Transcript zona pellucida

PowerPoint® Lecture Slides
prepared by
Barbara Heard,
Atlantic Cape Community
College
CHAPTER
28
Pregnancy
and Human
Developme
nt: Part A
© Annie Leibovitz/Contact Press Images
© 2013 Pearson Education, Inc.
Pregnancy
• Pregnancy - events that occur from
fertilization until infant born
• Conceptus - developing offspring
• Gestation period - time from last
menstrual period until birth (~280 days)
• Embryo - conceptus from fertilization
through week 8
• Fetus - conceptus from week 9 through
birth
© 2013 Pearson Education, Inc.
Figure 28.1 Diagrams showing the approximate size of a human conceptus from fertilization to the early fetal stage.
Embryo
Fertilization 1-week
conceptus
3-week
embryo
(3 mm)
5-week
embryo
(10 mm)
8-week embryo
(22 mm)
12-week fetus
(90 mm)
© 2013 Pearson Education, Inc.
From Egg to Zygote
• Oocyte viable for 12 to 24 hours
• Sperm viable 24 to 48 hours after
ejaculation
© 2013 Pearson Education, Inc.
From Egg to Zygote
• For fertilization to occur, coitus must occur
no more than
– Two days before ovulation
– 24 hours after ovulation
• Fertilization - sperm's chromosomes
combine with those of secondary oocyte to
form fertilized egg (zygote)
© 2013 Pearson Education, Inc.
Accomplishing Fertilization
• Ejaculated sperm
– Leak out of vagina immediately after
deposition
– Destroyed by acidic vaginal environment
– Fail to make it through cervix
– Dispersed in uterine cavity or destroyed by
phagocytes
– Few (100 to a few thousand) reach uterine
tubes
© 2013 Pearson Education, Inc.
Accomplishing Fertilization
• Sperm must become motile
• Sperm must be capacitated before they
can penetrate oocyte
– Motility must be enhanced; membranes must
become fragile to release hydrolytic enzymes
• Secretions of female tract weaken
acrosome membrane
• Sperm follow "olfactory trail" to reach
oocyte
© 2013 Pearson Education, Inc.
Acrosomal Reaction and Sperm Penetration
• Sperm must breach oocyte coverings
– Corona radiata and zona pellucida
• Sperm weaves through corona radiata,
then binds to zona pellucida and
undergoes acrosomal reaction
– Enzymes released to digest holes in zona
pellucida
– Hundreds of acrosomes release enzymes to
digest zona pellucida
© 2013 Pearson Education, Inc.
Figure 28.2 Sperm Penetration and the Cortical Reaction.
Sperm, delivered to the vagina and
capacitated in the female reproductive
tract, stream toward a secondary
oocyte.
Slide 1
2 Acrosomal reaction.
Binding of the sperm to sperm-binding
receptors in the zona pellucida causes
the Ca2+ levels within the sperm to rise,
triggering the acrosomal reaction.
Acrosomal enzymes from many sperm
digest holes through the zona pellucida,
clearing a path to the oocyte membrane.
3 Binding.
The sperm’s
membrane
binds to the
oocyte’s
Sperm-binding
receptors.
4 Fusion.
The sperm and
oocyte plasma
membranes
fuse, allowing
sperm contents
to enter the
oocyte.
1 Approach. Aided by
enzymes on its surface, a
sperm cell weaves its way
past granulosa cells of the
corona radiata.
5 Block of polyspermy.
Entry of the sperm’s
contents causes Ca2+ levels
in the oocyte’s cytoplasm
to rise, triggering the
cortical reaction
(exocytosis of cortical
granules). As a result,
the zona pellucida hardens
and the sperm receptors
are clipped off (slow block
to polyspermy).
