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Practical Audio
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BGD Cycle A 2010 Audio - Dr Mark Hill Monday 17th May 2010 3-5pm G2G4.
- Note - this is a live unedited recording from the practical and may contain errors in either descriptions or content.
listen Part 6 | download (2.13 Mb MP3 18:36)
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Hormones
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Roles
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Progesterone
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- maintains pregnancy - initially synthesized by corpus luteum, then levels maintained by placenta
- hyperpolarizes myometrial cells (-65 mV), reduces excitability and conductivity
- Level in plasma may fall just before parturition, definitely decreases following delivery of placenta
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Estrogens
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- Group of steroidal hormones, peak when parturition begins
- induce increased synthesis of actomyosin and ATP in myometrial cells
- alter membrane potential (-50 Mv) enhances excitation/conduction
- act to directly increase myometrial contraction
- indirectly by increasing oxytocin from pituitary gland
- Estriol - synthesized by fetus and placenta
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Oxytocin
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- Peptide hormone (8aa) from maternal posterior pituitary, initiation and maintenance of labour (synthetic form labour induction)
- myometrium sensitivity to oxytocin (increased by estrogen, decreased by progesterone)
- stimulus for release - mechanical stimulation of uterus, cervix and vagina (ethanol inhibits release)
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Prostaglandins
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- hydroxy fatty acids - sythesized by placenta, amniotic fliud contains mainly PGF2 alpha, causes myometrial contraction (also in maternal plasma)
- prostaglandin F2 alpha (PGF2 alpha) and prostaglandin E2 (PGE2) - used to induce labour (intravenous, oral, intravaginal, intraamniotic)
- Aspirin inhibitor of PG synthesis - leads to increased duration of pregnancy
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Endocrine
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Birth
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Labour Stages
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Changes
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Time
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Roles
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Stage 1
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Dilatation
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7 to 12 hours longer for first child
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Uterine contractions 10 minutes apart, function to dilate cervix fetal membranes rupture releasing amnion.
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Stage 2
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Expulsion
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20 to 50 minutes
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Uterine contractions 2 to 3 minutes apart, function to push fetus through cervix and vagina.
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Stage 3
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Placental
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15 minutes
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Uterine contractions following child delivery expel placenta. Haematoma separates placenta from uterine wall, separation occurs at spongy layer of decidua basalis.
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Stage 4
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Recovery
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2+ hours
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Uterine contractions continue and myometrial contraction closes spiral arteries, also begins to reduce uterine volume.
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Labour Stages
Labour Stages
|
Changes
|
Time
|
Roles
|
Stage 1
|
dilatation
|
7 to 12 hours longer for first child
|
uterine contractions 10 minutes apart, function to dilate cervix fetal membranes rupture releasing amnion
|
Stage 2
|
expulsion
|
20 to 50 minutes
|
uterine contractions push fetus through cervix and vagina, contractions 2-3 minutes apart
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Stage 3
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placental
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15 minutes
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following child delivery contractions continue to expel placenta. haematoma separates placenta from uterine wall, separation occurs at spongy layer of decidua basalis
|
Stage 4
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recovery
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2+ hours
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continued myometrial contraction closes spiral arteries
|
Hormones
|
Roles
|
Progesterone
|
- maintains pregnancy - initially synthesized by corpus luteum, then levels maintained by placenta
- hyperpolarizes myometrial cells (-65 mV), reduces excitability and conductivity
- Level in plasma may fall just before parturition, definitely decreases following delivery of placenta
|
Estrogens
|
- Group of steroidal hormones, peak when parturition begins
- induce increased synthesis of actomyosin and ATP in myometrial cells
- alter membrane potential (-50 Mv) enhances excitation/conduction
- act to directly increase myometrial contraction
- indirectly by increasing oxytocin from pituitary gland
- Estriol - synthesized by fetus and placenta
|
Oxytocin
|
- Peptide hormone (8aa) from maternal posterior pituitary, initiation and maintenance of labour (synthetic form labour induction)
- myometrium sensitivity to oxytocin (increased by estrogen, decreased by progesterone)
- stimulus for release - mechanical stimulation of uterus, cervix and vagina (ethanol inhibits release)
|
Prostaglandins
|
- hydroxy fatty acids - sythesized by placenta, amniotic fliud contains mainly PGF2 alpha, causes myometrial contraction (also in maternal plasma)
- prostaglandin F2 alpha (PGF2 alpha) and prostaglandin E2 (PGE2) - used to induce labour (intravenous, oral, intravaginal, intraamniotic)
- Aspirin inhibitor of PG synthesis - leads to increased duration of pregnancy
|
Endocrine Development
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External Environment
- mainly shown in other species parturition occurs in peaceful undisturbed surroundings, stress may have an inhibitory effect on oxytocin release
- Most human births occur at night (peak at 3am) diurnal rhythm influence