Download pregnancy and human development

PREGNANCY
AND
HUMAN DEVELOPMENT
Pregnancy and Human Development
•
•
•
•
•
Pregnancy: events that occur from the
time of fertilization (conception) until the
infant is delivered
– The pregnant woman’s developing
offspring is called the conceptus
– Time during which development occurs
is referred to as the gestation period
and extends from the last menstrual
period until birth, approximately 280
days
• Thus, at the moment of
fertilization, the mother is
officially (but illogically) two
weeks pregnant
Two weeks following fertilization, the
conceptus undergoes preembryonic
development and is known informally as a
preembryo
Week 3—week 8 after fertilization, the
embryonic period, the conceptus is called an
embryo
Week 9 through birth, the fetal period, the
conceptus is called the fetus
At birth, it is an infant
EMBRYONIC DEVELOPMENT
From Egg to Embryo
Accomplishing Fertilization
• Oocyte is viable for 12 to 24 hours after it is cast out
of the ovary
– Chance of pregnancy drops to almost zero the next day
• Sperm retain their fertilizing power for 24 to 72 hours
after ejaculation
• For fertilization to occur, coitus must occur no more
than three days (72 hours) before ovulation and no
later than one day (24 hours) after ovulation, at
which point the oocyte is approximately one-third of
the way down the length of the uterine tube
• Fertilization occurs when a sperm fuses with an egg
to form a fertilized egg, or zygote, the first cell of the
new individual
From Egg to Embryo
Accomplishing Fertilization
• Fertilization occurs when a sperm fuses with an egg to form a
zygote
• During copulation, millions of sperm ejaculated into the female
reproductive tract are lost due to leakage from the vaginal
canal, destruction by the acidic environment of the vagina,
inability to pass the cervical mucus, or destruction by defense
cells of the uterus
– Those that do reach the uterus are subjected to forceful
uterine contractions that act to disperse them throughout
the uterine cavity, where thousands are destroyed by
resident phagocytes
• Only a few thousand (and sometimes fewer than 200 sperm),
out of the millions in the male ejaculate, finally enter the uterine
tubes, where the oocyte may be moving leisurely toward the
uterus
From Egg to Embryo
Accomplishing Fertilization
• In order to fertilize an egg, sperm must be
capacitated, a process involving weakening of the
sperm cell membrane in order to allow release of
acrosomal hydrolytic enzymes
• As sperm swim through the cervical mucus, uterus,
and uterine tubes, membrane proteins are removed
and the cholesterol that keeps the acrosomal
membranes tough and stable is depleted
– The sperm undergo a gradual capacitation over the next 6-8
hours
• Thus, even though the sperm may reach the oocyte
within a few minutes, they must wait around for
capacitation to occur
From Egg to Embryo
Accomplishing Fertilization
• The ovulated oocyte is
encapsulated by the corona
radiata and the deeper zona
pellucida, a thick layer of
extracellular matrix, and
both must be breached
before the oocyte can be
penetrated
– Surface hyaluronidase
and sperm hypermobility
are sufficient to get the
sperm to this point
SPERM PENETRATION AND THE
CORTICAL REACTION
From Egg to Embryo
Accomplishing Fertilization
•
Once a sperm binds to the zona
pellucida, it undergoes the
acrosomal reaction:
– Triggered by Ca2+
– Acrosomal enzymes
(acrosin, proteases, and
others) are released in the
immediate vicinity of the
oocyte
– Hundreds of acrosomes
(sperms) must rupture to
break down the intercellular
cement, rich in hyaluronic
acid, that holds the
granulosa cells together and
to digest holes in the zona
pellucida
SPERM PENETRATION AND THE
CORTICAL REACTION
From Egg to Embryo
Accomplishing Fertilization
• The sperm that arrive first on
the scene “sacrifice
themselves” for the good of
their brothers
– A sperm that comes along
later, after hundreds of
sperm have undergone
acrosomal reactions to
expose the oocyte
membrane, is in the best
position to be the fertilizing
sperm
• Once a sperm cell binds to
membrane receptors on the
oocyte membrane, its nucleus
is pulled into the cytoplasm
