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CAMPBELL BIOLOGY IN FOCUS
Urry • Cain • Wasserman • Minorsky • Jackson • Reece
36
Reproduction
and Development
Lecture Presentations by
Kathleen Fitzpatrick and Nicole Tunbridge
© 2014 Pearson Education, Inc.
Overview: Pairing Up for Sexual Reproduction
 Each sea slug produces sperm and eggs and thus
acts as both mother and father to the next generation
 Animal reproduction takes many forms
 A population outlives its members only by
reproduction, the generation of new individuals
from existing ones
© 2014 Pearson Education, Inc.
Figure 36.1
© 2014 Pearson Education, Inc.
Concept 36.1: Both asexual and sexual
reproduction occur in the animal kingdom
 Sexual reproduction is the creation of an offspring
by fusion of a male gamete (sperm) and female
gamete (egg) to form a zygote
 Asexual reproduction is the creation of offspring
without the fusion of egg and sperm
© 2014 Pearson Education, Inc.
Mechanisms of Asexual Reproduction
 Many invertebrates reproduce asexually by budding,
in which new individuals arise from outgrowths of
existing ones
 Also common among invertebrates is fission, the
separation of a parent organism into two individuals
of approximately equal size
Video: Hydra Budding
© 2014 Pearson Education, Inc.
Figure 36.2
© 2014 Pearson Education, Inc.
 Fragmentation is breaking of the body into pieces,
some or all of which develop into adults
 Fragmentation must be accompanied by
regeneration, regrowth of lost body parts
 Parthenogenesis is the development of a new
individual from an unfertilized egg
© 2014 Pearson Education, Inc.
Sexual Reproduction: An Evolutionary Enigma
 Sexual females have half as many daughters as
asexual females; this is the “twofold cost” of sexual
reproduction
 Despite this, almost all eukaryotic species reproduce
sexually
© 2014 Pearson Education, Inc.
Figure 36.3-1
Sexual reproduction
Asexual reproduction
Female
Generation 1
Female
Generation 2
Male
© 2014 Pearson Education, Inc.
Figure 36.3-2
Sexual reproduction
Asexual reproduction
Female
Generation 1
Female
Generation 2
Male
Generation 3
© 2014 Pearson Education, Inc.
Figure 36.3-3
Sexual reproduction
Asexual reproduction
Female
Generation 1
Female
Generation 2
Male
Generation 3
Generation 4
© 2014 Pearson Education, Inc.
 Sexual reproduction results in genetic recombination
 The resulting increased variation among offspring
may enhance the reproductive success of parents in
changing environments
© 2014 Pearson Education, Inc.
Reproductive Cycles
 Most animals exhibit reproductive cycles related to
changing seasons
 Reproductive cycles are controlled by hormones and
environmental cues
 Because seasonal temperature is often an important
cue in reproduction, climate change can decrease
reproductive success
© 2014 Pearson Education, Inc.
Figure 36.4
© 2014 Pearson Education, Inc.
 In some species of whiptail lizards, the members of
breeding pairs alternate roles
 Reproduction is exclusively asexual, and there are
no males
 However, courtship and mating behavior still take
place, with one female of each pair mimicking male
mating behavior
 The two alternate roles two or three times during
the breeding season
© 2014 Pearson Education, Inc.
Hormone
level
Ovary
size
Figure 36.5
Estradiol
Ovulation
Ovulation
Progesterone
Behavior
Time
(a) A. uniparens females
© 2014 Pearson Education, Inc.
Female
Male- Female
like
(b) The sexual behavior of A. uniparens is
correlated with the cycle of ovulation.
Malelike
Figure 36.5a
(a) A. uniparens females
© 2014 Pearson Education, Inc.
Hormone
level
Ovary
size
Figure 36.5b
Estradiol
Ovulation
Ovulation
Progesterone
Behavior
Time
Female
Male- Female
like
(b) The sexual behavior of A. uniparens is
correlated with the cycle of ovulation.
© 2014 Pearson Education, Inc.
Malelike
Variation in Patterns of Sexual Reproduction
 For many animals, finding a partner for sexual
reproduction may be challenging
 One solution is hermaphroditism, in which each
individual has male and female reproductive systems
 Any two hermaphrodites can mate, and some
hermaphrodites can self-fertilize
© 2014 Pearson Education, Inc.
 Individuals of some species undergo sex reversals
 For example, in a coral reef fish, the bluehead
wrasse, a lone male defends a group of females
 If the male dies, the largest female in the group
transforms into a male
 Within a few weeks, this individual can begin to
produce sperm instead of eggs
© 2014 Pearson Education, Inc.
External and Internal Fertilization
 Sexual reproduction requires fertilization, the
union of sperm and eggs
 In external fertilization, eggs shed by the female
are fertilized by sperm in the external environment
 In internal fertilization, sperm are deposited in or
near the female reproductive tract, and fertilization
occurs within the tract
© 2014 Pearson Education, Inc.
