Physiology of Pregnancy and Lactation Flashcards
summarise the stages of fertilisation from ovulation to implantation
fimbrae sweep ovum into oviduct, carried by smooth muscle contraction and cilia
fertilisation occurs in ampulla of fallopian tube (day 1)
cleavage, division and differentiation
morula
blastocyst containing inner cell mass (becomes fetus) and trophoblast (accomplishes implantation and develops into fetal portions of placenta)
blastocysts reaches uterus day 4-5 and implants days 5-7
how does implantation occur
cords of trophoblastic cells invade the endometrium
as they carve deeper into endometrium make hole for the blastocyst and the boundaries between the cells in the advancing trophoblastic tissue disintergrate
when implantation is finished the blastocyst is completely buried in the endometrium (day 12)
what happens to the different parts of the blastocyst
inner cells become embyro outer cells (trophoblastic cells) burrow into endometrium and become the placenta
do maternal and foetal circualtions mix
no
what tissue is the placenta derived from
both trophoblast and decidual tissue (endometrium during pregnancy)
how is the placenta formed
trophoblast cells (chorion) differentiate into mulinucleate cells (syncytiotrophoblasts) which invade decidua and break down capillaries to form cavities filled with maternal blood
developing embryo send capillaries into syncytiotrophoblast projections to form placental villi
each villus contains foetal capillaries separated from maternal blood by a thin layer of tissue (no direct contact between bloods)
what gestation is the placenta functional
week 5
what exchange occurs at placenta
2 way exchange of resp gases, nutrients, metabolites
largely down diffusion gradient
what does hCG do to the corpus luteum
signals it to continue secreting progesterone
what does progesterone do to decidual cells
stimulates them to concentrate glycogen, proteins and lipids
as the placenta develops it extends villi into the uterine wall, what does this do
increases contact area between uterus and placenta meaning more nutrients and waste materials can be exchanged
what provides the early nutrition for the embryo
corpus luteum
what is the intervillous space and what is its function
within villi mothers blood is in intervillous soace along with blood vessels from the embryo. these re separated by a thin membrane
circulation within the intervillous space acts as an arteriovenous shunt (passage between artery and vein)
what structure acts as the fetal lungs
the placenta
what is the respiratory function of the placenta
supplies O2
removes CO2
how does the placental exchange of gas happen
maternal O2 rich blood
umbilical blood is a mix of arterial and venous blood, O2 poor
O2 diffuses from maternal into foetal circulation system (PO2 maternal> PO2 fetal)
CO2 partial pressure is elevated in fetal blood, follows a reversed gradient
what happens to the blood after placental gas exchange
O2 rich fetal blood returns to fetus via umbilical vein
maternal O2 low blood flows back into the uterine veins
how does the fetus receive sufficient oxygenation
fetal Hb has increased ability to carry O2
higher Hb concentration in fetal blood (50% more than in adults)
bohr effect (fetal Hb can carry more O2 in low pCO2 than in high pCO2)
how does water cross placenta
along its osmotic gradient (exchange increases during pregnancy up to 35th week)
how do electrolytes cross placenta
follow H20
which electrolytes can only go from mother to fetus and not back
iron and Ca2+ - why anaemia common in pregnancy
how does glucose cross placenta
(fetus’ main source of energy)
passes the placenta via simplified transport
(high glucose need in 3rd trimester)
how do fatty acids cross placenta
free diffusion
what is diffusion of waste products across placenta based on
concentration gradient
what teratogenic drugs can cross the placenta
thalidomide carbamazepine coumarins tetracycline alcohol, nicotine, heroin, cocaine, caffeine
drugs (exclusing alcohol) cause 3% of all congenital malformations
what effect does hCG have
prevents involution of the corpus luteum
affect on the testes of the male fetus (development of sex organs)
when does hCG peak
8-12 weeks
what is the role of human placental lactogen
produced from week 5 of pregnancy
