Uterine Motility Flashcards
what are the three layers of the uterus
- perimetric (serosa)
- myometrium (thick muscle)
- endometrium (glandular layer)
what do uterine contractions depend on
gap jun actions for phasic propagation of depolarisation (connexion 43)
• Minimal influence of autonomic innervation on contractions under physiological conditions.
what are gap junctions
Membrane proteins form a tunnel between cells (called connexons) and this allows cells to communicate with each other, share nutrients and transfer chemical and electrical signals
what is the structure of the connexins that make up the gap junctions
each has 6 connexins that form a hemichannel, and each hemichannel is specific to another hemi channel that it will connect to
where are gap junctions found
- in cells/tissue that spread action potential
cardiac muscles
nervous tissue in the brain
gap junctions in caridac muscle
– Constitutively expressed.
– Arranged in intercalated discs.
– Depolarisation starts from the sinoatrial (SA) node (pacemaker).
gap junctions in uterine smooth muscle
– Inducible (especially hormonally).
– Fundal dominance during labour – May arise from anatomical
arrangement of expressed gap junctions.
the sympathetic outflow effect in the uterus depends on what
receptor type:
– a-adrenoceptors - contraction.
– b-adrenoceptors - relaxation.
• Ratio of sympathetic receptor types influenced by hormonal status.
what produces ADH and Oxytocin
the hypothalamus, the posterior pituitary secretes these into the blood stream
why can ADH act on uterine muscle
because they are both 9 amino acid peptides, 2 amino acids which are different which means they have a very similar structure
what effects oxytocin receptor numbers
sex hormone levels
at term what happens in the uterus
– Falling placental progesterone with sustained oestrogen levels.
– Stimulates prostaglandin biosynthesis.
– Oxytocin receptor expression.
whaat is the role of oxytocin in contractions
- Uterine smooth muscle sensitive prior onset of labour.
- Stimulates increasingly regular, co-ordinated contractions that travel from the fundus to the cervix (fundal dominance).
- Uterus relaxes completely between contractions
• Uterine stimulants (oxytocics).
– Induce abortion / miscarriage
– Induce and accelerate labour.
– Contract the uterus after delivery to control postpartum haemorrhage (PPH).
• Uterine relaxants (tocolytics).
– Delay or treat preterm labour.
– Facilitate obstetric manoeuvres.
– Counteract (iatrogenic) uterine hyperstimulation.
– Treat menstrual cramps/dysmenorrhoea
what makes up oxytocics
– Oxytocin.
• IV infusion to induce or accelerate labour.
• IV or IM injection after delivery to control postpartum
haemorrhage (PPH).
– Ergometrine.
– E & F series prostaglandins.
Ergometrine
• Ergometrine found to be the component responsible for the actions on the uterus.
chemical original form a rye fungus
Still useful for bleeding related to early pregnancy complications such as miscarriage (oxytocin is not effective).
• Causes sustained powerful uterine contractions.
• Largely obsolete for postpartum haemorrhage (PPH) prophylaxis owing to stability, inadvisability in the presence of hypertension (vasoconstriction), adverse effect of nausea/vomiting.
• Syntometrine is the combination of oxytocin and ergometrine for the third stage of labour
Menstrual symptoms - Dysmenorrhoea (painful periods) and menorrhagia (excessive blood loss)
prostaglandins may play a role.
– Imbalance of prostaglandin E vs prostaglandin F in endometrium.
Nonsteroidalanti-inflammatorydrugs(NSAIDs)are effective for
pain relief, unclear whether via uterine relaxation or central analgesic effect.
– Ibruprofen, naproxen, mefenamic acid.
- Reduce menstrual blood loss
- More effective if combined with (Antifibrinolytics, i.e. tranexamic acid).
