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Human Biology lecture notes about labor and the stages of labor and lactation.
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Lecture 24Labor and Lactation
B Nursing II HUB228 2022
Dept. Medical Biosciences
University of the Western Cape
, Labor
Labor = series of events that expel the fetus from the uterus
Parturition or birth = forcible expulsion of the fetus
Labor consists of three stages:
1) Dilation stage
2) Expulsion stage
3) Placental stage
• but before labor is triggered, a number of chemical events are first
initiated…
, Initiation of labor
1) Estrogen levels peak during the last weeks of pregnancy, leading
to:
- increased expression of oxytocin receptors on myometrial cells (smooth
muscle cells) of uterus
- suppression of inhibitory influence of progesterone (the levels of which
peak before parturition, inhibiting contraction of myometrial cells)
→ myometrium becomes increasingly irritable
→ weak, irregular uterine contractions called Braxton Hicks contractions (false
labor pains) occur
2) Oxytocin and prostaglandins convert false labor into true labor:
- certain fetal cells begin to produce oxytocin, which causes the placenta to
release prostaglandins
→ both hormones produce powerful, frequent uterine contractions
(myometrium “primed” to respond to oxytocin because of increased receptor
expression caused by estrogen peak)
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