of the oocyte
SPERM PENETRATION AND THE
CORTICAL REACTION
From Egg to Embryo
Accomplishing Fertilization
• Each sperm carries a special
two-part binding apparatus
on its surface:
– The beta protein part acts
first as it binds to a receptor
on the oocyte membrane:
• This event engages the
alpha protein part, causing
it to insert into the
membrane:
– This somehow causes the
egg and sperm
membranes to open and
fuse together with such
perfect contact that the
contents of both cells are
combined within a single
membrane
SPERM PENETRATION AND THE
CORTICAL REACTION
Blocks to Polyspermy
• Polyspermy, or fertilization by more than
one sperm cell, leads to a lethal number of
chromosomes, and must be prevented
Blocks to Polyspermy
• Two mechanisms ensure monospermy: the one
sperm condition:
– 1. When the plasma membrane of one sperm contacts the
oocyte membrane, sodium channels open and Na+ diffuses
into the oocyte from the extracellular space, causing its
membrane to depolarize:
• This electrical event, called the fast block to polyspermy,
prevents other sperm from fusing with the oocyte membrane
• Once the sperm has entered, Ca2+ is released by the oocyte’s
endoplasmic reticulum into its cytoplasm, which activates the
oocyte to prepare for cell division
– It also causes the cortical reaction, in which granules located just deep
to the plasma membrane spill their enzymes into the extracellular
space beneath the zona pellucida
» These enzymes, called zonal inhibiting proteins (ZIPS),
destroy the sperm receptors, preventing further sperm entry
Blocks to Polyspermy
• 2. The spilled material binds
water, and as it swells it
detaches all sperm still
bound to receptors on the
oocyte membrane,
accomplishing the
permanent slow block to
polyspermy
• In rare cases of polyspermy
that do occur, the embryos
contain too much genetic
material and are nonviable
(die)
Completion of Meiosis II and Fertilization
• After a sperm enters
an oocyte, it loses
its tail and midpiece,
and migrates to the
center of the oocyte
while the secondary
oocyte completes
meiosis II, forming
the nucleus and
ejecting the second
polar body (a + b)
EVENTS FOLLOWING SPERM
PENETRATION
Completion of Meiosis II and Fertilization
•
•
•
•
The ovum and sperm nuclei
swell, becoming female and
male pronuclei, and approach
each other
A mitotic spindle develops
between them (c), and the
pronuclei membranes rupture,
releasing their chromosomes
into the immediate vicinity of the
spindle
The true moment of fertilization
occurs as the maternal and
paternal chromosomes
combine and produce the
diploid zygote, or fertilized egg
(d)
Almost as soon as the male and
female pronuclei come together,
their chromosomes replicate
– The first mitotic division of
the conceptus begins
EVENTS FOLLOWING SPERM
PENETRATION
Preembryonic Development
•
Preembryonic development begins with
fertilization and continues with the
movement of the preembryo to the
uterus, where it implants in the uterine
wall
•
The mitotic divisions after
fertilization occur without much
growth between divisions, resulting
in progressively smaller cells (high
surface-to-volume ratio, which
enhances their uptake of nutrients
and oxygen), a process called
cleavage
– Cleavage forms two identical
cells, blastomeres (36 hours),
which then form a morula, a
hollow ball of cells, by 72 hours
– After 4-5 days, the blastocyst
escapes from the degrading
zona pellucida to implant in the
uterine wall
CLEAVAGE
Preembryonic Development
• The blastocyst is a fluid
filled hollow sphere
composed of a single layer
of large, flattened cells
called trophoblast cells and
a small cluster of rounded
cells, called the inner cell
mass, located at one side:
– Trophoblast cells take
part in placenta
formation
– Inner cell mass becomes
the embryonic disc,
which forms the embryo
proper
CLEAVAGE
Implantation
•
Occurs after 6-7 days; the trophoblast
adheres to the endometrium, and
produces enzymes that irritate (takes on
the characteristics of an inflammation
site) the endometrium
– Uterine capillaries become
permeable and leaky, and
inflammatory cells including
lymphocytes, natural killer cells, and
macrohages invade the area
