B8.016 Physiology of the Pregnancy Flashcards
goal of cyclicity within HPG axis?
- prepare a fertilizable oocyte
- establish a uterine environment that promotes:
- gamete movement (primarily via estrogen)
- implantation (progesterone)
when is the oocyte viable
18 hr following ovulation
what occurs to stimulate luteolysis?
decreased sensitivity to LH
loss of blood start
decreased P4 and E2
leads to apoptosis
describe the movement of the conceptus
resides in oviduct/fallopian tube for 3 days
resides within uterus for 3 days prior to attachment of blastocyst to uterine wall
when does implantation occur
day 6-7
follicular phase overview
estrogen predominates
gland mitosis
endometrial sensitization
luteal phase overview
progesterone dominates and causes changes in the endometrial stroma
what is pre-decidualization
p4 dependent transformation of the cells
uterine secretions help nourish the blastocyst since it is in an avascular environment
decidualization
further differentiation of the endometrium which is associated with implantation
roles of decidualization
- controls invasion
- nutrition
- prevents immune rejection
- Prolactin secretion
estrogen function on uterus
proliferation
myometrium (gamete movement)
estrogen function on other sites in the body
vagina/cervix (mucous)
liver (increased binding protein production)
water retention
anabolic
progesterone function on uterus
development of glands and vasculature
myometrium
decidua cells
progesterone function on other sites
vagina/cervix (mucous)
catabolic
for how long is the blastocyst in a hypoxic environment?
first 12 weeks
small amount of blood surrounding the blastocyst, but not highly oxygenated yet
communication from lacunae filled with maternal blood
where is fetal circulation located at the invasion site?
within the villous tree
where is the maternal circulation located at the invasion site
intervillous space
what comprises the fetal circulation?
umbilical vein carried oxygenated blood to the fetus
umbilical artery carries deoxygenated blood to the placenta
function of syncytiotrophoblast layer
transport of nutrients
endocrine- production of CG, and PL
immune barrier
functional components of the placenta
- cytotrophoblasts: stem cells which fuse to generate a multinucleated layer of cells
- anchoring villous, columns of cytotrophoblasts
- invasive cytotrophoblasts
- syncytiotrophoblasts
function of invasive cytotrophoblasts
tap into maternal vasculature (spiral arteries) after week 12 of gestation
decidua help in controlling depth of invasion
function of anchoring villi
cytotrophoblasts replace the maternal endothelium and degrade the surrounding smooth muscle (decreased vascular resistance)
how do cytotrophoblasts remodel spiral arteries?
surround arteries
increase volume and decrease vascular resistance
what types of substances are transported across the placenta/trophoblast barrier?
O2
CO2
nutrients
waste
why is CG produced by syncytiotrophoblasts?
prevents mother from beginning another menstrual cycle
in maternal serum 7-9 days following surge of LH
binds to LH receptors and stimulates P4 production from corpus luteum (rescues)
**establishment and maintenance of pregnancy
CG half life
hours to days
highly glycosylated
how does progesterone impact gonadotropes
suppresses LH secretion
first 6-8 weeks of gestation are relatively independent of gonadotropin support from the pituitary
placental lactogen
produced by placenta/trophoblast
starts low and correlates to size of placenta
levels of pituitary GH (GH1) during pregnancy
decrease steadily over 20 weeks, and then flatline at almost 0 for remainder
levels of placental GH (GH2) during pregnancy
rise exponentially from 5 weeks to a peak at 35 weeks and then drop slightly
levels of IGF1 during pregnancy
rise from 25-35 weeks
drop slightly after 35 week mark
where does placental steroidogenesis take place
Syncytiotrophoblasts
takes over for ovary at around 8 weeks as the primary P4 producer
what enzymes does the placenta lack?
- cholesterol synthesis enzymes
- requires maternal cholesterol transported in - 17-alphaOH and 17-20 desmolase
- no androgen production (transports P4 out to the mother and fetus for conversion to DHEA)
what enzymes does the placenta have?
- 3beta-HSD
- converts pregnenolone to P4 - aromatase
- converts androgens to estrogens
- DHEA-S to E1 and E2
- 16OHDHEAS to E3
what metabolism is controlled by the fetal adrenal?
conversion of pregnenolone to DHEAS
what metabolism is controlled by the fetal liver?
conversion of DHEAS to 16OH DHEAS
list all placental hormones and their origins
P4: maternal cholesterol
E2 & E1: maternal and fetal DHEA-S
E3: fetal (only) 16-OH DHEAS
estrogen potency
estradiol > estrone > estriol
why is P4 particularly important in pregnancy?
suppresses uterine contractility
antagonizes estrogen actions
why is DHEA sulfated in the fetal adrenal?
inactivates it within the fetus so the fetus is not exposed to high levels of androgens during gestation
cortisol levels in fetal development
low prior to 30 wk of gestation
placental enzymes
sulfatase: removes sulfate from fetal DHEA
3BHSD: makes P4
aromatase: E1, E2
17BHSD: E3
hormonal control of myometrial contraction for labor
labor requires organized contractions (electrical activity) within the myometrium; this is achieved via gap junctions
-inhibited by P4, stimulated by estrogens
hormonal control of cervical maturation
collagen breakdown
-inhibited by P4, stimulated by E, relaxin, PGE2
relaxin
secreted by CL/decidua/placenta: inhibits myometrial contractility
induces collagenase activity, softens pelvic joints and the cervix canal (prep for birth)
estrogens in labor and delivery
stimulates uterine contractions (gap junctions)
stimulates PGF2a synthesis
induces expression of oxytocin receptors (increased response)
prostaglandins in labor and delivery
PGI2- vasodilator
PGF2a- stimulates cervix softening and uterine contractions
oxytocin in labor
stimulates uterine contractions
constricts blood vessels
regulated by a neuroendocrine reflex loop
most prominent stimuli leading to release of oxytocin
- suckling
2. uterine contractions in parturition
oxytocin Ferguson reflex positive feedback loop
CNS > supraoptic/paraventricular nuclei > posterior pituitary > oxytocin > uterus > contractions > stretch > back to hypothalamic nuclei
2 main functions of oxytocin
- stimulate myoepithelial cells surrounding alveoli of the mammary glands (promotes milk let down)
- stimulate myometrial contractility (labor)
development of mammary glads in pregnancy
development during pregnancy, regulated by hormones produces during pregnancy
estrogen function on mammary gland
duct growth
fat deposition
INHIBITS milk synthesis
progesterone function on mammary gland
growth of the alveolar epithelium
INHIBITS milk synthesis
insulin function on mammary gland
gland growth and development
glucocorticoid function on mammary gland
gland growth and development
milk protein synthesis
Prolactin, GH, PL function on mammary gland
gland growth
milk synthesis
oxytocin function on mammary gland
contraction of myoepithelial cells (secretion)
hormone control of mammary glands during parturition
fall in P4 and E (placenta is gone), maintenance of prolactin secretion
removes the block P4 and E have on milk synthesis
hormone control of mammary glands during lactation
prolactin stimulates milk secretion and lipase activity
oxytocin propels milk through the ducts to the nipples
why does prolactin cause amenorrhea?
inhibits GnRH, thus suppresses the HPG axis
what causes hyperprolactinemia
usually associated with a pituitary tumor
-often effectively treated with a dopamine agonist
hypothalamic control of prolactin secretion
usually tonically inhibited
dopamine seems to be the main player in this inhibitory control
oxytocin suckling positive feedback loop
CNS > supraoptic/paraventricular nuclei > posterior pituitary > oxytocin > mammary glands > milk let down > suckling > back to CNS
