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30THE TIMING OF BIRTH - induce production of enzymes in the...

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THE TIMING OF BIRTH Scientific American March 1999 p 68-75 Partuition: uterine and cervical changes that make labor possible. Happens in the last 2 weeks of pregnancy (gestation) During gestation – Uterus is a “relaxed bag of disconnected smooth muscle” maintained by progesterone (estrogen opposes progesterone in promoting contractility) Partuition occurs when estrogen levels (among several other forces like weight on cervix) override the blocking by progesterone Increased estrogen leads to: the myometrium synthesizing connexin that electrically (within cell membranes) links the cells allowing for co-ordinated contractions. an increase in oxytocin receptors in the myometrium. increased manufacture of prostaglandins by the placenta overlying the cervix. These in turn
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Unformatted text preview: induce production of enzymes in the cervix that digest collagen (allowing for dilation). Increased cortisol (made by fetal adrenal gland) matures infant’s lungs (production of surfactants) In humans, corticotropin releasing hormone (CRH) made in the placenta (placental clock) causes the pituitary to secrete adrenocorticotropin (ACTH) into the fetal circulation. Values of maternal CRH in the 16-20 th weeks can predict delivery dates. Early increases lead to premature birth. ACTH causes the adrenals to produce cortisol which activates the placental enzymes to convert DHEA-S (dihydroxyepiandrosterone sulfate) into estrogen. Increased estrogen levels (and decreasing progesterone) from this process contribute to the actions mentioned above....
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