St A - Uterine Motility

Question 1

Describe the anatomy of the uterus

Answer 1

• Perimetrium (serosa, it is a thin outer layer of epithelium.
• Myometrium (thick middle layer of smooth muscle).
• Endometrium ( inner layer with glands, blood vessels, lymphatics and epithelial cells)

Question 2

What do uterine contractions depend on and what are they influenced by?

Answer 2

They depend on gap junctions for phasic propagation of depolarisation and are hormonally influenced, especially in the menstrual cycle, pregnancy and labour.

Question 3

What are the functions of gap junctions?

Answer 3

They allow cells to communicate with each other, share nutrients and transfer chemical/electrical signals

Question 4

Describe structural features of gap junctions

Answer 4

They are made up of proteins called connexin. Each cell has 6 connexins that form a hemi-channel and each hemi-channel is specific to another hemi-channel which it will connect to.

Question 5

Explain the innervation of the uterus

Answer 5

Has SNS, PSNS and sensory innervation.

Question 6

The sympathetic outflow effect depends on??

Answer 6

The receptor type; alpha adrenoceptors (contraction) and beta adrenoceptors (Relaxation)

Question 7

Describe the effects of the posterior pituitary hormones

Answer 7

Both stimulate contraction of the uterus however there are far more oxytocin receptors

Question 8

What is the function of oxytocin at term?

Answer 8

Prior to the onset of labour the uterine smooth muscle becomes sensitive to oxytocin. It stimulates regular, co-ordinated contractions that travel from fundus to the cervix. The uterus completely relaxes between contractions but doesn’t go down to its original length

Question 9

What are some of the uses of uterine stimulants (oxytocics)

Answer 9

• Induce abortion/miscarriage,
• Induce and accelerate labour,
• Contraction of the uterus after delivery to control postpartum haemorrhage

Question 10

What are some of the uses of uterine relaxants? (tocolytics)

Answer 10

• Delay or treat preterm labour,
• Facilitate obstertric manoeuvres,
• Counteract uterine hyperstimulation,
• Treat menstrual cramps/dysmenorrhoea

Question 11

Name some examples of uterine stimulants (oxytocics)

Answer 11

• Oxytocin via IV infusion to induce/accelerate labour and IV/IM injection to control PPH.
• Ergometrine (vasoconstrictor),
• E and F series prostaglandins

Question 12

What are some of the uses of ergometrine in practice?

Answer 12

• Bleeding in early pregnancy complications eg, miscarriage.
• combined with oxytocin to form syntometrine for third stage labour

Question 13

Name some examples of prostaglandins

Answer 13

Dinoprostone - equivalent to prostaglandin E2,
Carboprost (analogue of prostaglandin F2a),

Gemeprost (analogue of PGE1).
Misoprostol (analogue of PGE1)

Question 14

What is misoprostol used for?

Answer 14

• Medical abortion following myometrium sensitisation by mifepristone.
• Induction of labour,
• Control of PPH

Question 15

Name some uterine relaxants (tocolytics)

Answer 15

• Beta 2 agonists such as terbutaline and salbutamol. These increase cAMP levels in smooth muscle.
• Calcium channel blockers such as Nifedipine which is used to delay preterm labour. It prevents intracellular calcium increase in SM.
• NSAIDS (idomethacin),
• Oxytocin receptor antagonist (atosiban)
• Nitrates

Question 16

Describe the treatment of menstrual symptoms

Answer 16

NSAIDs such as ibuprofen, naproxen mefenamic acid. They can also reduce menstrual blood loss especially when combined with antifibrinolytics like tranexamic acid.