Physiology of Pregnancy Flashcards
Name the cardiovascular changes that occur during pregnancy
Increased: plasma volume, total blood volume, erythrocyte numbers, cardiac output
Decreased: diastolic blood pressure, peripheral vascular resistance
Describe the timeline of blood volume changes in pregnancy?
Blood volume starting to increase in first trimester, rapidly increasing in second, and increasing more slowly in third trimester.
Why may pregnant women experience ‘dilutional anaemia’?
Plasma volume increases first, before total erythrocyte number, however, even then the volume of erythrocytes in comparison to the plasma volume increase is small and this leads to reduced haemoglobin concentrations from pre-pregnancy to third trimester
Describe the mechanism of increase in plasma volume in pregnancy
Vasodilation, decreased peripheral vascular resistance, activation of RAAS system, retention of sodium and an increase in total body water
Describe the mechanism of increase in erythrocytes in pregnancy
Increased renal EPO production –> increased erythropoiesis
Why does cardiac output increase in the first trimester?
Due to an increased heart rate and stroke volume (SV caused by increase plasma and erythrocyte volume)
What is the cause of decreased diastolic BP
Decrease in peripheral vascular resistance in early pregnancy facilitated by oestrogen, progesterone, NO, relaxin and calcitonin gene-related peptide
When does normal blood pressure resume in pregnancy?
Decreases until 24 weeks and then increases to normal levels thereafter
What is haemostasis?
Body’s response to blood vessel injury and bleeding. It involves a coordinated effort between platelets and numerous blood clotting proteins (or factors), resulting in the formation of a blood clot and subsequent stopping of the bleed
Define ‘hypercoagulable’
Abnormally increased tendency towards blood clotting
What is fibrinolysis?
Normal breakdown of clots (during healing phase)
What haematological changes occur during pregnancy?
Presentation of a hyperoagulable state - thought to be important in maintaining placental function and to prevent excessive bleeding during delivery
Describe the mechanism behind the production a hypercoagulable state in pregnant women
General increase in the majority of coagulation factors: fibrinogen, clotting factors (except XI and tissue factor), decrease in coagulation inhibits, increased platelet production, decreased platelet count (due to increased activity and consumption) and inhibition of fibrinolysis activity (due to decrease in tissue plasminogen activator)
What are the leading causes of direct deaths in pregnancy?
Venous thromboembolism and thrombosis due to excess clotting in pregnancy
Name the respiratory system changes that occur in pregnancy
Increased alveolar ventilation, increased minute ventilation, increased tidal volume, slightly increased respiratory rate
What is alveolar ventilation?
The amount of air that reaches the alveoli
Why does alveolar ventilation increase in pregnancy?
So that more air reaches the alveoli and therefore more oxygen is available to the blood in gaseous exchange
What is the consequence of an increased minute ventilation?
A fall in pCO2 and a slight rise in PO2
What is minute ventilation?
The volume of gas inhales of exhaled per minute
Why does respiratory rate increase slightly in pregnancy?
Due to progesterone-mediated hypersensitivity to CO2; the progesterone stimulates the respiratory centre directly in order to increase the sensitivity to carbon dioxide
Outline the changes in lung volumes during pregnancy
Decrease in total lung capacity, decrease in expiratory reserve volume, decrease in residual volume and increased tidal volume
Why are there changes to lung volumes during pregnancy?
Because the expanding uterus causes elevation of the diaphragm which can restrict the maximum expiratory reserve volume and therefore, decrease residual volume and total lung capacity
How is chronic respiratory alkalosis, caused by hyperventilation, compensated for by the body?
Renal compensation, whereby there is greater bicarbonate loss (HCO3-) and H+ retention in the kidneys in order to neutralise the change
Outline the changes to the kidneys during pregnancy
Increased kidney length, dilation of structures within the kidney, increased GFR, increased urea/creatine/urate and HCO3- clearance
Explain why there is dilation of structures within the kidney during pregnancy
Due to progesterone working to relax the smooth muscle within the structures
Explain why there is an increased GFR in pregnancy
There is an increased CO which increases renal plasma flow and subsequently increases the glomerular filtration rate
How is the renin-angiotensin-aldosterone system affected in pregnancy?
Increased activity, therefore this leads to water retention and decreased plasma osmolarity
How is the RAAS system controlled in pregnancy?
Not fully understood but there is potential for their to be direct action on the system facilitated by progesterone and oestrogen to stimulate RAAS
Why is there increased aldosterone secretion in pregnancy, and what is the consequence of this?
As a result of increased stimulation of the RAAS system; this leads to increased reabsorption of salt and water in the kidneys
How may oestrogen facilitate stimulation of the RAAS system?
May act directly to increases the secretion of renin from granular cells OR may upregulate angiotensinogen production in the liver
Outline the changes to the liver than occur during pregnancy
Increase alkaline phosphatase concentration in the blood as a result of placental production, spider naevi and palmar erythema may occur but these are normal in pregnancy
Outline the gastrointestinal changes that occur in pregnancy
Heart burn, decrease in tone and motility in the bowel, constipation and haemorrhoids
Outline the endocrine system changes that occur during pregnancy
Increased proliferation of insulin-secreting cells in the pancreas (beta cells) –> increase in insulin production, glycosuria due to a decrease in glucose reabsorption
Explain why cardiac output increases during labour
Due to auto-transfusion of the contracting uterus (placental blood being returned to the mother) and pain or anxiety may stimulate the sympathetic nervous system leading to an increase in heart rate and blood pressure
Outline the changes that occur in the body post-partum
Blood volume, heart rate and cardiac output decrease back to non-pregnant levels within 2-3 weeks and dilatation of the bladder, ureters and renal pelvis which persists for greater than 3 months
When is the breast fully developed for milk production?
Middle of pregnancy
Describe the physiological changes that occur during pregnancy to prepare for lactation
Lobular ductal-alveolar system in the mammary tissue undergoes hypertrophy where there is proliferation of the ducts; alveoli maturation and deposition of fat between the lobules, and this is controlled by placental steroids e.g. oestradiol, progesterone, hPL etc.
Describe the role of prolactin in lactation
It initiates milk production (it’s a primary lactogenic hormone) and it is present at high levels throughout gestation
Describe the role of oxytocin in lactation (let-down reflex)
Released in response to baby suckling and this causes the contraction of the myoepithlial cells which release milk from the alveoli and small ducts into the large ducts and sinuses, out of the nipple and into the baby’s mouth
Why don’t women lactate during their pregnancy?
Although prolactin works to initiate milk production and is present at high levels throughout gestation, oestrogen and progesterone inhibit secretion and lactogenesis is then triggered after parturition by a fall in the steroid secretion
Why may a pregnant women experience heartburn?
Due to increase in intra-abdominal pressure as a result of the foetus and progesterone also mediates a reduction in LOS tone
Why may a woman be constipated during pregnancy?
Stimulation of the RAAS system in pregnancy leads to increased water reabsorption in the kidney