Extracellular
space
Sperm
Sperm
Zona
pellucida
Polar body
Oocyte nucleus
arrested in
meiotic
metaphase II
Granulosa cells
of corona radiata
Zona pellucida
Sperm-binding
receptors
Oocyte
spermbinding
membrane
receptors
Cortical
granules
Microtubules
from sperm
flagellum
Mitochondria
Zona pellucida
Extracellular space
Oocyte plasma membrane
© 2013 Pearson Education, Inc.
Sperm
nucleus
Figure 28.2 Sperm Penetration and the Cortical Reaction.
Sperm, delivered to the vagina and capacitated in the
female reproductive tract, stream toward a secondary
oocyte.
1 Approach. Aided by
enzymes on its surface, a
sperm cell weaves its way
past granulosa cells of the
corona radiata.
Extracellular
space
Sperm
Sperm
Zona
pellucida
Polar body
Granulosa cells
of corona radiata
Oocyte nucleus
arrested in
Meiotic
metaphase II
Zona pellucida
Extracellular space
Oocyte plasma membrane
© 2013 Pearson Education, Inc.
Slide 2
Figure 28.2 Sperm Penetration and the Cortical Reaction.
2 Acrosomal reaction. Binding of the sperm
to sperm-binding receptors in the zona pellucida causes the
Ca2+ levels within the sperm to rise, triggering the
acrosomal reaction. Acrosomal enzymes from many sperm
digest holes through the zona pellucida, clearing a path
to the oocyte membrane.
© 2013 Pearson Education, Inc.
Zona pellucida
Sperm-binding receptors
Slide 3
Acrosomal Reaction and Sperm Penetration
• Sperm head approaches oocyte
• Rear portion of acrosomal membrane
binds to oocyte plasma membrane 
– Oocyte and sperm membranes fuse
– Gametes fuse as sperm's cytoplasmic
contents enter oocyte
• Only one sperm allowed to penetrate
oocyte (monospermy)
© 2013 Pearson Education, Inc.
Figure 28.2 Sperm Penetration and the Cortical Reaction.
3 Binding. The
sperm’s membrane
binds to the oocyte’s
Sperm-binding
receptors.
© 2013 Pearson Education, Inc.
Oocyte sperm-binding
Membrane receptors
Slide 4
Figure 28.2 Sperm Penetration and the Cortical Reaction.
4 Fusion. The sperm and
oocyte plasma membranes
fuse, allowing sperm
contents to enter the oocyte.
© 2013 Pearson Education, Inc.
Cortical granules
Slide 5
Block to Polyspermy
• Upon entry of sperm, Ca2+ surge from ER
causes cortical reaction
– Cortical granules release enzymes (zonal
inhibiting proteins, or ZIPs)
– ZIPs destroy sperm receptors
– Spilled fluid binds water and swells, detaching
other sperm (slow block to polyspermy)
© 2013 Pearson Education, Inc.
Figure 28.2 Sperm Penetration and the Cortical Reaction.
5 Block of polyspermy. Entry of the sperm’s
contents causes Ca2+ levels in the oocyte’s
cytoplasm to rise, triggering the cortical reaction
(exocytosis of cortical granules). As a result, the
zona pellucida hardens and the sperm receptors
are clipped off (slow block to polyspermy).
Microtubules
from sperm
flagellum
© 2013 Pearson Education, Inc.
Mitochondria
Sperm nucleus
Slide 6
Figure 28.2 Sperm Penetration and the Cortical Reaction.
Sperm, delivered to the vagina and
capacitated in the female reproductive
tract, stream toward a secondary
oocyte.
Slide 7
2 Acrosomal reaction.
Binding of the sperm to sperm-binding
receptors in the zona pellucida causes
the Ca2+ levels within the sperm to rise,
triggering the acrosomal reaction.
Acrosomal enzymes from many sperm
digest holes through the zona pellucida,
clearing a path to the oocyte membrane.
3 Binding.
The sperm’s
membrane
binds to the
oocyte’s
Sperm-binding
receptors.
4 Fusion.
The sperm and
oocyte plasma
membranes
fuse, allowing
sperm contents
to enter the
oocyte.
