Physiology of pregnancy Flashcards
Plasma volume changes in pregnancy
Plasma volume increases by 40%
- 2.5–> 3.7 L
8-10kg fluid weight gain (from 11-13 kg weight gain)
Oncotic pressure falls
- Fluid into extracellular space
- Oedema
Mechanism in increased plasma volume
Increase in oestrogen causes stimulation of angiotensinogen pathway.
Progesterone stimulates aldosterone secretion.
Aldosterone increases fluid absorption from the kidneys via Na+ absorption.
- Decreased ANP
- Decreased thirst threshold
- Osmostat resetting [regulates osmolality of EC fluid]
Changes in red blood cells
Red cell mass increases but massive plasma volume increase
- Dilutional anaemia–> decreased concentration of haemoglobin
Increased delivery of blood to uterus
- 3.5 fold
Iron changes in pregnancy
Fall in ferritin
- Body compensated by increasing iron absorption in gut
- Iron essential for increase in red cell mass.
Haemostasis in pregnancy
Hypercoagulable
- Increased plasma fibrogen
- Increased platelets, factor VIII, vWF
During delivery, increase in haemorrhage
- Placental separation
- Myometrial contraction
Changes in WBC during pregnancy
Total WBC increases
Increased neutrophils–> decreased apoptosis
Increases significantly around delivery
Effects of increased blood volume
Increase in cardiac output
- Partially compensates decreased vascular resistance
Decreased
peripheral resistance (35%)
- Progesterone causes increased vasodilatation
Increased BP
Heart changes during pregnancy
Heart enlarges
- Increases venous return
Presence of innocent systolic murmurs
Diastolic murmurs in around 20%
- Must rule out other pathologies
Effects of pregnancy on respiratory system
Increased pulmonary blood flow=
- Increased tidal flow
- Decreased maternal pCO2
- Increased maternal pO2
Increased O2 creates higher concentration gradient for diffusion in placenta.
Effects of pregnancy on renal system
Increase in kidney size (1cm)
Increase in GFR and effective renal plasma flow (50%)
- GFR decreases during third trimester
Tubular reabsorption is not affected
- Glycosuria
Decreased plasma creatinine and urea.
Progesterone–> dilation of renal pelvis and ureter= increased UTI
Effects of pregnancy on GIT
Reflux
- 70%
- Increased abdominal and reduced pyloric pressure
- Backwash of bile
Slowed gut motility (progesterone)
- Constipation
Reflux treatment
Avoid fat and alcohol
Upright posture
Antacids
Glucose metabolism
- First trimester
Increased sensitivity to insulin
- Increased glycogenesis and lipogenesis
Glucose metabolism
- Second trimester
Insulin resistance
Cortisol, progesterone, HPL and oestrogen antagonise insulin–> Increase in FA, glucose levels.
Importance of folate in pregnancy
DNA synthesis, repair and regulation
- Deficiency= neural tube defects
- Supplement given 3 months preconception to prevent NTDs
RBC development
- Deficiency= macrolytic anaemia.
