1. Reproduction and Development Figures 26.1 – 26.2
CHAPTER 26
Reproduction and Development
Figures 26.1 – 26.2

2. During ejaculation, a man releases up to 500 million sperm, only one of which may fertilize an egg
You have trillions of cells in your body, and they all arose from one original cell

3. An American woman is 4 times more likely to deliver triplets today than 25 years ago
Even though a woman is born with up to half a million developing gametes, she will only use about 500 during her lifetime

4. BIOLOGY AND SOCIETY: RISE OF THE SUPERTWINS
On November 19, 1997, news reports heralded the arrival of the Iowa septuplets
Figure 26.1

5. Other sets of multiple births soon followed
What accounted for the sudden rash of multiple births?

6. All of these multiple births were by women who had taken fertility drugs because they couldn’t become pregnant naturally
Couples turn to fertility drugs to overcome their natural reproductive limitations

7. UNIFYING CONCEPTS OF ANIMAL REPRODUCTION
Reproduction is the creation of new individuals from existing ones

8. In asexual reproduction
One parent produces genetically identical offspring

9. Binary fission Is the simplest type of asexual reproduction
Involves a single parent cell splitting through mitosis into two genetically identical offspring cells

10. Some multicellular organisms reproduce by a similar means called fission, in which one organism splits into two or more individuals
Figure 26.2a

11. Fragmentation is the breaking of a parent body into several pieces
Regeneration, which follows fragmentation, is the regrowth of a whole animal from the pieces

12. Budding Is the splitting off of new individuals from existing ones
Figure 26.2b

13. Asexual reproduction has a number of advantages
It allows a species to perpetuate itself if its individual members are sessile or isolated from one another
It allows organisms to multiply quickly

14. One potential disadvantage of asexual reproduction is that it produces genetically uniform populations

15. Sexual Reproduction Sexual reproduction
Involves the fusion of gametes (sperm and egg) from two parents
Increases the genetic variability among offspring

16. Some animals can reproduce both sexually and asexually
Figure 26.3a

17. Some species are hermaphrodites with both male and female reproductive systems
Figure 26.3b

18. The mechanics of fertilization play an important part in sexual reproduction

19. Many organisms use external fertilization, in which parents discharge their gametes into the water, where fertilization occurs
Figure 26.3c

20. Other organisms use internal fertilization, which occurs within the female’s body
Internal fertilization requires copulation, or sexual intercourse

21. Both sexes of humans have
HUMAN REPRODUCTION
Both sexes of humans have
A pair of gonads, the organs that produce gametes
Ducts to store and deliver the gametes
Structures to facilitate copulation

22. Female Reproductive Anatomy
The ovaries
Are the site of gamete production in human females
Ovaries
Oviduct
Follicles
Corpus luteum
Uterus
Wall of uterus
Endometrium (lining of uterus)
Cervix
(“neck” of uterus)
Vagina
Figure 26.4

23. The ovaries contain follicles
Each follicle consists of a single developing egg cell surrounded by layers of cells that nourish and protect it
The follicles also produce estrogen, the female sex hormone

24. Ovulation
Is the process by which an egg cell is ejected from the follicle
Figure 26.5

25. The egg enters the oviduct, which is a tube in which cilia sweep the egg toward the uterus

26. The uterus is the actual site of pregnancy
The cervix, the narrow neck at the bottom of the uterus, opens into the vagina, or birth canal
During copulation, the vagina serves as a repository for sperm

27. Female reproductive anatomy
Oviduct
Ovary
Rectum (digestive system)
Uterus
Bladder (excretory system)
Pubic bone
Cervix
Urethra (excretory system)
Vagina
Shaft
Glans
Clitoris
Prepuce
Labia minora
Labia majora
Vaginal opening
Figure 26.6

28. Male Reproductive Anatomy
The penis
Contains erectile tissue

29. The testes Are the male gonads, enclosed in a sac called the scrotum
Produce sperm

30. Several glands
Contribute to the formation of the fluid that carries, nourishes, and protects sperm
Semen
Consists of this fluid and sperm

31. Male reproductive anatomy, side view
Bladder (excretory system)
Seminal vesicle
Pubic bone
Rectum (digestive system
Erectile tissue of penis
Vas deferens
Urethra
Prostate gland
Vas deferens
Glans of penis
Epididymis
Testis
Prepuce
Scrotum
Figure 26.7a

32. Male reproductive anatomy, front view
Bladder (excretory system)
Seminal vesicle (behind bladder)
Prostate gland
Urethra
Erectile tissue of penis
Vas deferens
Scrotum
Epididymis
Testis
Glans of penis
Figure 26.7b