growth hormone like effects - protein tissue formation
decreases insulin sensitivity in mother- more glucose for the fetus
involved in breast development
what is the role of progesterone in pregnancy
development of decidual cells
decreases uterus contractility- makes uterus relax
preparation for lactation
what are the forms of oestrogen that are secreted in higher volumes as pregnancy progresses
estradiol (most secreted)
estriol
estrone
what is the role of estrogens in pregnancy
enlargement of uterus
breast development
relaxation of ligaments
what can relaxation of ligaments in pregnancy cause
pelvic girdle pain
how do hCG levels increase in a normal pregnancy
should double (or increase by >60%) every 48 hours in a singleton early pregnancy
what can hCG levels be used to help diagnose
ongoing viable pregnancy (doubling, or >60% rise) ectopic pregnancy (static or slow rising) failing pregnancy (falling)
what are the side effects of hCG
nausea and vomiting
what can cause high levels of hCG
multiple pregnancy
molar pregnancy
when do hCG levels start to fall
from 12-14 weeks
what does placental release of CRH (corticotrophin releasing hormone) cause
ACTH release in mother increase aldosterone (=hypertension) and cortisol (= oedema and insulin resistance = gestational diabetes)
what does HCG (HC thryotropin) released from the placenta cause
hyperthyroidism in the mother
what does increased Ca2+ demands of the placenta cause
hyperparathyroidism in the mother
what happens to cardiac output in pregnancy
is increased by 30-50% (begins 6wk gestation and peaks at 24 wks) due to demands of the uteroplacental circulation
decreases in last 8 weeks (becomes sensitive to body position, uterus compresses vena cava)
increases 30% more during labour
what causes the cardiac output to increase in pregnancy
placental circulation
increased metabolism
skin thermoregulation
renal circulation
what can the increase CO cause in pregnant mothers
ECG changes functional murmurs (usually mild systolic and normal but always investigate) heart sounds
what happens in HR in pregnancy
increases with to 90/min to increase cardiac output
what happens to BP in pregnancy
drops during 2nd trimester (uteroplacental circulation expands and peripheral resistance decreases - vasodilation)
with multiple pregancies cardiac output increases more and BP drops lower
lowest at 17-24 wks, rises after this back to normal (36wks) then can go higher than BP before pregnancy
what haematologic changes happen in pregnancy
plasma volume increases proportionally with cardiac output (50%)
erythropoesis (RBC) increases (25%)
Hb is decreases by dilution (this decreases blood viscosity)
iron requirements increase significantly (6-7 mg/ day in 2nd trim)- supplements usually needed
why lung changes happen in pregnancy
increase in progesterone (signals brain to lower CO2 levels)
enlarging uterus interferes with lung function - works to lower CO2
how does progesterone lower CO2 levels
increases CO2 sensitivity in respiratory centres of brain
what happens in O2 consumption in pregnancy
increases to meet metabolic needs of fetus, placenta and mother (20% above normal)
how is CO2 physically reduced in pregnancy
RR increases
tidal and minute volume increases (50%)
pCO2 decreases slightly
vital capacity and PO2 dont change
what happens to the urinary system in pregnancy
GFR and renal plasma flow increase (up to 30-50%, peaks at 16-24 wks)
increased re-absorption of ions and water (due to placental steroids and aldosterone)
slight increase in urine formation
how do postural changes affect renal function
when in:
up right position renal function decreased
supine position increased
lateral position during sleep increased significantly
what is pre-eclampsia
pregnancy induced hypertension and proteinuria
what are the features of pre-eclampsia
increasing BP since 20th week- hypertension
kidney function declines causing salt and water retention- oedema of face and hands
renal blood flow and GFR decreases
what causes pre eclampsia
?extensive secretion of placental hormones
?immune response to fetus
insufficient blood supply to placenta- ischaemia
who is pre-eclampsia more common in
women with pre existing hypertension, diabetes, autoimmune disease (e.g. lupus), renal disease, FHx of pre-eclampsia, obesity, multiple gestations (twins)
