physiology of pregnancy Flashcards
why do physiological adaptations need to occur?
to;
o Support the developing fetus
o Prepare the mother for labour
what cardiovascular changes occur during pregnancy?
increased plasma volume increase in erythrocyte production increased cardiac output fall in blood pressure hypercoagulable state
how does blood volume change over the course of pregnancy?
- Blood volume starts to increase during 1st trimester
- Expands rapidly during 2nd trimester
- Rises at a lower rate during 3rd trimester
how much can plasma volume increase overall during pregnancy?
45%
what follows an increase in plasma volume during pregnancy?
increase in total erythrocyte volume
how does dilution anaemia occur?
• Increase in RBC is smaller relative to that of plasma volume
how does Hb concentration change during pregnancy?
falls from around 150g/l pre-pregnancy to 120g/l during the third trimester
what stimulates erythropoiesis?
an increase in renal erythropoietin production
how does cardiac output change over the course of pregnancy?
- Cardiac output increases by 35-40% in the first trimester
* CO increases slightly during 2nd and 3rd trimesters, approx. 50% at term
what causes increased CO?
increased HR and SV
why does stroke volume increase during pregnancy?
o Increase in ventricular wall muscle mass
o Heart is physiologically dilated
o Myocardial contractility is increased
how does the distribution of CO change during pregnancy?
o Mainly increase blood flow to uterus (2% 17%)
oSlight increase to breast
how does MABP change during pregnancy?
MABP stays the same/falls slightly
when does BP reach its lowest point during pregnancy?
between 17-24 weeks of pregnancy
how is MAP calculated?
CO x TPR
how does TPR change during pregnancy and why?
decreased TPR bc CO is increased to maintain BP around the same state
how does peripheral vascular resistance change during pregnancy?
falls by 50% during early pregnancy
what causes peripheral vasodilation?
o Progesterone – key role in relaxing smooth muscle.
o Oestrogen, nitric oxide, relaxin and calcitonin gene-related peptide are also implicated in causing vasodilation
o Other influences include placenta, an additional organ – contributes an extra blood vessel circuit
what is the effect of an enlarged uterus on blood flow?
• Enlarged uterus (around 3rd trimester) can cause compression of vena cava –> impedes venous return to heart –> reduction in CO and BP (contributes to maternal hypotension)
how should pregnant women be positioned for BP measurements?
on the side - not supine
what is pre-eclampsia characterised by?
characterised by high blood pressure with proteinuria and oedema
what is haemostasis?
the process of coagulation depending on enzymatic activity, which culminates in the form of a stable, vascular plug
what is fibrinolysis?
clot dissolution that occurs during the healing phase
what is a hypercoagulable state?
– increased tendency towards blood clotting
why is it important for pregnancy to induce a hypercoagulable state?
important to maintain placental function during pregnancy and as prep to prevent excessive bleeding during delivery
which clotting factors increase during pregnancy?
all clotting factors gradually increase - EXCEPT XI and Tissue factor (TF)
do coagulation inhibitors increase or decrease during pregnancy?
decrease
what haemostatic changes occur in pregnancy?
o Increased platelet production
o Decreased platelet count (reflects increased activity and consumption)
o Inhibition of fibrinolysis activity
what is thrombosis/thromboembolism?
localised blood clot forming where it shouldnt
who is affected by thrombosis/thromboembolism?
Affects 1/1000 women under the age of 35
what physiological changes to the respiratory system occur during pregnancy?
increased O2 consumption
increased alveolar ventilation
increased minute ventilation
large increase in tidal volume
why is there increased O2 consumption during pregnancy?
maintains the additional metabolic requirements of pregnancy
what is alveolar ventilation?
amount of air that reaches the alveoli and is available for gas exchange with the blood
what is minute ventilation?
volume of gas inhaled/exhaled from lungs/min
why is minute ventilation increased?
large increase in tidal volume
respiratory rate slightly increased
what are the mechanisms of increase in ventilation?
- Progesterone-mediated hypersensitivity to CO2
* Progesterone stimulates the respiratory centre directly to increase sensitivity to carbon dioxide
what changes in lung volume occur during pregnancy?
- Decrease in total lung capacity
- Increased tidal volume
- Decrease in expiratory reserve volume
- Decrease in residual volume
- Expanding uterus
what changes does increased ventilation cause to an ABG?
fall in PaCO2 and slight rise in PaO2
what acid-base changes does hyperventilation lead to? how is this compensated?