33. Gametogenesis Gametogenesis Human gametes Is the production of gametes
Are haploid cells that develop by meiosis

34. Oogenesis is the development of eggs within the ovaries
Diploid cell in embryo
Differentiation and onset of meiosis I
Ovary
Primary oocyte,
arrested in prophase of meiosis I; present at birth
Completion of meiosis I and onset of meiosis II
Corpus luteum
First polar body
Secondary oocyte,
Growing follicle
arrested at metaphase of meiosis II; released from ovary
Entry of sperm triggers completion of meiosis II
Mature follicle
Second polar body
Ovulation
Ovum
Ruptured follicle
(haploid)
Sperm
Figure 26.8

35. Spermatogenesis
Spermatogenesis
Is the formation of sperm cells

36. Differentiation and onset of meiosis I Seminiferous tubule
Epididymis
Penis
Testis
Scrotum
Diploid cell
Testis
Differentiation and onset of meiosis I
Seminiferous tubule
Primary spermatocyte
Cross section of seminiferous tubule
Meiosis I completed
Secondary spermatocyte
Meiosis II
Developing spermatids
Differentiation
Sperm cells
(haploid)
Center of seminiferous tubule
Figure 26.9

37. The Female Reproductive Cycle
Human females have a reproductive cycle, a recurring series of events that produces gametes, makes them available for fertilization, and prepares the body for pregnancy

38. The female reproductive cycle involves two sets of changes
The ovarian cycle controls the growth and release of an ovum
The menstrual cycle prepares the uterus for possible implantation of an embryo

39. Hormones
Synchronize cyclical changes in the ovaries and uterus

40. The female reproductive cycle
Control by hypothalamus
Inhibited by combination of estrogen and progesterone
Hypothalamus
Stimulated by high levels of estrogen
Releasing hormone
Anterior pituitary
(a) 1
Pituitary hormones in blood 4
(b) 2
FSH stimulates follicle to grow
LH peak triggers ovulation
Ovarian cycle 5
Growing follicle
Mature follicle
Ovulation
Corpus luteum
Degenerating corpus luteum
(c)
Estrogen secreted by growing follicle
Progesterone and estrogen secreted by remnant of follicle
Figure 26.10a–c

41. (d) (e) Ovarian hormones in blood Peak causes LH surge 3 7 Estrogen
Progesterone 6
(d)
Progesterone and estrogen promote thickening of endometrium
Low levels trigger menstruation
Menstrual cycle
Endometrium
(e)
Menstruation
Figure 26.10d, e

42. Two issues of human reproductive health
Contraception
Transmission of disease

43. Contraception
Contraception
Is the deliberate prevention of pregnancy

44. There are many forms of contraception, each with varying degrees of reliability
Figure 26.11

45. Contraceptive methods and their effectiveness
Table 26.1

46. Sexually Transmitted Diseases
Sexually transmitted diseases (STDs)
Are contagious diseases spread by sexual contact

47. Viral STDs, such as AIDS, genital herpes, and genital warts, cannot be cured but can be controlled by medications

48. STDs caused by bacteria, protozoans, and fungi are generally curable with drugs
Table 26.2

49. REPRODUCTIVE TECHNOLOGIES
Can help solve problems related to the inability to conceive a child

50. Infertility Infertility
Is the inability to have children after one year of trying
Is most often due to problems in the man, such as underproduction of sperm or impotence

51. Female infertility can result from a lack of eggs or a failure to ovulate
There are technologies available to help treat the many forms of infertility

52. In Vitro Fertilization
In vitro fertilization (IVF)
Happens under artificial, laboratory conditions

53. IVF
Begins with the surgical removal of eggs and the collection of sperm
Involves fertilization of eggs in a petri dish
Figure 26.12

54. IVF Offers choices that nature does not
Raises many moral and legal issues

55. Embryonic development
HUMAN DEVELOPMENT
Embryonic development
Begins with fertilization, the union of sperm and egg to form a zygote

56. Fertilization
Copulation releases hundreds of millions of sperm into the vagina, but only a few hundred survive the trip to the egg, and only one will fertilize it
Figure 26.13

57. A mature human sperm
Has a streamlined shape that suits its need to swim through fluids in the vagina, uterus, and oviduct
Head
Plasma membrane
Mitochondria
Nucleus
Acrosome
Figure 26.14

58. The events of fertilization3
The plasma membranes of the sperm and egg fuse. 2
The sperm’s acrosomal enzymes digest the zona pellucida. 1
The sperm squeezes through cells left over from the follicle. 4
The sperm enters the egg cytoplasm.
Acrosomal enzymes
Sperm
Nucleus
Acrosome
Sperm nucleus 5
The nuclei of sperm and egg join.
Follicle cell
Cytoplasm
Plasma membrane
Zona pellucida
Egg nucleus
Egg cell
Zygote nucleus
Figure 26.15

59. Basic Concepts of Embryonic Development
The key to development in all organisms is that each stage of development takes place in a highly organized fashion

60. Zygote
2 cells
Cleavage
4 cells
8 cells
Many cells (solid ball)
Inner cell mass
Blastocyst (hollow ball)
Cross section of blastocyst
Ectoderm
Gastrulation
Mesoderm
Gastrula
(cross section)
Endoderm
Figure 26.16

