Flashcards in Repro Session 8 Deck (142):
What does the yolk sac become after the primitive gut tube has formed?
Proximal umbilical cord
What causes the amniotic sac to increase in size?
Foetus and fluid
What is the chorionic sac occupied by?
Expanding amniotic sac
What obliterates the chorionic cavity?
What are the aims of implantation?
Establish basic unit of exchange, anchor placenta and to establish maternal bloodflow
How is the basic unit of exchange established in implantation?
Describe the different stages of villi in their development.
Primary: early finger-like projections of trophoblast
Secondary: invasion of mesenchyme into core
Tertiary: invasion by foetal BV
Why is implantation said to be interstitial?
Uterine epithelium is breached and the conceptus implants in the stroma
Why is the placental membrane said to be haemomonochorial during implantation?
1 layer of trophoblast between maternal blood and foetal capillaries
Is there usually mixing of maternal and foetal blood?
No due to haemomonochorial placental layer
How is the placenta anchored in implantation?
Establishment of outermost cytotrophoblast shell
What has happened in embryonic development by the end of the 2nd week?
Conceptus has implanted; embryo, amniotic cavity and yolk sac are suspended by the connecting stalk in the chorionic cavity
What are the alternative names of the smooth and villous chorion?
Smooth = chorionic sac. Villous = placenta
What can uncontrolled invasion by the blastocyst at an inappropriate site of implantation lead to?
What is placenta praevia?
Implantation in lower 1/3 of uterine segment
When is C-section necessary in placenta praevia?
If internal os is occluded
What is there a risk of in placenta praevia?
What is placenta accreta?
Excessive invasion of chorionic villi
How do placenta accreta, increta and percreta differ?
Accreta = invasion of myometrium
Increta = into myometrium
Percreta = through myometrium
What is the pathogenesis of pre-eclampsia?
Failure of epithelial to endothelial transformation at 20+ wks results in unknown circulating factor causing maternal hypertension and proteinuria
What is the cycle of events in placental insufficiency?
Failure of maternal artery remodelling to low resistance; increased vascular resistance in fetoplacental vascular bed; deceased metabolically active placenta
What are prepared in each uterine cycle in anticipation of implantation?
Why can pre-decidual cells be considered "check point" cells?
Decidual reaction provides balancing force for invasive trophoblast
How far does the trophoblast invade into the endometrium normally?
To spiral arterioles but no further
What happens when the cytotrophoblast from ends of anchoring villi attach to terminal ends of spiral arteries?
Undergo epithelial to endothelial transformation
How are the BV of the endometrium altered upon implantation?
From small diameter with high resistance to large diameter, low resistance vessels
How do the villi on the surface of the chorion develop?
Those on chorionic pole grow to form chorion frondosum. On aembryonic pole they degenerate to form chorion laeve
What decidua layer covers the chorion frondosum?
What is the decidua basalis?
Decidual plate with glycogen that will form placenta
What happens to the decidua capsularis membrane over the chorion laeve?
Stretches and degenerates
What does the chorion laeve fuse with?
How can foetal membranes be shared by monozygotic twins?
One zygote with separate implantation sites--> 2 amnions and chorions. One morula with 2 intracellular masses and bilaminar discs forms 2 amnions and 1 chorion. One blastocyst and bilaminar disc with 2 primitive streaks forms shared amnion and chorion
What is there a risk of in a shared amnion and chorion between monozygotic twins?
What layers are present in the first trimester placenta?
Complete syncytiotrophoblast and cytotrophoblast layer
What forms the foetal component of the first trimester placenta?
Trophoblast with secondary and tertiary villi and extramebryonic mesoderm (chorionic plate)
What forms the maternal component of the first trimester placenta?
What are stem villi?
Extensions of mesoderm from chorionic plate to cytotrophoblast shell to give extraembryonic vasculature
What happens in endovascular invasion of the first trimester placenta?
Maternal vessels are eroded so that blood flows into intevillous spaces
How do the stem villi in the first trimester placenta?
Free villi extend from them
What happens to the syncytium in the first trimester placenta?
Becomes thin and breaks off as syncytial knots in maternal circulation
How does the foetal aspect of the placenta appear?
Umbilical vessels radiate to chorionic vessels under transparent amnion
How does the maternal aspect of the placenta appear?
Surrounding amniochorion ruptured, cotyledons separated by decidual septa and covered by thin layer of decidua basalis
What changes have occurred from the first trimester to term placenta?
SA for exchange dramatically increased, placental barrier thin, cytotrophoblast layer lost, discoid with 15-25 cm diameter
Why is a small population of cytotrophoblast cells retained in the term placenta?