1 Approach. Aided by
enzymes on its surface, a
sperm cell weaves its way
past granulosa cells of the
corona radiata.
5 Block of polyspermy.
Entry of the sperm’s
contents causes Ca2+ levels
in the oocyte’s cytoplasm
to rise, triggering the
cortical reaction
(exocytosis of cortical
granules). As a result,
the zona pellucida hardens
and the sperm receptors
are clipped off (slow block
to polyspermy).
Extracellular
space
Sperm
Sperm
Zona
pellucida
Polar body
Oocyte nucleus
arrested in
meiotic
metaphase II
Granulosa cells
of corona radiata
Zona pellucida
Sperm-binding
receptors
Oocyte
spermbinding
membrane
receptors
Cortical
granules
Microtubules
from sperm
flagellum
Mitochondria
Zona pellucida
Extracellular space
Oocyte plasma membrane
© 2013 Pearson Education, Inc.
Sperm
nucleus
Completion of Meiosis II and Fertilization
• As sperm nucleus moves toward oocyte
nucleus it swells to form male pronucleus
• The Ca2+ surge triggers completion of
meiosis II  ovum + second polar body
• Ovum nucleus swells to become female
pronucleus
• Fertilization – moment when membranes
of two pronuclei rupture and chromosomes
combine
© 2013 Pearson Education, Inc.
Figure 28.3a Events of fertilization.
Extracellular space
Corona radiata
Zona pellucida
Second meiotic
division of oocyte
Second meiotic
division of first
polar body
Sperm nucleus
1 After the sperm
penetrates the
secondary oocyte, the
oocyte completes
meiosis II, forming the
ovum and second
polar body.
Male pronucleus
Female pro-nucleus
(swollen ovum
nucleus)
Polar bodies
2 Sperm and ovum
nuclei swell, forming
pronuclei.
Male pronucleus
Mitotic spindle
Centriole
Female pronucleus
3 Pronuclei approach
each other and mitotic
spindle forms between
them.
Zygote
© 2013 Pearson Education, Inc.
4 Chromoomes of the
pronuclei intermix. Fertilization
is accomplished. Then, the DNA
replicates in preparation for the
first cleavage division.
Slide 6
Figure 28.3b Events of fertilization.
Male and female
pronuclei
Polar bodies
© 2013 Pearson Education, Inc.
Events of Embryonic Development: Zygote
to Blastocyst Implantation
• Cleavage
– Occurs while zygote moves toward uterus
– Mitotic divisions of zygote
– First cleavage at 36 hours  two daughter
cells (blastomeres)
– At 72 hours  morula (16 or more cells)
• At day 4 or 5, blastocyst (embryo of ~100
cells) reaches uterus
© 2013 Pearson Education, Inc.
Embryonic Development
• Blastocyst - fluid-filled hollow sphere
composed of
– Trophoblast cells
• Display immunosuppressive factors
• Participate in placenta formation
– Inner cell mass
• Becomes embryonic disc ( embryo and three of
embryonic membranes)
© 2013 Pearson Education, Inc.
Figure 28.4 Cleavage: From zygote to blastocyst.
4-cell stage
2 days
Zygote
(fertilized egg)
Morula (a solid ball
of blastomeres).
3 days
Zona
pellucida
Degenerating
zona
pellucida
Sperm
Blastocyst
cavity
Uterine
tube
Fertilization
(sperm
meets and
enters egg)
Early blastocyst
(Morula hollows out,
fills with fluid, and
“hatches” from the
zona pellucida).
4 days
Implanting blastocyst
(Consists of a sphere
of trophoblast cells and
an eccentric cell cluster
called the inner cell
mass). 7 days
Ovary
Oocyte
(egg)
Trophoblast
Ovulation
Uterus
Endometrium
Cavity of
uterus
© 2013 Pearson Education, Inc.