 A moist habitat is almost always required for external
fertilization to prevent gametes from drying out and to
allow sperm to swim to eggs
 Many aquatic invertebrates simply shed gametes into
the surrounding water
 In this case, timing of release of gametes is crucial to
ensure that sperm and egg encounter one another
 If external fertilization is not synchronous across a
population, courtship behaviors might lead to
fertilization
© 2014 Pearson Education, Inc.
Figure 36.6
© 2014 Pearson Education, Inc.
 However fertilization occurs, the mating animals
may use pheromones, chemicals released by one
organism that can influence physiology and
behavior of another individual of the same species
© 2014 Pearson Education, Inc.
Ensuring the Survival of Offspring
 Internal fertilization is typically associated with
production of fewer gametes but the survival of a
higher fraction of zygotes
 Internal fertilization is also often associated with
mechanisms to provide protection of embryos and
parental care of young
© 2014 Pearson Education, Inc.
 The embryos of some terrestrial animals develop in
eggs with calcium- and protein-containing shells and
several internal membranes
 Some other animals retain the embryo, which
develops inside the female
 In many animals, parental care helps ensure survival
of offspring
© 2014 Pearson Education, Inc.
Figure 36.7
© 2014 Pearson Education, Inc.
Concept 36.2: Reproductive organs produce and
transport gametes
 Sexual reproduction in animals relies on sets of
cells that are precursors for eggs and sperm
© 2014 Pearson Education, Inc.
Variation in Reproductive Systems
 Many (but not all) animals have gonads, organs that
produce gametes
 Some simple systems do not have gonads, but
gametes form from undifferentiated tissue
 More elaborate systems include sets of accessory
tubes and glands that carry, nourish, and protect
gametes and sometimes developing embryos
© 2014 Pearson Education, Inc.
 Most insects have separate sexes with complex
reproductive systems
 In many insects, the female has a spermatheca in
which sperm is stored during copulation
© 2014 Pearson Education, Inc.
 A cloaca is a common opening between the external
environment and the digestive, excretory, and
reproductive systems
 A cloaca is common in nonmammalian vertebrates;
mammals usually have a separate opening to the
digestive tract
© 2014 Pearson Education, Inc.
Human Male Reproductive Anatomy
 The male’s external reproductive organs are the
scrotum and penis
 The internal organs are gonads that produce sperm
and reproductive hormones, accessory glands that
secrete products essential to sperm movement, and
ducts that carry sperm and glandular secretions
Animation: Male Reproductive Anatomy
© 2014 Pearson Education, Inc.
Figure 36.8
(Urinary bladder)
Seminal
vesicle
(Urinary duct)
(Rectum)
(Pubic bone)
Vas deferens
Ejaculatory
duct
Prostate gland
Bulbourethral
gland
© 2014 Pearson Education, Inc.
Erectile
tissue
Urethra
Vas deferens
Epididymis
Testis
Scrotum
Glans
Prepuce
Penis
Testes
 The male gonads, or testes, produce sperm in
highly coiled tubes called seminiferous tubules
 Production of normal sperm cannot occur at the
body temperatures of most mammals
 The scrotum, a fold of the body wall, maintains testis
temperature at about 2oC below the core body
temperature
© 2014 Pearson Education, Inc.
Ducts
 From the seminiferous tubules of a testis, sperm
pass into the coiled duct of the epididymis
 During ejaculation, sperm are propelled through
the muscular vas deferens and the ejaculatory
duct and then exit the penis through the urethra
© 2014 Pearson Education, Inc.
Accessory Glands
 Semen is composed of sperm plus secretions from
three sets of accessory glands
 The two seminal vesicles contribute about 60% of
the total volume of semen
 The prostate gland secretes its products directly
into the urethra through several small ducts
 The bulbourethral glands secrete a clear mucus
before ejaculation that neutralizes acidic urine
remaining in the urethra
© 2014 Pearson Education, Inc.
Penis
 The human penis is composed of three cylinders of
spongy erectile tissue
 During sexual arousal, erectile tissue fills with blood
from the arteries, causing an erection
 The head of the penis, or glans, has a thinner skin
covering than the shaft
 The prepuce, or foreskin, is a fold of skin covering
the glans; it is removed when a male is circumcised
© 2014 Pearson Education, Inc.
Human Female Reproductive Anatomy
 The female external reproductive structures include
the clitoris and two sets of labia
 The internal organs are a pair of gonads and a
system of ducts and chambers that carry gametes
and house the embryo and fetus
Animation: Female Reproductive Anatomy
© 2014 Pearson Education, Inc.
Figure 36.9
Oviduct
Ovary
Uterus
(Urinary
bladder)
(Pubic bone)
(Rectum)
(Urethra)
Cervix
Vagina
Body
Clitoris
Glans
Prepuce
Major vestibular
gland
Labia minora
Vaginal opening
© 2014 Pearson Education, Inc.