What blood vessels are present in the umbilical cord?
2 umbilical arteries carrying deoxygenated blood from foetus to mother and 1 umbilical vein carrying oxygenated blood from placenta to foetus
Which blood vessels in the umbilical cord are oxygen rich and poor?
Umbilical arteries are oxygen poor, veins oxygen rich
What are the metabolic functions of the placenta?
Synthesis of glycogen, cholesterol and fatty acids
Why does the latent a synthesis cholesterol?
For steroid hormone synthesis
What are the endocrine functions of the placenta?
Produce protein and steroid hormones
What protein hormones does the placenta produce?
hCG, hCsommatomammotrophin (placental lactogen), hCthyrotrophin, hCcorticotrophin
What is hCG and analogue of?
What is the function of placental lactogen?
Diabetogenic mother and breast development
What steroid hormones does the placenta synthesise?
Progesterone and oestrogen
What effect does progesterone have on appetite in the pregnant female?
Why do trophoblast disease and choriocarcinoma cause very raised hCG?
Endocrine function of placenta is in syncytiotrophoblast
What does the placenta take over steroid hormone production from in the 11th week?
What happens to hCG levels when the placenta takes over steroid hormone production?
What is a molar pregnancy?
When the outer cell mass only develops
What is choriocarcinoma?
Malignant trophoblast if cancer
How is exchange of water, electrolytes, urea and uric acid achieved by the placenta?
How is AT of a.a. And iron achieved by the placenta?
Specific transporters in syncytiotrophoblast
How is glucose transported across the placenta?
Describe gas exchange across the placenta.
O2, CO2 and CO via simple diffusion limited by flow
Why does gas exchange across the placenta need careful monitoring, especially in childbirth?
Cord compression can be rapidly fatal as foetal oxygen stores are small
What makes complement components in the first trimester?
What happens at 14wks that causes development of passive immunity for the foetus?
Maternal IgG transported via receptor-mediated process so foetal [IgG] exceeds those in maternal circulation
What does development of passive immunity depend on?
Mother's exposure to pathogens
Is the placenta a protective or true barrier and why?
Protective because some substances readily access foetus via placenta
Give some examples of known teratogens.
Thalidomide, alcohol, therapeutic drugs, drugs of abuse
What effect does maternal smoking have on pregnancy via an unknown mechanism?
Causes embryon and placental disruption
How do infectious agents lead to birth defects?
Cross placenta to cause foetal infection and subsequent cell death
Give some examples of infectious agents that can lead to birth defects.
Varicella zoster, CMV, treponema pallidum, toxoplasma gondii, rubella
What is rubella syndrome?
Microcephaly, PDA and cataracts
What is the affect of alcohol crossing the placental barrier?
Inhibits bronchial apparatus and CNS development
How does haemolytic disease of the newborn arise?
Exposure of maternal blood to foetal circulation mounts maternal antibodies against foetal rhesus group which in a following pregnancy cross placenta and ellicit haemolysis
Why is haemolytic disease of the newborn now uncommon?
Mother and father rhesus groups are tested and prophylaxis offered if necessary
How is routine antenatal screening conducted?
History and examination for risk factors and FHx, blood tests and urinalysis
What is assessed in antenatal blood tests?
Blood group for comparison with father's, Hb levels for anaemia and any infection
Why is UTI a potential problem pregnancy?
Can lead to pre-term labour
What change is seen in cardiac output during pregnancy?
Increase of 40% from T1
What change is seen in stroke volume during pregnancy?
Increase of 35% from T1
Why does cardiac output increase in pregnancy?
To account for potential significant haemorrhage at birth
Why does stroke volume increase in pregnancy?
Blood volume has significantly increased
What changes are seen in TPR during pregnancy?
Decreases 25-30% from T1
Why does TPR change during pregnancy?
Foetal gas exchange depends on flow
How does blood pressure change during pregnancy?
Decreases during T1 and T2 but returns to normal in T3
What causes blood pressure changes during pregnancy?
Decreased vascular resistance due to progesterone
Why should women in T3 not lie on their back?
Causes aortocaval compression by gravid uterus leading to hypotension
What is the treatment for pre-eclampsia?
How is pre-eclampsia identified?
Maternal hypertension and proteinuria
What changes in renal perfusion are seen during pregnancy?
Increases by 60-80%
Why does RPF change in pregnancy?
Cardiac output increases
What change is seen in GFR during pregnancy?
Increases of 55%
Why does GFR change in pregnancy?
Progesterone causing afferent and efferent dilation
What complications can progesterone action on GFR cause?