Blastocyst
cavity
Inner cell
mass
Implantation
• Blastocyst floats for 2–3 days
– Nourished by uterine secretions
• Implantation begins 6–7 days after
ovulation
– Trophoblast cells adhere to site with proper
receptors and chemical signals
– Inflammatory-like response occurs in
endometrium
• Uterine blood vessels more permeable and leaky;
inflammatory cells invade area
© 2013 Pearson Education, Inc.
Figure 28.5a Implantation of the blastocyst.
Endometrium
Uterine endometrial
epithelium
Inner cell mass
Trophoblast
Blastocyst cavity
Lumen of uterus
© 2013 Pearson Education, Inc.
Implantation
• Trophoblasts proliferate and form two
distinct layers
– Cytotrophoblast (cellular trophoblast) inner layer of cells
– Syncytiotrophoblast (syncytial
trophoblast) - cells in outer layer lose plasma
membranes, invade and digest endometrium
• Blastocyst burrows into lining surrounded
by pool of leaked blood; endometrial cells
cover and seal off implanted blastocyst
© 2013 Pearson Education, Inc.
Figure 28.5c Implantation of the blastocyst.
Endometrial stroma
with blood vessels
and glands
Syncytiotrophoblast
Cytotrophoblast
Blastocyst cavity
Lumen of uterus
© 2013 Pearson Education, Inc.
Implantation
• Implantation completed by twelfth day
after ovulation
– Menstruation must be prevented
– Corpus luteum maintained by hormone
human chorionic gonadotropin (hCG)
© 2013 Pearson Education, Inc.
Figure 28.5d Implantation of the blastocyst.
Endometrial stroma
with blood vessels
and glands
Syncytiotrophoblast
Cytotrophoblast
Lumen of uterus
© 2013 Pearson Education, Inc.
Hormonal Changes During Pregnancy
• Human chorionic gonadotropin (hCG)
– Secreted by trophoblast cells; later chorion
– Prompts corpus luteum to continue secretion
of progesterone and estrogen
– Promotes placental development via its
autocrine growth factor activity
– hCG levels rise until end of second month,
then decline as placenta begins to secrete
progesterone and estrogen; low values at 4
months and rest of pregnancy
© 2013 Pearson Education, Inc.
Figure 28.6 Hormonal changes during pregnancy.
Relative blood levels
Human chorionic
gonadotropin
Estrogens
Progesterone
0
4
8
Ovulation
and fertilization
© 2013 Pearson Education, Inc.
12
16
24
20
28
Gestation (weeks)
32
36
Birth
Placentation
• Formation of placenta from embryonic
and maternal tissues
– Temporary organ
– Embryonic tissues
• Mesoderm cells develop from inner cell mass; line
trophoblast
• Together these form chorion and chorionic villi
© 2013 Pearson Education, Inc.
Placentation
• Cores of chorionic villi invaded by new
blood vessels; extend to embryo as
umbilical arteries and vein
• Erosion  blood-filled lacunae (intervillous
spaces) in stratum functionalis
• Villi lie in intervillous spaces, immersed in
maternal blood
© 2013 Pearson Education, Inc.
Placentation
• Maternal portion of placenta
– Decidua basalis (stratum functionalis
between chorionic villi and stratum basalis of
endometrium)
• Fetal portion of placenta
– Chorionic villi
© 2013 Pearson Education, Inc.
Figure 28.7a–c Events of placentation, early embryonic development, and extraembryonic membrane formation.
Endometrium
Lacuna (intervillous
space) containing
maternal blood
Maternal
blood vessels
Proliferating
syncytiotrophoblast
Chorionic villus
• Ectoderm
Chorion
• Mesoderm
Amnion
• Endoderm
Cytotrophoblast
Amniotic cavity
Yolk sac
Implanting 71/2 -day blastocyst.
The syncytiotrophoblast is eroding
the endometrium. Cells of the
embryonic disc are now separated
from the amnion by a fluid-filled
space.
© 2013 Pearson Education, Inc.
