Download - Free Documents

EXTRAEMBRYONER STRUCTURES
PLACENTA AND FOETAL MEMBRANES
PLACENTA and FETAL MEMBRANES
Placenta Chorion / Maternal Decidua Chorion Trophoblasts / Extraembryonic Mesoderm
Amnion Epiblast / Extraembryonic Mesoderm Yolk Sac Hypoblast / Extraembryonic
Mesoderm Allantois Embryonic Hindgut
PARTURITION AMNION SAC AND AMNION FLUID VITTELLINE SAC ALLANTOIS
OBJECTIVES
Describe the differentiation of the trophoblast layer of the blastocyst upon implantation.
Describe the fetal syncytiotrophoblast and cytotrophoblast separate roles in the primitive
placenta. Understand the decidual reaction of the endometrium. Understand the definition of
the types of villi that develop sequentially. Understand the cell layers that separate maternal
from fetal blood. Understand the nutritive role of the placenta. Understand the maternal and
fetal components that can cross the placenta barrier. Understand the endocrine role of the
placenta. Understand abnormalities of placental development than can occur. Describe the
cause and consequences of erythroblastosis fetalis.
. plakuos flat cake is a maternofetal organ which begins developing at implantation of the
blastocyst and is delivered with the fetus at birth. gas exchange.PLACENTA
INTRODUCTION The placenta Gk. endocrine and immune support for the developing fetus.
waste removal. During that month period it provides nutrition.
PLACENTA GENERAL SPECIFICATION The placenta continues to grow and develop
throughout pregnancy and at term is an organ of about cm in diameter. with a thickness of
cm and a weight of about g. The decidual septa define regions of the placenta called
cotyledon. . The erosion of the decidua basalis is incomplete uneroded regions called
decidual septa. The rate of maternal blood flow to the uterus is in the range of ml/min with of
that destined to supply the placenta Martal and Cdard. The chorionic villi have an enormous
area of exchange. reaching m at term and the capillaries within them have a length of km. .
. hemochorial.PLACENTA CLASSIFICATION Human plancentation type is discoid.
. cm long.Placental Anatomy Maternal Surface Cotyledons Form cobblestone appearance
Originally placental septa formed grooves Overed with maternal decidua basalis Fetal
Surface Covered with amniotic membrane attached to chorionic plate. Umbilical cord
attachment. Umbilical vessels branch into chorionic vessels. Cord cm diameter.
.not associated with the embryo.DEC DUA Decidual Reaction stromal cells accumulate
glycogen and lipid. associates with the chorion frondosom Decidua capsularis Superfical
layer overlying the entire embryoblast. called Decidual Cells Decidua basalis forms maternal
component of the placenta. This layer eventually degenerates. associates with the chorion
laeve Decidua parietalis All remaining parts of the endometrium .
Amniotic Sac Between the epiblast and trophoblast. a slitlike cavity appears and enlarges to
form the amniotic sac.Early Development of the Placenta Growth of the embryoblast
outstrips the trophoblast . . Cells from the epiblast migrate upwards to completely line this
new cavity. Primary Yolk Sac The cells of the hypoblast migrate downwards to line the
blastocoele and form the primary yolk sac. This cavity called the amniotic cavity The next
significant step in embryogenesis is separation of embryoblast from trophoblast This disc will
soon come to sit between two sacs. the amniotic sac and yolk sac. As a consequence the
former begins pulling away from later forming another cavity.
the lacunae form interconnections so that the syncytiotrophoblast or syncytium takes on a
quotspongyquot appearance . As the trophoblast grows outward rapidly. it erodes into dilated
uterine capillaries called sinusoids. Maternal blood from the sinusoids rushes into the
syncytiotrophoblast cell mass and fills cavities called lacunae. But at the stalk where it
remains attached to the cytotrophoblast. By day . The direct contact of the
syncytiotrophoblast with maternal blood allows for diffusion to take place and forms the
beginning of uteroplacental circulation. Oxygen and nutrients from maternal blood diffuse
across the trophoblast to supply the developing embryo. The cavitations grow larger and
eventually join to form a large cavity that completely surrounds the embryo all.Early
Uteroplacental Circulation As the syncytiotrophoblast invades the uterine wall. while wastes
from the embryo diffuse across the trophoblast into the lacunae to be removed by the uterine
veins. cavitations appear within the extraembryonic mesoderm. .
