Download chapter 27 Reproduction

Chapter 27
Reproduction and Embryonic
Development
PowerPoint Lectures for
Campbell Biology: Concepts & Connections, Seventh Edition
Reece, Taylor, Simon, and Dickey
© 2012 Pearson Education, Inc.
Lecture by Edward J. Zalisko
Introduction
 Fertility drugs
– increase the number of eggs that are ovulated and
– have allowed thousands of infertile couples to have
babies.
 Ten percent of women taking fertility drugs become
pregnant with more than one embryo.
© 2012 Pearson Education, Inc.
Introduction
 Newborns from multiple births are
– more likely to be premature,
– more likely to have lower birth weights, and
– less likely to survive.
© 2012 Pearson Education, Inc.
Figure 27.0_1
Chapter 27: Big Ideas
Asexual and Sexual
Reproduction
Human Reproduction
Principles of Embryonic
Development
Human Development
Figure 27.0_2
ASEXUAL AND SEXUAL
REPRODUCTION
© 2012 Pearson Education, Inc.
27.1 Asexual reproduction results in the
generation of genetically identical offspring
 Asexual reproduction
– is the creation of genetically identical offspring by one
parent,
– is a very rapid form of reproduction, and
– can proceed via
– budding,
– fission, or
– fragmentation/regeneration.
Video: Hydra Budding
© 2012 Pearson Education, Inc.
Figure 27.1A
Figure 27.1B
27.2 Sexual reproduction results in the generation
of genetically unique offspring
 Sexual reproduction
– is the creation of offspring by fertilization and
– joins two haploid sex cells or gametes to form a diploid
(2n) zygote.
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27.2 Sexual reproduction results in the generation
of genetically unique offspring
 The male gamete, the sperm,
– is relatively small and
– moves by means of a flagellum.
 The female gamete, the egg,
– is a much larger cell and
– is not self-propelled.
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27.2 Sexual reproduction results in the generation
of genetically unique offspring
 Some organisms, such as sea anemones, can
reproduce both
– asexually and
– sexually.
Video: Hydra Releasing Sperm
© 2012 Pearson Education, Inc.
Figure 27.2A
Eggs
Two
offspring
arising by
fission
27.2 Sexual reproduction results in the generation
of genetically unique offspring
 Some animals exhibit hermaphroditism in which an
individual has both female and male reproductive
systems.
 Hermaphroditism makes it easier to find a mate for
animals that are solitary or less mobile.
 Hermaphrodites may
– exchange gametes with other individuals or
– fertilize their own eggs.
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Figure 27.2B
27.2 Sexual reproduction results in the generation
of genetically unique offspring
 External fertilization
– occurs when eggs and sperm are discharged near each
other and
– is used by many fish and amphibian species.
 Internal fertilization
– occurs when sperm is deposited in or near the female
reproductive tract and
– is used by some fish and amphibian species and nearly
all terrestrial animals.
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Figure 27.2C
Egg
HUMAN REPRODUCTION
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27.3 Reproductive anatomy of the human female
 Both sexes in humans have
– a set of gonads where gametes are produced,
– ducts for gamete transport, and
– structures for copulation.
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27.3 Reproductive anatomy of the human female
 Ovaries contain follicles that
– nurture eggs and
– produce sex hormones.
 An immature egg is ejected from the follicle in a
process called ovulation.
Animation: Female Reproductive Anatomy
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27.3 Reproductive anatomy of the human female
 Oviducts convey eggs to the uterus where a
fertilized egg develops.
 The uterus opens into the vagina through the
cervix.
 The vagina
– receives the penis during sexual intercourse and
– forms the birth canal.
