Download Chapter 27

Chapter 27
Reproduction and Embryonic
Development
PowerPoint Lectures for
Biology: Concepts and Connections, Fifth Edition
– Campbell, Reece, Taylor, and Simon
Lectures by Chris Romero
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Baby Bonanza
• The increased use of fertility drugs has caused
an increase in the number of multiple births in
the United States
• Infertility affects about one in seven couples in
the United States
• Fertility drugs are an example of technology
affecting the normal reproductive cycle
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
ASEXUAL AND SEXUAL REPRODUCTION
27.1 Sexual and asexual reproduction are both
common among animals
• In asexual reproduction, one parent produces
genetically identical offspring
– Budding, fission, fragmentation/
regeneration
– Allows isolated animals to reproduce
without having to find mates
– Produces offspring quickly
– Diminishes genetic diversity of offspring
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• 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 selfpropelled
– Increases genetic variability among
offspring
– May enhance reproductive success in
changing environments
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• Many animals can reproduce both sexually
and asexually
– Rotifer
• Asexual in good environmental conditions
• Sexual in more stressful conditions
– Hermaphrodites
• Each individual has both female and male
reproductive systems
• Most mate with another member of their
species
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
LE 27-01c
“Head”
Intestine
Ovary
Eggs
Video: Rotifer
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• 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
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
LE 27-01e
Eggs
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
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• 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
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• 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
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
– 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
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
LE 27-02a
Ovaries
Oviduct
Follicles
Corpus luteum
Wall of uterus
Uterus
Endometrium
(lining of uterus)
Cervix
(“neck” of uterus)
Vagina
LE 27-02c
Oviduct
Ovary
Uterus
Rectum
(digestive
system)
Urinary bladder
(excretory system)
Pubic bone
Cervix
Urethra
(excretory system)
Vagina
Shaft
Glans
Bartholin’s gland
Anus
(digestive
system)
Clitoris
Prepuce
Labia minora
Vaginal opening
Labia majora
LE 27-02b
Egg
cell
Ovary
Animation: Female Reproductive Anatomy
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
27.3 Reproductive anatomy of the human male
• Testes, housed outside the body in the
scrotum, produce sperm
• Pathway of sperm from testis to outside
– Epididymis
– Vas deferens
– Ejaculatory duct
– Ejaculation through urethra in penis
• Connection between reproductive and
excretory systems
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• Several glands contribute to the formation of
fluid that nourishes and protects sperm
– Seminal vesicles
– Prostate gland
– Bulbourethral glands
– Semen combines sperm and glandular
secretions
Animation: Male Reproductive Anatomy
Animation: Male Hormones
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
LE 27-03a
Rectum
(digestive
system)
Seminal
vesicle
Urinary bladder
(excretory
system)
Vas deferens
Pubic bone
Ejaculatory
duct
Erectile tissue
of penis
Prostate gland
Bulbourethral
gland
Vas deferens
Epididymis
Testis
Scrotum
Urethra
(excretory
system)
Glans of penis
Prepuce
Penis
LE 27-03b
Urinary bladder
(excretory
system)
Seminal
vesicle
(behind
bladder)
Prostate gland
Bulbourethral
gland
Erectile tissue
of penis
Vas deferens
Urethra
Scrotum
Epididymis
Testis
Glans of
penis
• The process of ejaculation involves
coordinated contractions and expulsion of
fluids
• Hormones control sperm production by the
testes through a negative-feedback system
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
LE 27-03c
Sphincter
contracts
Contractions
of vas deferens
Urinary
bladder
Urethra region here
expands and fills
with semen
Contractions
of seminal
vesicle
Contractions
of prostate
gland
First stage
Sphincter
contracts
Sphincter remains
contracted
Contractions
of epididymis
Semen expelled
Contractions
of muscles
around base
of penis
Sphincter
relaxes
Second stage
Contractions
of urethra
LE 27-03d
Stimuli from other
areas in the brain
Hypothalamus
Anterior
pituitary
FSH
LH
Androgen
production
Testis
Sperm
production
Negative feedback
Releasing
hormone
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
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
LE 27-04a
Epididymis
Testis
Scrotum
Penis
Diploid cell
2n
Differentiation and
onset of Meiosis I
2n
Primary spermatocyte
(in prophase of Meiosis I
Meiosis I completed
Cross section of
seminiferous
tubule
Secondary spermatocyte
(haploid; double chromatids)
n
n
Testis
Seminiferous tubule
Meiosis II
n
n
n
n
Developing sperm cells
(haploid; single chromatids)
Differentiation
n
n
n
n
Sperm cells
(haploid)
Center of
seminiferous tubule
•
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
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
LE 27-04b
Diploid cell
2n
In embryo
Differentiation and
onset of Meiosis I
Primary oocyte