Labia majora
Ovaries
 The female gonads, a pair of ovaries, lie in the
abdominal cavity
 Each ovary contains many follicles, which consist
of a partially developed egg, called an oocyte,
surrounded by support cells
© 2014 Pearson Education, Inc.
Oviducts and Uterus
 Upon ovulation, a mature egg cell is released
 It travels from the ovary to the uterus via an oviduct
 Cilia in the oviduct convey the egg to the uterus,
also called the womb
 The uterus lining, the endometrium, has many
blood vessels
 The neck of the uterus is the cervix, which opens
into the vagina
© 2014 Pearson Education, Inc.
Vagina and Vulva
 The vagina is a muscular but elastic chamber that
is the repository for sperm during copulation and
serves as the birth canal
 The vagina opens to the outside at the vulva, which
consists of the labia majora, labia minora, hymen,
and clitoris
© 2014 Pearson Education, Inc.
Mammary Glands
 The mammary glands are not part of the
reproductive system but are important to mammalian
reproduction
 Within the glands, small sacs of epithelial tissue
secrete milk
© 2014 Pearson Education, Inc.
Gametogenesis
 Gametogenesis is the production of gametes
 There is a close relationship between the structure
and function of the gonads
Video: Flagella in Sperm
Video: Sperm Flagellum
© 2014 Pearson Education, Inc.
Figure 36.10a
Epididymis
Seminiferous tubule
Testis
Primordial germ cell in embryo
Cross section of
seminiferous tubule
Mitotic divisions
Spermatogonial
stem cell
Sertoli cell
nucleus
2n
Mitotic divisions
Spermatogonium
2n
Mitotic divisions
Primary spermatocyte
2n
Meiosis I
Secondary spermatocyte
Lumen of
seminiferous
tubule
Tail
Plasma
membrane
Neck
Midpiece
n
Meiosis II
Spermatids
(two stages)
Early
spermatid
n
n
n
n
Differentiation
(Sertoli cells
provide nutrients)
Head
Acrosome
Nucleus
Mitochondria
© 2014 Pearson Education, Inc.
n
Sperm cell
n
n
n
n
Figure 36.10aa
Epididymis
Seminiferous tubule
Sertoli cell
nucleus
Testis
Spermatogonium
Primary
spermatocyte
Secondary
spermatocyte
Cross section of
seminiferous tubule
Spermatids
(two stages)
Sperm cell
Lumen of
seminiferous tubule
© 2014 Pearson Education, Inc.
Figure 36.10ab
Primordial germ cell in embryo
Mitotic divisions
Spermatogonial
stem cell
2n
Mitotic divisions
Spermatogonium
2n
Mitotic divisions
Primary spermatocyte
2n
Meiosis I
Secondary spermatocyte
n
n
Meiosis II
Early
spermatid
Sperm cell
© 2014 Pearson Education, Inc.
n
n
n
n
Differentiation
(Sertoli cells
provide nutrients)
n
n
n
n
Figure 36.10ac
Tail
Plasma
membrane
Neck
Midpiece
Head
Acrosome
Nucleus
Mitochondria
© 2014 Pearson Education, Inc.
Figure 36.10b
Ovary
Primary oocyte
within follicle
In embryo
Primordial germ cell
Mitotic divisions
2n
Oogonium
Growing
follicle
Mature follicle
Mitotic divisions
Primary oocyte
(present at birth), arrested
in prophase of meiosis I
2n
Completion of meiosis I
and onset of meiosis II
First
polar n
body
n
Secondary oocyte,
arrested at metaphase of
meiosis II
Ruptured
follicle
Ovulated
secondary oocyte
Ovulation, sperm entry
Completion of meiosis II
Second
polar n
body
n
© 2014 Pearson Education, Inc.
Fertilized egg
Corpus luteum
Degenerating
corpus luteum
Figure 36.10ba
Ovary
Primary
oocyte
within
follicle
Growing
follicle
Ruptured
follicle
Ovulated
secondary
oocyte
Mature
follicle
Corpus
luteum
Degenerating
corpus
luteum
© 2014 Pearson Education, Inc.
Figure 36.10bb
In embryo
Primordial germ cell
Mitotic divisions
2n
Oogonium
Mitotic divisions
2n
© 2014 Pearson Education, Inc.
Primary oocyte
(present at birth), arrested
in prophase of meiosis I
Figure 36.10bc
Completion of meiosis I
and onset of meiosis II
First
polar n
body
n
Secondary oocyte,
arrested at metaphase of
meiosis II
Ovulation, sperm entry
Completion of meiosis II
Second
polar n
body
n
© 2014 Pearson Education, Inc.
Fertilized egg
 Spermatogenesis, the development of sperm, is
continuous and prolific (millions of sperm are
produced per day); each sperm takes about 7 weeks
to develop
 Oogenesis, the development of a mature egg, is a
prolonged process
 Immature eggs form in the female embryo but do not
complete their development until years or decades
later
© 2014 Pearson Education, Inc.