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Figure 27.3A
Ovaries
Oviduct
Follicles
Corpus luteum
Uterus
Wall of uterus
Endometrium
(lining of uterus)
Vagina
Cervix
(“neck” of uterus)
Figure 27.3B
Egg
cell
Ovary
Figure 27.3C
Oviduct
Ovary
Uterus
Rectum
(digestive system)
Cervix
Vagina
Anus
(digestive system)
Urinary bladder
(excretory system)
Pubic bone
(skeletal system)
Urethra
(excretory system)
Shaft
Prepuce Clitoris
Glans
Labia minora
Labia majora
Vaginal opening
Vulva
Figure 27.3C_1
Oviduct
Ovary
Uterus
Rectum
(digestive system)
Cervix
Vagina
Anus
(digestive system)
Figure 27.3C_2
Oviduct
Ovary
Uterus
Urinary bladder
(excretory system)
Pubic bone
(skeletal system)
Urethra
(excretory system)
Shaft
Prepuce Clitoris
Glans
Vulva
Labia minora
Labia majora
Vaginal opening
27.4 Reproductive anatomy of the human male
 Testes (singular, testis) produce
– sperm and
– male hormones.
 The epididymis stores sperm as they develop
further.
 Several glands contribute to semen. These are the
– seminal vesicles,
– prostate gland, and
– bulbourethral glands.
Animation: Male Reproductive Anatomy
© 2012 Pearson Education, Inc.
Figure 27.4A
Urinary bladder
(excretory
system)
Seminal
vesicle
(behind
bladder)
Prostate gland
Bulbourethral
gland
Urethra
Erectile tissue
of penis
Vas deferens
Scrotum
Epididymis
Testis
Glans of
penis
Figure 27.4B
Rectum
(digestive
system)
Urinary bladder
(excretory system)
Seminal vesicle
Vas deferens
Pubic bone
(skeletal system)
Ejaculatory
duct
Prostate gland
Erectile
tissue
Bulbourethral gland
Anus
(digestive system)
Vas deferens
Testicle
Urethra
(excretory
system)
Epididymis
Testis
Glans of penis
Scrotum
Prepuce
Penis
Figure 27.4B_1
Rectum
(digestive
system)
Seminal vesicle
Vas deferens
Ejaculatory
duct
Prostate gland
Bulbourethral gland
Anus
(digestive system)
Figure 27.4B_2
Urinary bladder
(excretory system)
Pubic bone
(skeletal system)
Erectile
tissue
Testicle
Vas deferens
Urethra
(excretory
system)
Epididymis
Glans of penis
Testis
Scrotum
Prepuce
Penis
27.4 Reproductive anatomy of the human male
 During ejaculation
– sperm is expelled from the epididymis,
– the seminal vesicles, prostate, and bulbourethral glands
secrete into the urethra, and
– semen is formed and expelled from the penis.
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Figure 27.4C
Contractions
of vas deferens
Sphincter
contracts
Urinary
bladder
Urethral region here
expands and fills
with semen
Contractions
of seminal
vesicle
Contractions
of prostate
gland
1
Sphincter
contracts
Sphincter remains
contracted
Contractions
of epididymis
Semen expelled
Contractions
of muscles
around base
of penis
Sphincter
relaxes
2
Contractions
of urethra
27.4 Reproductive anatomy of the human male
 Sperm production
– is regulated by a negative feedback system of hormones
and
– involves the
– hypothalamus,
– anterior pituitary, and
– testes.
Animation: Male Hormones
© 2012 Pearson Education, Inc.
Figure 27.4D
Stimuli from other
areas in the brain
Releasing
hormone
Anterior
pituitary
FSH
LH
Androgen
production
Testis
Sperm
production
Negative feedback
Hypothalamus
27.5 The formation of sperm and egg cells
requires meiosis
 Spermatogenesis occurs in seminiferous tubules.
– Primary spermatocytes
– are formed by mitosis and
– divide by meiosis I to produce secondary spermatocytes.
– Secondary spermatocytes
– divide by meiosis II to produce round spermatids,
– spermatids differentiate into elongate sperm, and
– mature sperm are released into seminiferous tubules.