– The trophoblast proliferates, forming
two distinct layers;
• Inner cytotrophoblast: cells
retain their cell boundaries
• Outer syncytiotrophoblast: cells
that lose their plasma membranes
and form a multinuclear
cytoplasmic mass
– Invade the endometrium and
rapidly digests the uterine
cells it contacts
– Implanted blastocyst is covered over
and sealed off from the uterine
cavity by proliferation of the
endometrical cells
Implantation
•
•
Takes about a week and is
usually completed by the 14th
day after ovulation—just when
the endometrium normally
begins to slough off in menes
(must be prevented if the
pregnancy is to continue)
Trophoblast cells secrete
human chorionic gonadotropin
(hCG), which acts on the corpus
luteum:
– Bypasses pituitary-ovarian
controls at this critical time and
prompts the corpus luteum to
continue secreting progesterone
and estrogen
– Pregnancy test used today are
antibody tests that detect hCG
in blood or urine
IMPLANTATION
IMPLANTING BLASTOCYST AND FORMATION
OF THE EMBRYONIC MEMBRANES
Implantation
• The chorion, which develops
from the trophoblast after
implantation, continues this
hormonal stimulus; thus, the
developing conceptus takes
over the hormonal control of
the uterus during this early
phase of development
• Between the 2nd and 3rd
month, the placenta
assumes the role of
progesterone and estrogen
production for the remainder
of the pregnancy
– The corpus luteum
degenerates and the ovaries
remain inactive until after
birth
RELATIVE CHANGES IN MATERNAL BLOOD LEVELS OF HUMAN
CHORIONIC GONADOTROPIN, ESTROGENS, AND
PROGESTERONE DURING PREGNANCY
Placentation
• Is the formation of the
placenta:
– Temporary organ that
originates from both
embryonic (trophoblastic)
and maternal
(endometrical) tissues
– The process of proliferation
of the trophoblast gives rise
to a layer of
extraembryonic mesoderm
on its inner surface that
becomes the chorion (b)
IMPLANTING BLASTOCYST AND FORMATION
OF THE EMBRYONIC MEMBRANES
Placentation
• The chorion develops
fingerlike chorionic villi,
which are especially
elaborate where they
are in contact with
maternal blood (c):
– The mesodermal cores of
the chorionic villi become
richly vascularized by
newly forming blood
vessels, which extend to
the embryo as the umbilical
arteries and veins
IMPLANTING BLASTOCYST AND FORMATION
OF THE EMBRYONIC MEMBRANES
Placentation
• The chorionic villi come to lie in spaces
between the maternal blood
Placentation
Placentation
Placentation
• The placenta is fully
functional as a nutritive,
respiratory, excretory,
and endocrine organ by
the end of the third
month of gestation
• Although the maternal
and embryonic blood
supplies are very close,
they normally do not
intermix
Placentation
• Throughout pregnancy, blood levels of
estrogens and progesterone continue
to increase, encouraging growth and
further differentiation of the mammary
glands and readying them for lactation
• The placenta also produces other
hormones, such as human placental
lactogen, human chorionic thyrotropin,
and relaxin
EVENTS
OF
EMBRYONIC DEVELOPMENT
•
Formation and Roles of the
Embryonic Membranes:
–
–
While implantation is occurring, the
blastocyst is being converted into a
gastrula, in which three primary
germ layers form (ectoderm,
mesoderm, and endoderm) and
embryonic membranes develop
Embryonic membranes:
•
•
•
•
The amnion forms the transparent sac
ultimately containing the embryo, and
provides a buoyant environment that
protects the embryo from physical
trauma
The yolk sac forms part of the gut,
produces the earliest blood cells and
blood vessels, and is the source of
germ cells that migrate into the embryo
to seed the gonads
The allantois is the structural base for
the umbilical cord that links the embryo
to the placenta, and becomes part of
the urinary bladder
The chorion helps to form the placenta,
and encloses the embryonic body and
all other membranes
Placentation
EVENTS
OF
EMBRYONIC DEVELOPMENT
• Gastrulation: Germ Layer Formation
– Gastrulation is the process of transforming the
two-layered embryonic disc to a three-layered
embryo containing three germ layers: ectoderm,
mesoderm, and endoderm
– Gastrulation begins with the appearance of the