 Spermatogenesis differs from oogenesis in three
ways
 All four products of meiosis develop into sperm, while
only one of the four becomes an egg
 Spermatogenesis occurs throughout adolescence and
adulthood
 Sperm are produced continuously without the
prolonged interruptions in oogenesis
© 2014 Pearson Education, Inc.
Concept 36.3: The interplay of tropic and sex
hormones regulates reproduction in mammals
 Human reproduction is coordinated by hormones
from the hypothalamus, anterior pituitary, and
gonads
 Gonadotropin-releasing hormone (GnRH) is secreted
by the hypothalamus and directs the release of FSH
(follicle-stimulating hormone) and LH (luteinizing
hormone) from the anterior pituitary
© 2014 Pearson Education, Inc.
 FSH and LH regulate processes in the gonads and
the production of sex hormones
 The major androgen is testosterone and major
estrogens are estradiol and progesterone
 Both males and females produce androgens and
estrogens but differ in their blood concentrations of
particular hormones
 For example, males have testosterone levels about
10 times higher than females
© 2014 Pearson Education, Inc.
 Sex hormones regulate gamete production both
directly and indirectly
 They serve many additional functions including
sexual behavior and the development of primary and
secondary sex characteristics
 Androgens are responsible for male vocalizations
and courtship displays
© 2014 Pearson Education, Inc.
Figure 36.11
© 2014 Pearson Education, Inc.
Hormonal Control of the Male Reproductive
System
 FSH and LH act on different cells in the testes to
direct spermatogenesis
 Sertoli cells, found in the seminiferous tubules,
respond to FSH by nourishing developing sperm
 Leydig cells, connective tissue between the
tubules, respond to LH by secreting testosterone
and other androgens, which promote
spermatogenesis
Animation: Male Hormones
© 2014 Pearson Education, Inc.
Figure 36.12
Hypothalamus
GnRH
FSH
LH
Leydig cells
Sertoli cells
Inhibin
Spermatogenesis
Testis
© 2014 Pearson Education, Inc.
Testosterone
Negative feedback
Negative feedback
Anterior pituitary
 Two negative feedback mechanisms control sex
hormone production in males
 Testosterone regulates the production of GnRH,
FSH, and LH through negative feedback
mechanisms
 Sertoli cells secrete the hormone inhibin, which
reduces FSH secretion from the anterior pituitary
© 2014 Pearson Education, Inc.
Hormonal Control of Female Reproductive Cycles
 Females produce eggs in cycles
 Prior to ovulation, the endometrium thickens with
blood vessels in preparation for embryo implantation
 If an embryo does not implant in the endometrium,
the endometrium is shed in a process called
menstruation
© 2014 Pearson Education, Inc.
 Hormones closely link the two cycles of female
reproduction
 Changes in the uterus define the menstrual cycle
(also called the uterine cycle)
 Changes in the ovaries define the ovarian cycle
Animation: Ovulation
Animation: Post-Ovulation
© 2014 Pearson Education, Inc.
Figure 36.13
(a)
Control by hypothalamus
Inhibited by combination of
estradiol and progesterone
Hypothalamus
Stimulated by high levels
of estradiol
GnRH
1
Anterior pituitary
2
FSH
Inhibited by low levels of
estradiol
LH
Pituitary gonadotropins
in blood
(b)
6
LH
FSH
FSH and LH stimulate
follicle to grow
3
(c)
Ovarian cycle
7
Growing follicle
Maturing
follicle
8
Follicular phase
Corpus
luteum
Ovulation
Degenerating
corpus luteum
Luteal phase
Estradiol secreted
by growing follicle in
increasing amounts
4
(d)
LH surge triggers
ovulation
Progesterone and
estradiol secreted
by corpus luteum
Ovarian hormones
in blood
Peak causes
LH surge
(see 6 )
5
10
9
Estradiol
Progesterone
Estradiol level
very low
(e)
Progesterone and estradiol promote thickening
of endometrium
Uterine (menstrual) cycle
Endometrium
Days
Menstrual flow phase
© 2014 Pearson Education, Inc.
0
5
Proliferative phase
10
14 15
Secretory phase
20
25
28
Figure 36.13a
(a)
Control by hypothalamus
Inhibited by combination of
estradiol and progesterone
Hypothalamus
Stimulated by high levels
of estradiol
GnRH
1
Anterior pituitary
2
FSH
Inhibited by low levels of
estradiol
LH
Pituitary gonadotropins
in blood
(b)
6
LH
FSH
Days
3
0
© 2014 Pearson Education, Inc.
FSH and LH stimulate
follicle to grow
5
10
LH surge triggers
ovulation
14 15
20
25
28
Figure 36.13b
(b)
Pituitary gonadotropins
in blood
6
LH
FSH
3
Days
(c)
FSH and LH stimulate
follicle to grow
Ovarian cycle
7
Growing follicle
Maturing
follicle
LH surge triggers
ovulation
8
Corpus
luteum
Follicular phase
Ovulation
Estradiol secreted
4
by growing follicle in
increasing amounts
0
© 2014 Pearson Education, Inc.