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Figure 27.5A
Penis
Epididymis
Testis
Seminiferous
tubule
Scrotum
Testis
2n
Diploid cell
Differentiation and
onset of meiosis I
2n
Primary
spermatocyte
Cross section of
seminiferous tubule
(diploid; in prophase
of meiosis I)
Meiosis I completed
n
Secondary
spermatocyte
n
(haploid)
Developing
sperm cells
Meiosis II
n
n
n
n
Differentiation
Sperm cells
(haploid)
Mature sperm released into center of
seminiferous tubule
n
n
n
n
Figure 27.5A_1
Penis
Epididymis
Testis
Seminiferous
tubule
Scrotum
Testis
Cross section of
seminiferous tubule
Figure 27.5A_2
2n
Diploid cell
Differentiation and
onset of meiosis I
2n
Primary
spermatocyte
(diploid; in prophase
of meiosis I)
Meiosis I completed
n
Secondary
spermatocyte
n
(haploid)
Meiosis II
Developing
sperm cells
n
Sperm cells
(haploid)
n
Mature sperm released into center of
seminiferous tubule
n
n
n
Differentiation
n
n
n
Figure 27.5A_3
2n
Diploid cell
Differentiation and
onset of meiosis I
Primary
spermatocyte
(diploid; in prophase
of meiosis I)
Secondary
spermatocyte
(haploid)
2n
Meiosis I
completed
n
n
Figure 27.5A_4
n
Secondary
spermatocyte
(haploid)
Meiosis II
Developing
sperm cells
n
Sperm cells
(haploid)
n
Mature sperm released into
center of seminiferous tubule
n
n
n
n
Differentiation
n
n
n
27.5 The formation of sperm and egg cells
requires meiosis
 Oogenesis begins before birth when a diploid cell in
each developing follicle begins meiosis.
– Each month about one primary oocyte resumes meiosis.
– A secondary oocyte arrested at metaphase of meiosis II
is ovulated.
– Meiosis of the ovum is completed after fertilization.
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Figure 27.5B
Before
birth
Ovary
Diploid cell
Differentiation
and onset
of meiosis I
Primary
oocyte
within
follicle
Primary oocyte
(arrested in prophase
of meiosis I; present
at birth)
Growing
follicle
Completion of meiosis I
and onset of meiosis II
Mature
follicle
Ruptured
follicle
First
polar body
Secondary oocyte
Ovulated
secondary oocyte
(arrested at metaphase
of meiosis II; released
from ovary)
Entry of sperm triggers
completion of meiosis II
Corpus luteum
Second
polar body
Mature egg
(ovum)
Degenerating
corpus luteum
Figure 27.5B_1
Before
birth
Ovary
Diploid cell
Differentiation
and onset
of meiosis I
Primary
oocyte
Primary oocyte
within
(arrested in prophase
follicle of meiosis I; present
at birth)
Figure 27.5B_2
Growing
follicle
Completion of meiosis I
and onset of meiosis II
Mature
follicle
Ruptured
follicle
First
polar body
Secondary oocyte
(arrested at metaphase
Ovulated
secondary oocyte of meiosis II; released
from ovary)
Figure 27.5B_3
Ruptured
follicle
First
polar body
Secondary oocyte
Ovulated
secondary oocyte
(arrested at metaphase
of meiosis II; released
from ovary)
Entry of sperm triggers
completion of meiosis II
Corpus luteum
Second
polar body
Mature egg
(ovum)
Degenerating
corpus luteum
27.5 The formation of sperm and egg cells
requires meiosis
 Oogenesis and spermatogenesis are
– alike in that both produce haploid gametes but
– different in that
– oogenesis produces only one mature egg and polar bodies that
degenerate and
– spermatogenesis produces four mature gametes.
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27.6 Hormones synchronize cyclic changes in the
ovary and uterus
 About every 28 days
– the hypothalamus signals the anterior pituitary to secrete
follicle-stimulating hormone (FSH) and luteinizing
hormone (LH),
– which trigger the growth of a follicle and ovulation, the
release of an egg.
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Table 27.6
27.6 Hormones synchronize cyclic changes in the
ovary and uterus
 After ovulation, the ovarian follicle becomes the
corpus luteum.
