8 Flashcards
When does the development of the placenta begin?
- during second week of development
- very first structure that develops
- no healthy pregnancy without a healthy placenta
What tissue is the placenta made from?
- trophoblast (outer cell mass)
- specifically the synctiotrophoblast and the cytotrophoblast
What day does implantation begin?
-day 6 of pregnancy
What has happened by the end of the 2nd week?
- conceptus has implanted
- embryo has 2 cavities, amniotic cavity and yolk sac
- embryo is suspended by connecting stalk
- embryo is contained within the chorionic cavity
What is the fate of the embryonic spaces?
- yolk sac disappears
- amniotic sac enlarges as the embryo enlarges which displaces the chorionic sac
- amniotic and chorionic membrane fuse to become a single cavity
What does implantation achieve?
- establishes the basic unit of exchange
- primary villi: early finger-like projections of trophoblast
- secondary villi: invasion of mesenchyme into core
- tertiary villi: invasion of mesenchymal core by fetal vessels
- anchor the placenta
- establish maternal blood flow within the placenta
What happens to the placental membrane as the needs of the fetus increase?
- becomes progressively thinner
- in the end only one layer of trophoblast ultimately separates maternal blood from fetal capillary wall to optimize transport
- 2 circulations never mix
What is a chorionic villus?
- initial unit of exchange
- branch out like a tree
- outer layer is synctiotrophoblast and core is made of CT where fetal blood vessels develop
- maternal blood vessels surround the villi
- look at placenta slide 11
What are some implantation defects?
Implantation in the wrong place
- ectopic pregnancy
- placenta praevia
Incomplete invasion
- placental insufficiency
- pre-eclampsia
Look at placenta slide 13-14
What is decidua?
- cells of endometrium that are specialized to modulate the degree of invasion of the conceptus once it has been implanted
- happens through a decidual reaction and is balanced by promoting and inhibiting factors
- important b/c if conceptus implants into an area with no decidua then there is no inhibition of invasion, so no control of degree of invasion
- if implantation is in correct place but the decidual reaction is subpar, then pregnancy may not be maintained
- look at placenta slide 15
Describe the structure of the chorionic villus
- first trimester villus: thicker barrier
- placenta itself changes as embryo grows
- third trimester villus: barrier at optimal “thinnes”
- cytotrophoblast has basically vanished
- fetal capillaries pushed up against synctitiotrophoblast
- see placenta slides 18-20
Describe the blood vessels of the placenta
Maternal blood vessels
- endometrial arteries and veins
- bathe the outside of the villi in maternal blood for exchange to occur
Fetal blood vessels
-bring waste products to the villi through the umbilical PAIRED arteries (deoxygenated blood from fetus to placenta) and nutrients/oxygen to the fetus via the SINGULAR umbilical vein
Describe the endocrine function of the placenta
- produces steroid hormones such as progesterone and oestrogen
- responsible for maintaining the pregnant state
- produces protein hormones such as:
- human chorionic gonadatrophin (hcg)
- human chorionic somatomammotrophin
- human chorionic thyrotrophin
- human chorionic corticotrophin
What produces hcg?
Synctiotrophoblast
What hormone sustains the corpus luteum in the first trimester?
Hcg
How do placental hormones influence maternal metabolism?
Progesterone
-increased appetite to allow an increased fat deposition to help support the fetus and breastfeeding
HCS/hPL
- human placental lactose increases glucose availability to fetus by creating a diabetogenic state to cause insulin resistance in mother
- same function in HCS
Describe transport functions of the placenta
Simple diffusion
-molecules move across a concentration gradient
Eg. Water, electrolytes, gases, urea and Uric acid
Facilitated diffusion
-applies to glucose transport
Active transport
- specific “transporters” expressed by the synctiotrophoblast
- amino acids, iron, vitamins
See placenta slide 30
Describe gas exchange in the placenta
- FLOW LIMITE not diffusion limited
- simple diffusion
- fetal O2 stores are small therefore maintenance of adequate flow is essential
- need good uteroplacental circulation
- if compromised then for example, during labour the contraction can lead to compression of the blood vessels and “fetal distress”
Describe the transfer of passive immunity
- fetal immune system immature
- so antibodies are transported from placenta to fetal circulation
- specifically IgG
Describe the pathophysiology of placental transport. Give an example
- placenta is not a true “barrier”
- teratogens can access the fetus via the placenta (especially in early pregnancy since this is when the body systems develop)
- ex. Rhesus disease of the new-born can occur where maternal antigens can cross into the fetal circulation and attack fetal blood cells
- pregnancy is considered to be an immune-compromised state for the mother so infections may be prevalent
What armful substances can affect the placenta and how?
