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Lecture 12
Pregnancy and Human Development
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
• Sperm has a limited amount of time to reach the
ovulated secondary oocyte
• Oocyte is viable for 12 to 24 hours
• Sperm viable 24 to 48 hours after ejaculation
• Maximum likelihood of fertilization: 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
The Roadblocks
• Most sperm don’t reach the oocyte
• 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
Capacitation
• Fresh sperm are incapable of penetrating an
oocyte
– capacitated before they can penetrate oocyte
– occurs 2 – 10 hrs after ejaculation
– Sperm must become motile
– Secretions of female tract weaken acrosome
membrane
• helps in the release of hydrolytic enzymes needed to
penetrate oocyte
• Calcium uptake to trigger motility
Sperm can smell
• Sperm have olfactory receptors that respond
to chemical stimuli
– presumed to be coming from the oocyte or
surrounding area
Sperm Penetration
• Sperm must breach oocyte coverings
– Corona radiata and zona pellucida
• Corona radiata easier to get through
• Zona pellucida requires an acrosomal reaction
– Hyaluronidase, acrosin, proteases released to
digest holes in zona pellucida
ZP3 Glycoprotein
• Zone pellucida receptor protein for sperm to
bind
• Binding opens a Ca2+ channel in sperm that
activates the acrosomal reactions
Plasma Membrane Fusion
• Sperm head approaches oocyte
– Rear portion of acrosomal membrane binds to
oocyte plasma membrane
• Binding has two consequences:
– Oocyte forms microvilli that surround sperm and
fuse membranes
– Cytoplasmic contents of sperm enter the oocyte,
leaving PM behind
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
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
Monospermy
• Upon entry of sperm, Ca2+ surge from ER
causes cortical reaction:
– Cortical granules release enzymes (zonal inhibiting
proteins, or ZIPs)
– ZIPs inactivate sperm receptors
– Activates oocyte to prepare for second meiotic
division
Formation of the Zygote
• Sperm nucleus moves toward oocyte nucleus and
swells to form male pronucleus
• Ovum nucleus swells to become female
pronucleus
• Fertilization – moment when membranes of two
pronuclei rupture and chromosomes combine
– zygote
Figure 28.3b Events of fertilization.
Male and female
pronuclei
Polar bodies
© 2013 Pearson Education, Inc.
Embryonic Development
• Occurs while zygote moves toward uterus
• Proccess called cleavage
– rapid mitotic divisions without growth
Cleavage
• 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
The Blastocyst
• 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)
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
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Blastocyst
cavity
Inner cell
mass
Implantation
• Blastocyst floats for 2–3 days
• Nourished by uterine secretions
• Implantation begins 6–7 days after ovulation
• Dependent on proper endometrial layer
– minimum of 67% of all zygotes formed fail to implant
– 30% of implanted zygotes miscarry due to varied
factors
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
• Endometrial cells cover and seal off implanted
blastocyst
Figure 28.5a Implantation of the blastocyst.
Endometrium
Uterine endometrial
epithelium
Inner cell mass
Trophoblast
Blastocyst cavity
Lumen of uterus
© 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
– just before endometrium normally begins to slough
off
• Menstruation must be prevented
• Viability of corpus luteum maintained by
hormone human chorionic gonadotropin (hCG)
Human chorionic gonadotropin (hCG)
• Initially secreted by trophoblast cells
– Prompts corpus luteum to continue secretion of
progesterone and estrogen
– Promotes placental development
• hCG levels rise until end of second month,
then decline as placenta begins to secrete
progesterone and estrogen
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
• Orginates from embryonic and endometrial
tissues
• Inner mass cells give rise to extraembryonic
mesoderm layer
– under the inner surface of trophoblast
– This becomes the chorion
Chorion and Chorionic villi
• Chorion – outmost membrane that helps form
the placenta
– chorion grown outward to make chorionic villi
– extending further into the endometrium layer that
is growing new blood vessles
• Maternal endometrium becomes the decidua
basalis
Placentation
• Maternal portion of placenta
– Decidua basalis
– stratum functionalis between chorionic villi and
stratum basalis of endometrium)
• Fetal portion of placenta
– Chorionic villi
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.
