Developmental - Maternal physiology during pregnancy Flashcards
What is beta HCG, where is it secreted from? and when can it be detected in the maternal circulation versus maternal urine.
beta human chorionic gonadotropin is a glycoprotein hormone with structure similar to that of LH, FSH, TSH.
secreted from the placenta
Detectable in maternal circulation: 10 days
Detectable in maternal urine: 10 days
Describe the rise of hcg during pregnancy. How fast is the rise and when is the peak reached
Rapid rise
Doubles every 2 days until peak is reached after 10 weeks gestation
Describe the endocrine process that prevents miscarriage in early pregnancy
- In the 2nd half of the menstrual cycle, the corpus luteum secretes progesterone and a small amount of oestrogen.
- after 14 days and without implantation, corpus luteum degenerates into corpus albicans
- If embryo implants in uterus or fallopian tube (ectopic) then syncytiotrophoblast cells of the newly formed placenta produce beta hcg which stimulates the corpus luteum to keep secreting progesterone. This prevents sloughing of the placenta which would cause miscarriage
What are the functions of the hormone beta hcg
- Prevent degeneration of the corpus luteum after implantation of a zygote
- To suppress the maternal immune response, protecting the placenta and embryo from immune destruction.
What happens to beta hcg concentration at 10 weeks? Why does this occur
Peak beta hcg levels are reached. At this point the placenta takes over progesterone synthesis and secretion from the corpus luteum. The beta hcg level then falls and the corpus luteum degenerates
What is Human Placental Lactogen (hPL). Where is it secreted from
Polypeptide hormone similar to GH
Secretion: syncytiotrophoblast cells of placenta
Describe the rise of human Placental Lactogen (hPL) levels during pregnancy
hPL levels increase through pregnancy in proportion to fetal and placental growth, peaking near term
What are the functions of human Placental Lactogen
Ensure provision of nutrients for the growing fetus through manipulation of maternal metabolism.
- Increased maternal lipolysis (ffas availability)
- Decreased maternal insulin sensitivity (glucose avail)
- Stimulation of breast growth and development
What type of hormone is progesterone
A steroid hormone
How is progesterone secreted during pregnancy
Corpus Luteum up to 10 weeks (thanks to beta hcg)
Then placenta takes over in second and third trimester
What are the main functions of progesterone
The ‘pregnancy hormone’
- Prepare endometrium for implantation
- Promote endometrial growth following implantation
- Uterine muscle relaxation (prevent miscarriage)
- Formation of cervical mucus plug (protect developing fetus from ascending infection)
- Development of milk glands in preparation for lactation
Also responsible for many other physiological changes during pregnancy
Name the three types of oestrogen synthesized by the placenta. How is the synthesis of these types determined and which is the important type during pregnancy
Oestradiol
Oestrone
Oestriol
Each are made from different precursors
The amount of precursors for each available determines the synthesis of each type.
Oestriol is produced from a fetal adrenal precursor called dehydroepiandrostenedione sulphate. Hence oestriol production is under the control of the growing fetus
What controls uteroplacental blood flow during pregnancy. How is this control achieved
The fetus.
The fetal adrenals produce the precursor dehydroepiandrostenedione sulphate which are delivered to the placenta and favour the synthesis and secretion of oestriol (over oestrone and oestradiol).
Oestriol Increases uteroplacental blood flow.
(oestradiol is the oestrogen that regulates the menstrual cycle)
What are the roles of oestrogens during pregnancy
- To increase uteroplacental blood flow
- Stimulate uterine growth
- Sensitise myometrium to oxytocin (reduce PPH)
- Procoagulant (reduce PPH, VTE risk)
Describe the changes to thyroid hormones during pregnancy
Oestriol –> liver: synthesis of more thyroxine-binding globulin –> decrease unbound T3 and T4 –> sensed by hypothalamus –> increase TRH –> increase TSH –> T3 and T4 back to normal
What is Sheehan’s syndrome
Oestrogen –> dramatic increase PRL during pregnancy to prep the breasts for lacatation –> pituitary gland doubles in size with much higher metabolic demands: vulnerable to ischaemia. If effective circulating volume diminished during PPH –> ischaemia/infarction of the pituitary gland.
Which hormone causes increased secretion of prolactin during pregnancy and doubling in size of the pituitary gland as a result
Oestrogen
Discuss maternal calcium regulation during pregnancy
Fetal demand Ca is high. Ca+ moved from maternal into fetal circulation across placenta –> reduced maternal ionized calcium –> Increased maternal PTH –> increased renal reabsorption Ca, activation of vit D and resorption of bone.
In combination with LMWH –> osteopaenia of bone
When do the respiratory changes in pregnancy become significant
> 20 weeks
How is the airway affected during pregnancy
- Capillary engorgement (oestrogen) –> oedema and swelling of oropharyngeal and laryngeal mucosa
- Weight gain
——> larger breasts
——> short neck - Increased mucosal vascularity and bleeding (worsened by low plt in PET)
How is the minute ventilation affected in pregnancy
At term: Ve increase by 50%
- Vt increases 40%
- RR increases 10%
How does pregnancy affect minute ventilation
Progesterone:
- VT increased by 40% at term
- RR increased 10% at term
- Ve increased 50% at term and even further during la our due to pain
How is anatomical dead space affected by pregnancy
Progesterone
Causes bronchodilation—> increased (minimally) anatomical dead space
Progesterone induced smooth muscle relaxation
What is the normal PaCO2 and HCO3 in pregnancy and why.
PaCO2 —> 4.3
HCO3- —> 20
Fetus: increased CO2 production
Mother: increased Ve
Overall: PaCO2 down
Kidneys respond to respiratory alkalosis by excreting more HCO3-