Forming
umbilical
cord
Allantois
Bilayered
embryonic disc
• Epiblast
• Hypoblast
Endometrial
epithelium
Amniotic
cavity
Primary
germ layers
Extraembryonic
mesoderm
Chorion
being formed
Lumen of uterus
12-day blastocyst. Implantation
is complete. Extraembryonic
mesoderm is forming a discrete
layer beneath the cytotrophoblast.
Extraembryonic
coelom
16-day embryo. Cytotrophoblast and associated
mesoderm have become the chorion, and
chorionic villi are elaborating. The embryo exhibits
all three germ layers, a yolk sac, and an allantois,
which forms the basis of the umbilical cord.
Placentation
• Decidua capsularis - part of endometrium
at uterine cavity face of implanted embryo
• Placenta fully formed and functional by
end of third month
– Nutritive, respiratory, excretory, endocrine
functions
• Placenta also secretes human placental
lactogen, human chorionic thyrotropin, and
relaxin
© 2013 Pearson Education, Inc.
Figure 28.7d Events of placentation, early embryonic development, and extraembryonic membrane formation.
Decidua basalis
Maternal blood
Chorionic villus
Umbilical blood
vessels in
umbilical cord
Amnion
Amniotic cavity
Yolk sac
Extraembryonic
coelom
Lumen
of uterus
Chorion
Decidua
capsularis
41/2 -week embryo. The decidua capsularis, decidua basalis, amnion, and
yolk sac are well formed. The chorionic villi lie in blood-filled intervillous
spaces within the endometrium. The embryo is nourished via the umbilical
vessels that connect it (through the umbilical cord) to the placenta.
© 2013 Pearson Education, Inc.
Figure 28.7e Events of placentation, early embryonic development, and extraembryonic membrane formation.
Placenta
Decidua basalis
Chorionic villi
Yolk sac
Amnion
Amniotic
cavity
Umbilical
cord
Decidua
capsularis
Extraembryonic
coelom
13-week fetus.
© 2013 Pearson Education, Inc.
Uterus
Lumen of
uterus
Placentation
• If placental hormones inadequate,
pregnancy aborted
• Throughout pregnancy blood levels of
estrogens and progesterone increase
• Prepare mammary glands for lactation
© 2013 Pearson Education, Inc.
Placentation
• Maternal and embryonic blood supplies
normally do not intermix
• Embryonic placental barriers include
– Membranes of chorionic villi
– Endothelium of embryonic capillaries
© 2013 Pearson Education, Inc.
Figure 28.8 Detailed anatomy of the vascular relationships in the mature decidua basalis.
Placenta
Chorionic
villi
Decidua
basalis
Maternal
arteries
Umbilical
cord
Decidua
capsularis
Uterus
Lumen of
uterus
Chorionic villus
containing fetal
capillaries
Maternal blood
in lacuna
(intervillous
space)
Fetal arteriole
Fetal venule
Amnion
Umbilical cord
© 2013 Pearson Education, Inc.
Maternal
veins
Myometrium
Stratum
basalis of
endometrium
Maternal
portion of
placenta
(decidua
basalis)
Fetal portion
of placenta
(chorion)
Umbilical arteries
Umbilical vein
Connection to
yolk sac
Events of Embryonic Development: Gastrula
to Fetus
• Germ Layers
– During implantation, blastocyst begins
conversion to gastrula
• Inner cell mass develops into embryonic disc
(subdivides into epiblast and hypoblast)
• Three primary germ layers form; extraembryonic
membranes develop
© 2013 Pearson Education, Inc.
Extraembryonic Membranes
• Amnion - epiblast cells form transparent
sac filled with amniotic fluid
– Provides buoyant environment that protects
embryo
– Helps maintain constant homeostatic
temperature
– Allows freedom of movement; prevents parts
from fusing together
– Amniotic fluid comes from maternal blood,
and later, fetal urine
© 2013 Pearson Education, Inc.
