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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
ASEXUAL vs. SEXUAL REPRODUCTION
Sexual & asexual reproduction common
• Asexual reproduction: 1 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
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Fragmentation / Regeneration
• Ex. sea star regenerating lost arm
• Regeneration results from repeated cell
divisions
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8.3 Prokaryotes reproduce by binary fission
Prokaryotic cells divide asexually
•
Chromosome replicates  then cell divides into
two cells = binary fission
Prokaryotic chromosomes
Figure 8.3B
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Binary fission of a prokaryotic cell
Plasma
membrane
Prokaryotic
chromosome
Cell wall
Duplication of chromosome
and separation of copies
Continued growth of the cell
and movement of copies
Division into
two cells
Figure 8.3A
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Asexual reproduction (seen here in a hydra)
Figure 8.11C
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Sexual Reproduction
• Sexual reproduction: 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
External vs. Internal Fertilization
• External fertilization common in aquatic
animals
– Parents release gametes into the
environment, fertilization occurs outside
body
• Internal fertilization occurs in nearly all
terrestrial animals
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
LE 27-01e
Eggs
HUMAN REPRODUCTION
Reproductive anatomy of the human female
• Both sexes in humans
– Have set of gonads where gametes are
produced
– Have ducts for delivery of the gametes and
structures for copulation
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FEMALE
• Ovaries
– Produce egg cells (ova)
– Follicles protect and nourish eggs and
produce estrogen
• Ovulation - one egg released every 28 days,
starting at puberty
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
• 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
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- ectopic pregnancy, embryo implants
somewhere other than uterus
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MALE
• Testes, housed outside the body (a few
degrees cooler than body temp) 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
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
LE 27-03d
Stimuli from other
areas in the brain
Hypothalamus
Anterior
pituitary
FSH
LH
Androgen
production
Testis
Sperm
production
Negative feedback
Releasing
hormone
LE 27-04c
Degenerating
corpus luteum
Start:
Primary oocyte
within follicle
Corpus luteum
Growing
follicles
Mature follicle
Secondary
oocyte
Ovary
Ovulation
Ruptured follicle
MENSTRUAL CYCLE
Changes in ovary and uterus
– Ovarian cycle: produces the oocyte
– Menstrual/Uterine cycle: involves the
monthly changes in the uterus
– Hormonal messages synchronize the two
cycles through intricate feedback systems
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Figure 46.15 The reproductive cycle of the human female
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Uterine Cycle—3 Phases
1. Menstruation: shedding of the old uterine
lining, the endometrium. Days 1-5 of the
menstrual cycle.
2. Proliferation Phase: new Uterine lining
(endometrium) is built. Under the control of
Estrogen, which is secreted by the ovary
during this phase. Days 6 to 13
3. Secretory Phase: new uterine lining thickened
and maintained in preparation for a possible
pregnancy. Under the control of
Progesterone. Days 14 to 28. Ends when
progesterone levels fall & menstruation
begins again (if no fertilization)
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Ovarian Cycle—3 Phases
1. Follicular Phase: Days 1-13
FSH from the anterior pituitary causes development
of a follicle in the ovary—a maturing oocyte and its
surrounding cells. They in turn secrete Estrogen
which effects the uterine lining
2. Ovulation: Day 14
Release of the oocyte from the follicle into the
Fallopian tube (oviduct). Caused by a large surge in
LH from the anterior pituitary due to surge in
Estrogen.
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Luteal Phase
3. Luteal Phase: Days 14 – 28
LH turns what’s left of the follicle into the Corpus
Luteum, a structure that secretes Progesterone (some
estrogen) which has an effect on maintaining the Uterine
lining. Estrogen drop so LH drop. CL dies and
progesterone & estrogen levels fall off, uterine lining
sheds
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
OK—Menstrual Cycle again
• 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
What if. . . .
. . the Ovum is fertilized?
• resulting embryo releases hCG (human chorionic
gonadotropin)
•This has the effect of prolonging the Corpus Luteum
longer, so it continues to secrete progesterone
•Progesterone levels never fall & the uterine lining does
not shed
•This is the first sign of pregnancy
•hCG levels stay high for the 1st 3-4 months, then the
placenta takes over the production of progesterone
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Animation: Ovulation
Animation: Post Ovulation
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
FERTILIZATION
Fertilization  zygote  embryonic development
1. Gametes are formed (spermatogenesis &
oogenesis produce haploid cells)
2. Ovum fertilized in Fallopian tube. Sperm
swim up through the cervix & uterus to find
the egg.
Sperm contain digestive enzymes in
Acrosome to penetrate protective barriers
around the ovum
Video: Hydra Releasing Sperm
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
LE 27-09b
Plasma membrane
Middle
piece
Neck
Head
Tail
Mitochondrion
(spiral shape)
Nucleus
Acrosome
SPERM
• 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 27-09c
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
3. Zygote formed. Once sperm has penetrated
the ovum, sperm and ovum nuclei fuse producing
Diploid cell.
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4. Cleavage produces a ball of cells from the
zygote
• Cleavage 1st major stage of embryonic
development
• rapid series of cell divisions produces a solid
ball of cells called a Morula from the zygote
• Fluid-filled blastocoel forms in the center of
the embryo
• Blastula, a hollow ball of cells, is final 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
5. Implantation in the
Uterus.
Continues to divide and
hollows out producing a
Blastocyst.
Inner cells become the
embryo. The outer ring of
cells becomes the
placenta.
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
6. The Embryonic Stage (implantation to Week 8)
Gastrulation produces a three-layered embryo
– Endoderm: inner linings of respiratory,
digestive, reproductive, and urinary
systems; for glandular organs: liver,
pancreas, salivary glands)
– Mesoderm: Middle strucutres—bones,
blood vessels, heart, kidneys, uterus,
gonads
– Ectoderm: External structures—skin, hair,
nails, linings of mouth/anus, all nervous
system structures
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
7. Neurulation & Organogenesis
Organs formation after gastrulation, ex. nervous
system
– 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
HUMAN DEVELOPMENT
• 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
OVERVIEW OF EMBRYONIC DEVELPMENT
– Fertilization in the oviduct
– Cleavage (morula) -> blastula (implantation)
-> gastrula and organ formation
– Blastocyst implanted in endometrium
• Fluid-filled cavity
• Trophoblast (outer layer cells of the
Blastocyst)
– 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
EXTRAEMBRYONIC MEMBRANES
– Amnion = enclose 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 27-16e
Chorion
Amnion
Allantois
Yolk sac
Chorionic villi
Embryo:
Ectoderm
Mesoderm
Endoderm
PLACENTA
• 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
CHILDBIRTH
hormonally induced /occurs in 3 stages
• happens 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