61. Development begins with cleavage, a series of rapid cell divisions that results in a multicellular ball
Cleavage continues as the embryo moves down the oviduct toward the uterus
About 6–7 days after fertilization, the embryo has reached the uterus as a fluid-filled hollow ball of about 100 cells called a blastocyst

62. The next stage of development is gastrulation, a process that produces the three embryonic tissue layers

63. Tissues and organs take shape in a developing embryo as a result of many different changes in the cells
Outer layer of ectoderm
Neural tube
Figure 26.17

64. In the process called induction, one group of cells influences the development of an adjacent group of cells
Lens ectoderm
Optic cup
Cornea
Future brain
Lens
Optic vesicle
Future retina
Optic stalk 1 2 3 4
Figure 26.18

65. Pregnancy and Early Development
Pregnancy, or gestation
Is the carrying of developing young within the female reproductive tract
Is measured as 40 weeks from the start of the last menstrual cycle in humans

66. The early stages of human development begin with fertilization and cleavage in the oviduct
Cleavage starts
Fertilization of ovum
Ovary
Oviduct
Secondary oocyte
Ovulation
Blastocyst (implanted)
Endometrium
Uterus
Figure 26.19

67. About one week after conception
The embryo, which has become a blastocyst, implants itself in the uterine wall
The outer cell layer, the trophoblast, becomes part of the placenta

68. Endometrium Inner cell mass Cavity
Blood vessel (maternal)
Inner cell mass
Future embryo
Multiplying cells of trophoblast (future placenta)
Cavity
Future yolk sac
Trophoblast
Trophoblast
Uterine cavity
(a) Blastocyst (6 days after conception)
(b) Implantation underway (about 7 days)
Figure 26.20

69. The embryo after about a month after conception
Mother’s blood vessels
Allantois (forms part of the umbilical cord)
Placenta
Amnion
Yolk sac
Embryo
Chorion
Chorionic villi
Figure 26.21

70. Four structures develop that assist the developing embryo
The amnion, a fluid filled sac that encloses and protects the embryo
The yolk sac, which produces the embryo’s first blood and germ cells

71. The allantois, which forms part of the umbilical cord
The chorion, which becomes part of the placenta

72. The Stages of Pregnancy
Pregnancy is divided into three trimesters

73. A human embryo about 5 weeks after fertilization
The First Trimester
A human embryo about 5 weeks after fertilization
Figure 26.22

74. A human embryo, now called a fetus, about 9 weeks after fertilization
Figure 26.23

75. By the end of the first trimester
The fetus looks like a miniature human being
The sex of the fetus can be determined by ultrasound
Figure 26.24

76. The Second Trimester
The main developmental changes during the second and third trimesters involve an increase in size and general refinement of the human features

77. A fetus at 14 weeks, 2 weeks into the second trimester
Figure 26.25

78. At 20 weeks, the fetus
Is about 19 cm (7.6 in.) long and weighs about half a kilogram (1 lb)
Has the face of an infant
Figure 26.26

79. The Third Trimester The third trimester Is a time of rapid growth
Includes many important physical changes

80. At birth
A typical baby is about 50 cm (20 in.) long and weighs 2.7–4.5 kg (6–10 lb)
Figure 26.27

81. Childbirth
The birth of a child is brought about by a series of strong, rhythmic contractions of the uterus called labor

82. Hormones play a key role in inducing labor
Estrogen, oxytocin, and prostaglandins are all involved
Estrogen
Oxytocin
from ovaries
from fetus and pituitary
Induces oxytocin receptors on uterus
Positive feedback
Stimulates uterus to contract
Stimulates placenta to make
Prostaglandins
Simulate more contractions of uterus
Figure 26.28

83. The three stages of labor
Figure 26.29

84. EVOLUTION CONNECTION: MENOPAUSE AND THE GRANDMOTHER HYPOTHESIS
Typically between the ages of 46 and 54, human females undergo menopause, the cessation of ovulation and menstruation

85. Why does the reproductive system shut down?
One group of researchers proposed that menopause actually increases a woman’s evolutionary fitness in the long run
Postreproductive women contribute to raising grandchildren

86. SUMMARY OF KEY CONCEPTS
Gametogenesis
Oogenesis
Spermatogenesis
Primary oocyte
Primary spermatocyte
Once per month
Polar body
Secondary oocyte
Secondary spermatocyte
Spermatid
Fertilization
Sperm
Polar body
Ovum
Zygote
Visual Summary 26.1

87. In Vitro Fertilization
Collected egg
Implantation
8-cell embryo
Zygote
In vitro fertilization
Collected sperm
Visual Summary 26.2

88. Basic Concepts of Embryonic Development
Cleavage
Gastrulation
Ectoderm
Mesoderm
Endoderm
Zygote
2-cell embryo
Gastrula (cross section)
Many-celled solid ball
Blastocyst (cross section)
Visual Summary 26.3

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