Early Development of the Placenta .
spiral arteries and endometrial veins Enlargement includes further branching of the
anchoring villus. chorion frondosum.Placental Development By weeks Chorionic stem villi
over the entire surface of the chorionic sac Those villi associated with the decidua basalis
increase in size and more villi form. The villi project into a blood filled intervillous space
resulting from the erosion of the decidua basalis.this region is called the chorion leave .
Endometrial vessels. Villi associated with the decidua capsularis degenerate .
cytotrophoblasts frorm fingerlike extensions Secondary chorionic villi have a core of loose
connective tissue. trophoblastic shell cells syncitiotrophoblasts. Extraembryonic mesoderm
grows into villi.Structure of the Placenta Primary chorionic villi Late Week Day are solid
outgrowths of cytotrophoblast that protrude into the syncytiotrophoblast. covers entire
surface of chorionic sac Tertiary chorionic villi Late Third Week Day contain embryonic blood
vessels that develop from mesenchymal cells in the loose connective tissue core. which
grows into the primary villi about the midthird week Day of development. mesenchyme
differentiates into blood vessels and cells forms arteriocapillary network fuse with placental
vessels developing in connecting stalk .
Placental Development Chorionic Villi Stem or anchoring villi cytotrophoblast cells attached
to maternal tissue Branched villi or terminal grow from sides of stem villi region of main
exchange surrounded by maternal blood in intervillous spaces maternal sinusoids .
Late Second Week Fingerlike protrusions into endometrium contains syncytiotrophoblast.
solid mass of trophoblast Cytotrophoblastic shell Surrounds embryo.chorionic arteries and
veins derived from extraembryonic mesoderm. Hemichorial type placenta Maternal blood
baths villi Cytotrophoblastic cell column Terminal villi. Secondary stem villi day Mid Third
Week Extraembryonic mesoderm invasion into villi core. cytotrophoblast.PLACENTAL
STRUCTURE OVERVIEW Chorionic Plate Stem villi extends from this tissue Primary stem
villi day . direct contact with maternal decidual cells Anchoring Villi give off cytotrophoblastic
extensions anchoring because they represent the real maternoembryoner link Floating Villi
branches off anchoring villi suspends freely in maternal blood . Tertiary stem villus day Mid
Third Week Extraembryonic vessels .
umbilical vein Maternal. Freeflowing lake Spiral arteries open into intervillous space and bath
the villi ml of maternal blood in the intervillous space Exchanged. return baths the villi .
Contained within vessels Umbilical Arteries chorionic plate branches to stem villi capillaries in
terminal villi return via .PLACENTAL CIRCULATION Fetal. times/minute Reduced blood
pressure in intervillous space Oxygenated blood to the chorionic plate.
PLACENTAL CIRCULATION .
PLACENTAL CIRCULATION .
The vitelline contributes to the portal system And the systemic embryonic matures into the
cardiovascular system. systemic and vitelline.FOETAL CIRCULATION There are essentially
separate aortic/venous circulatory systems Umbilical. . The umbilical system is is lost at birth.
PLACENTAL BARRIERS Placental barrier decreases with gestation Placental Barrier
syncytiotrophoblast basal lamina. no major histocompatibility antigens . basal lamin fetal
capillary endothelium Syncytiotrophoblasts many microvilli.
CHORION Chorionic cavity extraembryonic coelomlined with extraembryonic mesoderm
Chorionic cavity expands separating amnion from cytotrophoblast Chorionic sac consist of
Cytotrophoblastic layer Syncytiotrophoblastic layer Extraembryonic somatic mesoderm The
Chorion / maternal endometrium forms the placenta Chorion forms stem villi .
solid mass of trophoblast Cytotrophoblastic shell Surrounds embryo.STEM VILLI Chorionic
Plate Stem villi extends from this tissue Primary stem villi day Fingerlike protrusions into
endometrium contains syncytiotrophoblast. cytotrophoblast. Tertiary stem villus day
Extraembryonic vessels . Secondary stem villi day Extraembryonic mesoderm invasion into
villi core. Hemichorial type placenta Maternal blood baths villi Cytotrophoblastic cell column
Terminal villi. direct contact with maternal decidual cells Anchoring Villi give off
cytotrophoblastic extensions anchoring because they represent the real maternalembryo link
Floating Villi branches off anchoring villi dangles freely in maternal blood .chorionic arteries
and veins derived from extraembryonic mesoderm.