2n
(arrested in prophase
of Meiosis I)
Present at birth
Completion of Meiosis I
and onset of Meiosis II
Secondary oocyte
(arrested at metaphase of Meiosis II;
released from ovary)
n
n
First
polar body
Entry of sperm triggers
completion of Meiosis II
Ovum
(haploid)
n
n
Second
polar body
• 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
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
LE 27-04c
Degenerating
corpus luteum
Start:
Primary oocyte
within follicle
Corpus luteum
Growing
follicles
Mature follicle
Secondary
oocyte
Ovary
Ovulation
Ruptured follicle
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
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• Events in the menstrual cycle are coordinated
with the ovarian cycle
– Events synchronized by five hormones
– Menstrual cycle prepares uterus for
implantation of embryo
– Menstruation lasts 3-5 days, corresponding
to pre-ovulatory phase of ovarian cycle
– Continues through time of ovulation (20-25
days)
– If no embryo is implanted, menstruation
begins again
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• 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
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• 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
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
– 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
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
LE 27-05
Control by hypothalamus
Inhibited by combination of
estrogen and progesterone
Hypothalamus
Stimulated by high levels
Releasing hormone of estrogen
Anterior pituitary
FSH
LH
Pituitary hormones
in blood
LH peak triggers
ovulation and
corpus luteum
formation
LH
FSH
LH
FSH
Ovarian cycle
Growing follicle
Mature
follicle
Ovulation
Pre-ovulatory phase
Estrogen
Corpus
luteum
Degenerating
corpus luteum
Post-ovulatory phase
Progesterone
and estrogen
Ovarian hormones
in blood
Estrogen
Progesterone
Estrogen
Progesterone
and estrogen
Animation: Ovulation
Animation: Post Ovulation
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
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
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
CONNECTION
27.7 Sexual activity can transmit disease
• Sexually transmitted diseases (STDs) are
contagious diseases spread by sexual contact
• Viral diseases are not curable but can be
controlled by medication
• Many STDs can cause long-term problems or
even death if untreated
• STDs are most prevalent among teenagers
and young adults
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
CONNECTION
27.8 Contraception can prevent unwanted
pregnancy
• Contraception is the deliberate prevention of
pregnancy
• Contraception must be used correctly to
prevent failure
• "Safe sex" provided by condoms can prevent
both unwanted pregnancy and sexually
transmitted disease
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• Common contraceptive methods
– Abstinence
– Tubal ligation or vasectomy
– Rhythm method (natural family planning)
– Withdrawal
– Barrier methods: condom, diaphragm
• Most effective if used with spermicide
– Oral contraceptives
– Morning after pills
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
LE 27-08
Skin patch
Condom
Diaphragm
Spermicide
Birth control pills
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
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• The properties of sperm cells
– Streamlined shape an adaptation for
swimming
– Thick head contains haploid nucleus
– Acrosome at tip of head contains enzymes
that help sperm penetrate the egg
– High-energy nutrients absorbed from semen
provide energy for propulsion and
penetration
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
LE 27-09b
Plasma membrane
Middle
piece
Neck
Head
Tail
Mitochondrion
(spiral shape)
Nucleus
Acrosome
•
The process of fertilization
1. Sperm approaches egg
2. Sperm's acrosomal enzymes digest egg's
jelly coat
3. Proteins on sperm head bind to egg
receptors
4. Plasma membranes of sperm and egg
fuse
5. Sperm nucleus enters egg cytoplasm
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
6. Fertilization envelope forms, preventing
other sperm from entering egg
7. Nuclei of sperm and egg fuse, producing
diploid nucleus of zygote
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
LE 27-09c
The sperm
approaches
the egg
Sperm
The sperm’s
acrosomal enzymes
digest the egg’s
jelly coat
Proteins on the sperm
head bind to egg
receptors
The plasma
membranes of sperm
and egg fuse
Sperm
head
Nucleus
The sperm nucleus
enters the egg
cytoplasm
Acrosome
Plasma
membrane
Acrosomal
enzymes
Vitelline
layer
A fertilization
envelope forms
Receptor protein
molecules
Plasma
membrane
Sperm
nucleus
Cytoplasm
Egg
nucleus
Jelly
coat
Egg cell
The nuclei of
sperm and egg
fuse
Zygote nucleus
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
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
LE 27-10
Zygote
2 cells
4 cells
8 cells
Blastocoel
Many
cells
(solid
ball)
Blastula
(hollow ball)
Cross section
of blastula
Video: Sea Urchin Embryonic Development
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• Cleavage makes two important contributions to
early development
– Creates a multicellular embryo from a
single-celled zygote
– Partitions the embryo into developmental
regions
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
27.11 Gastrulation produces a three-layered
embryo