what is eclampsia
extreme pre-eclampsia (lethal without Tx)
vascular spasms, extreme hypertension, chronic seizures and coma
what is the treatment for eclampsia
vasodilation and cesarean section
what is the average maternal weight gain (and what causes it )
11 kg
- fetus (3.5 kg)
- extra-embryonic fluid/ tissues (2 kg)
- uterus (1 kg)
- breasts (1 kg)
- body fluid (2.5 kg)
- fat accumulation (1 kg)
how much extra food is needed in pregnancy
200 extra calories/ day
30g/ day or protein
end of pregnancy fetus needs 5mg/kg/min of glucose= 2.5mg/kg/min for mother
what causes the increased metabolic demand in pregnancy
85% fetal metabolism
15% stored as maternal fat
what are the 2 metabolic phases of pregnancy
1st-20th week= mothers’ anabolic phase:
- anabolic metabolism of mother
- small nutritional demands of the conceptus
21st-40th week (esp last trim) catabolic stage
- high metabolic demands of fetus
- accelerated starvation of mother
why should starvation of mother be avoided in pregnancy
as circulating ketones bad for babies brain
what happens physiologically in the anabolic phase of pregnancy
- normal/ increased sensitivity to insulin
- lower plasmatic glucose level
- lipogenesis, glycogen stores increase
- growth of breasts, uterus, weight gain
what happens physiologically in the catabolic phase of pregnancy (accelerated starvation)
- maternal insulin resistance
- increased transport of nutrients through placental membrane
- lipolysis
what causes insulin resistance in pregnancy
HPL, cortisol and growth hormone
what are the special nutritional needs in pregnancy
folic acid- reduces risk of neural tube defects, ideally taken before conception
vit D supplements (esp if mother overweight)
high protein diet (higher energy intake)
iron supplements may be required
B vitamins for erythropoesis
towards the end of pregnancy the uterus progressively becomes more excitable- what does this mean
it becomes more contractile
progesterone inhibits contractility of uterus while oestrogen increases it
how does the uterus become more excitable during end of pregnancy
estrogen: progesterone ratio changes
progesterone inhibits contractility of uterus while oestrogen increases it
oxytocin (from maternal posterior pituitary gland) increases contractions and excitability
mechanical stretch of uterine muscles and cervix by fetal head increases contractility
where is oxytocin release from
fetus
mothers posterior pituitary
what controls the timing of labour
oxytocin
adrenal glands
prostaglandins
what are braton hicks contractions
infrequent, irregular contractions that involve only mild cramping- preparing for birth, false labour
become more frequent and stronger then labour pains begin
what does cervical stretching cause the release of
oxytocin
what do strong uterine contractions and pain from the birth canal cause
neurogenic reflexes from spinal cord that induce intense abdominal muscle contractions
what is parturition
initiation of labour
what hormone induces oxytocin receptors on uterus
estrogen
what does oxytocin cause
uterine contractions
stimulates placenta to make prostaglandins
what do prostaglandins cause
more vigorous contractions of uterus
what is full dilation
10 cm
what can induce labour
vaginal prostaglandins and oxytocin injection
intracervical ballon/ sweep- mechanical stretch
what are contractions like in late labour
strong, 3-4 every 10 minutes
what are the stages of labour
1st- cervical dilation (8-24 hours)
2nd- passage through birth canal (few mins to 120 mins)
3rd- expulsion of placenta
how does estrogen affect production and release of milk
stimulates growth of ductile system
inhibit milk production
how does progesterone affect production and release of milk
development of lobule-alveolar system
inhibit milk production
how does prolactin affect production and release of milk
stimulates milk production steady rise in weeks 5-birth)
1-7 days after birth prolactin induces high milk production
stimulates colostrum (low volume, not fat- high in protein and immunoglobulins for fetal immunity)
what is the milk let down reflex
suckling stimulus (mechanoreceptors in nipple) or the sound of a childs cry causes release of prolactin (makes more milk) and oxytocin (causes breast to push out milk via smooth muscle contraction)