5
10
14 15
Degenerating
corpus luteum
Luteal phase
Progesterone and
estradiol secreted
by corpus luteum
20
25
28
Figure 36.13c
(c)
Ovarian cycle
7
Growing follicle
Maturing
follicle
8
Follicular phase
Ovulation
Ovarian hormones
in blood
5
Degenerating
corpus luteum
Luteal phase
Estradiol secreted
by growing follicle in
increasing amounts
4
(d)
Corpus
luteum
Progesterone and
estradiol secreted
by corpus luteum
Peak causes
LH surge
(see 6 )
10
9
Estradiol
Progesterone
Progesterone and estradiol promote thickening
of endometrium
Days
Estradiol level
very low
0
© 2014 Pearson Education, Inc.
5
10
14 15
20
25
28
Figure 36.13d
(d)
Ovarian hormones
in blood
Peak causes
LH surge
(see 6 )
5
10
9
Estradiol
Progesterone
Estradiol level
very low
(e)
Progesterone and estradiol promote thickening
of endometrium
Uterine (menstrual) cycle
Endometrium
Days
Menstrual flow phase
0
© 2014 Pearson Education, Inc.
5
Proliferative phase
10
14 15
Secretory phase
20
25
28
The Ovarian Cycle
 The sequential release of GnRH then FSH and LH
stimulates follicle growth
 Follicle and oocyte growth and an increase in the
hormone estradiol characterize the follicular phase
of the ovarian cycle
 Estradiol causes GnRH, FSH, and LH levels to rise
through positive feedback
 The final result is the maturation of the follicle
© 2014 Pearson Education, Inc.
 At the end of the follicular phase, the follicle
releases the secondary oocyte
 The follicular tissue left behind transforms into the
corpus luteum in response to LH; this is the luteal
phase
 The corpus luteum disintegrates, and ovarian steroid
hormones decrease by negative feedback
mechanisms
© 2014 Pearson Education, Inc.
The Uterine (Menstrual) Cycle
 Hormones coordinate the uterine cycle with the
ovarian cycle
 Thickening of the endometrium during the proliferative
phase coordinates with the follicular phase
 Secretion of nutrients during the secretory phase
coordinates with the luteal phase
 Shedding of the endometrium during the menstrual
flow phase coordinates with the growth of new
ovarian follicles
© 2014 Pearson Education, Inc.
Menopause
 After about 500 cycles, human females undergo
menopause, the cessation of ovulation and
menstruation
 Menopause is very unusual among animals
 Menopause might have evolved to allow a mother to
provide better care for her children and grandchildren
© 2014 Pearson Education, Inc.
Menstrual Versus Estrous Cycles
 Menstrual cycles are characteristic only of humans
and some other primates
 The endometrium is shed from the uterus in a
bleeding called menstruation
 Sexual receptivity is not limited to a time frame
© 2014 Pearson Education, Inc.
 Estrous cycles are characteristic of most mammals
 The endometrium is reabsorbed by the uterus
 Sexual receptivity is limited to a “heat” period
 The length and frequency of estrus cycles vary from
species to species
© 2014 Pearson Education, Inc.
Human Sexual Response
 Two reactions predominate in both sexes
 Vasocongestion, the filling of tissue with blood
 Myotonia, increased muscle tension
 The sexual response cycle has four phases:
excitement, plateau, orgasm, and resolution
 Excitement prepares the penis and vagina for coitus
(sexual intercourse)
© 2014 Pearson Education, Inc.
 Direct stimulation of genitalia maintains the plateau
phase and prepares the vagina for receipt of sperm
 Orgasm is characterized by rhythmic contractions of
reproductive structures
 In males, semen is first released into the urethra and
then ejaculated from the urethra
 In females, the uterus and outer vagina contract
© 2014 Pearson Education, Inc.
 During the resolution phase, organs return to their
normal state and muscles relax
© 2014 Pearson Education, Inc.
Concept 36.4: Fertilization, cleavage, and
gastrulation initiate embryonic development
 Across animal species, embryonic development
involves common stages occurring in a set order
 First is fertilization, which forms a zygote
 During the cleavage stage, a series of mitoses
divide the zygote into a many-celled embryo
 The resulting blastula then undergoes
rearrangements into a three-layered embryo called
a gastrula
© 2014 Pearson Education, Inc.
Figure 36.14
EMBRYONIC DEVELOPMENT
Sperm
Zygote
Adult
frog
Egg
Blastula
Metamorphosis
Larval
stages
Gastrula
Tail-bud
embryo
© 2014 Pearson Education, Inc.
Fertilization
 Molecules and events at the egg surface play a
crucial role in each step of fertilization
 Sperm penetrate the protective layer around the egg
 Receptors on the egg surface bind to molecules on
the sperm surface
 Changes at the egg surface prevent polyspermy, the
entry of multiple sperm nuclei into the egg
© 2014 Pearson Education, Inc.