UMBLICAL CHORD One umbilical vein. two umbilical arteries Whartons jelly mucoid
connective tissue surrounding vessels Allantois Yolk Stalk vitelline duct and vitelline vessels
early Intestinal loop umbilical hernia late .
UMBLICAL CHORD .
hCG Chorionic somatomammotropin Chorionic adrenocorticotropin cACTH Estriol
Progesteron Relaxin Human Placental Lactogen .Placental Function Main functions of the
placenta are a exchange of metabolic and gaseous products between maternal and fetal
bloodstreams and Exchange of gasses Exchange of Nutritients and Electrolytes
Transmission of Maternal Antibodies b production of hormones.
g. However in primates there is no clear evidence that a drop in progesterone levels is
needed for parturition to occur. the ewe Thorburn and Challis. . it should be noted however.
.The endocrine role of the placenta Progesterone Progesterone plays an important part in
maintaining pregnancy. e. Progesterone levels continue to increase during pregnancy but
there is a marked species variation in progesterone levels around parturition. . it seems that
in most species there is evidence that a drop in progesterone levels precedes parturition. this
led to the hypothesis that a drop in progesterone levels was needed for the uterine
contractions associated with parturition to occur Numan. this secretion of progesterone
inhibits the normal oestrus cycle and allows pregnancy to continue. . In summary. In the
human placenta progesterone is derived from maternal cholesterol bound to lowdensity
lipoprotein LDL Martal and Cdard.. . At conception progesterone production in the corpus
luteum is increased Bassett et al. In some species there is a marked drop in the levels of
progesterone just before the beginning of parturition. Progesterone production is continued
by the corpus luteum for about days after which time the cytotrophoblast and
syncytiotrophoblast of the placenta take over the production of progesterone Martal and
Cdard. . that the measurement of plasma levels of hormones may not be indicative of their
levels at the site of action.
Man is therefore said to posses a fetoplacental unit because both the fetus and the placenta
are required to complete the steroidogenic pathway. but as with progesterone there is a
difference of opinion as to what happens prior to parturition. . . pregnenolone and
progesterone. who lacks the necessary enzymes for this pathway. In the ewe the amount of
osteogen in the mothers plasma rise slowly until day of pregnancy when there is a sharp
increase in the level. oestrogen are produced from androgens secreted by the fetal adrenal
gland Wooding and Flint. in man.g. In some species oestrogen are produced entirely in the
placenta by synthesis from C steroid precursors e. however.The endocrine role of the
placenta Oestrogen Oestrogen play an important role in implantation and in mammary gland
development as well as in the release of prolactin at parturition. In humans. the levels of
oestrogen in maternal plasma appear to rise throughout pregnancy.
The endocrine role of the placenta Placental lactogen Placental lactogen PL also known as
chorionic somatomammotropin is a member of the growth hormone and prolactin family of
hormones. Ogren and Talamantes. . . because of this. . and the fact that hPL binds to both
hGH and PRL receptors most of the work done on the role of hPL in pregnancy has
examined processes that are regulated by growth hormones and PRLs. At the amino acid
level human placental lactogen hPL shows an homology to human growth hormone hGH and
a homology to prolactin PRL Martal and Cdard.
The regulation of maternal intermediary metabolism PL is thought to play a role in some of
the lipid and carbohydrate metabolism changes that occur in the mother during the third
trimester of pregnancy. This led early researchers into this field to believe that the main role
of PL was the regulation of maternal intermediary metabolism Ogren and Talamantes.The
regulation of steroidogenesis Human PL stimulates an increase in basal lipolysis Williams
and Coltart. and . hPL stimulates amino acid uptake.. Stimulation of fetal growth The potency
of PL in promoting growth is very low. impaired carbohydrate tolerance and an increase in
lipid mobilization. The seretuary rate of hPL increases gradually until term at which time the
placenta may be producing between .The endocrine role of the placenta These include i.