primitive streak, which establishes the long axis of the
embryo:
• The endoderm gives rise to epithelial linings of the gut,
respiratory, and urogenital systems, and associated glands
• The mesoderm gives rise to all types of tissues not formed
by ectoderm or endoderm, such as muscle tissue
• The ectoderm gives rise to structures of the nervous system
and the epidermis
GASTRULATION FORMATION OF THE THREE
PRIMARY GERM LAYERS
EVENTS
OF
EMBRYONIC DEVELOPMENT
• Organogenesis: Differentiation of the Germ Layers
– Organogenesis is the formation of organs and organ
systems; by the end of the embryonic period, all organ
systems are recognizable:
• Neurulation, the formation of the brain and spinal cord, is the first
event of organogenesis
• As the embryo develops from a flat plate of cells, it rolls into a tube
and the inferior endoderm becomes the lining of the primitive gut
• Mesodermal specialization forms the notochord, and gives rise to
the dermis, parietal serosa, bones, muscles, cardiovascular
structures, and connective tissues
• By 3 ½ weeks, the embryo has a blood vessel system and a
pumping heart
• Vascular modification include umbilical arteries and veins, a ductus
venosus, and the foramen ovale and ductus arteriosus
EVENTS OF NEURULATION
EVENTS OF NEURULATION
FOLDING OF THE EMBRYONIC BODY
ENDODERMAL DIFFERENTIATION TO FORM THE EPITHELIAL
LININGS OF THE DIGESTIVE AND RESPIRATORY TRACTS AND
ASSOCIATED GLANDS
EMBRYO
5 WEEKS
6 WEEK OLD EMBRYO
• Fingers, toes, and
external ears form
7 WEEK OLD EMBRYO
• HANDS AND FEET
8 WEEKS EMBRYO
• DISTNCT FINGERS
AND TOES
EARLY MESODERMAL
DIFFERENTIATION
EVENTS
OF
FETAL DEVELOPMENT
• The fetal period extends from weeks 938, and is a time of rapid growth of
body structures established in the
embryo
• During the first half of the fetal period,
cells are still differentiating into
specific cell types to form the body’s
distinctive tissues
• TABLE 28.2 page 1128
SECOND TRIMESTER
•
•
•
•
•
•
•
•
Middle 3 months of pregnancy
After 8th week
In beginning 5 cm
Called Fetus
Skeleton formed
Soft hair grows over the skin
Eyes open
At end is 32 cm
Circulation in Fetus and Newborn
• (a): Special adaptations for
embryonic and fetal life
• The umbilical vein carries
oxygen-and nutrient-rich blood
from the placenta to the fetus
• The umbilical arteries carry
waste-laden blood from the
fetus to the placenta
• Ductus arteriosus and foramen
ovale bypass the
nonfunctional lungs
• Ductus venosus allows blood
to partially bypass the liver
CIRCULATION IN FETUS AND NEWBORN
Circulation in Fetus and Newborn
• (b): Changes in the
cardiovascular system
at birth
• The umbilical vessels
are occluded
(obstructed), as are the
liver and lung bypasses
(ductus venosus and
arteriosus, and the
foramen ovale)
CIRCULATION IN FETUS AND NEWBORN
Events of Fetal Development
• The main events of the fetal period—weeks 9
through 38—are listed in TABLE 28.2
• Time of rapid growth of the body structures that
were established in the embryo
• First half of this period, differentiation is still
continuing
• Length (crown to rump): 30mm (1 inch) to 360
mm (14 inches)
– Total body length at birth is approximately 550 mm
(22 inches)
• Weight of approximately: 2g (0.06 ounce) to 2.74.1 Kg (6-10 ponds)
FETUS
11-12WEEK OLD FETUS
• NOTE PLACENTA
AND UMBILICAL
CORD
12 WEEK OLD FETUS
22 WEEK OLD FETUS
THIRD TRIMESTER
• Final 3 months of pregnancy
• Fetus becoming modified to survive in
the outside world
• Grows in size and weight
HOMEOSTATIC IMBALANCE
• Because many potentially harmful substances can cross placental
barriers and enter the fetal blood, a pregnant woman should be
aware of what she is taking into her body, particularly during the
embryonic period when the body’s foundations are laid down
• Teratogens: factors that may cause severe congenital
abnormalities or even fetal death include:
– Alcohol: fetal alcohol syndrome (FAS)
• Mental retardation, abnormal growth
– Nicotine: hinders oxygen delivery to the fetus
• Impairs normal growth and development
– Anticoagulants
– Sedatives: thalidomide (alleviated morning sickness)
• If taken during days 26-56
– Deformed infants with short flipperlike limbs