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
• Placenta fully formed and functional by end of
third month
• Nutritive, respiratory, excretory, endocrine
functions
• Placenta also secretes human placental lactogen,
human chorionic thyrotropin, hCG, and relaxin
– inadequate hCG induces spontaneous abortion
Placentation
• Maternal and embryonic blood supplies
normally do not intermix
• Embryonic placental barriers include
– Membranes of chorionic villi
– Endothelium of embryonic capillaries
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
Extraembryonic Membranes
• Amnion – transparent sac filled with amniotic
fluid
– Provides buoyant environment that protects
embryo
– Helps maintain constant homeostatic temperature
– Allows freedom of movement; isolates growing
fetus
– Amniotic fluid comes from maternal blood, and
later, fetal urine
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
Extraembryonic Membranes
• Allantois - small outpocketing at caudal end of
yolk sac
– Structural base for umbilical cord
– Becomes part of urinary bladder
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: From Gastrula to Fetus
• While implanting is occuring, the blastocyst is
being converted to a gastrula
– three germ layers form
– extraembroyonic membranes develop
• To start: inner mass cells subdivide into two
layers:
– upper epiblast
– lower hypoblast
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.
Gastrulation
• Occurs in week 3
• Embryonic disc forms three-layered embryo
with primary germ layers:
– Ectoderm, mesoderm, and endoderm
• Begins with appearance of primitive streak
– raised dorsal groove
– establishes longitudinal axis of embryo
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
Organogenesis
• Gastrulation sets stage for organogenesis
– Formation of body organs and systems
• At eighth week
– All organ systems recognizable
– End of embryonic period
Ectoderm, mesoderm, endoderm
• The primitive tissues from which all body organs derive
• Ectoderm – “outer skin”
– nervous system; skin epidermis
• Endoderm – “inner skin”
– epithelial linings of digestive, respiratory, urogenital
systems; associated glands
• Mesoderm – “middle skin”
– everything else
Organogenesis
• Embryo begins as flat plate
• Forms a cylindrical body resembling three
stacked sheets of paper folding laterally into
tube, and at both ends
Figure 28.10a Folding of the embryonic body, lateral views.
Head
Tail
Amnion
Yolk sac
Ectoderm
Mesoderm
Endoderm
© 2013 Pearson Education, Inc.
Trilaminar
embryonic
disc
Figure 28.10b Folding of the embryonic body, lateral views.
Lateral
fold
© 2013 Pearson Education, Inc.
Future gut
(digestive
tube)
Figure 28.10c Folding of the embryonic body, lateral views.
Somites
(seen
through
ectoderm)
Tail
fold
Head
fold
Yolk sac
© 2013 Pearson Education, Inc.
Figure 28.10d Folding of the embryonic body, lateral views.
Neural
tube
Notochord
Primitive
gut
Hindgut
© 2013 Pearson Education, Inc.
Yolk
sac
Foregut
Specialization of the Endoderm
• Primitive Gut
– becomes the epithelial lines of the GI tract
– Organs of GI tract become apparent, and oral and
anal openings perforate
– Mucosal lining of respiratory tract forms from
pharyngeal endoderm (foregut)
– Glands arise further along tract
Figure 28.11 Endodermal differentiation.
Pharynx
Parathyroid
glands and
thymus
Thyroid
gland
Esophagus
Trachea
Connection
to yolk sac
Right and
left lungs
Stomach
Liver
Umbilical
cord
Pancreas
Gallbladder
Small intestine
Allantois
Large intestine
© 2013 Pearson Education, Inc.
5-week embryo
Specialization of the Ectoderm
• Neurulation
– First major event of organogenesis
– Gives rise to brain and spinal cord
– Induced by chemical signals from notochord
– Ectoderm over notochord thickens, forming neural
plate
– Neural plate folds inward as neural groove with
neural folds
Specialization of the Mesoderm
• First evidence - appearance of notochord
– Eventually replaced by vertebral column
• Formation of somites
– mesodermal aggregates
• Formation of Intermediate mesoderm
• Formation of Lateral plate mesoderm
Figure 28.12a Neurulation and early mesodermal differentiation.
Head
Amnion
Amniotic cavity
Left
Right
Cut
edge of
amnion
Primitive
streak
Tail
Neural plate
Ectoderm
Mesoderm
Notochord
Endoderm
Yolk sac
© 2013 Pearson Education, Inc.
17 days. The flat three-layered
embryo has completed
gastrulation. Notochord and
neural plate are present.
Figure 28.12b Neurulation and early mesodermal differentiation.
Neural
crest
Neural
groove
Neural
fold
Coelom
© 2013 Pearson Education, Inc.
