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Mechanism of action of oxytocin
Gq receptors - increase contractility of uterine myometrium (increased amplitude/frequency)
Supplemented by prostaglandins - contraction (Via PLC) or relaxation (via cAMP)
Estrogen sensitizes the myometrium to oxytocin - increases gap junctions and number of receptors
Two theories of initiation of birthing
Increased estrogen/progesterone ratio
Increased levels of CRH
Changes in uterine structure before birthing
Two distinct sections (upper muscular section - for propulsion; lower thinner section - allows for ripening of cervix and vagina)
Increased number of oxytocin receptors
First stage of labor
Begins when uterine contractions are of sufficient freq, intensity and duration
Latent phase: rate of cervical dilation is slow (up to 3cm)
Active phase: rate of dilation is about 1cm/hr
Second stage of labor
Begins when dilation reaches 10cm.
Fetal head begins descent (Friedman curve - fetal head in relation to ischial spine to assess progress of labor)
Third stage of labor
Interval between delivery of the fetus and delivery of the placenta
During this stage the placenta separates and is expelled
Typically takes 5-30 minutes
Causes bleeding - but limited by continued uterine contractions (vasoconstriction/vasospasm)
Physiology of dystocia
Abnormally slow labor
Can be cause by: uterus, size of the fetus, positioning of the fetus and excess sedation/anesthesia
Cephalicopelvic disproportion - head is too big to fit through birth canal
Breast milk is good because:
- It is suitable for digestion by immature GIT
- Provides optimal water/electrolytes
- Immunological protection
- Contains hormones (vitamin D, TRH, GnRH, etc)
Major hormones associated with lactation
- Estrogens, (progesterone, prolactin, hCS, cortisol, insulin, GH, and others)
- Epithelial tissues expand and become activated
- Estrogen and prolactin leads to deposition of fat tissues
Milk production inhibition in pregnancy
- High levels of estrogen (inhibits terminal differentiation) and progesterone (inhibits lactogenesis)
- After birth, both drop dramatically
Prolactin and lactation
- Suckling inhibits DA and stimulates prolactin releasing factor
- Therefore, suckling creates a prolactin spike
- Needs multiple w/in 24-hours to sustain milk production
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