Endo-Repro L29 Flashcards
1st stage
Onset of regular uterine activity associated with effacement and dilation of the cervix, and descent of the presenting part. The latent phase of labour is from the onset of contractions until the cervix is fully effaced and the active phase is when the fully effaced cervix dilates.
→7-14 hours
2nd stage
Full dilation of the cervix to delivery time of the baby. Subdivided into the propulsive phase (when the head descends to the pelvic floor) and the expulsive phase (when the mother experiences a desire to push until the baby is delivered)
→1-3 hours
3rd stage
After delivery of the baby until the delivery of the Cervical ripening factors controlling:
placenta
→30 min, Contractions, tonic
Duration of pregnancy →
38-40 weeks
Duration of Labour →
→ 8-16 hours (reg. contractions every 5 mins)
Cervical ripening factors controlling:
- Prostaglandins
- Oestradiol
- Progesterone and antiprogesterone
- Relaxin
- Inflammatory mediators
- Nitric Oxide
- Apoptosis
Hormonal control of Labour →
- Progesterone
- Oestrogens
- Oxytocin
- Prostaglandins
- Fetal adrenal glands
Initiation of Labour →
Unknown → oxytocin • Prostaglandins • Growth Factors • Cytokines • Endothelins • Gap junction formation • Placental corticotrophin – releasing hormone • Nitric Oxide withdrawal
Role of fetus in Labour →
- Fetal adrenal glands, fetal cortisol.
2. Increase in the ratio of oestradiol to progesterone stimulates.
Progesterone
Is an anti-inflammatory agent, labour is inflammatory process. It inhibitis human myometrial contractions and decreases gap junction formation.
Exogenous progesterone
Does not postpone the onset of parturition at term.
Anti-progesterone
Activate many of the pathways involved in the onset of labour and induce uterine contractility and cervical ripening.
Suggests role in maintenance of pregnancy
- Hyperpolarises myometrial cells inhibits contractions
- Reduces oxytocin sensitivity
- Stabilises decidua and membranes (stops PG formation)
- Decreases gap junction formation.
Role in late pregnancy in initiation of labour
- Uncoupling of action (local metabolism of progesterone, progesterone inactivation by specific binding protein, by endogenous anti-progesterone, or by a change in number or affinity of progesterone receptors)
- Decline in progesterone sensitivity
- No fall in concentration
CRH is
A peptide hormone, hpothalalmic releasing factor, secreted by placental trophoblasts.
Maternal plasma CRH during pregnancy
Rise
Elevated CRH levels associated with
Preterm labour
CRH present are present in
Myometrium and fetal membranes
CRH is secreted by
Placenta trophoblasts
Three weeks before the onset of spontaneous labour
- Rise in plasma CRH concentrations
2. Abrupt fall in CRH-BP (blocks bio-availability of CRH) concentrations in the maternal circulation and amniotic fluid.
CRH action
- Stimulates the release of prostaglandins from human amnion and deciduas
- Potentiate the action of oxytocin (stimulating myometrial contractions)
- Potentiate the actions of prostaglandins
- Induces synthesis of prostaglandins and glucocorticoids
Induced synthesis of prostaglandins and glucocorticoids stimulates
Placental CRH secretion → positive feedback loop
Oestrogen and progesterone
- Synergises to stimulate uterine growth
* Oestrogens oppose the progesterone block on uterine contractions
Actions
Increase uterine contractions
• Increase actinomyosin and glycogen in myometrium
• Depolarises myometrial cells
• Increase gap junctions
• Increase oxytocin sensitivity (receptors)
• Destabilise decidua and membranes (prostaglandin formation)
Oxytocin and Labour Released from
The magnocellular neurosecretory neurones projecting directly to the posterior pituitary
Oxytocin and Labour Function
Potent stimulated of myometrium (if estrogen primed)
Oxytocin and Labour Stimulation
Dilation of cervix by fetal head
Oxytocin and Labour Levels
Rise in 1st and 2nd stage
Reduce in 3rd
Prostaglandins
Description
Local tissue hormones – rapidly destroyed in the circulation.
Prostaglandins Function
Powerful contractors of smooth muscle
Prostaglandins Control of PG synthesis
Via phospholipase from lysosomes
What liberates phospholipase
Increase in oestrogen: progesterone ratio and mechanical damage liberate phospholipase.
Levels in pregnancy of PGs
Rise in early labour
Can promote labour at any stage
PGs Mainly produced in
Endometrium but can be also in myometrium
Control of PG synthesis during labour
Oestrogen (increased) and progesterone (reduced) and mechanical disruption leads to conversion of phospholipids to arachadonic acid and then converted to PGE and PGF
→ Phosphoslipase and PG synthetase
Artificial induction of labour →
- Prostaglandins → ripen cervix
- Artificial rupture of membranes → Increases PG and puts head onto cervix
- Syntocinon → womb contraction
Main stimulation of breast tissue →
- Oestrogen (duct system) and progesterone (secretory system).
- Prolactin and GH and hPL from placenta contribute.
Initiation of secretion inhibition of mammary gland
Oestrogens
Progesterone
Stimulator of secretion from mammary glands
Prolactin (and hPL)
Maintenance of secretion from mammary gland
Prolactin released during sucking
• Sucking stimulus inhibits release of dopamine from hypothalamus
• Lactotrophs are free of dopamine inhibition and release prolactin
• Complete emptying of mammary gland
Control of milk removal:
Proper attachment
Active milk-ejection reflex
Suckling causes oestrogen release during suckling, acts on myoepithelial cells
Can be conditioned e.g. sound of baby