 The corpus luteum secretes estrogen and
progesterone, which
– stimulate the endometrium to thicken,
– prepare the uterus for implantation of the embryo, and
– inhibit the hypothalamus, reducing FSH and LH secretion.
Animation: Ovulation
Animation: Post Ovulation
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27.6 Hormones synchronize cyclic changes in the
ovary and uterus
 If the egg is fertilized
– the embryo releases hormones that maintain the uterine
lining and
– menstruation does not occur.
 If the egg is not fertilized
– the drop in LH shuts down the corpus luteum and its
hormones,
– menstruation is triggered, and
– the hypothalamus and pituitary stimulate development of
a new follicle.
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Figure 27.6
Control by hypothalamus
A
Inhibited by combination of
estrogen and progesterone
Hypothalamus
Stimulated by high levels
of estrogen
Releasing hormone
Anterior pituitary
FSH
1
LH
B Pituitary hormones
in blood
4
LH peak triggers
ovulation and
corpus luteum
formation
6
LH
FSH
2
C
FSH stimulates
follicle to grow
LH surge
triggers ovulation
Ovarian cycle
Growing
follicle
5
Mature
follicle
Ovulation
Pre-ovulatory phase
Corpus Degenerating
corpus
luteum
luteum
Post-ovulatory phase
Progesterone and
estrogen secreted by
remnant of follicle
Estrogen secreted
by growing follicle
Peak causes
LH surge
Ovarian
hormones
in blood
D
3
7
Estrogen
Progesterone
Progesterone and
estrogen promote
thickening of
endometrium
Low levels of
estrogen trigger
menstruation
E Menstrual cycle
8
Endometrium
0
5
Menstruation
10
14 15
Days
20
25
28
Figure 27.6_1
Control by hypothalamus
Hypothalamus
Releasing hormone
Anterior pituitary
FSH
LH
Inhibited by combination of
estrogen and progesterone
Stimulated by high levels
of estrogen
Figure 27.6_2
0
5
10
Pituitary hormones
in blood
Days
14 15
20
LH peak triggers
ovulation and
corpus luteum
formation
LH
FSH
FSH stimulates
follicle to grow
LH surge
triggers ovulation
25
28
Figure 27.6_3
0
10
5
Days
14 15
20
25
28
Ovarian cycle
Growing
follicle
Mature
follicle
Ovulation
Pre-ovulatory phase
Estrogen secreted
by growing follicle
Corpus Degenerating
corpus
luteum
luteum
Post-ovulatory phase
Progesterone and
estrogen secreted by
remnant of follicle
Figure 27.6_4
0
5
10
Days
14 15
20
25
28
Peak causes
LH surge
Ovarian
hormones
in blood
Estrogen
Progesterone
Low levels of
estrogen trigger
menstruation
Progesterone and
estrogen promote
thickening of
endometrium
Figure 27.6_5
Menstrual cycle
Endometrium
0
5
Menstruation
10
14 15
Days
20
25
28
27.7 CONNECTION: Sexual activity can transmit
disease
 Sexually transmitted diseases (STDs) caused by
bacteria can often be cured.
 Chlamydia
– is the most common bacterial STD,
– often produces no symptoms, and
– can lead to pelvic inflammatory disease and infertility.
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27.7 CONNECTION: Sexual activity can transmit
disease
 Viral diseases
– such as genital herpes and HIV,
– can only be controlled.
 The best way to avoid the spread of STDs is
abstinence.
 Latex condoms provide the best protection against
disease transmission for “safer sex.”
© 2012 Pearson Education, Inc.
Table 27.7
27.8 CONNECTION: Contraception can prevent
unwanted pregnancy
 Contraception is the deliberate prevention of
pregnancy.
 Several forms of contraception can prevent
pregnancy, with varying degrees of success.
© 2012 Pearson Education, Inc.