Video: Cortical Granule
Video: Calcium Release of Egg
Video: Calcium Wave of Egg
© 2014 Pearson Education, Inc.
Figure 35.15-1
Basal body
(centriole)
Sperm
head
Acrosome
Jelly coat
Spermbinding
receptors
© 2014 Pearson Education, Inc.
Vitelline layer
Egg plasma membrane
Figure 35.15-2
Basal body
(centriole)
Sperm
head
Acrosome
Jelly coat
Spermbinding
receptors
© 2014 Pearson Education, Inc.
Hydrolytic enzymes
Vitelline layer
Egg plasma membrane
Figure 35.15-3
Sperm
nucleus
Acrosomal
process
Basal body
(centriole)
Sperm
head
Acrosome
Jelly coat
Spermbinding
receptors
© 2014 Pearson Education, Inc.
Actin
filament
Hydrolytic enzymes
Vitelline layer
Egg plasma membrane
Figure 35.15-4
Sperm plasma
membrane
Sperm
nucleus
Acrosomal
process
Basal body
(centriole)
Sperm
head
Actin
filament
Fused
plasma
membranes
Acrosome
Jelly coat
Spermbinding
receptors
© 2014 Pearson Education, Inc.
Hydrolytic enzymes
Vitelline layer
Egg plasma membrane
Figure 35.15-5
Sperm plasma
membrane
Sperm
nucleus
Acrosomal
process
Basal body
(centriole)
Sperm
head
Acrosome
Jelly coat
Spermbinding
receptors
© 2014 Pearson Education, Inc.
Actin
filament
Cortical
Fused
granule
plasma
membranes
Perivitelline
Hydrolytic enzymes
space
Fertilization
Vitelline layer
envelope
Egg plasma membrane
 The events of fertilization also initiate metabolic
reactions that trigger the onset of embryonic
development, thus “activating” the egg
 Activation leads to events such as increased protein
synthesis that precede the formation of a diploid
nucleus
 Sperm entry triggers a release of Ca2+, which
activates the egg and triggers the cortical reaction,
the slow block to polyspermy
© 2014 Pearson Education, Inc.
Figure 36.16
Seconds
1
2
3
4
6
8
10
20
30
40
50
1
Binding of sperm to egg
Acrosomal reaction: plasma membrane
depolarization (fast block to polyspermy)
Increased intracellular calcium level
Cortical reaction (slow block to polyspermy)
Formation of fertilization envelope complete
Minutes
2
3
4
5
Increased protein synthesis
10
20
30
40
60
90
© 2014 Pearson Education, Inc.
Fusion of egg and sperm nuclei complete
Onset of DNA synthesis
First cell division
Cleavage and Gastrulation
 Fertilization is followed by cleavage, a period of
rapid cell division without growth
 Cleavage partitions the cytoplasm of one large cell
into many smaller cells
 The blastula is a ball of cells with a fluid-filled cavity
called a blastocoel
 The blastula is produced after about five to seven
cleavage divisions
Video: Cleavage of Egg
© 2014 Pearson Education, Inc.
Figure 36.17
50 m
(a) Fertilized egg
© 2014 Pearson Education, Inc.
(b) Four-cell stage (c) Early blastula
(d) Later blastula
Figure 36.17a
50 m
(a) Fertilized egg
© 2014 Pearson Education, Inc.
Figure 36.17b
50 m
(b) Four-cell stage
© 2014 Pearson Education, Inc.
Figure 36.17c
50 m
(c) Early blastula
© 2014 Pearson Education, Inc.
Figure 36.17d
50 m
(d) Later blastula
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 After cleavage, the rate of cell division slows
 The remaining stages of embryonic development
are responsible for morphogenesis, the cellular
and tissue-based processes by which the animal
body takes shape
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 During gastrulation, a set of cells at or near the
surface of the blastula moves to an interior location,
cell layers are established, and a primitive digestive
tube forms
 The hollow blastula is reorganized into a two- or
three-layered embryo called a gastrula
© 2014 Pearson Education, Inc.
 The cell layers produced by gastrulation are called
germ layers
 The ectoderm forms the outer layer and the
endoderm the inner layer
 In vertebrates and other animals with bilateral
symmetry, a third germ layer, the mesoderm,
forms between the endoderm and ectoderm
© 2014 Pearson Education, Inc.
Figure 36.18
Animal
pole
Blastocoel
Mesenchyme cells
Vegetal plate
Vegetal
pole
Blastocoel
Filopodia
Archenteron
Mesenchyme cells
Blastopore
Key
Future ectoderm
Future mesoderm
Future endoderm
50 m
Blastocoel
Ectoderm
Mouth
Mesenchyme
(mesoderm forms
future skeleton)
© 2014 Pearson Education, Inc.
Archenteron
Blastopore
Digestive tube (endoderm)
Anus (from blastopore)
Figure 36.18a-1
Animal
pole
Blastocoel
Mesenchyme
cells
Vegetal plate
Vegetal
pole
© 2014 Pearson Education, Inc.