Extraembryonic Membranes
• Yolk sac - sac that hangs from ventral
surface of embryo
– Forms part of digestive tube
– Source of earliest blood cells and blood
vessels
© 2013 Pearson Education, Inc.
Extraembryonic Membranes
• Allantois - small outpocketing at caudal
end of yolk sac
– Structural base for umbilical cord
– Becomes part of urinary bladder
• Chorion - helps form placenta
– Encloses embryonic body and all other
membranes
© 2013 Pearson Education, Inc.
Figure 28.7a–c Events of placentation, early embryonic development, and extraembryonic membrane formation.
Endometrium
Lacuna (intervillous
space) containing
maternal blood
Maternal
blood vessels
Proliferating
syncytiotrophoblast
Chorionic villus
• Ectoderm
Chorion
• Mesoderm
Amnion
• Endoderm
Cytotrophoblast
Amniotic cavity
Yolk sac
Implanting 71/2 -day blastocyst.
The syncytiotrophoblast is eroding
the endometrium. Cells of the
embryonic disc are now separated
from the amnion by a fluid-filled
space.
© 2013 Pearson Education, Inc.
Forming
umbilical
cord
Allantois
Bilayered
embryonic disc
• Epiblast
• Hypoblast
Endometrial
epithelium
Amniotic
cavity
Primary
germ layers
Extraembryonic
mesoderm
Chorion
being formed
Lumen of uterus
12-day blastocyst. Implantation
is complete. Extraembryonic
mesoderm is forming a discrete
layer beneath the cytotrophoblast.
Extraembryonic
coelom
16-day embryo. Cytotrophoblast and associated
mesoderm have become the chorion, and
chorionic villi are elaborating. The embryo exhibits
all three germ layers, a yolk sac, and an allantois,
which forms the basis of the umbilical cord.
Figure 28.7d Events of placentation, early embryonic development, and extraembryonic membrane formation.
Decidua basalis
Maternal blood
Chorionic villus
Umbilical blood
vessels in
umbilical cord
Amnion
Amniotic cavity
Yolk sac
Extraembryonic
coelom
Lumen
of uterus
Chorion
Decidua
capsularis
41/2 -week embryo. The decidua capsularis, decidua basalis, amnion, and
yolk sac are well formed. The chorionic villi lie in blood-filled intervillous
spaces within the endometrium. The embryo is nourished via the umbilical
vessels that connect it (through the umbilical cord) to the placenta.
© 2013 Pearson Education, Inc.
Gastrulation
• Occurs in week 3
• Embryonic disc  three-layered embryo
with primary germ layers present
– Ectoderm, mesoderm, and endoderm
• Begins with appearance of primitive
streak, raised dorsal groove; establishes
longitudinal axis of embryo
© 2013 Pearson Education, Inc.
Gastrulation
• Cells begin to migrate into groove
– First cells form endoderm
– Cells that follow push laterally, forming
mesoderm
• Notochord - rod of mesodermal cells that serves
as axial support
– Cells that remain on embryo's dorsal surface
form ectoderm
© 2013 Pearson Education, Inc.
Gastrulation
• Ectoderm, mesoderm, endoderm - primitive
tissues from which all body organs derive
• Epithelia cells
– Ectoderm  nervous system; skin epidermis
– Endoderm  epithelial linings of digestive,
respiratory, urogenital systems; associated glands
• Mesenchyme cells
– Mesoderm  everything else
© 2013 Pearson Education, Inc.
Figure 28.9 Formation of the three primary germ layers.
Amnion
Bilayered
embryonic disc
Head end of
bilayered
embryonic disc
Yolk sac
Frontal
section
3-D view
Section
view in (e)
Primitive
streak
Head end
Cut edge
of amnion
Epiblast
Yolk sac
(cut edge)
Right
Left
14-15 days
Hypoblast
Endoderm
Ectoderm
Primitive
streak
Tail end
Bilayered embryonic disc, superior view
© 2013 Pearson Education, Inc.
16 days Mesoderm Endoderm