These include increases in the basal and glucose stimulated insulin secretion. thymine
incorporation and insulinlike growth factor IGF production in fibroblast and skeletal muscle
myoblasts Hill et al. Recently. ii. This could be because of the similarity between hPL and the
animals own PRL iv.Stimulation of mammary gland secretary differentiation The predominant
role of hPL in the human mammary gland would appear to be to stimulate cell proliferation
rather than secretion although hPL stimulates lactogenesis in nonprimate species. iii. The net
effect of these changes being to freeup maternal glucose for the fetus. as well as stimulating
glucose uptake and utilisation Human placental lactogen is produced in the
syncytiotrophoblast from the th week of pregnancy and is secreted into the maternal
bloodstream. for example. development of insulin resistance by some tissues. . . it has been
found that hPL plays a role in regulating growthassociated processes in several fetal tissues.
g/day Martal and Cdard. .
Examination of the levels of hGHV and insulinlike growth factor IGF during pregnancy have
shown a correlation between their levels suggesting a possible role for hGHV in regulating
IGF production in the second half of pregnancy Caufriez et al... . Its role appears to be similar
to pituitary growth hormone in that it has a somatogenic activity and during the second half of
pregnancy it may regulate many of the processes normally regulated by pituitary growth
hormone in nonpregnant individuals Ogren and Talamantes. its concentration increases until
about week and then remains constant for the remainder of pregnancy Caufriez et al. . .. .
.The endocrine role of the placenta Growth Hormone A variant of human growth hormone
hGH hGHV which differs in amino acid positions from hGH has been found in the placenta.
Human growth hormone variant is produced by the syncytiotrophoblast cells and is found in
the maternal blood from about weeks to . It is possible that hGHV is in the maternal blood
system from week at low levels since mRNAs for hGHV are present in placenta from that
time Liebhabner et al.
with absence of decidua basalis placenta percreta villi penetrate myometrium placenta
previa placenta overlies internal os of uterus abnormal bleeding cesarian delivery .Placental
Abnormalities placenta accreta abnormal adherence.
AMNION Amnionic membrane is two cell layers epiblast derived extraembryonic ectodermal
layer thin nonvascular extraembryonic mesoderm As the amnion enlarges it encompasses
the embryo on the ventral side. . merging around the umbilical cord. Amnion forms the
epithelial layer of the umbilical cord With embryo growth the amnion obliterates the chorionic
cavity Amnionic sac is fluid filled called amnionic fluid the embryo is bathed in the fluid.
fluid is similar to fetal serum keratinization After weeks Contribution from urine. Hydraminos
Excess fluid gt ml. renal agenesis .AMNIONIC FLUID Up to week . Near birth . esophageal
atresia Oligohydramnios Insufficient fluid lt ml. filtration from fetal vessels in cord. maternal
serum filtered thru endothelium of nearby vessels.can contain fetal feces called meconium
Near birth Amnionic fluid ml exchanges every hrs across the amnion exchange with maternal
fluids. fetal swallowing ml/hour to gut adsorption by fetus out the umbilical cord to placenta.
AMNION FUNCTION Mechanical protection hydrostatic pressure Allows free movement
.which aids in neuromuscular development Antibacterial Allow for fetal growth Protection
from adhesions .
VITELLINE SAC Hypoblast . epithelium of the respiratory and digestive tracts .Second wave
of cell migration .the primary yolk sac or Heusers membrane. Day .YOLK SAC .forms
definitive yolk sac Composed of extrembryonic endoderm Early nutrition weeks for the
embryo .later shrinking nonfunctional Meckels diverticulum outpocketing of small intestine
Connects to midgut via the yolk sac stalk Derivatives Early blood cells forms from blood
islands Primordial germ cells The early gut.
artery and vein becomes the umbilical vessels Remnants of Allantois becomes the urachus
ligament that connects the belly button to the bladder .ALLANTOIS Endodermal origin.
caudal outpocketing of the yolk sac Invades the connecting stalk extraembryonic mesoderm
that suspends the embryo in the chorionic cavity Involved in early hematopoiesis up to
months The allantois blood vessels .
