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Western University Health Science 4320B Final Exam Study Guide (Weeks 5-9)
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This is a full study guide for UWO's Health Science 4320B Final Exam. This is part 2 of 3 and covers weeks 5-9.
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WEEK 5 REVIEW Chorionic cavity is established, embryo will fill and pushLecture 1 - Placentation (Review from Implantation) against this
Uterine Lining: Perimetrium (outer layer); Myometrium Obliteration of Chorion (E.E mesoderm and villi):
(muscular layer); Endometrium (embryo interacts with Early on, the entire conceptus is covered by chorionic villi
this, undergoes decidualization) (for ~8 weeks); As baby grows, fills chorionic cavity and
Trophectoderm cells of blastocyst bind to endometrium; amnion fills rapidly with more fluid (faster than growth of
differentiate into cytotrophoblasts and chorionic cavity); Villi become concentrated where the
syncytiotrophoblasts (invading cells) Lecture 2 - Placentation (continued) umbilicus and placenta are; Area with no chorionic villi =
Day 9: breakdown of blood vessels into pools (lacunae), Primary Villus: cytotrophoblasts start invading smooth chorion - will press against uterine endometrial
lacunar network with syncytiotrophoblasts and intervillous syncytiotrophoblasts and get covered by them = primary wall and push it into the uterine lumen
space chorionic villi
Day 12: extra-embryonic mesoderm b/w embryo and Secondary Villus (~16 days): core of extraembryonic
cytotrophoblasts, also have trilaminar embryo mesoderm (mesenchymal cells - "mesenchymal core")
Day 15: extra-embryonic mesoderm surrounds outside and penetrates primary villus = secondary chorionic villi
inside around embryo (somatic/somatopleure = around Tertiary Villus (~21 days): capillaries containing fetal blood
amnion; splanchnic = around umbilical vesicle) now established in the mesenchymal core; allows
Connecting stalk (eventually umbilical cord) communication and nutrients for embryo
Cytotrophoblasts invade into syncytiotrophoblasts, then
past them to make "outer shell" (support and structure for
placenta); Extensions known as "secondary villi"?
Week 3-20: somatopleure invades into the
cytotrophoblasts to make tertiary villi
3 layers: syncytiotrophoblasts, cytotrophoblasts,
somatopleure mesoderm The Chorion: conceptus (embryo + cavity) is completely
Embryo folding, umbilical cord now attached to chorionic surrounded by villus in the endometrial lining (embryo
itself covered in somatic/splanchnic mesoderm) Fetal Membranes and Placenta:
plate At 4 weeks, heart already beating, organ systems start
2 main arteries in opposite directions (deoxygenated blood As the embryo grows, the uterine lining surrounding it will
be pushed to the other side of the uterus developing b/w 4-6 weeks (large nutritional demands), gas
to placenta; acts like "lungs"), 1 vein (oxygenated blood exchange with maternal starting
from placenta to embryo) Chorionic plate (somatopleure) is what the different villi
extend off from Significant changes at ~9 weeks as nutritional demands
Branching of vasculature off the umbilical vesicle through increase (organ systems developed); increase in SA b/w
the villi; mesoderm making blood cells at blood islands As fetal membranes mature, the chorionic plate, villi and
uterine lining will all start to change maternal and fetal components (placenta getting bigger);
Maternal blood in intervilli space interacts and exchanges changes in fetal membranes as more amniotic fluid
material with the villi Uterus in Menstrual Cycle:
Decidualization - large growths from decidua that separate 2 layers of endometrial layer - basalis and functionalis
the villi into different compartments (cotyledons - (embryo embedded, undergoes decidualization)
represent mature placenta) -Functionalis layer of endometrial layer known as 'decidua'
The whole structure = "frondosum" once pregnancy is established; 3 layers of decidua:
Decidua Basalis: deep to conceptus, forms maternal
portion of placenta; where lacunae form, spiral arteries
transform, gas exchange occurs, and where tertiary villi
from fetus grow into
Decidua Capsularis: superficial portion overlying conceptus
Decidua Parietalis: remaining parts of decidua that are not
What we know about the chorion:
in contact with embryo or conceptus
Establishing fetal circulatory system that will mix with
-Mucous plug forms at cervix to prevent infection; Usually
maternal; Conceptus will be enveloped in the amnion
lost 1-2 weeks before delivery, sign of impending labor
during body folding; Secondary umbilicus will eventually
leave
,Amniochorionic Membrane: complications, present SGA; May also result from
Villi become compressed and degenerated at decidua placental insufficiency - placenta did not mature properly
capsularis - avascular smooth chorion produced; amnion and establish enough vasculature, insufficient oxygen and
expands faster than chorionic sac nutrients; Not all SGA babies have pathology, but IUGR
Amnion fuses to the decidua capsularis to form the babies are SGA
amniochorionic membrane ("amniotic membrane") - Large for Gestational Age (LGA)
decidua capsularis eventually degenerates at 22-24 weeks, May be associated with gestational diabetes/regular
so then decidua parietalis is fused with amnion diabetes, high levels of glucose in the maternal blood
This membrane ruptures prior to parturition/ birth (a supplying the baby, baby keeps absorbing it to keep
woman's "water broke") - around 1 L of water growing
Cotyledons: incorporate spiral arteries, lacunae, and Pre-eclampsia: Elevated blood pressure in mother and
tertiary villi; mix b/w fetal and maternal contributions to high levels of proteinuria; Can escalate to eclampsia:
the placenta seizure, death of baby and mother; Occurs in 5% of
pregnancies, can present as early as 20 weeks
Oxygen and nutrients supplied to fetus, but harmful -if it does present this early, can lead to premature