Table 27.8
Figure 27.8
Skin patch
PRINCIPLES OF
EMBRYONIC DEVELOPMENT
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27.9 Fertilization results in a zygote and triggers
embryonic development
 Embryonic development begins with fertilization,
– the union of sperm and egg,
– to form a diploid zygote.
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Figure 27.9A
27.9 Fertilization results in a zygote and triggers
embryonic development
 Sperm are adapted to reach and fertilize an egg.
Sperm have
– a streamlined shape, which moves easily through fluids,
– many mitochondria, which provide ATP for tail
movements, and
– a head that contains a haploid nucleus and is tipped with
an acrosome containing enzymes that help it penetrate
the egg.
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Figure 27.9B
Plasma membrane
Middle
piece
Head
Tail
Mitochondria
Nucleus
Acrosome
27.9 Fertilization results in a zygote and triggers
embryonic development
 During fertilization,
1. sperm squeeze past follicle cells,
2. acrosomal enzymes digest the egg’s jelly coat,
3. a sperm binds to egg receptors,
4. sperm and egg plasma membranes fuse,
5. the sperm nucleus enters the egg cytoplasm,
6. The vitelline layer separates and becomes impenetrable,
and
7. the egg and sperm nuclei fuse.
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Figure 27.9C
1
A sperm touches
the egg’s jelly
coat, and its
acrosome
releases enzyme
molecules.
2
The sperm’s
acrosomal
enzymes digest the
egg’s jelly coat.
3
Proteins on the
sperm head bind
to egg receptors.
4
The plasma membranes
of sperm and egg fuse.
Acrosomal
enzymes
Sperm
5
The sperm nucleus enters
the egg cytoplasm.
Plasma
membrane
6
The vitelline
layer
separates
and becomes
impenetrable.
Nucleus
Acrosome
Plasma
membrane
Receptor protein
molecules
n Sperm
nucleus
Vitelline
layer
Cytoplasm
Jelly
coat
Egg cell
n
Egg
nucleus
n
n
7
The nuclei of sperm
and egg fuse.
2n
Zygote nucleus
Figure 27.9C_1
A sperm touches
the egg’s jelly
coat, and its
acrosome
releases enzyme
molecules.
Sperm
The sperm’s
acrosomal
enzymes
digest the
egg’s jelly
coat.
Proteins on the
sperm head bind
to egg receptors.
Acrosomal
enzymes
Plasma
membrane
Nucleus
Acrosome
Jelly
coat
Plasma
membrane
Vitelline
layer
Receptor protein
molecules
Figure 27.9C_2
The plasma membranes
of sperm and egg fuse.
The sperm nucleus enters
the egg cytoplasm.
The vitelline
layer
separates
and becomes
impenetrable.
n Sperm
nucleus
Figure 27.9C_3
n Sperm
nucleus
n
Egg
nucleus
n
n
The nuclei of sperm
and egg fuse.
2n
Zygote nucleus
27.10 Cleavage produces a ball of cells from the
zygote
 Cleavage is a rapid series of cell divisions that
produces
– more cells,
– smaller cells, and
– a fluid-filled embryo called a blastula.
Video: Sea Urchin Embryonic Development
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Figure 27.10_s1
Zygote
2 cells
Figure 27.10_s2
Zygote
2 cells
4 cells
8 cells
Figure 27.10_s3
Zygote
2 cells
4 cells
8 cells
Many cells (solid ball)
Figure 27.10_s4
Zygote
2 cells
4 cells
8 cells
Many cells (solid ball)
Blastocoel
Blastula Cross section
(hollow ball) of blastula
27.11 Gastrulation produces a three-layered
embryo
 During gastrulation
– cells migrate to new locations,
– a rudimentary digestive cavity forms, and
– the basic body plan of three layers is established with
– ectoderm outside—becomes skin and nervous systems,
– endoderm inside—becomes digestive tract,
– mesoderm in the middle—becomes muscle and bone.
