Uterine Motility

Question 1

what are the three layers of the uterus

Answer 1

• perimetric (serosa)
• myometrium (thick muscle)
• endometrium (glandular layer)

Question 2

what do uterine contractions depend on

Answer 2

gap jun actions for phasic propagation of depolarisation (connexion 43)
• Minimal influence of autonomic innervation on contractions under physiological conditions.

Question 3

what are gap junctions

Answer 3

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

Question 4

what is the structure of the connexins that make up the gap junctions

Answer 4

each has 6 connexins that form a hemichannel, and each hemichannel is specific to another hemi channel that it will connect to

Question 5

where are gap junctions found

Answer 5

• in cells/tissue that spread action potential

cardiac muscles
nervous tissue in the brain

Question 6

gap junctions in caridac muscle

Answer 6

– Constitutively expressed.
– Arranged in intercalated discs.
– Depolarisation starts from the sinoatrial (SA) node (pacemaker).

Question 7

gap junctions in uterine smooth muscle

Answer 7

– Inducible (especially hormonally).
– Fundal dominance during labour – May arise from anatomical
arrangement of expressed gap junctions.

Question 8

the sympathetic outflow effect in the uterus depends on what

Answer 8

receptor type:
– a-adrenoceptors - contraction.
– b-adrenoceptors - relaxation.

• Ratio of sympathetic receptor types influenced by hormonal status.

Question 9

what produces ADH and Oxytocin

Answer 9

the hypothalamus, the posterior pituitary secretes these into the blood stream

Question 10

why can ADH act on uterine muscle

Answer 10

because they are both 9 amino acid peptides, 2 amino acids which are different which means they have a very similar structure

Question 11

what effects oxytocin receptor numbers

Answer 11

sex hormone levels

Question 12

at term what happens in the uterus

Answer 12

– Falling placental progesterone with sustained oestrogen levels.
– Stimulates prostaglandin biosynthesis.
– Oxytocin receptor expression.

Question 13

whaat is the role of oxytocin in contractions

Answer 13

• 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

Question 14

• Uterine stimulants (oxytocics).

Answer 14

– Induce abortion / miscarriage
– Induce and accelerate labour.
– Contract the uterus after delivery to control postpartum haemorrhage (PPH).

Question 15

• Uterine relaxants (tocolytics).

Answer 15

– Delay or treat preterm labour.
– Facilitate obstetric manoeuvres.
– Counteract (iatrogenic) uterine hyperstimulation.
– Treat menstrual cramps/dysmenorrhoea

Question 16

what makes up oxytocics

Answer 16

– Oxytocin.
• IV infusion to induce or accelerate labour.
• IV or IM injection after delivery to control postpartum
haemorrhage (PPH).
– Ergometrine.
– E & F series prostaglandins.

Question 17

Ergometrine

Answer 17

• 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

Question 18

Menstrual symptoms - Dysmenorrhoea (painful periods) and menorrhagia (excessive blood loss)

Answer 18

prostaglandins may play a role.

– Imbalance of prostaglandin E vs prostaglandin F in endometrium.

Question 19

Nonsteroidalanti-inflammatorydrugs(NSAIDs)are effective for

Answer 19

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).