Somite
Intermediate
mesoderm
20 days. The neural folds form
by folding of the neural plate, which
then deepens, producing the
neural groove. Three mesodermal
Lateral plate aggregates form on each side of
the notochord (somite,
mesoderm
intermediate mesoderm, and
lateral plate mesoderm).
Figure 28.12c Neurulation and early mesodermal differentiation.
Surface
ectoderm
Neural
crest
Neural
tube
Somite
Notochord
© 2013 Pearson Education, Inc.
22 days. The neural folds have
closed, forming the neural tube
which has detached from the
surface ectoderm and lies
between the surface ectoderm
and the notochord. Embryonic
body is beginning to undercut.
Figure 28.12d Neurulation and early mesodermal differentiation.
Neural tube
(ectoderm)
Somite
Dermatome
Myotome
Sclerotome
Kidney and gonads
(intermediate
mesoderm)
Epidermis
(ectoderm)
Gut lining
(endoderm)
Lateral plate
mesoderm
• Limb bud
• Smooth
muscle of gut
• Visceral serosa
Peritoneal cavity
(coelom)
© 2013 Pearson Education, Inc.
• Parietal serosa
• Dermis
End of week 4. Embryo
undercutting is complete. Somites
have subdivided into sclerotome,
myotome, and dermatome, which
form the vertebrae, skeletal
muscles, and dermis respectively.
Body coelom present.
Figure 28.13 Flowchart showing major derivatives of the embryonic germ layers.
Epiblast
ECTODERM
MESODERM
Notochord
Somite
Intermediate
mesoderm
ENDODERM
Lateral plate
mesoderm
Somatic
mesoderm
• Epidermis, hair,
nails, glands of skin
• Brain and spinal
cord
Nucleus
pulposus of
intervertebral
discs
• Neural crest and
derivatives (e.g.,
cranial, spinal, and
sympathetic
ganglia and
associated nerves;
chromaffin cells of
the adrenal
medulla; pigment
cells of the skin)
© 2013 Pearson Education, Inc.
• Sclerotome:
vertebrae and
ribs
• Dermatome:
dermis of
dorsal body
region
• Myotome:
trunk and limb
musculature
• Kidneys
• Parietal serosa
• Gonads
• Dermis of ventral
body region
• Connective
tissues of limbs
(bones, joints,
and ligaments)
Splanchnic
mesoderm
• Wall of
digestive and
respiratory
tracts (except
epithelial
lining)
• Visceral serosa
• Heart
• Blood vessels
Epithelial lining
and glands of
digestive and
respiratory
tracts
Effects of Pregnancy: Anatomical
Changes
• Uterus expands, occupying most of abdominal
cavity
• Ribs flare to widen thorax
• Relaxin causes pelvic ligaments and pubic
symphysis to relax to ease birth passage
– secreted by the placenta
Effects of Pregnancy: Anatomical
Changes
• Good nutrition vital: 300 additional daily calories
• Multivitamins
– folic acid reduce fetal risk of neurological problems (spina
bifida, anencephaly, and spontaneous preterm birth)
• Poor fetal environment may not show for decades later
– Below-normal birth rate increases risk of type2-diabetes
(women) and cardiovascular disease (men and women)
Effects of Pregnancy: Metabolic
Changes
• Placental hormones
– Human placental lactogen (hPL)
– maturation of breasts, fetal growth, and glucose
sparing in mother (reserving glucose for fetus)
– thought to be the cause of gestational diabetes in
10% pregnant women
Effects of Pregnancy: Metabolic
Changes
• Parathyroid hormone and vitamin D levels
high throughout pregnancy
– Mutivitamin generally includes calcium
– adequate calcium for fetal bone mineralization
• Remember: bone is site for Ca2+ storage and
will be removed regardless of bone integrity
Effects of Pregnancy: Physiological
Changes
• GI tract
– Morning sickness believed due to elevated levels
of hCG, estrogen and progesterone
• Urinary system
– Urine production due to maternal metabolism
and fetal wastes
Effects of Pregnancy: Physiological
Changes
• Respiratory system
– Estrogens may cause nasal edema, congestion and
nose bleeds
– Tidal volume increases
• respond for greater need for oxygen
• progesterone enhances sensitivity of the medullary
respiratory center to CO2
Effects of Pregnancy: Physiological
Changes
• Cardiovascular system
– Blood volume increases 25–40%
– Safeguards against blood loss during childbirth
– Cardiac output rises as much as 35-40%
• Propels greater volume around body
– Venous return from lower limbs may be impaired,
resulting in varicose veins
Parturition
• Giving birth to baby
• Labor
– Events that expel infant from uterus
– Series of steps for induction
Events for Labor
• Fetal cortisol simulate placenta to release
large amounts of estrogen
• Increased production of surfactant protein A
(SP-A) by fetal lungs trigger inflammatory
response in the cervix
– occurs weeks before delivery
– stimulates its softening in preparation
Rise of Estrogen
• Three important consequences:
– Stimulates myometrial cells to form oxytocin
receptors
– Promotes formation of gap junctions between uterine
smooth muscle
– Antagonizes progesterone's influence on uterine
muscle
• Result: Myometrium becomes irritable and weak
– cause of false labor
Initiation of Labor
• Fetus determines own birth date
– Fetal secretion of cortisol stimulates placenta to
secrete more estrogen
– Rise of estrogen has its effects
– Fetal oxytocin causes placenta to produce
prostaglandins
– Oxytocin and prostaglandins - powerful uterine
muscle stimulants
– leads to Braxton Hicks contractions in uterus
Figure 28.17 Hormonal induction of labor.