FOETAL MEMBRANES .
growth Third Trimester weeks organ function and rapid growth Fetus to neonate involves
three phases Transition Phases Late gestation Parturition processes needed to establish
independent homoeostatic regulation after separation from the placenta.PARTURITION Fetal
Growth First Trimester weeks embryonic and early fetal Second Trimester weeks organ
development and function. following expelled after birth . parturitio childbirth expelling the
fetus. Phases are regulated by a series of fetal and placental endocrine events. Childbirth
Parturition L. placenta and fetal membranes probably initiated by fetus not mother Labor
uterine contractions and dilation of cervix process under endocrine regulation Placenta and
Fetal Membranes secundina L.
LABOR STAGES
stage dilatation
uterine contractions minutes apart function to dilate cervix fetal membranes rupture
releasing amnion hours longer for first child
stage expulsion
uterine contractions push fetus through cervix and vagina uterine contractions minutes apart
minutes
stage placental
following child delivery contractions continue to expel placenta haematoma separates
placenta from uterine wall separation occurs at spongy layer of decidua basalis minutes
stage recovery
continued myometrial contraction closes spiral arteries hours
DELIVERY
CHILD BIRTH
. About Months about Days after Fertilization, at the end of a Full Term Pregnancy, the Fetus
is ready for Birth. By this time, it has usually moved so that its Head is against the Cervix. .
When it is time A Hormone known as OXYTOCIN is released from the Pituitary Gland, that
affects a group of large Involuntary Muscles that surrounds the Uterus. . WEAK, Irregular
Contractions may occur for Several Weeks before birth. False Labor. . As these Muscles are
stimulated, they begin a series of Rhythmic Contractions knows as LABOR that Expands the
opening of the CERVIX so that it will be large enough about cm to allow the baby to pass
through it. . As contractions continue, they become more Powerful PAINFUL and more
Frequent, occurring once every minute or two. . Little by little, in a process LABOR that last
from to hours, the baby is FORCED toward the Vagina as labor continues.
and the fluid it contains rushes out of the Vagina. The baby is finally Forced out of the
Uterus and the Vagina. Breathing starts almost immediately. . . Head First. still attached to its
mother by the Umbilical Cord. leaving a Scar known as Navel or Belly Button. . The Baby will
begin to cough or cry in order to rid its lungs of the fluid with which they have been filled. .
.CHILD BIRTH . collectively called AFTER BIRTH are expelled from the mothers body about
minutes after the baby is born. The Amniotic Sac Breaks Breaking Water. In the final
contractions the Placenta. The Umbilical Cord is clamped and cut. Amniotic Sac and the
Uterine Lining. The process of Childbirth is complete. .
two chorions.e. . Dizygotic twins are only as closely genetically related as any two
siblings.CLINICAL CORRELATIONS Multiple Pregnancy Dizygotic Fraternal twins are
derived from two zygotes that were fertilized independently i. two oocytes and two
spermatozoa. they are associated with two amnions. which may or may not be fused. and
two placentas.. Consequently.
.
This type of twins commonly has two amnions. but may have physical differences due to
differing developmental environments e.g. one chorion. If the embryo splits early in the
second week after the amniotic cavity has formed. the twins will have one amnion.MULTIPLE
PREGNANCY Monozygotic twins are derived from one zygote that splits into two parts. one
chorion. Monozygotic twins are genetically identical. unequal division of placental circulation.
and one placenta.. . and one placenta.
CONJOINED SIAMESE TWINS .
FETUS PAPYRACEUS amp TWINS TRANSFUSION SYNDROME .
CLINICAL CORRELATIONS Placenta Previa The fetus implants in such a way that the
placenta or fetal blood vessels grow to block the internal os of the uterus. . See implantation.
When fetal erythrocytes are Rh positive but the mother is Rh negative. which cross the
placental barrier and destroy the fetus. the mothers body can form antibodies to the Rh
antigen.CLINICAL CORRELATIONS Erythroblastosis Fetalis Some erythrocytes produced in
the fetus routinely escape into the mothers systemic circulation. The immunological memory
of the mothers immune system means this problem is much greater with second and
subsequent pregnancies. .