Thalidomide -limb defects Alcohol -FAS and ARND Therapeutic drugs -anti-epileptic drugs -warfarin -ACE inhibitors Drugs of abuse -dependency in the fetus and newborn Maternal smoking
Describe how teratogenesis can affect the fetus at different stages of development
Pre-embryonic -lethal effects Embryonic -super sensitive -narrow windows for some sensitive Fetal -becomes less critical apart from CNS -see placenta slide 34
Why does the body need to adapt for pregnancy?
Volume support -volume expansion -vasodilation Nutrition -increase in respiration -insulin resistance -increase in absorption Waste Clearance -increase in GFR -hepatocellular stimulation Pregnancy maintenance -uterine quiescence -immunologic sequestration Childbirth -msk -clotting
What drive the maternal body adaptations?
- hcg
- estrogen
- progesterone
- relaxin
- hPL
- see mat phys slide 4
In regards to immunity, what does the baby need, what does the mom need and how is this achieved?
Baby -thrives as a parasite Mom -needs to be a good host (must regulate her immune system) Acheived -through immune regulation
Describe the immunological changes during pregnancy
Fetus= hemi-allograft
- recognized by maternal immune system
- incited also-response is not cytotoxic
Pregnancy= “Immunosuppressed” state
- higher attack rate and severity of certain viral pathogens i.e. varicella
- may improve certain autoimmune conditions
-see mat phys slide 7
In regards to respiratory, what does the baby and mom need and hw is this acheived?
Baby
-O2 delivery
-CO2 clearance
Mom
-continued O2 delivery to her organs and periphery
-increased O2 supply to meet metabolic demand
-increased CO2 clearance
-mom needs 20% more O2 than in normal adults
Achieved
-increased ventilation
Describe the respiratory changes that occur during pregnancy
- more susceptible to respiratory disease
- tidal volume and oxygen uptake increase
- increased awareness of the desire to breath (DYSPNOEA)
- increase in tidal volume lowers the pCO2
- is induced by progesterone directly acting on the resp centre
- see mat phys slide 9
What does dyspnoea commonly happen in pregnant women?
- multifactorial
- most likely due to hyperventilation and deceased pCO2
- see mat phys slide 11
In regards to CVS and haematology, what does the baby and mom need and how is this acheived?
Baby
-delivery of nutrients
Mom
-fill uterine-placental-fetal circulation
-oxygenate growing uterus, very vascular! High demand
-protect from impaired venous return
-prepare for potential blood loss during delivery
Achieved
-volume expansion
-clotting mechanisms
What CVS changes occur in pregnancy?
- pregnancy is a pro-thrombotic state due to increased clotting factors and fibrinogen as well as reduced fibrinolysis
- can lead to thromboembolic disease in pregnancy
- BUT cannot be treated with warfarin since warfarin is TERATOGENIC
- progesterone relaxes smooth muscle meaning BP and SVR decrease
- red cell may also increases but not to the extent of blood volume so anaemia could occur
- anaemia can also happen from iron and/or folate deficiency
- see mat phys slide 13-14
What are some CVS consequences during pregnancy?
Increased RAAS
-peripheral edema
Change in plasma volume»_space; change in RBC volume
-dilution always anaemia
Clotting: hypercoagulale state
-increased number of thromboembolic events
-uterus can compress the vena cava and cause venous stasis
In regards to renal, what does the baby and mom need and how is this acheived?
Baby -clear wastes Mom -increased clearance of wastes Acheived -increased GFR
How does the renal and urinary tract change in pregnancy?
Systemic vasodilation = increased RBF -so increased GFR to 160% of normal -increased creatinine clearance -decreased serum urea and creatinine by 25% Decreased PCT absorption -glucosuria Structural: smooth muscle relaxation and obstruction -increased size of kidneys and ureters -decreased speed of urine passage
See mat phys slide 18
In regards to GI, what does the baby and mom need and how is this achieved?
Baby -nutrients Mom -feed herself and her baby -increased absorption of minerals and vitamins Achieved -slow transit time
How does the GI change in regards to pregnancy?
- progesterone causes smooth muscle relaxation throughout GI tract
- causes slow gastric emptying
- causes common symptoms of nausea, constipation and heartburn
- gallbladder emptying is reduced
- uterus displaces bowel which can cause mechanical obstruction
- liver function test will show increased ALP levels due to placental synthesis
- see mat phys slide 20
In regards to endocrine, what does the baby and mom need and how is this acheived?