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Figure 27.11_s1
Blastula
(end of cleavage)
Animal pole
Blastocoel
Vegetal pole
Figure 27.11_s2
Blastula
(end of cleavage)
Animal pole
Blastocoel
Vegetal pole
Gastrulation
(cell migration)
Blastocoel
shrinking
Formation of a
simple digestive
cavity
Blastopore
Figure 27.11_s3
Blastula
(end of cleavage)
Animal pole
Blastocoel
Vegetal pole
Gastrulation
(cell migration)
Blastocoel
shrinking
Gastrula
(end of gastrulation)
Simple
digestive
cavity
Formation of a
simple digestive
cavity
Blastopore
Ectoderm
Mesoderm
Endoderm
Table 27.11
27.12 Organs start to form after gastrulation
 Organs develop from the three embryonic layers.
– The stiff notochord forms the main axis of the body and
is later replaced by the vertebral column in most
chordates.
– The neural tube develops above the notochord and will
become the
– brain and
– spinal cord.
Video: Frog Embryo Development
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Figure 27.12A
Neural Neural
fold
plate
Notochord
Ectoderm
Mesoderm
Endoderm
Neural folds
Figure 27.12A_1
Neural folds
Figure 27.12B
Neural
fold
Neural plate
Outer layer
of ectoderm
Neural tube
27.12 Organs start to form after gastrulation
 As the embryo elongates, paired somites
– form along the sides of the notochord,
– hollow out to form a coelom, and
– eventually contribute to muscles, bone, and other
connective tissues.
 Other systems develop at the same time.
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Figure 27.12C
Neural tube
Notochord
Somite
Coelom
Somites
Digestive
cavity
Eye
Tail bud
Figure 27.12C_1
Somites
Eye
Tail bud
Figure 27.12D
27.13 Multiple processes give form to the
developing animal
 Tissues and organs develop by
– changes in cell shape,
– cell migration, and
– programmed cell death (also called apoptosis).
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Figure 27.13A
Figure 27.13A_1
Figure 27.13A_2
Figure 27.13B
Apoptosis
Dead cell engulfed and
digested by adjacent cell
27.13 Multiple processes give form to the
developing animal
 Through induction, adjacent cells and cell layers
– influence each other’s differentiation
– via chemical signals.
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27.14 EVOLUTION CONNECTION: Pattern
formation during embryonic development is
controlled by ancient genes
 Pattern formation,
– the emergence of the parts of a structure in their correct
relative positions,
– involves the response of genes to spatial variations of
chemicals in the embryo, and
– results in tissues and organs developing in their proper
positions at the correct times.
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Figure 27.14A
Anterior
Limb bud
Limb bud
develops
Anterior
Ventral
Distal
Proximal
Dorsal
Limb buds
Posterior
Posterior
27.14 EVOLUTION CONNECTION: Pattern
formation during embryonic development is
controlled by ancient genes
 Homeotic genes
– contain common nucleotide sequences (homeoboxes),
– guide pattern formation in embryos, and
– occur in diverse groups such as
– prokaryotes,
– yeast,
– plants, and
– animals.
– Homeotic genes reveal the shared evolutionary history
of life.
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Figure 27.14B
Fly chromosome
Mouse chromosomes
Fruit fly embryo (10 hours)
Mouse embryo (12 days)
Adult fruit fly
Adult mouse
HUMAN DEVELOPMENT
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27.15 The embryo and placenta take shape during
the first month of pregnancy
 Pregnancy, or gestation, is the carrying of
developing young within the female reproductive
tract.
 Human pregnancy
– averages 266 days (38 weeks) from fertilization or
– 40 weeks (9 months) from the start of the last menstrual
period.
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27.15 The embryo and placenta take shape during
the first month of pregnancy
 Human development begins with fertilization in the
oviduct.
 Cleavage produces a blastocyst whose
– inner cell mass becomes the embryo and the
– trophoblast, the outer cell layer, which
– attaches to the uterine wall and
– forms part of the placenta.
 Gastrulation occurs and organs develop from the
three embryonic layers.
© 2012 Pearson Education, Inc.