Hydroureter and urinary stasis
What change is seen in creatinine clearance in pregnancy?
Increases by 40-50%
What happens in protein excretion during pregnancy?
What happens to urea levels during pregnancy?
Decreases by 50%
What accounts for the changes in creatinine clearance, protein excretion and urea levels in pregnancy?
Filtration capacity of kidneys
What change is seen in bicarbonate levels during pregnancy?
What change is seen in creatinine levels during pregnancy?
Why does the bicarbonate level change during pregnancy?
Functional renal reserve decreases as GFR increases
What do normal non-pregnant ranges of urea, bicarbonate and creatinine indicate in pregnancy?
What respiratory changes are seen during pregnancy?
Oxygen consumption increases, resting minute ventilation increases, tidal volume increases, RR VC and FEV1 remain constant
What causes physiological dyspnoea during pregnancy?
Increased respiratory drive due to progesterone
Why does tidal volume increase during pregnancy?
AP and transverse diameters of thorax increase
Why does FRC decrease in T3?
Diaphragm is displaced by gravid uterus
Why are vital capacity and FEV1 constant in pregnancy?
Diaphragm and changes in thorax diameters balance each other out
Why is PaCO2 reduced in pregnancy?
Increased metabolic CO2 is blown off by physiological hyperventilation
Why does physiological hyperventilation not lead to respiratory alkalosis?
Renal bicarbonate excretion increases
Why are pregnant women predisposed to metabolic acidosis?
Renal bicarbonate excretion is increased
What changes to carbohydrate metabolism are seen on pregnancy?
Increased maternal peripheral insulin resistance, switch to gluconeogenesis
What stimulates changes to carbohydrate metabolism in pregnancy?
Human placental lactogen mainly but prolactin, oestrogen, progesterone and cortisol also contribute
What happens to fasting blood glucose pregnancy?
What happens to post-prandial blood glucose in pregnancy?
What is gestational diabetes?
Carbohydrate intolerance first recognised in pregnancy that does not persist after delivery
What are risk factors for developing gestational diabetes?
PCOS, FHx, high maternal age, T2DM, ethnicity, obesity
What are the possible consequences of gestational diabetes?
Macrosomic foetus, stillbirth, congenital defects
What builds fat stores in early pregnancy for lipolysis in T2?
What is the benefit of lipolysis in T2?
Increases plasma free FA that cannot cross placenta therefore increasing glucose available for foetal metabolism
Which fatty acids are able to cross the placenta?
Why are pregnant women at a higher risk of ketoacidosis?
Increased FA synthesis combined with physiological increase in renal bicarbonate excretion
Why might TSH be low in normal pregnancies?
hCG minimises its function
Why does hCG and TSH not lead to high free T4?
Very active liver produces thyroid binding globulins
What happens to the appendix during pregnancy?
Moved to RUQ
What are the effects of progesterone on the smooth muscle of the GI tract?
Delayed emptying and stasis in biliary tract
Why are pregnancy women at an increased risk of pancreatitis?
Progesterone on smooth muscle of biliary racy causes stasis and stone formation
Why is pregnancy a pro-thrombotic state?
Need for fibrin deposition at the implantation site and risk of haemorrhage at birth
What are the effects of progesterone on the blood during pregnancy?
Increased fibrinogen and clotting factors, decreased fibrinolysis, stasis and venodilation
Why can thromboembolic disease in pregnancy not be treated with warfarin?
It is a teratogen
How does a physiological aneamia arise during pregnancy?
Due to dilution as red cell mass increases but does not match the plasma volume increase
When does iron and folate deficiency anaemia arise in pregnancy?
If increased demands during pregnancy are not met
What are the complications of sickle cell disease in pregnant homozygotes?
More frequent crises, pre-eclampsia, thrombosis and infections
What are the consequences of sickle cell disease in pregnancy heterozygotes?
May develop crises
What are the implications for pregnancy for homozygous beta-thalassaemia pts?
Anaemia in pregnancy is unusual due to iron overload
What is the treatment for pregnant homozygous beta-thalassaemia pts with anaemia?
Folic acid without iron
What are the consequences for heterozygous beta-thalassameia pts during pregnancy?
Worsening of chronic anaemia
Why is non-specific local immune system suppression needed at the materno-foetal interface?
Foetus is an allograft
How is the immune system suppression at the materno-foetal interface identified histologically?
Different lymphocytes are found at the trophoblast-endometrial boundary
How can a foetus develop an abnormal thyroid state?
Exchange of maternal autoantibodies e.g. In Graves or Hashimoto's disease
What is the treatment for haemolytic disease of the newborn?
IM anti-RH antibodies