Baby -nutrients -good environment Mom -way to give glucose to baby -LOTS of calcium -keep metabolism under control Achieved -thyroid regulation -parathyroid activation -insulin “resistance”
What thyroid changes occur in pregnancy?
- pregnancy is a euthyroid state meaning it has imbalanced levels
- estrogen stimulates TBG hepatic production
- need to increase thyroxine production
- hcg has a similar alpha-subunit to TSH
- weak stimulating effect on thyroid
What PTH and calcium changes occur in pregnancy?
- PTH rises despite small Ca drop
- placenta produces additional hydroxylase and calcitriol, which leads to increased intestinal absorption of calcium
- if adequate dietary intake of calcium, minimal bone resorption should occur
- see mat phys slide 24
How is insulin changed in pregnant women?
- they are diabetogenic
- insulin resistance
- increased insulin secretion
What happens if a pregnant pt. Had impaired glucose metabolism BEFORE getting pregnant?
- need more insulin to compensate for the resistance
- pancreas will start burning out a bit which can result in hyperglycaemia
- can get gestational diabetes
- see mat phys slide 26-27
In regards to MSK and skin, what does the baby and mom need and how is this acheived?
Baby -room to grow -a way out Mom -cope with additional weight -cope with change in centre of gravity -prepare body for childbirth Achieved -make everything loose and stretchy -relaxin helps to do this
What MSK changes occur during pregnancy?
Back pain, shoulder pain, tension headaches
- changes in centre of gravity due to increased lordosis and kyphosis and forward flexion of neck
- due to stretching of abd muscles, which impedes posture and strains paraspinal muscles
Pelvic pain
- increased mobility of sacroiliac joints and pubic symphysis
- anterior tilt of pelvis
- stance is widened to maintained trunk movement
- widened genital hiatus
- fluid retention can compress structures such as median nerve (i.e. carpal tunnel)
- see mat phys slide 30
What skin changes occur during pregnancy?
- Caused by increased oestrogen
- cholasma aka melisma
- palmar erythema
- vascular spiders
- linea nigra
- see mat phys slide 31
What is pre-eclampsia?
- condition relating to placental insufficiency which becomes a clinical syndrome in pregnancy of hypertension and proteinuria
- usually presents in third trimester
- resolves after delivery
- multisystem disorder
What are the risk factors of pre-eclampsia?
- chronic or gestational HTN
- pre-existing renal disease
- diabetes (any type)
- obesity
- family history
- first pregnancy
- extremes of age
- pre-eclampsia in print pregnancy
- multiple gestation
- IVF
What is the pathogenesis of pre-eclampsia?
- impaired invasion of trophoblast leading to shallow invasion of spiral arteries
- remain small caliber and of high resistance
- leads to hypoperfusion and ischaemia
- systemic endothelial dysfunction
- spiral arteries become shallow and have high resistance which can lead to ischaemia
- see mat phys slide 33
What complications for the mother and fetus can occur in pre-eclampsia?
Maternal
- can get excessive peripheral edema
- seizure (eclampsia)
- cerebral hemorrhage
- renal failure
- pulmonary edema
- DIC and thrombocytopenia
- hepatic failure or rupture
Fetal
- growth restriction
- oligohydramnios
- placental infarct or abruption (EMERGENCY)
- premature delivery
- stillbirth
How can we treat pre-eclampsia?
- stabilize BP
- monitor blood results
- monitor baby
- MgSO4 for neuroprotection and seizure prevention
- fluid restrict and monitor output
- deliver!
- difficult decision regarding timing if <37/40
If you know the date that a menstrual bleed began, how menstrual cycle, and in particular whether ovulation is occurring would you most accurately calculate when the previous regularly ovulation had occurred?
Subtract 14 days from start of menstruation
Which hormone provides evidence that ovulation has
infertility occurred?
LH
Why is it useful to keep a daily record of body temperature on rising in the morning? Why does the temperature have to be taken at the same time each day?
- increased temperature during luteal phase due to progesterone
- when it starts rising, ovulation has occurred
- done same time to make it reliable but also due to circadian rhythm
How, in principle, might you test whether Fallopian tubes are patent?
Hysterosalpingogram
What are the two most common causes of secondary amenorrhoea?
- pregnancy
- weight
What is clomiphene?
- “anti-oestrogen”
- used in treating infertility
- HPG is blind to the increasing fake oestrogen
- the fake ones block oestrogen receptors and reduces their concentration
What will be the effects of clomiphen on the secretion of GnRH and the plasma levels of FSH and LH?
They would all increase so ovulation would be stimulated