CLINICAL CORRELATIONS Oligohydramnios Deficiency of amniotic fluid less than ml in late
pregnancy. It can result from renal agenesis because the fetus is unable to contribute urine
to the amniotic fluid volume. Hydraminos Excess fluid gt ml. esophageal atresia .
PRENATAL DIAGNOSIS .
amniocentesis. . genetic abnormalities. including ultrasound.Prenatal Diagnosis The
perinatologist has several approaches for assessing growth and development of the fetus in
utero. In combination. The use and development of in utero therapies have heralded a new
concept in which the fetus is now a patient. maternal serum screening. and chorionic villus
sampling. these techniques are designed to detect malformations. such as placental or
uterine abnormalities. overall fetal growth. and complications of pregnancy.
Placental position and umbilical blood flow. Multiple gestations are present .Ultrasonography
Ultrasonography is a relatively noninvasive technique that uses highfrequency sound waves
reflected from tissues to create images. The approach may be transabdominal or
transvaginal. Presence or absence of congenital anomalies. Status of the uterine
environment. including the amount of amniotic fluid. Important parameters revealed by
ultrasound include characteristics Fetal age and growth. with the latter producing images with
higher resolution.
such as omphalocele and gastroschisis. and abdominal circumference are used Congenital
malformations that can be determined by ultrasound include The neural tube defects
anencephaly and spina bifida. A fter that. including the biparietal diameter BPD of the skull.
femur length.Ultrasonography Fetal age and growth are assessed by crownrump length
during the th to th weeks of gestation. a combination of measurements. Heart and facial
defects. . Abdominal wall defects. including cleft lip and palate.
.
bladder exstrophy. peaks at approximately weeks. . These conditions are also associated
with lower serum concentrations of human chorionic gonadotropin hCG and unconjugated
estriol. as. AFP levels increase in amniotic fluid and maternal serum. AFP concentrations
increase in maternal serum during the second trimester and then begin a steady decline after
weeks of gestation. sacrococcygeal teratoma. In cases of neural tube defects and several
other abnormalities. AFP concentrations decrease. gastroschisis.Maternal Serum Screening
A search for biochemical markers of fetal status led to development of maternal serum
screening tests. and leaks into the maternal circulation via the placenta. One of the first of
these tests assessed serum afetoprotein AFP concentrations. Thus. In other instances. for
example. AFP is produced normally by the fetal liver. amniotic band syndrome. and intestinal
atresia. sex chromosome abnormalities. including omphalocele. and triploidy. trisomy . in
Down syndrome.
such as AFP and acetylcholinesterase. more sophisticated molecular analyses using
polymerase chain reaction PCR and genotyping assays will increase the level of detection for
genetic abnormalities. fetal cells. can be recovered and used for metaphase karyotyping and
other genetic analyses. but it is less in centers skilled in the technique. With special stains
Giemsa and highresolution techniques. a needle is inserted transabdominally into the
amniotic cavity and approximately to mL of fluid is withdrawn. . The fluid itself is analyzed for
biochemical factors. Because of the amount of fluid required. the procedure is not usually
performed before weeks gestation. In addition. The risk of fetal loss as a result of the
procedure is . sloughed into the amniotic fluid. now that the human genome has been
sequenced. chromosome banding patterns can be determined.Amniocentesis During
amniocentesis. when sufficient quantities are available without endangering the fetus.
Furthermore.
The risk of fetal loss from CVS is approximately twofold greater than with
amniocentesis.Chorionic Villus Sampling Chorionic villus sampling CVS involves inserting a
needle transabdominally or transvaginally into the placental mass and aspirating
approximately to mg of villus tissue. . such as diabetes. an abnormal ultrasound or serum
screening test. these prenatal diagnostic tests are not used on a routine basis Indications for
using the tests include the following advanced maternal age years and older. such as the
parents having had a child with Down syndrome or a neural tube defect. Generally. the
presence of maternal disease. previous family history of a genetic problem. and there have
been indications that the procedure carries an increased risk for limb reduction defects.