Future ectoderm
Future mesoderm
Future endoderm
Figure 36.18a-2
Animal
pole
Blastocoel
Mesenchyme
cells
Vegetal plate
Vegetal
pole
Future ectoderm
Future mesoderm
Future endoderm
Filopodia
Archenteron
© 2014 Pearson Education, Inc.
Figure 36.18a-3
Animal
pole
Blastocoel
Mesenchyme
cells
Vegetal plate
Vegetal
pole
Future ectoderm
Future mesoderm
Future endoderm
Filopodia
Archenteron
Blastocoel
Archenteron
Blastopore
© 2014 Pearson Education, Inc.
Figure 36.18a-4
Animal
pole
Blastocoel
Mesenchyme
cells
Vegetal plate
Vegetal
pole
Future ectoderm
Future mesoderm
Future endoderm
Filopodia
Archenteron
Blastocoel
Ectoderm
Mouth
Mesenchyme
(mesoderm forms
future skeleton)
© 2014 Pearson Education, Inc.
Archenteron
Blastopore
Digestive tube (endoderm)
Anus (from blastopore)
Figure 36.18b
Blastocoel
Filopodia
Archenteron
Mesenchyme
cells
Blastopore
© 2014 Pearson Education, Inc.
50 m
 Cell movements and interactions that form the germ
layers vary among species
 One distinction is whether the mouth develops at the
first opening that forms in the embryo (protostomes)
or the second (deuterostomes)
 Sea urchins and other echinoderms are
deuterostomes, as are chordates
© 2014 Pearson Education, Inc.
 Each germ layer contributes to a distinct set of
structures in the adult animal
 Some organs and many organ systems derive from
more than one germ layer
© 2014 Pearson Education, Inc.
Figure 36.19
ECTODERM (outer layer of embryo)
• Epidermis of skin and its derivatives (including sweat glands,
hair follicles)
• Nervous and sensory systems
• Pituitary gland, adrenal medulla
• Jaws and teeth
• Germ cells
MESODERM (middle layer of embryo)
• Skeletal and muscular systems
• Circulatory and lymphatic systems
• Excretory and reproductive systems (except germ cells)
• Dermis of skin
• Adrenal cortex
ENDODERM (inner layer of embryo)
• Epithelial lining of digestive tract and associated organs
(liver, pancreas)
• Epithelial lining of respiratory, excretory, and reproductive tracts
and ducts
• Thymus, thyroid, and parathyroid glands
© 2014 Pearson Education, Inc.
Human Conception, Embryonic Development,
and Birth
 Conception, fertilization of an egg by a sperm,
occurs in the oviduct
 The resulting zygote begins cleavage about 24 hours
after fertilization and produces a blastocyst after
4 more days
 A few days later, the embryo implants into the
endometrium of the uterus
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 The condition of carrying one or more embryos in
the uterus is called gestation, or pregnancy
 Human pregnancy averages 38 weeks from
fertilization
 Gestation varies among mammals, from 21 days in
many rodents to more than 600 days in elephants
 Human gestation is divided into three trimesters of
about three months each
© 2014 Pearson Education, Inc.
Figure 36.20
3 Cleavage
4 Cleavage
continues.
Ovary
2 Fertilization
Uterus
1 Ovulation
5 Implantation
Endometrium
(a) From ovulation to implantation
Endometrium
Inner
cell
mass
Cavity
Blastocyst
(b) Implantation of blastocyst
© 2014 Pearson Education, Inc.
Trophoblast
 During the first trimester, the embryo secretes
hormones that signal its presence and regulate the
mother’s reproductive system
 Human chorionic gonadotropin (hCG) acts to
maintain secretion of progesterone and estrogens by
the corpus luteum through the first few months of
pregnancy
© 2014 Pearson Education, Inc.
 Occasionally an embryo splits during the first month
of development, resulting in identical or monozygotic
twins
 Fraternal, or dizygotic, twins arise when two eggs
are fertilized and implant as two genetically distinct
embryos
 Some embryos cannot complete development due to
chromosomal or other abnormalities
 These spontaneously abort, often before a woman is
aware of her pregnancy
© 2014 Pearson Education, Inc.
 During its first 2 to 4 weeks, the embryo obtains
nutrients directly from the endometrium
 Meanwhile, the outer layer of the blastocyst, called
the trophoblast, mingles with the endometrium and
eventually forms the placenta
 Materials diffuse between maternal and embryonic
circulation to supply the embryo with nutrients,
immune protection, and metabolic waste disposal
© 2014 Pearson Education, Inc.
 The first trimester is the main period of
organogenesis, development of the body organs
 All the major structures are present by 8 weeks, and
the embryo is called a fetus
Video: Ultrasound of Fetus
© 2014 Pearson Education, Inc.
Figure 36.21
(a) 5 weeks
© 2014 Pearson Education, Inc.
(b) 14 weeks
(c) 20 weeks
Figure 36.21a
(a) 5 weeks
© 2014 Pearson Education, Inc.
