Physiology of Pregnancy

Question 1

Name the cardiovascular changes that occur during pregnancy

Answer 1

Increased: plasma volume, total blood volume, erythrocyte numbers, cardiac output
Decreased: diastolic blood pressure, peripheral vascular resistance

Question 2

Describe the timeline of blood volume changes in pregnancy?

Answer 2

Blood volume starting to increase in first trimester, rapidly increasing in second, and increasing more slowly in third trimester.

Question 3

Why may pregnant women experience ‘dilutional anaemia’?

Answer 3

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

Question 4

Describe the mechanism of increase in plasma volume in pregnancy

Answer 4

Vasodilation, decreased peripheral vascular resistance, activation of RAAS system, retention of sodium and an increase in total body water

Question 5

Describe the mechanism of increase in erythrocytes in pregnancy

Answer 5

Increased renal EPO production –> increased erythropoiesis

Question 6

Why does cardiac output increase in the first trimester?

Answer 6

Due to an increased heart rate and stroke volume (SV caused by increase plasma and erythrocyte volume)

Question 7

What is the cause of decreased diastolic BP

Answer 7

Decrease in peripheral vascular resistance in early pregnancy facilitated by oestrogen, progesterone, NO, relaxin and calcitonin gene-related peptide

Question 8

When does normal blood pressure resume in pregnancy?

Answer 8

Decreases until 24 weeks and then increases to normal levels thereafter

Question 9

What is haemostasis?

Answer 9

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

Question 10

Define ‘hypercoagulable’

Answer 10

Abnormally increased tendency towards blood clotting

Question 11

What is fibrinolysis?

Answer 11

Normal breakdown of clots (during healing phase)

Question 12

What haematological changes occur during pregnancy?

Answer 12

Presentation of a hyperoagulable state - thought to be important in maintaining placental function and to prevent excessive bleeding during delivery

Question 13

Describe the mechanism behind the production a hypercoagulable state in pregnant women

Answer 13

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)

Question 14

What are the leading causes of direct deaths in pregnancy?

Answer 14

Venous thromboembolism and thrombosis due to excess clotting in pregnancy

Question 15

Name the respiratory system changes that occur in pregnancy

Answer 15

Increased alveolar ventilation, increased minute ventilation, increased tidal volume, slightly increased respiratory rate

Question 16

What is alveolar ventilation?

Answer 16

The amount of air that reaches the alveoli

Question 17

Why does alveolar ventilation increase in pregnancy?

Answer 17

So that more air reaches the alveoli and therefore more oxygen is available to the blood in gaseous exchange

Question 18

What is the consequence of an increased minute ventilation?

Answer 18

A fall in pCO2 and a slight rise in PO2

Question 19

What is minute ventilation?

Answer 19

The volume of gas inhales of exhaled per minute

Question 20

Why does respiratory rate increase slightly in pregnancy?

Answer 20

Due to progesterone-mediated hypersensitivity to CO2; the progesterone stimulates the respiratory centre directly in order to increase the sensitivity to carbon dioxide

Question 21

Outline the changes in lung volumes during pregnancy

Answer 21

Decrease in total lung capacity, decrease in expiratory reserve volume, decrease in residual volume and increased tidal volume

Question 22

Why are there changes to lung volumes during pregnancy?

Answer 22

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

Question 23

How is chronic respiratory alkalosis, caused by hyperventilation, compensated for by the body?

Answer 23

Renal compensation, whereby there is greater bicarbonate loss (HCO3-) and H+ retention in the kidneys in order to neutralise the change

Question 24

Outline the changes to the kidneys during pregnancy

Answer 24

Increased kidney length, dilation of structures within the kidney, increased GFR, increased urea/creatine/urate and HCO3- clearance

Question 25

Explain why there is dilation of structures within the kidney during pregnancy

Answer 25

Due to progesterone working to relax the smooth muscle within the structures

Question 26

Explain why there is an increased GFR in pregnancy

Answer 26

There is an increased CO which increases renal plasma flow and subsequently increases the glomerular filtration rate

Question 27

How is the renin-angiotensin-aldosterone system affected in pregnancy?

Answer 27

Increased activity, therefore this leads to water retention and decreased plasma osmolarity

Question 28

How is the RAAS system controlled in pregnancy?

Answer 28

Not fully understood but there is potential for their to be direct action on the system facilitated by progesterone and oestrogen to stimulate RAAS

Question 29

Why is there increased aldosterone secretion in pregnancy, and what is the consequence of this?

Answer 29

As a result of increased stimulation of the RAAS system; this leads to increased reabsorption of salt and water in the kidneys

Question 30

How may oestrogen facilitate stimulation of the RAAS system?

Answer 30

May act directly to increases the secretion of renin from granular cells OR may upregulate angiotensinogen production in the liver

Question 31

Outline the changes to the liver than occur during pregnancy

Answer 31

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

Question 32

Outline the gastrointestinal changes that occur in pregnancy

Answer 32

Heart burn, decrease in tone and motility in the bowel, constipation and haemorrhoids

Question 33

Outline the endocrine system changes that occur during pregnancy

Answer 33

Increased proliferation of insulin-secreting cells in the pancreas (beta cells) –> increase in insulin production, glycosuria due to a decrease in glucose reabsorption

Question 34

Explain why cardiac output increases during labour

Answer 34

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

Question 35

Outline the changes that occur in the body post-partum

Answer 35

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

Question 36

When is the breast fully developed for milk production?

Answer 36

Middle of pregnancy

Question 37

Describe the physiological changes that occur during pregnancy to prepare for lactation

Answer 37

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.

Question 38

Describe the role of prolactin in lactation

Answer 38

It initiates milk production (it’s a primary lactogenic hormone) and it is present at high levels throughout gestation

Question 39

Describe the role of oxytocin in lactation (let-down reflex)

Answer 39

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

Question 40

Why don’t women lactate during their pregnancy?

Answer 40

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

Question 41

Why may a pregnant women experience heartburn?

Answer 41

Due to increase in intra-abdominal pressure as a result of the foetus and progesterone also mediates a reduction in LOS tone

Question 42

Why may a woman be constipated during pregnancy?

Answer 42

Stimulation of the RAAS system in pregnancy leads to increased water reabsorption in the kidney