Physiology Flashcards
how does the endocrine system adapt to pregnancy?
- progesterone and oestroegn levels increase (made by placenta)
- increase total T3 and T4 (free T3/T4 same as increase in TBG)- this ensures constant supply thyroxine for fetal development
- lactogen, prolactin and cortisol increase due to increases in P and O, these are anti insulin so increase insulin resistance for constant supply of glucose for fetus
- increased lipolysis so fatty acids becomes substrate for maternal metabolism, however this can result in ketogenesis so increased risk ketoacidosis in pregnancy
- progesterone also stimulated fat deposition in first half of pregnancy so can use it later and let fetus use glucose
How the cardiovascular system adapt to pregnancy
- increased progesterone which decreases systemic vascular resistance and so decreases diastolic BP during 1st and 2nd trimester
- in response to this the CO increases by about 30-50%
- pregnancy activates RAAS system which increases sodium levels and water retention so total blood volume increases
how does the resp system adapt to pregnancy
- growth of fetus causes upward displacement of diaphragm, however total lung volume doesnt decrease much as there is transverse and AP increase in diameters of the thorax
- Many women experience hyperventilation due to increased resp drive from progesterone and increased carbon dioxide release- this results in resp alkalosis and is compensated by kidneys
How does the GI system adapt to pregnancy?
- upward diaplacement of stomach (predisposes to reflux and N+V)
- appendix moves to RUQ as uterus elnarges
- increased progesterone results in smooth muscle relaxation which can lead to constipation and biliary tract stasis (gall stones)
How does the urinary system adapt to pregnancy
- increased CO and vasodilation of arterioles due to progesterone leads to GFR increase by about 50-60% which activates RAAS
- this leads to increased renal excretion and levels or urea and creatinine are lower
- progestserone affects collecting system and relaxation of ureter and bladder, which causes urinary stasis and predisposes to UTIs and pyelonephritis
Describe the haematological changes in pregnancy
- increase fibrinogen and clotting factors and decrease fibrinolysis
- increase in progesterone causes venodilation and stasis of blood so VTE risk increases
- plasma volume increases due to RAAS activation but red cell mass doesnt as much so get physiological dilutional anaemia
Describe the fetal blood flow at the placenta
- umbilical arteries carry deoxygenated blood to the placenta from baby
- umbelical veins carry oxygenated blood away
- O2 moves from mum to baby as fetal blood has low pO2 so diffusion gradient + fetal hb (a+y) has higher affinity for O2 than mothers (a+b) + double bohr effect (her blood has lower CO2 due to physiological hyperventilation due to projesterone- , bohr effect, maternal hb has lower affinity for O2, O2 moves into foetal Hb
+ maternal production of 2,3 BPG due to physiological resp alkalosis means her Hb lower affinity for O2 + double haldane effect
What is normal HR for a fetus and when can it be measured?
- 120-160 BPM
- USS detects at 5-6 week
- doppler stethoscopy at 8 weeks
- normal stethoscope at 20 weeks
What is thought to initiate labour
- prostaglandins from surfactant protein A in baby, progesterone drops, fetal cortisol, cervical stretching
- prostaglandins are produced in myometrium and decidua
- cause contractions of smooth muscle and involved in cervical ripening
- oestrogen remains high when P drops, this increases gap junctions between smooth muscle cells which increases excitability
- contractions are caused by oxytocin, which is usually inhibited throughout pregancy by progesterone, high Oestrogen at end of pregnancy causes increase in oxytocin receptors
Describe the process of cervical ripening
- process where cervix goes from strong structure which keeps the fetus in to something it passes through
- reduction in collagen
- increased glycosaminoglycans
- increased hylauronic acid
- reduced aggregation of collagen
- mediated by relaxin throught pregnancy and prostaglandins at the end
Describe the grades of perineal tear
1st: skin only
2nd: involvement of perineal muscles but not sphincters
- 3rd: involvement of anal sphincters
- 4th: sphincters and rectal mucosa
What is the first stage of labour
- defined as interval between onset of labour (4cm cervix dilation and regular contractions) and full dilation (10cm) of cervix
- contractions start to push baby into birth canal
- latent phase first- slow cervical dilation and softening
- ## active phase- faster, regular contractions begin
What is the second phase of labour
- time between full dilation and delivery
- uterine contractions become expulsive, fetus descends through birth canal and is delivered
- passive stage: descent and rotation of head
- active phase: maternal effort to expel fetus and achieve birth
What is the 3rd phase of labour?
- time between completed birth and complete expulsion of placenta and membranes
- usually lasts between 5-15 mins but may be 30-60 depending on circumstance
how is blood loss limited after normal delivery?
- powerful contractions of uterus constricts blood vessels
- pressure exerted in placental site by walls of contracted uterus prevent bleeding
- blood clots