– Antihypertensives
– Some antibiotics
– Maternal infections (German Measles)
THALIDOMIDE
EFFECTS OF PREGNANCY ON
THE MOTHER
• Anatomical Changes:
– The female reproductive organs and breasts become
increasingly vascular and engorged with blood
– The uterus enlarges dramatically, causing a shift in the woman’s
center of gravity and an accentuated lumbar curvature (lordosis)
– Placental production of the hormone relaxin causes pelvic
ligaments and the pubic symphysis to soften and relax
• This increases motility for easier birth passage
– There is a normal weight gain of around 28 pounds, due to
growth of the fetus, maternal reproductive organs, and
breasts, and increased blood volume
EFFECTS OF PREGNANCY ON
THE MOTHER
• Good nutrition is necessary all through
pregnancy if the developing fetus is to have all
the building materials (especially proteins,
calcium, and iron) needed to form its tissues
• Multivitamins containing folic acid seem to
reduce the risk of having babies with
neurological problems, including such birth
defects as spina bifida and anencephaly
(absence of brain and cranial vault with cerebral
hemisphere missing or reduced in size)
RELATIVE SIZE OF THE UTERUS BEFORE
CONCEPTION AND DURING PREGNANCY
EFFECTS OF PREGNANCY ON
THE MOTHER
• Metabolic Changes:
– As the placenta enlarges, it produces human
placental lactogen, which works with estrogen and
progesterone to promote maturation of the breasts for
lactation
– Human placental lactogen (hPL) also promotes the
growth of the fetus, and exerts a glucose-sparing
effect on maternal metabolism
• Consequently, maternal cells metabolize more fatty acids and
less glucose than usual, sparing glucose for use by the fetus
– Human chorionic thyrotropin from the placenta
increases maternal metabolic rate
EFFECTS OF PREGNANCY ON
THE MOTHER
• Physiological Changes:
– Many women suffer morning sickness during the first few months of
pregnancy, until their systems adapt to elevated levels of estrogen and
progesterone
– Heartburn often results from the displacement of the esophagus (uterus
pushing on body organs), and constipation may result due to the
decreased motility of the digestive tract
– The kidneys produce more urine, since there is additional fetal
metabolic waste
• Increased urination frequency due to uterus pressing on urinary bladder
– Vital capacity and respiratory rate increases, but there is a decrease
in residual volume, and many women suffer from difficult breathing, or
dyspnea
– Blood volume increases to accommodate the needs of the fetus, so
blood pressure and heart rate rise, increasing cardiac output
PARTURITION (BIRTH)
• Parturition is the process of giving birth,
and usually occurs within 15 days of
the calculated due date, which is 280
days from the last menstrual period
Initiation of Labor
•
•
Several events and hormones
interlock to trigger labor
During the last few weeks of
pregnancy, estrogens reach their
highest levels in the mother’s blood
–
Studies indicate that the fetus
determines its own birth date
•
–
Rising levels of fetal adrenocortical
hormones (especially cortisol) late in
pregnancy are a major stimulus for
the placenta to release such large
amounts of estrogens
This has two important consequences:
•
•
It stimulates the myometrical cells of the
uterus to form abundant oxytocin
receptors
It antagonizes progesterone’s
quieting influence on uterine muscle
–
–
Myometrium becomes increasingly
irritable, and weak, irregular uterine
contractions begin to occur
These contractions (Braxton Hicks
contractions) have caused many
women to go to the hospital, only to
be told that they were in false labor
and sent home
HORMONAL INDUCTION OF LABOR
Initiation of Labor
•
As birth nears, two more
chemical signals cooperate to
convert these false labor pains
into the real thing:
– Certain fetal cells begin to
produce oxytocin, which
causes the placenta to
release prostaglandins:
• Both hormones are
powerful uterine muscle
stimulants, and since
the myometrium is now
highly sensitive to
oxytocin, contractions
become more frequent
and more vigorous
Initiation of Labor
•
•
•
•
Increasing emotional and physical
stresses activate the mother’s
