sperm nucleus Egg nucleus Egg cell Cytoplasm Zygote nucleus The nuclei of sperm and egg fuse The sperm nucleus enters the egg cytoplasm

90. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 27.10 Cleavage produces a ball of cells from the zygote Cleavage is the first major stage of embryonic development A rapid series of cell divisions produces a ball of cells from the zygote – The number of cells doubles with each cleavage division Fluid-filled blastocoel forms in the center of the embryo A blastula, a hollow ball of cells, is the product of cleavage

91. LE 27-10 Zygote 2 cells 8 cells Many cells (solid ball) Blastula (hollow ball) Cross section of blastula 4 cells Blastocoel

92. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Cleavage makes two important contributions to early development – Creates a multicellular embryo from a single-celled zygote – Partitions the embryo into developmental regions

93. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 27.11 Gastrulation produces a three-layered embryo Gastrulation adds more cells to the embryo and sorts them into three layers – Ectoderm: forms outer skin of gastrula – Endoderm: forms embryonic digestive tract (archenteron) – Mesoderm: partly fills space between ectoderm and endoderm – These layers develop into all parts of the adult animal

94. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Mechanics of gastrulation 1.Blastula 2.Blastopore formation 3.Cell migration to form layers 4.Completion of gastrulation

95. LE 27-11 Animal pole Vegetal pole Blastula Blastocoel Gastrulation Archenteron Gastrulation Blastopore forming Blastopore forming Blastocoel shrinking Archenteron Ectoderm Mesoderm Endoderm Yolk plug Gastrula

96. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 27.12 Organs start to form after gastrulation The three embryonic tissue layers differentiate into tissues and organs Frog development in first few hours after gastrulation – Notochord in mesoderm Will become core of the backbone – Hollow nerve cord in ectoderm Neural plate forms neural tube, which will become the brain and spinal cord

97. LE 27-12a Neural folds Archenteron Endoderm Mesoderm Ectoderm Notochord Neural fold Neural plate 15 

98. LE 27-12b Neural fold Neural plate Outer layer of ectoderm Neural tube

99. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Relative positions of neural tube, notochord, and archenteron preview the basic body plan Changes about 12 hours later – Somites from mesoderm; will give rise to segmented structures such as vertebrae – Hollow coelom (body cavity) By 5-8 days after beginning of development, all body tissues and organs would have emerged from cells of the three original layers

100. LE 27-12c Neural tube Somite Notochord Coelom Archenteron (digestive cavity) Somites Tail bud Eye SEM 15 

103. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 27.13 Changes in cell shape, cell migration, and programmed cell death give form to the developing animal Changes in cell shape – Folds of ectoderm become the start of the brain and spinal cord Migration of cells – Move to specific destinations – Join together, held by glycoproteins – Take on characteristics of a tissue

104. LE 27-13a Ectoderm

105. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Programmed cell death, or apoptosis – Controlled by "suicide" genes – Essential for normal development and differentiation of body structures

106. LE 27-13b Apoptosis Dead cell engulfed and digested by adjacent cell

107. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 27.14 Embryonic induction initiates organ formation All developmental processes depend on signals between cells Induction: the mechanism by which one group of cells influences development of an adjacent group A sequence of inductive signals leads to increasingly greater specialization of cells into organs

108. LE 27-14 Future brain Optic vesicle Optic stalk Lens ectoderm Optic cup Cornea Lens Future retina

109. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 27.15 Pattern formation organizes the animal body Pattern formation is emergence of a body form with specialized parts in the right places Positional signals determine which master control genes will be expressed In vertebrates, pattern-forming zones provide positional information to other cells through chemical signals A major goal of developmental research is to learn how information in DNA directs development of 3-D animal form

110. LE 27-15a Anterior Ventral Limb bud Bird embryo Distal Proximal Dorsal Posterior Limb bud develops Normal wing

111. LE 27-15b Wing with duplication Host limb bud develops Host pattern- forming zone Graft Host limb bud Donor limb bud Donor cells Graft of cells from pattern- forming zone

112. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings HUMAN DEVELOPMENT 27.16 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 – Gestation period varies considerably within animal species

113. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings An overview of human developmental events – Fertilization in the oviduct – Blastocyst implanted in endometrium Fluid-filled cavity Cell mass that will form baby Trophoblast – Secretes enzymes enabling implantation; forms part of placenta Extraembryonic membranes

114. LE 27-16a Ovary Cleavage starts Oviduct Fertilization of ovum Secondary oocyte Ovulation Blastocyst (implanted) Uterus Endometrium

115. LE 27-16b Endometrim Inner cell mass Cavity Trophoblast

116. LE 27-16c Endometrium Future yolk sac Future embryo Trophoblast Multiplying cells of trophoblast Blood vessel (maternal) Uterine cavity Actual size

117. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Roles of the extraembryonic membranes – Amnion has grown to enclose the embryo – Yolk sac produces embryo's first blood cells and germ cells – Allantois forms part of umbilical cord and part of urinary bladder – Chorion becomes embryo's part of placenta HCG maintains production of estrogen and progesterone during early pregnancy

118. LE 27-16d Chorion Amnion Amniotic cavity Mesoderm cells Yolk sac

119. LE 27-16e Chorion Amnion Allantois Yolk sac Chorionic villi Embryo: Ectoderm Mesoderm Endoderm

120. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The placenta: composite organ consisting of chorionic villi closely associated with blood vessels of mother's endometrium – Chorionic villi Absorb food and oxygen from the mother's blood – Chorionic blood vessels Carry food, oxygen, protective antibodies, some viruses and toxins to fetus Carry wastes back to mother's bloodstream

121. LE 27-16f Yolk sac Allantois Mother’s blood vessels Placenta Amniotic cavity Amnion Embryo Chorion Chorionic villi

122. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 27.17 Human development from conception to birth is divided into three trimesters First trimester – All organs and appendages are built in essentially a human pattern – By 9 weeks, embryo is called a fetus – Sex is evident, and heartbeat can be detected

123. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Second trimester – Main changes involve an increase in size and a general refinement of human features – Placenta takes over secretion of progesterone and estrogen – Corpus luteum degenerates – Eyes are open, and teeth are forming

124. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Third trimester – Fetus grows rapidly and gains strength needed to survive outside uterus – Circulatory and respiratory system change to allow air breathing – Fetus gains ability to maintain its own temperature – Bones harden, muscles thicken

130. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 27.18 Childbirth is hormonally induced and occurs in three stages The birth of a child is brought about by a series of strong, rhythmic contractions of the uterus Several hormones play key roles, under positive feedback control – Estrogen – Oxytocin – Prostaglandins

131. LE 27-18a Stimulate more contractions of uterus Stimulates placenta to make Prostaglandins Stimulates uterus to contract Positive feedback from ovaries OxytocinEstrogen Induces oxytocin receptors on uterus from fetus and pituitary

132. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Labor occurs in three stages 1.Dilation of the cervix 2.Expulsion: delivery of the infant 3.Delivery of the placenta

133. LE 27-18b Placenta Uterus Cervix Umbilical cord Expulsion: delivery of the infant Uterus Placenta (detaching) Umbilical cord Delivery of the placenta Dilation of the cervix

134. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings CONNECTION 27.19 Reproductive technology increases our reproductive options Couples may be unable to conceive or bear a child for a variety of reasons – Males: low sperm count, defective sperm, impotence – Females: lack of ova, failure to ovulate, blocked oviducts, uterus won't support growing embryo

135. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Reproductive technologies can help many cases of infertility – Drug or hormone therapies for both sexes – Penile implants – Sperm, ova from donors – Assisted reproductive technology In vitro fertilization – Very expensive – Entails some risks