Pregnancy Endocrinology Flashcards
4 main placental hormones
hCG, hPL, progesterone and oestrogen
Which hormones are hydrophobic and hydrophillic
Oestrogens and progestens are hydrophobic (lipid/steroids) and hCG/hPL/oxytocin are hydrophillic (proteins)
What is hCG and what does it do
- Secreted by synctiotrophoblasts and maintains corpus luteum, peaks around week 12 doubling every 48 hours before then. Reduces for remainder of pregnancy. - drops because placenta takes over steroid production.
Functions of hCG = maintains corpus luteum, stimulates DHEA production in the foetal adrenal gland and in males stimulates testosterone
Structure of hCG
It has an alpha and beta subunit
The alpha subunit is identical to that of LH, FSH and TSH and acts on LH receptors.
Beta subunit is excreted renally so can be used in to detect pregnancy – pregnancy test looks at levels of hCG
How does multiple pregnancies affect TSH levels?
Morning sickness is though to result from particularly potent hCG and risk of this increase with multiple pregnancies (hCG levels even higher)
Due to similar structure of hCG and TSH there is usually an increase in free T4 hormone and reduction in TSH
Function of corpus luteum
Produces progesterone and oestrogen to promote decidualisation rather than menstruation (disintergration)
What is hPL
Human placental lactogen, it affects breast development and fetal growth. Released from synctiotrophoblasts and increases steadily throughout pregnancy
Function of hPL
adjust maternal metabolism to promote foetal growth – this involves mobilisation of free fatty acids and antagonising actions of maternal insulin
Indirectly it is able to increase oestrogen concentration through acting on the ovaries as well as stimulating foetal bone plate growth and acinar breast gland development.
Also causes increase in IGF1 increase causing increased insulin resistance and breakdown of other substances to make glucose (lipolysis/gluconeogenesis)
This increases maternal insulin production and mobilises nutrients for the foetal needs
Antagonising maternal insulin leads to insulin resistant state in the mother that may lead to gestational diabetes.
Premature baby - hPL consequences
As hPL levels increase so do levels of glycogen storage in the foetal liver
infants born premature as they will have a lower glycogen store
This leads them to increased susceptibility of hypoglycaemic episode between feeds
What is PGH
-Placental growth hormone, released from weeks 15-20. Modifies glucose transport across fetus.
non-pulsatile secretion, correlates to placental size. -
stimulates maternal gluconeogeneisis and lipolysis, more glucose for baby.
3 different types of oestrogen
- Oestrone = predominant in menopause
- Oestradiol = regulates menstruation
- Oestriol = pregnancy specific
Oestrogen effects on mother
- Myometrium oestrogen acts in increase excitability and glycogen stores, hypertrophy and hyperplasia and stimulates oxytocin receptor expression at end of pregnancy
- Softens the cervix and pelvic ligaments, increase uterine blood flow, increases levels of renin, angiotensin and hormone binding globulins in blood
- Effects on metabolism such as increased cholesterol and triglyceride levels, decrease HDLs and decrease in glucose uptake
- Increase in clotting factors and decrease in fibrinolysis preventing haemorrhage in labour - However, this puts the mother at risk of deep vein thrombosis (DVT)
- Stimulates growth and development of breast and causes prolactin release
Effects of progesterone
levels are high through pregnancy with down-regulation of progesterone receptors at the end of pregnancy (labour)
- It acts to make endometrium receptive to implantation
- Relaxes the myometrium and smooth muscle in general
- Resets the respiratory centre to allow hyperventilation and decreased pCO2
- Increases body temp
- Increases protein breakdown to provide the foetus with more nutrients
- Promotes breast glandular development
Progrestorone in labour
Reduces collagen fibres causing shortening and effacement (thinning out) of the cervix during parturition
The change in cervical dilation from the latent to the active phase of partition takes on the shape of a sigmoid curve (known as Friedman’s partogram)
Multiparas (had children before) attain the active phase faster than nulliparas (never had children)
Where is progesterone produced
Corpus luteum until 12 weeks, then placenta.
Role of progesterone receptor B
downregulates contractile proteins (gap junctions, oxytocin) and negatively regulates hPL.
Balance between oestradiol and progesterone.
P suppresses contractions of myometrium to prevent birth, during labour it falls and estradiol causes contractions.
Giving P antagonist initiates contractions and stimulates labour.
Alternative pathway for oestradiol synthesis
Placenta lacks 17-alpha-hydroxylase, so can’t convert P to DHEA. -
Foetal adrenal gland lacks 3-Beta-hydroxysteroid dehydrogenase, so can’t convert pregnenolone to P.
These modifications mean more DHEA is converted to oestradiol.
Prostaglandins in pregnancy
Increase in intrauterine prostaglandin synthesis, due to increase in oestradiol and decrease in P.
PGF and PGE2 are procontractile
PGI2 is a vasodilator
TXA2 is anti-aggregating
Oxytocin Function
Nanopeptide released from neurones of the posterior pituitary
- Increase in intramyometrial prostaglandins, uterine contractions and cervical distension are sensed by these neurones
- This leads to a neuroendocrine reflex that causes the release of oxytocin in a positive feedback loop
- Oxytocin then promotes further uterine contractions and release of prostaglandins
Parturition can still occur when there is no oxytocin present as other factors substitute for it
Foetal Contribution to Initiation of labour
Placental CRH increases during gestation. DHEAs increase via fetal adrenal, converted into oestradiol in placenta and back into DHEA in maternal liver, causing procontractile effects.
Ferguson reflex
Contractions push down placenta, causing release of oxytocin, which causes Ca2+ influx and smooth muscle contractions. Oxytocin increases tone and number of contractions.
Changes in breasts
Oestrogen = increasing size and number of ducts in the breast
Progesterone = increasing number of alveolar cells but inhibits the lactogenic effects of hPL
hPL = stimulates development of acinar glands
Prolactin = promotes milk production
Oxytocin = promotes let down reflex
prolactin function
Prolaction is secreted from anterior pituitary when dopamine inhibition is released.
Secretion is increased throughout pregnancy by oestrogens and TRH.
Milk production via somatosensory pathway
Stimulation of the nipples has positive feedback to pituitary for prolactin release meaning as much milk can be produced as is needed
Oestrogen effects on prolactin
Oestrogen increases prolactin secretion either directly or by suppressing dopamine
Expulsion of the placental causes a fall in oestrogen and progesterone which initiates lactation
Let down reflex
Neuroendocrine reflex
Nipple stimulation by suckling leads to release of oxytocin which stimulates contractility of the myoepithelial cells in the breast
Results in release of milk from alveoli and ductal flow to the nipples
Adv. of breastfeeding for mother
Delays fertility reduces cancer risk emotional health weight loss osteoporosis.
Adv. of breastfeeding for baby
Protection against infections, illness, allergies.
Enhancement of intelligence and development.
Long-term health benefits.