hypothalamus, which signals for
oxytocin release by the posterior
pituitary
The elevated levels of oxytocin and
prostaglandins trigger the rhythmic
expulsive contractions of true labor
Once the hypothalamus is involved,
a positive feedback mechanism is
propelled into action—greater
contractile force causes the release
of more oxytocin, which causes
greater contractile force, and so on
These expulsive contractions are
aided by the fact that fetal
fibronectin, a natural “stickum”
(adhesive protein) that binds the
fetal and maternal tissues together
throughout pregnancy, changes to
a lubricant just before true labor
begins
HORMONAL INDUCTION OF LABOR
Initiation of Labor
• Both oxytocin and prostaglandins are
essential for initiating labor in humans
• Untimely spurts of oxytocin may provoke
some instances of premature birth, and
interfering with production of either of these
hormones will hinder onset of labor
– Example:
• Antiprostaglandin drugs such as ibuprofen (antiinflammatory) can inhibit the early stages of labor and such
drugs are used occasionally to prevent preterm births
HORMONAL INDUCTION OF LABOR
Stages of Labor
– The dilation stage of labor extends from onset of labor to
the time when the cervix is fully dilated by the baby’s head,
at about 10 cm in diameter
– The expulsion stage extends from full dilation until the time
the infant is delivered:
• When the baby is in the vertex, or head first, position, the skull
acts as a wedge to dilate the cervix
• Crowning occurs when the baby’s head distends the vulva, and
once the head has been delivered, the rest of the baby follows
much more easily
• After birth, the umbilical cord is clamped and cut
– During the placental stage, uterine contractions cause
detachment of the placenta from the uterine wall, followed
by delivery of the placenta and membranes (afterbirth)
Stages of Labor
• Stage 1: Dilation Stage
(a)
– Time from labor’s onset
until the cervix is fully
dilated by the baby’s
head (about 10 cm in
diameter)
– As labor starts, weak but
regular contractions begin
in the upper part of the
uterus and move toward
the vagina
– At first, only the superior
uterine muscle is active,
the contractions are 15-30
minutes apart, and they
last for 10-30 seconds
Stages of Labor
• Stage 1: Dilation Stage
(a)
– As labor progresses, the
contractions become
more vigorous and rapid,
and the lower uterine
segment gets involved
– As the infant’s head is
forced against the cervix
with each contraction,
the cervix softens, thins
(effaces), and dilates
– Eventually the amnion
ruptures, releasing the
amniotic fluid, an event
commonly called
“breaking the water”
Stages of Labor
• Stage 1: Dilation Stage (a)(b)
– The dilation stage is the
longest part of labor, lasting
6-12 hours or more
– Several events happen during
this phase:
• Engagement occurs when the
infant’s head enters the true
pelvis
• As descent continues
through the birth canal, the
baby’s head rotates so that
its greatest dimension is in
the anteroposterior line,
which allows it to navigate
the narrow dimensions of
the pelvic outlet
Stages of Labor
• Stage 2: Expulsion Stage (c)
– Lasts from full dilation to
delivery of the infant
– By the time the cervix is
fully dilated, strong
contractions are occurring
every 2-3 minutes and
lasting about 1 minute
• A mother undergoing labor
without local anesthesia
has an increasing urge to
push or bear down with the
abdominal muscles
– Although this phase may
last 2 hours, it is typically 50
minutes in a first birth and
around 20 minutes in
subsequent births
Stages of Labor
• Stage 2: Expulsion Stage (c)
– Crowning occurs when the
largest dimension of the
baby’s head distends the
vulva
– At this point, an episiotomy
(incision made to widen the
vaginal orifice) may be done
to reduce tissue tearing
– The baby’s neck extends as
the head exits from the
perineum, and once the head
has been delivered, the rest of
the baby’s body is delivered
much more easily
– After birth, the umbilical
cord is clamped and cut
Stages of Labor
• Stage 2: Expulsion Stage (c)
– When the infant is in the usual
vertex, or head-first,
presentation, the skull (its
largest diameter) acts as a
