1. Reproduction and Embryonic Development
Chapter 27
Reproduction and Embryonic Development

2. 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. ASEXUAL AND SEXUAL REPRODUCTION
27.1 Sexual and asexual reproduction are both common among animals
In asexual reproduction, one parent produces genetically identical offspring
Budding, fission, fragmentation/ regeneration
Allows isolated animals to reproduce without having to find mates
Produces offspring quickly
Diminishes genetic diversity of offspring

8. 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

9. 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

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

12. Video: Rotifer

13. External fertilization is common in aquatic animals
Parents release their gametes into the environment, where fertilization occurs
Internal fertilization occurs in nearly all terrestrial animals
Sperm are deposited in or close to the female reproductive tract
Gametes unite within the tract
Usually requires copulation

14. LE 27-01e
Eggs

15. 27.2 Reproductive anatomy of the human female
HUMAN REPRODUCTION
27.2 Reproductive anatomy of the human female
Both sexes in humans
Have a set of gonads where gametes are produced
Have ducts for delivery of the gametes and structures for copulation

16. Produce egg cells (ova)
Ovaries
Produce egg cells (ova)
Follicles protect and nourish the eggs and produce estrogen
Ovulation
One egg released every 28 days, starting at puberty
Remaining follicular tissue temporarily develops into corpus luteum
Secretes progesterone

17. Oviducts (fallopian tubes) Convey eggs to the uterus
Location of fertilization
Uterus (womb)
Thick wall and endometrium richly supplied with blood vessels
Actual site of pregnancy
Embryo: from first division of zygote until body structures begin to appear
Fetus: from about ninth week until birth

18. In ectopic pregnancy, embryo implants somewhere other than uterus
Cervix: narrow neck of uterus
Vagina: Muscular opening from uterus
Receives penis during intercourse
Forms the birth canal
Other structures of the female reproductive system
Labia minora and majora, clitoris, Bartholin's gland

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

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

21. LE 27-02b
Egg
cell
Ovary
LM 200

22. Animation: Female Reproductive Anatomy

23. 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

24. Animation: Male Reproductive Anatomy Animation: Male Hormones
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
Animation: Male Reproductive Anatomy
Animation: Male Hormones

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

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

27. The process of ejaculation involves coordinated contractions and expulsion of fluids
Hormones control sperm production by the testes through a negative-feedback system

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

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

30. 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

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

32. 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

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

34. 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

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

36. 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

37. 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

39. Hormonal events leading to ovulation
Hypothalamus signals the anterior pituitary to secrete FSH and LH
FSH stimulates growth of a follicle, with little estrogen secreted and negative feedback control of pituitary
Increased secretion of estrogen exerts positive feedback on hypothalamus
Pituitary secretes burst of FSH and LH levels
LH, FSH, and estrogen peak

40. Hormonal events at ovulation and after
LH stimulates completion of meiosis and rupture of follicle
Ovulation occurs
Follicle becomes the corpus luteum
Corpus luteum secretes estrogen and progesterone
High levels of estrogen and progesterone exert negative feedback on hypothalamus and pituitary

41. FSH and LH levels drop
Hypothalamus stimulates pituitary to secrete more FSH and LH, and a new cycle begins
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

42. LE 27-05 Control by hypothalamus Inhibited by combination of
estrogen and progesterone
Hypothalamus
Stimulated by high levels
of estrogen
Releasing hormone
Anterior pituitary
FSH LH
Pituitary hormones
in blood
LH peak triggers
ovulation and
corpus luteum
formation LH
FSH
FSH LH
Ovarian cycle
Growing follicle
Corpus
luteum
Degenerating
corpus luteum
Mature
follicle
Ovulation
Pre-ovulatory phase
Post-ovulatory phase
Estrogen
Progesterone
and estrogen
Ovarian hormones
in blood
Estrogen
Progesterone
Progesterone
and estrogen
Estrogen

43. Animation: Post Ovulation
Animation: Ovulation
Animation: Post Ovulation

44. 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

45. 27.7 Sexual activity can transmit disease
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

47. 27.8 Contraception can prevent unwanted pregnancy
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

48. 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

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

51. 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
Video: Hydra Releasing Sperm

53. 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

54. LE 27-09b Plasma membrane Middle piece Neck Head Tail Mitochondrion
(spiral shape)
Nucleus
Acrosome

55. The process of fertilization
Sperm approaches egg
Sperm's acrosomal enzymes digest egg's jelly coat
Proteins on sperm head bind to egg receptors
Plasma membranes of sperm and egg fuse
Sperm nucleus enters egg cytoplasm

56. Fertilization envelope forms, preventing other sperm from entering egg
Nuclei of sperm and egg fuse, producing diploid nucleus of zygote

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

58. 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

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

60. Video: Sea Urchin Embryonic Development

61. Cleavage makes two important contributions to early development
Creates a multicellular embryo from a single-celled zygote
Partitions the embryo into developmental regions

62. 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

63. Video: Frog Embryo Development
Mechanics of gastrulation
Blastula
Blastopore formation
Cell migration to form layers
Completion of gastrulation
Video: Frog Embryo Development

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

65. 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

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

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

68. 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

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

72. 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

73. LE 27-13a
Ectoderm

74. Programmed cell death, or apoptosis
Controlled by "suicide" genes
Essential for normal development and differentiation of body structures

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

76. 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

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

78. 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

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

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

81. 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

82. 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

83. Cleavage starts Fertilization of ovum Ovary Oviduct Secondary oocyte
Blastocyst
(implanted)
Ovulation
Endometrium
Uterus

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

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

86. 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

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

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

89. 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

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

91. 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

92. 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

93. Video: Ultrasound of Human Fetus 2
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
Video: Ultrasound of Human Fetus 2

99. 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

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

101. Labor occurs in three stages
Dilation of the cervix
Expulsion: delivery of the infant
Delivery of the placenta

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

103. 27.19 Reproductive technology increases our reproductive options
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

104. 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