Figure 36.21b
(b) 14 weeks
© 2014 Pearson Education, Inc.
Figure 36.21c
(c) 20 weeks
© 2014 Pearson Education, Inc.
 During the second trimester the fetus grows and is
very active
 The mother may feel fetal movements as early as
one month into the second trimester
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 During the third trimester, the fetus grows and fills
the space within the embryonic membranes
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 Childbirth begins with labor, a series of strong,
rhythmic contractions that push the fetus and
placenta out of the body
 Once labor begins, local regulators, prostaglandins
and hormones, induce and regulate further
contractions of the uterus
© 2014 Pearson Education, Inc.
 Lactation, the production of milk, is an aspect of
maternal care unique to mammals
 Suckling stimulates the release of prolactin, which in
turn stimulates mammary glands to produce milk,
and the secretion of oxytocin, which triggers milk
release from the glands
© 2014 Pearson Education, Inc.
Contraception
 Contraception, the deliberate prevention of
pregnancy, can be achieved in a number of ways
 Contraceptive methods fall into three categories
 Preventing development or release of eggs and sperm
 Keeping sperm and egg apart
 Preventing implantation of an embryo
© 2014 Pearson Education, Inc.
 A health-care provider should be consulted for
complete information on the choice and risks of
contraception methods
© 2014 Pearson Education, Inc.
Figure 36.22
Male
Method
Female
Event
Event
Method
Production of Production of
sperm
primary oocytes
Vasectomy
Sperm transport
Oocyte
down male
development
duct system and ovulation
Abstinence
Condom
Coitus
interruptus
(very high
failure rate)
Combination
birth control
pill (or injection,
patch, or
vaginal ring)
Abstinence
Female condom
Sperm
deposited
in vagina
Capture of the
oocyte by the
oviduct
Tubal ligation
Sperm
movement
through female
reproductive
tract
Transport
of oocyte in
oviduct
Spermicides;
diaphragm;
progestin alone
(as minipill
or injection)
Meeting of sperm and oocyte
in oviduct
Union of sperm and egg
Implantation of blastocyst
in endometrium
© 2014 Pearson Education, Inc.
Morning-after
pill; intrauterine
device (IUD)
Figure 36.22a
Male
Method
Female
Event
Event
Production of Production of
sperm
primary oocytes
Vasectomy
Oocyte
Sperm transport
development
down male
duct system and ovulation
Abstinence
Condom
Coitus
interruptus
(very high
failure rate)
Method
Combination
birth control
pill (or injection,
patch, or
vaginal ring)
Abstinence
Female condom
Sperm
deposited
in vagina
Capture of the
oocyte by the
oviduct
Tubal ligation
Spermicides;
diaphragm;
progestin alone
(as minipill
or injection)
© 2014 Pearson Education, Inc.
Figure 36.22b
Male
Method
Female
Event
Sperm
movement
through female
reproductive
tract
Event
Transport
of oocyte in
oviduct
Method
Meeting of sperm and oocyte
in oviduct
Union of sperm and egg
Implantation of blastocyst
in endometrium
© 2014 Pearson Education, Inc.
Morning-after
pill; intrauterine
device (IUD)
 The rhythm method, or natural family planning, is
temporary abstinence when conception is most
likely; it has a pregnancy rate of 10–20%
 Coitus interruptus, the withdrawal of the penis before
ejaculation, is unreliable
 Barrier methods block fertilization with a pregnancy
rate of less than 10%
 A condom fits over the penis
 A diaphragm is inserted into the vagina before
intercourse
© 2014 Pearson Education, Inc.
 Intrauterine devices (IUDs) are inserted into the
uterus and interfere with fertilization and implantation;
the pregnancy rate is less than 1%
 Female birth control pills are hormonal
contraceptives with a pregnancy rate of less than 1%
© 2014 Pearson Education, Inc.
Infertility and In Vitro Fertilization
 Infertility, the inability to conceive offspring, affects
about one in ten couples in the United States and
worldwide
 The causes are varied and equally likely to affect
men and women
 Sexually transmitted diseases (STDs) are the most
significant preventable causes of infertility
© 2014 Pearson Education, Inc.
 Some forms of infertility are treatable
 Hormone therapy can sometimes increase sperm or
egg production
 In vitro fertilization (IVF) mixes oocytes with sperm
in culture dishes and returns the embryo to the uterus
at the eight-cell stage
 Sperm may be injected directly into an oocyte as well
© 2014 Pearson Education, Inc.
Figure 36.UN01
© 2014 Pearson Education, Inc.
Figure 36.UN02
Human gametogenesis
Spermatogenesis
Oogenesis
Primary
spermatocyte
2n
Primary
oocyte
2n
Polar
n body
n
Secondary
spermatocytes
n
n
n
n
n
Spermatids
n
n
n
n
Sperm
n
Secondary
oocyte
n Polar body
n
© 2014 Pearson Education, Inc.
Fertilized
egg