substances could also be delivered to the fetus delivery and associated complications (reversible if baby is
delivered); Can also result in placental insufficiency = IUGR
-Risk Factors: previous history of pre-eclampsia, diabetes,
obesity, family history of pre-eclampsia
-Mechanism not completely known, most likely many
factors contributing to the same symptoms
Placental Delivery:
Full-Term Placenta: Normally delivered within 15-30 minutes after fetus is
Maternal Side = cotyledons covered by decidua basalis born; Involves the formation of hematoma (localized mass
Fetal Side = amnion and chorionic vessels of blood, helps with separation of placenta from uterine
wall); Myometrial contractions minimize blood loss (also
continue up to 6 months after birth to bring uterus back to
original size); Umbilical cord has its own clamping
mechanism within 5 minutes of delivery (Wharton's Jelly) -
induced by dramatic temperature change
Placental Functions: Retained Placenta - delivery takes 60 minutes or longer
Gas exchange (oxygen-carbon dioxide) Placental Anomalies:
Nutrient and waste exchange Placenta Previa - placenta grows in lowest part of uterus,
Maternal antibodies (fetus gains passive immunity) covers all or part of opening to the cervix; may be due to
Hormone production: Progesterone (end of 4th month); scar tissue from C-section or endometriosis; prevents or
Estrogen (stimulates uterine growth); hCG; disrupts normal delivery
Somatomammotrophin (placental lactogen - mammary Marginal - against cervix but not covering opening
gland development) Partial - placenta covers part of cervical opening
Placental Circulation: from maternal to fetal then back to Low-lying - placenta slightly higher up on wall
maternal; technically NO mixing b/w maternal and fetal Complete - placenta completely covers opening to cervix;
blood; 150 mL blood replenished every 3-4 minutes Head of baby needs to push against opening to stimulate
➔ Endometrial Arteries (spiral arteries - positive feedback loop of oxytocin and contractions;
functionalis); Blood enters intervillous space; Lecture 3 - Clinical Correlates: Placental Issues
complete coverage prevents this
Blood enters branch villi (some anchored, some Low Birth Weight:
free) Intrauterine Growth Restriction (IUGR) vs. Small for
➔ Umbilical Veins (O2 rich) Gestational Age (SGA)
➔ Umbilical Arteries (O2 poor); Blood back to villi IUGR babies have some underlying pathology from genetic
to be re-oxygenated or environmental factors (teratogens, congenital
➔ Endometrial Veins (if any waste products) infections, maternal health, SES), increased risk for health
, Placenta Accreta - placenta too deeply embedded into 2 possible ways to implant and grow:
uterine wall; may be due to past trauma to uterus (C- "Di-Di-Di" Twins: 2 separate amnions, chorions, and
section); may require hysterectomy placentas = SAFEST WAY TO HAVE TWINS
Increta - penetrates into myometrium
Percreta - penetrates entire uterine wall, may attach to
other organs - These would be retained placenta,
hematoma cannot form and placenta cannot be released;
can cause bleeding and trauma Problems with the Fetal Membranes/Amnion:
The Amnion: remember that amnion rapidly expands and
fills with fluid, reaches chorion by the end of 3rd month
and membranes fuse (amniochorionic membrane)
Amniotic Fluid: partly derived from amniotic cells (line
cavity), but mostly from maternal blood 2 separate amnions, 2 fused chorions, and 2 fused
Volume replaced every 3 hours placentas
Starting at 5th month, fetus drinks and urinates the fluid
Oligohydramnios: low volume of amniotic fluid; May be d/t
Placental Abruption - premature separation of placenta placental insufficiency, diminished placental blood flow,
from uterine wall; decreased supply of oxygen and pre-term rupture of membranes
nutrients to fetus; usually seen in 3rd trimester -Prevents baby from moving around and umbilical cord
Partial (concealed or apparent hemorrhage): Could cannot lengthen = development issues and pressure on
potentially save the pregnancy baby
Complete (concealed or apparent hemorrhage): Results in
immediate delivery of the baby; could lead to the death of
Monozygotic Twins: resulting from 1 fertilized oocyte, but
baby and the mother
the blastocyst split; 3 possible ways:
Division at 2-cell morula ("di-di"): each of the cells goes on
to form own blastocyst and implant separately; 2 separate
amnions, chorions, and placentas; could also have fused
placentas (35%)
Division of Embryoblast: just the inner cell mass splits;
Polyhydramnios: excess amniotic fluid; May be d/t leads to 2 amnions but shared chorion and placenta (65%)
maternal diabetes, multiple gestation, meroencephaly; Division of Embryonic Disc: at bilaminar stage, separation
Increases risk of severe defects of disc; leads to shared amnion, chorion, and placenta
Rh Incompatibility: technically fetal and maternal blood
does not mix, but some fetal blood cells can enter (rare)
maternal circulation (during placental formation, pre-natal - Separate Twins - separate and complete
screening, birth) - Conjoined Twins - not separate but complete
If mother is Rh factor negative, and the baby is Rh factor - Parasitic Twins - not separate or complete (some
positive, can trigger an immune response in mother structures of another baby develop attached to
against the newborn (Attack and hemolyze fetal red blood the baby)
cells - hemolytic disease of the newborn)
-Greater sensitivity with each successive pregnancy, may Twinning:
lead to the loss of future pregnancies; Can be prevented by Dizygotic - 2 zygotes (fraternal - boys, sororal - girls)
treatment with Anti-Rh immunoglobulin Monozygotic - 1 zygote (identical)
Labelling Twins: Baby A is closest to cervix and will be born
first if vaginal birth; Baby A is implanted higher up in
uterus, would most likely be born first in a C-section
Dizygotic Twins: result from 2 ovulated eggs that were
fertilized, each became blastocysts and implanted into
uterine wall
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