Figure 27.15A–B
Cleavage starts
Fertilization
of mature
egg
Blastocyst
Trophoblast
Uterine
cavity
Cavity
Oviduct
Ovary
Inner cell mass
Blastocyst
(implanted)
Secondary
oocyte
Ovulation
Endometrium
Uterus
Uterine
cavity
Figure 27.15C
Endometrium
Uterine cavity
Multiplying
cells of
trophoblast
(contribute to
future placenta) Trophoblast
Embryo
Future
yolk sac
Blood vessel
(maternal)
27.15 The embryo and placenta take shape during
the first month of pregnancy
 Four extraembryonic membranes develop.
1. The amnion
– surrounds the embryo and
– forms a fluid-filled amniotic cavity that protects the embryo.
2. The yolk sac,
– in reptiles, stores yolk,
– in humans, does not store yolk but is a source of the first germ
cells and blood cells.
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27.15 The embryo and placenta take shape during
the first month of pregnancy
3. The allantois
– contributes to the umbilical cord,
– forms part of the urinary bladder, and
– in reptiles, stores embryonic waste.
4. The chorion
– contributes to the placenta and
– secretes human chorionic gonadotropin (HCG), which
prevents menstruation in mammals.
© 2012 Pearson Education, Inc.
Figure 27.15D
Yolk sac
Chorion
Amnion
Amniotic
cavity
Mesoderm
cells
Figure 27.15E
Embryo:
Endoderm
Mesoderm
Ectoderm
Chorionic
villi
Chorion
Amnion
Allantois
Yolk
sac
Figure 27.15F
Placenta
Amnion
Amniotic
cavity
Embryo
Mother’s
blood Allantois
vessels
Yolk
sac
Chorion
Chorionic
villi
27.15 The embryo and placenta take shape during
the first month of pregnancy
 The placenta is a
– close association of
– embryonic chorion and
– mother’s blood vessels, and
– site of
– gas exchange—from mother to embryo,
– nutrient exchange—from mother to embryo, and
– waste exchange—from embryo to mother.
© 2012 Pearson Education, Inc.
27.16 Human development from conception to
birth is divided into three trimesters
 The first trimester is the period of greatest change.
– The embryo forms, looking like other vertebrate embryos.
– Extraembryonic membranes form.
– All major organ systems are established.
– After 9 weeks after fertilization, the embryo is called a
fetus and
– can move its arms and legs and
– starts to look distinctly human.
Video: Ultrasound of Human Fetus 1
Video: Ultrasound of Human Fetus 2
© 2012 Pearson Education, Inc.
Figure 27.16A–C
January
0
Conception
February
35 days
March
April
63 days
98 days
Figure 27.16A
5 weeks (35 days)
Figure 27.16B
9 weeks (63 days)
27.16 Human development from conception to
birth is divided into three trimesters
 During the second trimester,
– there is a great increase in the size of the fetus, and
– human features are refined.
– At 20 weeks, the fetus
– is about 19 cm long (7.6 in.) and
– weighs about 0.5 kg (1 lb.).
© 2012 Pearson Education, Inc.
Figure 27.16C
14 weeks (98 days)
Figure 27.16D–E
May
June
July
August
September
October
280 days
140 days
Figure 27.16D
20 weeks (140 days)
27.16 Human development from conception to
birth is divided into three trimesters
 The third trimester is also a time of rapid growth.
– The circulatory and respiratory systems mature.
– Muscles thicken and the skeleton hardens.
– The third trimester ends with birth.
– Babies born as early as 24 weeks may survive only with
extensive medical care.
© 2012 Pearson Education, Inc.
Figure 27.16E
At birth (280 days)
27.17 Childbirth is induced by hormones and
other chemical signals
 Hormonal changes induce birth.
– Estrogen makes the uterus more sensitive to oxytocin.
– Oxytocin acts with prostaglandins to initiate labor.
– The cervix dilates to about 10 cm.
– The baby is expelled by strong uterine contractions.
– The placenta dislodges and is expelled after the baby.
© 2012 Pearson Education, Inc.
