Repro Session 10 Flashcards
Term given to expulsion of products of conception before 24 wks of gestation?
spontaneous abortion
what is premature/pre-term labour?
labour (expulsion of conception products after 24 wks of gestation) occurring before 37th wk of gestation
3 processes expulsion of fetus requires? (3 stages of labour)
creation of birth canal- release of structures which normally retain fetus in utero, and enlargement and realignment of cervix and vagina
expulsion of fetus
expulsion of placenta and changes to minimise blood loss from mother
when does uterus 1st become palpable?
around 12 wks of gestation
when does uterus reach level of umbilicus?
by 20 wks gestation
when does uterus reach xiphisternum?
by 36 wks gestation
boundaries of pelvic inlet?
poster: sacral promontory
laterl: ilio-pectinal line
anter: superior pubic rami and upper margin of PS
commonest lie of fetus?
longitudinally
how is cervical dilatation produced?
forceful contractions of uterine smooth muscle- 1st thin cervix and then dilate it
describe cervical ripening which facilitates cervical dilatation
marked reduction in collagen and increase in GAGs which decreases aggregation of collagen fibres. Keratin sulfate (GAG) increases at expense of dermaton sulfate, so collagen bundles loosen. Also inflammatory cell influx and increase in NO output.
All changes triggered by PGs-E2 and F2x
which 2 hormones cause sudden increase in frequency and force of uterine contractions at labour onset, and how do they work?
PGs and oxytocin
PGs: enhance release of Ca2+ from IC stores
Oxytocin: lowers threshold for triggering APs
how is PG synthesis increased in endometrium?
fall in progesterone or rise in oestrogen, which alters release of phospholipase from liposomes
PG release may also be stimulated by oxytocin
how are uterine smooth muscle cells made more sensitive to oxytocin?
by fall in progesterone levels relative to oestrogen which increases the receptor pop.
how does +ve feedback occur to make uterine contractions more forceful and frequent?
sensory receptors in cervix and vagina are stimulated by contractions, and excitation passes via afferent nerves to hypothalamus to promote massive oxytocin release
what is brachystasis?
property of uterine smooth muscle that means at each contraction, muscle fibres shorten but do not relax fully, so uterus, partic. fundal part, shortens progressively, which pushes presenting part into birth canal and stretches cervix over it
how is progress in labour plotted?
graphically on a partogram
what occurs in the first stage of labour?
creation of birth canal- max size determined by pelvis
what determines max size of birth canal?
pelvis- size of pelvic inlet may be increased by softening of ligaments
normal size of pelvic inlet?
11 cm
typical diameter of presentaion?
9.5cm
2 requirements for birth canal formation?
structural changes: will enable expansion to take place, =cervical ripening
lot of force: uterine smooth muscle contractions will actually produce birth canal through dilatation of cervix
uterine smooth muscle contractions cause what before dilating the cervix?
effacement= thinning of cervix
PGs causing cervical ripening= structural changes where cervix softened in order to allow dilatation mediated by contractions to form birth canal?
E2 and F2x
what is the Ferguson reflex?
+ve feedback mechanism in which strong uterine contractions mediates increased oxytocin secretion which further stimulates smooth muscle contraction. Contractions stimulate sensory receptors in cervix and vagina, afferent nerves transmit excitation back to hypothalamus, and this promotes massive oxytocin release causing more frequent and forceful myometrial contractions