Uterine Motility Flashcards
Describe the layers of the uterus
- perimetrium: serosa of single outer layer of epithelium
- myometrium: thick middle layer of smooth muscle
- endometrium: inner layer with glands, blood vessels, lymphatics and epithelial cells
- thickens and becomes decidua in pregnancy
Summarise the influences of uterine motility
- contractions depend on gap junctions (connexin 43) between muscle fibre cells allowing communication of signals and transfer of nutrients
- hormonally influenced by menstrual cycle, pregnancy and labour
- minimal influence of autonomic innervation of contractions under physiological conditions
Describe the structure of the connexins
- proteins that make up gap junctions
- 6 connexins form hemi-channel (each cell has hemi channel that join with each other to form full gap junction)
- each hemi channel is specific to another hemi-channel (the one it connects to)
Describe features of the gap junctions in the uterine smooth muscle
- inducible (esp hormonally)
- fundal dominance during labour
- may arise from anatomical arrangement of expressed gap junctions
Describe the innervation of the uterus
- sympathetic, parasympathetic and sensory
- innervation only of vascular smooth muscle and myometrium
- sympathetic outflow depends on receptor (a-adrenoreceptor = contraction, b-adrenoreceptor = relaxation)
- ratio of sympathetic receptor type depends on hormonal status
Describe the effect of oxytocin on the uterus
- uterine smooth muscle sensitive prior to onset of labour
- stimulates increasingly regular, coordinated contractions that travel from fundus to cervix
- uterus relaxes completely between contractions
What are the uses for uterine stimulants (oxytocics)?
- induce abortion/miscarriage
- induce and accelerate labour (IV infusion oxytocin)
- contract the uterus after delivery to control post partum haemorrhage (IV/IM injection oxytocin after delivery)
What are the uses for uterine relaxants (tocolytics)?
- delay or treat pre-term labour
- facilitate obstetric manoeuvres
- counteract (iatrogenic) uterine hyperstimulation
- treat menstrual cramps (dysmenorrhoea)
What are oxytocics and name the types?
- drugs that stimulate uterine contractions
Made up of:
- oxytocin
- ergometrine (vasoconstrictor)
- E and F series prostaglandins
Describe the uses of ergometrine in practice
- bleeding related to early pregnancy complications such as miscarriage (oxytocin not useful)
- causes sustained powerful uterine contractions
- post partum haemorrhage prophylaxis
- syntometrine is combo of oxytocin and ergometrine for third stage of labour
Describe the types of prostaglandins
- prostaglandin F2a generated in large amounts by endo/myometrium
- prostaglandin I2 and E2 occur naturally
- F series is more vasoconstrictor
- E series more vasodilator
(F and E both act on cervical ripening and induce oxytocin receptors)
Name the different prostaglandin drugs and the types of prostaglandin they are
- dinoprostone (prostaglandin E2, naturally occuring)
- carboprost (synthetic analogue of F2a)
- gemeprost (synthetic analogue of E1)
- misoprostol (synthetic of E1)
What are the therapeutic uses of misoprostol?
- treatment/prevention of peptic ulcers
- medical abortion (mifepristone given then misoprostol)
- induction of labour
- control of PPH (secondary to uterine atony)
What drugs are under uterine relaxants (tocolytics), its mechanism of action and examples?
- B2 agonists (ritodrine, terbutaline, salbutamol): increase cAMP
- CCBs (nifedipine, magnesium sulphate): prevent intracellular increase in calcium in smooth muscle
- NSAIDs (indomethacin): inhibit prostaglandin synthesis
- oxytocin receptor antagonist (atosiban)
- nitrates: NO donors
What causes dysmenorrhoea and menorrhagia (excessive blood loss), and its treatment?
- imbalance of prostaglandin E and F in endometrium
- NSAIDs treatment (ibuprofen, naproxen etc): either uterine relaxation or central analgesic effect