wedge to dilate the cervix
– The head-first presentation
also allows the baby to be
suctioned free of mucus and
to breathe even before it has
completely exited from the
birth canal
– In breech (buttock-first) and
other nonvertex
presentations, these
advantages are lost and
delivery is much more
difficult, often requiring the
use of forceps
HOMEOSTATIC IMBALANCE
• If a women has a deformed or malelike
pelvis, labor may be prolonged and
difficult (dystocia)
– Besides extreme maternal fatigue, another
consequence is fetal brain damage
– To prevent these outcomes, a cesarean (Csection) is performed in many such cases
– A C-section is delivery of the infant
through n incision made through the
abdominal and uterine walls
Stages of Labor
•
Stage 3: Placental Stage (d)
– Delivery of the placenta
– Accomplished within 30 minutes
after birth of the infant
– The strong uterine contractions
that continue after birth
compress uterine blood
vessels, limit bleeding, and
cause placental detachment
– The placenta and its attached
fetal membranes, collectively
called the afterbirth, are then
easily removed by a gentle tug
on the umbilical cord
– It is very important that all
placental fragments be
removed to prevent continued
uterine bleeding after birth
(postpartum bleeding)
TWINS
• Identical:
– One embryo splits into two separate embryos
• Probably during the blastocyst stage
• Fraternal:
– Two eggs are fertilized by different sperm
AFTERBIRTH
•
Baby still attached to the placenta by means of the umbilical cord:
– Once tied and cut, the baby no longer obtains food and oxygen from the mother
– Navel is the spot where your umbilical cord was attached to your body
•
Lung filled with amniotic fluid:
– First cries rid the lungs of fluid and fill them with air
– Newborn begins to breathe on its own
•
In the uterus most of the blood bypassed the lungs:
– Right ventricle through a duct into the systemic system
– Duct closes at birth
– Right ventricle begins pumping to the lungs
•
Before birth, an opening exists between the right and left atria:
– Normally this opening closes shortly after birth preventing oxygenated and
deoxygenated blood from mixing
•
The remains of the placenta and amnion are then expelled from the
mother’s body about 10 minutes after the birth of the baby (afterbirth)
ADJUSTMENTS OF THE INFANT
TO EXTRAUTERINE LIFE
• Neonatal period is the four-week period
immediately after birth
• Birth represents quite a shock to the infant
–
–
–
–
Exposed to physical trauma during the birth process
Suddenly cast out of its watery, warm environment
Its placental life supports are severed
NOW must do for itself
ADJUSTMENTS OF THE INFANT
TO EXTRAUTERINE LIFE
• At 1 and 5 minutes after birth, the infant’s
physical status is assessed based on five
signs:
– Each observation is given a score of 0 to 2
•
•
•
•
•
Heart rate
Respiration
Color
Muscle tone
Reflexes (tested by slaps on the feet)
– Total is called the Apgar score
• Score of 8 to 10 indicates a healthy baby
• Lower scores reveal problems in one or more of the
physiological functions assessed
ADJUSTMENTS OF THE INFANT
TO EXTRAUTERINE LIFE
• Taking the First Breath:
– Once carbon dioxide is no longer removed by the
placenta, it accumulates in the baby’s blood, causing
central acidosis
– This excites respiratory control centers in the
baby’s brain and triggers the first inspiration
– The first breathe requires a tremendous effort
• The airways are tiny, and the lungs are collapsed
• Once the lungs have been inflated in full-term babies,
surfactant in alveolar fluid reduces surface tension in the
alveoli, and breathing is easier
– The rate of respiration is rapid (about 45
respirations/min) during the first two weeks and then
gradually declines to normal levels
ADJUSTMENTS OF THE INFANT
TO EXTRAUTERINE LIFE
• Keeping the lungs inflated is much more
difficult for premature infants (those
weighing less than 2500 g, or about 5.5
pounds, at birth) because surfactant
production occurs during the last
months of prenatal life
– Consequently, preemies are usually put on
respiratory assistance (a ventilator) until
their lungs are mature enough to function
on their own
