The human placenta is haemomonochorial, what does this mean?
There is only one layer of trophoblast separating maternal blood from foetal capillary wall
What is placenta praevia?
Implantation in lower uterine segment, requires C-section and can cause haemorrhage
How is the endometrium prepared for implantation?
“Pre-decidual” cells in preparation for decidualisation
Elaboration of spiral arterial supply
What is decidualisation?
A reaction balancing the force of invasion of the trophoblast. can occur in ectopic pregnancy
How are the spiral arteries remodelled?
Low resistance vascular bed created
Maintains high flow
Describe the development of the foetal membranes?
Initially chorion has villi all round (wk5)
Villi are lost leaving them only in decidua basalis (wk12)
Amnion joins chorion to become one membrane
What is twinning?
The degree to which membranes are shared in monozygotic twins
What are the three degrees of twinning?
Share both amnion and chorion
Share neither
Share just chorion
Describe the placenta in 1st trimester
Established
Barrier still thick
Complete cytotrophoblast layer beneath syncytiotrophoblast
Describe the placenta at term
SA for exchange increased lots
Placental barrier thin
Cytotrophoblast layer lost
How many umbilical arteries are there? What is their function?
2 - carry deoxygenated blood foetus -> placenta
How many umbilical veins are there? What is their function?
1 - carries oxygenated blood placenta -> foetus
What are the three main functions of the placenta?
Metabolism
Endocrine
Transport
What are the metabolic functions of the placenta?
Synthesis of glycogen, cholesterol and FAs
What are the endocrine functions of the placenta?
Production of; hCG, hC Somatomammotrophin, hC thyrotrophin, hC corticotrophin, progesterone and oestrogen
What are the functions of human chorioni gonadotrophin?
Supports secretion by corpus luteum
Pregnancy specific and excreted in maternal urine so can be test
Reduces risk of trophoblast disease
At what point does the corpus luteum stop producing progesterone and oestrogen? Why?
11th week - placenta takes over
How do placental hormones influence maternal metabolism?
Progesterone increases appetite
hCS/hPL increase glucose availability to foetus
How is gas exchange limited in the foetus?
Flow-limited i.e. foetal stores are small
How is active transport carried out between foetus and mother?
“Transporters” expressed by syncytiotrophoblast; AAs, iron, vitamins
How is passive immunity established initially in the foetus?
IgG only - conc. higher in foetal plasma than maternal circulation
What is a teratogen?
An agent or factor causing malformation of an embryo
List some common teratogens
Thalidomide
Alcohol
Cigarette smoke
Why are teratogens significant to the placenta?
As it is not a “true” barrier they can access foetus through it
List some infectious agents relevant to the placenta
Varicella zoster
Cytomegalovirus
Treponema pallidum
Rubella
How does the maternal cardiovasuclar system change during pregnancy?
Blood volume increase
CO, SV and HR increase
BP drops T1-2, normal in T3
What caues low BP in pregnancy?
Progesterone reduces sytemic vascular resistance
What casues the return to normal BP in T3 of pregnancy?
Aortocaval compression by gravid uterus
what is the role of the endothelium in pregnancy?
Controls vascular permeability
Contributes to control of vascular tone
What is pre-eclampsia?
A defect in placentation; vasoconstriction causing high BP with contracted plasma
Which aspects of the maternal urinary system increase during pregnancy?
Renal plasma flow
GFR
Creatinine clearance
Protein excretion
Which aspects of the maternal urinary system decrease in pregnancy?
Urea
Uric acid
Bicarbonate
Creatinine
What are the consequences of changes to the maternal urinary system in pregnancy?
Progesterone causes hydroureter
Possible pyelonephritis
What changes occur in the respiratory system of pregnant women?
Diaphragm displaced Diameters of thorax increase Increased ventilation Increased tidal volume Decreased functional residual capacity
What problems can occur in the respiratory system of pregnant women?
Physiological hyperventialtion; increased CO2 production, progesterone increases respiratory drive
How does pregnancy alter carbohydrate metabolism?
Increased maternal peripheral insulin resistance due to action of hPL, switch to alternative fuels
What is gestational diabetes?
Carbohydrate intolerance first recognised in pregnancy but not persisting after delivery
List some risk factors of gestational diabetes
Prediabetes
Hypertension
FH of it or type II DM
How is lipid metabolism altered in pregnancy?
Increase in lipolysis from T2
Increased plasma FFAs on fasting
How is the thyroid gland alterd in pregnancy?
Thyroid binding globulin production increased
T3&4 increased
hCG directly affects TSH (can lower it)
How does pregnancy alter the haematological state of the mother?
Pro-thrombotic state
++ fibrin at implantation site
More fibrinogen & clotting factors
Reduced fibrinolysis
Why can warfarin not be used in thromboembolic disease during pregnancy?
Crosses the placenta and is teratogenic
How can physiological anaemia occur in pregnancy?
Blood volume increase not met with sufficient red cell mass increase