Start
Estrogen
Oxytocin
from
placenta
from fetus
and mother's
posterior pituitary
Induces oxytocin
receptors on uterus
Stimulates uterus
to contract
Stimulates
placenta to release (+)
Prostaglandins
Stimulate more
vigorous contractions
of uterus
© 2013 Pearson Education, Inc.
Positive feedback
(+)
Delivery Events
• Cervix thins and dilates fully to 10 cm
• Amnion ruptures, releasing amniotic fluid
– “water breaking”
• Engagement occurs
– head enters true pelvis
– head rotates to navigate body through pelvis
Delivery
• Crowning
– when largest dimension of head distends vulva
• Episiotomy may be done to reduce tearing
– also easier to repair and heal
• Once head has been delivered, rest of body
delivered much easier
Delivery Positions
• Vertex position – head-first
– Skull dilates cervix; early suctioning allows
breathing prior to complete delivery
• Breech position – buttock-first
– Delivery more difficult; often forceps required, or
C-section (delivery through abdominal and uterine
wall incision)
But wait, there’s more!
• Strong contractions continue
– detachment of placenta and compression of
uterine blood vessels
– Delivery of afterbirth (placenta and membranes)
occurs ~30 minutes after birth
• All placenta fragments must be removed to
prevent postpartum bleeding
Apgar Score
• Neonatal period
– four-week period immediately after birth
– infant must adjust to dramatic environmental changes
• Physical status assessed minutes after birth
– 0–2 points each:
– Heart rate, Muscle tone, Respiration, Reflexes and
Color
• Score of 8–10 - healthy
Baby’s First Breath
•
CO2 in body due to loss of placenta
– central acidosis which stimulates respiratory control
centers to trigger first inspiration
• Breathing ain’t easy:
– airways tiny; lungs collapsed (never used)
• Surfactant in alveolar fluid helps reduce surface
tension
– occurs in last months
– breathing difficulties in premature births
Lactation
• Production of milk by mammary glands
• Toward end of pregnancy
– Placental estrogens, progesterone, and human
placental lactogen stimulate hypothalamus to
release prolactin-releasing factors (PRFs)
– Anterior pituitary releases prolactin
– mammary glands secrete colostrum
Colostrum
• Released first 2–3 days
– Less lactose but more protein, vitamin A, and
minerals; almost no fat
• Yellowish secretion rich in IgA antibodies
– IgA resistant to digestion; may protect infant against
bacterial infection; absorbed into bloodstream for
immunity
• Followed by true milk production
Lactation
• Prolactin release wanes after birth
• Lactation sustained by mechanical stimulation of
nipples - suckling
– Suckling causes afferent impulses to hypothalamus
– Prolactin stimulates milk production
– oxytocin activates let-down reflex
• both mammary glands fill with milk regardless of suckling
Advantages of Breast Milk
• Fats and iron better absorbed; amino acids more easily
metabolized as compared with cow's milk or formula
– some formula contains high fructose corn syrup and linked
to obesity in infants
• Beneficial chemicals
– IgA, complement, lysozyme, interferon, and
lactoperoxidase (protect from infections)
– Interleukins and prostaglandins prevent inflammatory
responses
– Glycoprotein deters ulcer-causing bacterium from
attaching to stomach mucosa
Lab for Today
• Exersise 43
– Understand the steps of spermatogenesis and
oogenesis
– Understand the menstrual cycle (pg. 652)
• Exercise 44
– Understand human development and placental
structure