Occlusion of Special Fetal Blood
Vessels and Vascular Shunts
•
After birth, the umbilical arteries and veins
constrict and become fibrosed (fibrous tissue,
scar)
– Proximal parts of the umbilical arteries
persist as the superior vesical arteries that
supply the urinary bladder
– Distal parts of the umbilical arteries become
the medial umbilical ligaments
– Umbilical vein becomes the round ligament
of the liver, or ligamentum teres, that
attaches the umbilicus (scar that marks the
former attachment of the umbilical cord to the
fetus) to the liver
– Ductus venosus collapses as blood stops
flowing through the umbilical vein and is
eventually converted to the ligamentum
venosum on the liver’s undersurface
– Pulmonary shunts close
– Flap of the foramen ovale (hole between the
atria) is pushed to the shut position fusing to
form the septal wall (fossa ovalis)
– Ductus arteriosus constricts, becoming the
ligamentum arteriosus
The Transitional Period
• Infants pass through an unstable
transitional period:
– 6-8 hours after birth
– Characterized by intermittent waking periods
in which the infant’s heart rate, respiratory
behavior, and body temperature fluctuate
LACTATION
• Lactation is the production of milk by the
hormone-prepared mammary glands:
– Rising levels of placental estrogens, progesterone,
and lactogen toward the end of pregnancy stimulate
the hypothalamus to produce prolactin-releasing
hormone (PRH), which promotes secretion of
prolactin by the anterior pituitary
– After a delay of two to three days, true milk production
begins
LACTATION
• During the delay of milk production, a yellowish fluid
called colostrum is secreted:
– Comparison to milk:
•
•
•
•
•
Has less lactose than milk
Almost no fat
Higher in protein
Higher in Vitamin C
Higher in minerals
– Like milk, colostrum is rich in IgA antibodies:
• Since these antibodies are resistant to digestion in the stomach,
they may help to protect the infant’s digestive tract against bacterial
infection
• These antibodies are absorbed by endocytosis and subsequently
enter the bloodstream to provide even broader immunity
LACTATION
• After birth, prolactin (placenta) release gradually
wanes, and continual milk production depends on
mechanical stimulation of the nipples, normally
provided by the sucking infant:
– Mechanoreceptors in the nipples send afferent nerve impulses
to the hypothalamus, stimulating secretion of Prolactin
releasing hormone (PRH)
• Which stimulates the anterior pituitary to secrete prolactin
– Nipple stimulation during nursing sends neural signals to the
hypothalamus, resulting in production of PRH and a burst of
prolactin from the anterior pituitary resulting in the stimulation of
milk production for the next feeding
LACTATION
• Mechanoreceptors (nipples)
also prompt hypothalamic
release of oxytocin from the
posterior pituitary via a
positive feedback
mechanism
– Oxytocin causes the letdown reflex:
• Ejection of milk from the
alveoli of the mammary
glands of both breast, not
just the suckled one
• During nursing oxytocin
also simulates the recently
emptied uterus to contract,
helping it to return to
(nearly) its prepregnant size
POSITIVE FEEDBACK MECHANISM OF THE
MILK LET-DOWN REFLEX
LACTATION
•
Advantages of breast milk are:
–
–
–
–
–
–
–
–
Its fats and iron are better absorbed
Its amino acids are metabolized more efficiently than those of cow’s milk
IgA antibodies
Lysozyme: protect infants from infections
Interferon: protect infants from infections
Lactoperoxidase: protect infants from infections
Interleukins and prostaglandins: prevent overzealous inflammatory responses
Glycoprotein: deters the ulcer-causing bacterium from attaching to the stomach
mucosa
– Naturally laxative: helps cleanse the bowels
• Removes meconium (green-black paste containing sloughed-off epthelial cells, bile,
bilirubin, etc.)
– Prevents physiological jaundice
– Encourages bacteria that are the source of Vitamins K and some Bs to
colonize the large intestine
POSITIVE FEEDBACK MECHANISM OF THE
MILK LET-DOWN REFLEX
LACTATION
• When nursing is discontinued, the stimulus
for prolactin release and milk production
ends, and the mammary glands stop
producing milk
CONTRACEPTION