• Gastrulation adds more cells to the embryo
and sorts them into three layers
– Ectoderm: forms outer skin of gastrula
– Endoderm: forms embryonic digestive tract
(archenteron)
– Mesoderm: partly fills space between
ectoderm and endoderm
– These layers develop into all parts of the
adult animal
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
•
Mechanics of gastrulation
1. Blastula
2. Blastopore formation
3. Cell migration to form layers
4. Completion of gastrulation
Video: Frog Embryo Development
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
LE 27-11
Animal pole
Blastocoel
Blastula
Vegetal pole
Gastrulation
Blastopore
forming
Blastopore
forming
Blastocoel
shrinking
Archenteron
Archenteron
Ectoderm
Mesoderm
Endoderm
Yolk plug
Yolk plug
Gastrula
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
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
LE 27-12a
Neural Neural
fold
plate
Notochord
Ectoderm
Mesoderm
Endoderm
Archenteron
Neural folds
LE 27-12b
Neural
fold
Neural plate
Outer layer
of ectoderm
Neural tube
• 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
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
LE 27-12c
Neural tube
Notochord
Somite
Coelom
Archenteron
(digestive cavity)
Somites
Tail bud
SEM 15
Eye
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
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
LE 27-13a
Ectoderm
• Programmed cell death, or apoptosis
– Controlled by "suicide" genes
– Essential for normal development and
differentiation of body structures
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LE 27-13b
Apoptosis
Dead cell
engulfed and
digested by
adjacent cell
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
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
LE 27-14
Lens ectoderm Optic cup
Cornea
Future
brain
Lens
Optic
vesicle
Optic
stalk
Future
retina
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
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
LE 27-15a
Anterior
Bird
embryo
Ventral
Limb bud
Limb bud develops
Distal
Dorsal
Proximal
Posterior
Normal wing
LE 27-15b
Donor
limb
bud
Graft of cells
from patternforming
zone
Donor cells
Host
limb
bud
Graft
Host limb bud
develops
Host patternforming zone
Wing with duplication
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
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• An overview of human developmental events
– Fertilization in the oviduct
– Blastocyst implanted in endometrium
• Fluid-filled cavity
• Cell mass that will form baby
• Trophoblast
– Secretes enzymes enabling
implantation; forms part of placenta
• Extraembryonic membranes
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
LE 27-16a
Cleavage starts
Fertilization
of ovum
Ovary
Oviduct
Secondary
oocyte
Ovulation
Blastocyst
(implanted)
Endometrium
Uterus
LE 27-16b
Endometrim
Inner cell mass
Cavity
Trophoblast
LE 27-16c
Endometrium
Future embryo
Future
yolk sac
Blood vessel
(maternal)
Multiplying cells
of trophoblast
Trophoblast
Actual
size
Uterine cavity
• 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
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
LE 27-16d
Amniotic
cavity
Mesoderm
cells
Amnion
Chorion
Yolk sac
LE 27-16e
Chorion
Amnion
Allantois
Yolk sac
Chorionic villi
Embryo:
Ectoderm
Mesoderm
Endoderm
• 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
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
LE 27-16f
Mother’s blood
vessels
Allantois
Yolk sac
Placenta
Amniotic
cavity
Amnion
Embryo
Chorion
Chorionic
villi
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
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• Second trimester
– Main changes involve an increase in size
and a general refinement of human features
– Placenta takes over secretion of
progesterone and estrogen
– Corpus luteum degenerates
– Eyes are open, and teeth are forming
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• Third trimester
– Fetus grows rapidly and gains strength
needed to survive outside uterus
– Circulatory and respiratory system change
to allow air breathing
– Fetus gains ability to maintain its own
temperature
– Bones harden, muscles thicken
Video: Ultrasound of Human Fetus 2
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
27.18 Childbirth is hormonally induced and
occurs in three stages
• The birth of a child is brought about by a series
of strong, rhythmic contractions of the uterus
• Several hormones play key roles, under
positive feedback control
– Estrogen
– Oxytocin
– Prostaglandins
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
LE 27-18a
from
ovaries
Oxytocin
from fetus
and pituitary
Induces oxytocin
receptors on uterus
Stimulates uterus
to contract
Stimulates
placenta to make
Prostaglandins
Stimulate more
contractions
of uterus
Positive feedback
Estrogen
•
Labor occurs in three stages
1. Dilation of the cervix
2. Expulsion: delivery of the infant
3. Delivery of the placenta
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
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
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
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• Reproductive technologies can help many
cases of infertility
– Drug or hormone therapies for both sexes
– Penile implants
– Sperm, ova from donors
– Assisted reproductive technology
• In vitro fertilization
– Very expensive
– Entails some risks
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings