Physiology of Pregnancy Flashcards
Structure of hCG
what it is produced by
Two chain hormone, with the alpha chain the same as TSH, LH and FSH
Produced by STB of placenta and trophectoderm of preimplantation blastocyst
How is BhCG used?
To detect pregnancy by urine or blood if need be
levels raise to about 10 weeks gestation, then start to drop
Function of b hCG
important for maintaining pregnancy!
Transmits signals similar to LH
Causes the corpus luteum to produce progesterone and estrogen in the first 6-8 weeks. Prevents regression, and size will double.
After 6-8 weeks, placenta takes over as main source of progesterone, so hCG function is to keep uterus from returning to normal cyclic pattern by keeping CL producing P and E
hCG and cancer
hCG and male sexual diff
thyroid
Cancer: levels can be monitored in things like choriocarcinoma and hyaditiform mole
Sex diff.: hCG targets leydig cells prior to pituitary development to produce testosterone
Thyroid: similar to TSH, can stimulate thyroid hyperthyroidism
Progesterone: Synthesis Fetus role Receptor location Concentration on graph
Synthesis: STB (thus in cancers present). Can not from from acetate so use LDL from circulation (LDL receptors)
Fetus: Does not partake in production. (note ovaries can be removed after 6 weeks)
Receptor location: Endometrial glands and stroma
On graph, slight increase (CL) then after 10 weeks steady increase
Function of progesterone
- Maintain uterine quiescence (relaxes myometrium)
- Along with oestrogen, provide uterine environment adapt for pregnancy
- induces decidual formation (remember decidua not necessary for implantation) and maintains
What requirements are there for oestrogen production in pregnancy?
note 1000 fold increase during pregnancy
1) Live fetus
2) Fetal adrenals functioning
3) intact feto-placental circulation
4) functioning placenta
Why can’t the placenta make estrogen?
It does not contain the enzyme 17 alpha hydroxylase
(moles and choriocarcinomas can not produce)
However can aromatise testosterone, just can not form androgens
How are oestrogens made in pregnancy?
Placenta makes progesterones, which travel into fetal circulation.
In the fetal adrenals and liver, these are converted to androgens
Androgens travel back in fetal circulation to the placenta
Are aromatised in the STB into free oestrogens which are secreted in maternal blood
What can be said about the STB and steroid production/release?
Most oestrogens and progesterone end up in maternal circulation due to close contact.
However maternal blood to fetus is a longer distance
What is preeclampsia?
A dangerously elevated maternal blood pressure associated with proteinurea or multiorgan dysfunction.
Affects most maternal organs; only in pregnancy; triggered by placenta; inflammatory response leading to vascular failure; normal vasculature fails to adapt, typically vasculature relaxes, so in this, higher peripheral resistance
What are the cardiovascular adaptations to pregnancy?
when do they occur?
Increase cardiac ouput (10% SV and 10-15% HR); starts early in gestation
Reduced peripheral vascular resistance to compensate for increased BP (if it does not preeclampsia?)
9 weeks
What causes the CV change in pregnancy (4 hormones)
NB idea of placental vesicles preventing endothelial cll activation
Oestrogen: Reduces vascular resistance; changes ratio of type 1 and 3 collagen in vessel wall. However fetal adrenals not making much at 9 weeks
Progesterone: may induce vascular relaxation in the placenta only. However low at 9/10 weeks also
Angiotensin: uteroplacental unit produces a lot, vasoconstricting effect. However effect is blunted in pregnancy
NO: made by endothelium. Nitric oxide synthetase activity is increased in some tissues in preg
What are the haemotological changes in pregnancy?
An increase in blood volume. the plasma increases at a much faster rate (1250 mL on average), resulting in a declining haemotocrit. (note this occurs after the CV changes, as increase in CO preceeds the volume change, showing it is not more blood that needs pumping around). Stable at 30 weeks
Lecture take home message
Pregnancy is a physiological state, not a disease. When looking at results check the normals for pregnancy not the standard norms
What is the purpose of the haematological change?
During delivery loss of 500mL roughly of blood.
The hypervolaemia accounts for this. Haemtocrit retuns slowly
How does the immune system adapt in pregnancy?
*- Seminal plasma dulls effects of immune response (immunosuppressive to a degree) tolerises to a degree
- some evidence of immune diminuition in pregnancy to some organisms meaning first encounter infection dealt with poorly
- Increase in white cell count, due to luteal phase, does not stop. Neutrophils peak at 30 weeks, then rise at labour.
- lymphocyte count does not change, bias towards TH2 cells, that drive towards antibody mediated response
What is special about the decidua’s immune system?
- No B cells and resident T cell population
- Has uterine NK cells. NK cells produce antibody dependent cell mediated cytotoxicity
- uNK cells lack the CD16, and instead produce growth factors
How does the uterus grow during pregnancy?
Growth is attributed to cell stretching.
Cell length goes from 50 microns to 400-600 microns
Cervical change during pregnancy
Softens and glands form to make up half the mass.
Water and GAG’s increase, collagen is lost.
Incompetent cervix associated with recurrent miscarriage
How does uteroplacental blood flow change during pregnancy
- First trimester: very limited due to trophoblast plugs (so as to make spiral arteries eroded, and have no tone). Remains like this for up to 10 weeks
- At about 13 weeks, flow into intervillous spaces can be recorded. Increases all the way up to term (10 weeks 50, 28 week 185, term 500-700)
Changes to abdominal wall and skin
Increased blood flow to skin, hands (peripheries)
Clammy hands
Skin pigmentation changes: Nipple and areola; linea nigra (belly); chloasma;
Hair loss reduced in pregnancy, but is then lost afterwards
