T2 L18 Physiology of pregnancy Flashcards
Why is there an increase in physiological demands for the foetus and placenta?
Nutrients - O2, amino acids, glucose
Amniotic fluid production
Removal of foetal waste products
How much does plasma volume increase in pregnancy?
40%
2.5 to 3.7L
8-10kg of fluid weight gain
What is the consequence of the fall in plasma colloid osmotic pressure?
Causes shift of fluid into extracellular space
Increased hydration of connective tissue
Oedema in lower limbs, hands and face
Describe the mechanism for an increase in plasma volume
Slight decrease in atrial natriuretic peptide
Decreased thirst threshold
Re-setting osmostat
What is the function of the renin angiotensin system in the placenta?
Responsible for local regulation of trophoblast invasion and uterine / placental blood flows
How much does red cell mass increase?
Increased by 25%
How is iron increased to meet the needs of the increased red cell mass?
Fall in ferritin levels
Increased iron absorption from the gut
How is blood delivered to the uterus?
Uterine artery
How much does uterine artery flow increase?
From 95 to 342ml/min
How much blood is lost at placental separation?
500ml/min
Describe the change in white blood cells during pregnancy
Concentration doesn’t fall during pregnancy
Total WBC increases in pregnancy
Marked increase around delivery
What does an increased blood volume have an impact on?
Cardiac output
Peripheral resistance
Blood pressure
Why is there an increase in CO?
Increase in stroke volume and heart rate
Why does peripheral resistance decrease?
Progesterone causes peripheral vasodilation
How much does the heart enlarge during pregnancy?
12%
Why does the heart enlarge?
There is increased venous return
How common are systolic murmurs in pregnancy?
Common - 90%
Why can you get an innocent diastolic murmur?
Reflects increased flow across atrioventricular valves
How much does the kidney increase in size during pregnancy?
1cm
How much do GFR and effective renal plasma flow increase during pregnancy?
≥50%
Why do you get glycosuria in pregnancy?
There is a decrease in glucose reabsorption
Why does the risk of a UTI increase during pregnancy?
Progesterone causes dilation of renal pelvis and ureter
Why does gastro-oesophageal reflux increase during pregnancy?
Increased abdominal pressure
Reduced pyloric sphincter with backwash of bile
How can gastro-oesophageal reflux be reduced?
Avoidance of fat and alcohol
Upright posture
Antacids
What is the effect of progesterone on the gut?
Slowing of gut motility and constipation
Describe glucose metabolism in the first trimester
Increased sensitivity to insulin
Increased glycogen synthesis and fat deposition
Describe glucose metabolism in the second trimester
Insulin resistance
Cortisol, progesterone, HPL and oestrogen are all insulin antagonists
Glucose levels may rise and there are an increase in fatty acids
What is the role of folate?
DNA synthesis, repair and regulation
RBC development
What is the change in folate requirement during pregnancy?
50mg to 400mg
How does thyroid function change during pregnancy?
Increased iodine absorption
Increased serum T3 and T4 levels
Increase in thyroid binding globulin due to oestrogen
What hormones are produced by the placenta?
hCG (human chorionic gonadotrophin) hPL (human placental lactogen) hPG (human placental gonadotrophin) CRH Progesterone Oestrogen
When is hCG first detectable?
8-9 days after ovulation
When does hCG peak?
8-10 weeks
When is hCG significantly lower?
Ectopic pregnancy
Risk of miscarriage
What is the alpha subunit of hCG similar to?
LH
FSH
TSH
What is the role of hCG?
Maintains corpus luteum secretion of progesterone and oestrogen
Decreases as placental production of progesterone increases
May have a role in maternal oestrogen secretion and modulation of maternal immune response later in pregnancy
What does hPL have a similar structure to?
Prolactin and growth hormone
What does hPL do?
Alters maternal carbohydrate and lipid metabolism to provide for foetal requirements
- mobilise maternal free fatty acids
- inhibit maternal peripheral uptake of glucose
- increase insulin release from pancreas
What is placental growth hormone responsible for?
Regulating foetal growth
Induces maternal insulin resistance
What does placental corticotrophin releasing hormone do?
Stimulates production of maternal ACTH and cortisol
Describe the effects of high levels of cortisol on the foetus
High levels early on are linked to slower rate of cognitive development post-partum
High levels later on are linked to accelerated cognitive development postpartum
What does progesterone do?
Maintains uterine quiescence by decreasing uterine electrical activity
Immune suppressor
Lobulo-alveolar development in breasts
Substrate for foetal adrenal corticosteroid synthesis
What is the effect of oestrogen?
Growth of uterus, cervical changes
Development of ductal system of breasts
Stimulation of prolactin synthesis
Stimulation of CBG, SHBG, TBG