- Leads to development of chronic respiratory alkalosis
* Renal compensation (HCO3- loss, H+ retention)
what changes occur to the kidneys during pregnancy?
- increase in length
- dilation of the renal calyces, pelvis and ureter mainly due to the action of progesterone to relax smooth muscle
- increased renal plasma flow
- increased glomerular filtration rate
- Increase in urea, creatinine, urate clearance and excretion of bicarbonate
what is glycosuria? why does it occur?
decrease in reabsorption of glucose
Due to increase in filtered load of glucose which is greater than the ability of the proximal tubule to reabsorb glucose
how do prorenin, renin and angiotensinogen change during pregnancy?
- Prorenin: peaks 8-12 weeks of gestation
- Renin: rises around 20 weeks of gestation
- Significant increase in Angiotensinogen
how does oestrogen affect renin secretion?
increases renin secretion from granular cells
how does oestrogen affect angiotensinogen?
upregulate angiotensinogen production in the liver
what does increased activity of RAAS in early pregnancy lead to?
leads to water retention + decrease in plasma osmolarity
what does increased aldosterone secretion during pregnancy lead to?
reabsorption of salt + water
name markers of liver function
alanine aminotransferase
aspartate transaminase
lactate dehydrogenase
gamma-glutamyl transferase
what are clinical signs of liver disease?
spider naevi and palmar erythema may occur
what action does pregnancy have on GI function?
- heartburn/reflux common
- Progesterone-mediated reduction in lower oesophageal sphincter tone
- • Predisposition to regurgitation and aspiration during anaesthesia
• Small and large bowel – decrease in tone and motility
• 60% increase in water absorption
• Constipation
• Haemorrhoid formation
why is heartburn/reflux common in pregnancy?
partly bc of increased intra-abdominal pressure (aggravated in supine position)
how is pancreatic function affected by pregnancy?
- Pancreatic islets of Langerhans – hyperplasia of insulin producing β-cells: Increased insulin production
- Early pregnancy tissues show an increased sensitivity to insulin and plasma glucose may fall
- Late pregnancy insulin response blunted by placental hormones and plasma glucose may rise.
- Increased placental glucose uptake
what is parturition?
labour or the act of giving birth
what are the 3 stages of labour?
o Dilation of cervix/uterine contractions
o Fetal expulsion
o Placental expulsion
what changes occur to cardiac output during labour?
o Increases bc “autotransfusion” from contracting uterus.
o Further increase in blood may be autotransfused as placenta delivered.
o Pain/anxiety and stimulation of sympathetic nervous system also increases heart rate and possibly blood pressure.
what postpartum changes are there to the cardiovascular system?
o Blood volume decreases by 20% in 72hrs postpartum
o Heart rate and CO decreases to baseline in 2 weeks
o Proteins and lipids decrease to baseline in 2-3 weeks
what postpartum changes are there to the urinary system?
o Functional change – prompt return to baseline with decreased blood volume
o Structural change - Dilatation of bladder, ureters and renal pelvis – persist for 3 months
when does the mammary gland start developing?
start of puberty
what hormones regulate the development of the non-pregnant adult mammary gland?
progesterone and oestrogen
how do mammary glands develop during puberty?
• Lactiferous ducts and alveoli (lobes) develop but the breast is not capable of large-scale mile production (lactogenesis)
how does the mammary gland develop during pregnancy?
- Lobular ductal-alveolar system undergoes hypertrophy.
- Proliferation of ducts.
- Alveoli mature.
- Deposition of adipose tissue between lobules of the gland
what hormones regulate development of the mammary gland during pregnancy?
- Controlled by placental steroids: estradiol and progesterone as well as placental peptide hormone (hPL).
- Pituitary growth hormone and prolactin may also have a role.
when is the breast fully developed for milk production?
middle of pregnancy
what is prolactin?
primary lactogenic hormone (initiates milk production)
what inhibits secretory activity of mammalian tissue?
steroid secretion (placental steroids: oestrogen and progesterone)
what triggers lactogenesis?
triggered post-delivery by fall in steroid secretion (placental steroids: oestrogen and progesterone).
what hormone is needed for the milk ejection reflex?
oxytocin
what stimulates oxytocin release?
in response to suckling
how does the milk ejection reflex occur?
oxytocin secreted
Contraction of myoepithelial cells – release milk from alveoli and small ducts into large ducts and sinuses