Figure 27.17A
Estrogen
from
ovaries
Oxytocin
from fetus and
mother’s pituitary
Induces oxytocin
receptors on uterus
Stimulates
placenta to make
Prostaglandins
Stimulate more
contractions
of uterus
Positive feedback
Stimulates uterus
to contract
27.17 Childbirth is induced by hormones and
other chemical signals
 Labor occurs in three stages:
1. dilation of the cervix,
2. expulsion, delivery of the infant,
3. delivery of the placenta.
© 2012 Pearson Education, Inc.
Figure 27.17B
Placenta
Umbilical
cord
Uterus
Cervix
1 Dilation of the cervix
2 Expulsion: delivery of the infant
Uterus
Placenta
(detaching)
Umbilical
cord
3 Delivery of the placenta
Figure 27.17B_1
Placenta
Umbilical
cord
Uterus
Cervix
1
Dilation of the cervix
Figure 27.17B_2
2
Expulsion: delivery of the infant
Figure 27.17B_3
Uterus
Placenta
(detaching)
Umbilical
cord
3
Delivery of the placenta
27.18 CONNECTION: Reproductive technologies
increase our reproductive options
 New techniques can help many infertile couples.
– About 15% of couples wanting children are infertile.
– Drug therapies can help address problems of impotence
(erectile dysfunction) and induce ovulation.
– Assisted reproductive technologies (ART) require
eggs to be harvested from the ovaries, fertilized, and
returned to a woman’s body.
– In vitro fertilization (IVF) is the most common assisted
reproductive technology. Fertilization occurs in a culture
dish and an early embryo is implanted in the uterus.
© 2012 Pearson Education, Inc.
Figure 27.18
Implantation
Zygote
Collected
egg
In vitro fertilization
Collected
sperm
8-cell
embryo
Figure 27.18_1
You should now be able to
1. Compare the types, advantages, and
disadvantages of asexual and sexual reproduction.
2. Describe the structures and functions of the female
and male human reproductive systems.
3. Describe and compare the processes and products
of spermatogenesis and oogenesis.
4. Describe the events of and control of the menstrual
cycle.
© 2012 Pearson Education, Inc.
You should now be able to
5. Describe the nature of the most common sexually
transmitted diseases.
6. Describe the most common forms of birth control
and explain how each works.
7. Relate the structure of sperm to its role in
fertilization.
8. Describe the process and results of cleavage.
9. Describe the process of gastrulation and the
resulting arrangement of the embryo.
© 2012 Pearson Education, Inc.
You should now be able to
10. Explain how organs form after the development of
a gastrula.
11. Explain how changes in cell shape, induction, cell
migration, and apoptosis contribute to
development.
12. Explain how the one-dimensional information in
DNA is used to direct the three-dimensional form
of an embryo.
13. Describe the initial embryonic stages and the
formation and functions of the extraembryonic
membranes in humans.
© 2012 Pearson Education, Inc.
You should now be able to
14. Describe the main changes that occur during each
of the trimesters of human development.
15. Explain how labor begins and describe the main
events of the three stages of labor.
16. Describe the common causes of human infertility
and the technologies currently available to help
couples conceive.
© 2012 Pearson Education, Inc.
Figure 27.UN01
Oogenesis
2n
Once per
month
Spermatogenesis
Primary
oocyte
Primary
spermatocyte
Continuously
n Polar body
n
Secondary
oocyte
2n
Secondary
spermatocyte
Developing n
sperm cells
n
n
n
n
Sperm n
Fertilization
Polar body n
Mature egg
n
2n
Zygote
n
Figure 27.UN02
Cleavage
Gastrulation
Ectoderm
Mesoderm
Endoderm
Zygote
2-cell
embryo
Many-celled Blastula
(cross
solid ball
section)
Gastrula
(cross
section)
Hormone level in blood
(arbitrary units)
Figure 27.UN03
50
Hormones (A–D)
40
C
30
D
20
A
10
B
0
0
Events (P–S)
5
10
15
Days
20
P
Q
R
S
25
28