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Reprooooooooo > Pharmacology of the uterus > Flashcards

Pharmacology of the uterus Flashcards

1
Q

What is the structure of the myometrium?

A

It’s the smooth muscle of the uterus

  • Outer longitudinal fibres
  • Middle figure of 8 fibres
  • Inner circular fibres
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2
Q

What does contraction of the myometrium mean?

A

Contraction means increase in uterine pressure forcing content towards the cervix and acts as a natural ligature to prevent blood loss

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3
Q

What are the mechanical properties of the myometrium?

A
  • Spontaneously active
  • Produce regular contractions without neuronal or hormonal input
  • Highly sensitive to neurotransmitters and hormones
  • Rhythmic contractions for parturition
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4
Q

How is synchronous contraction achieved?

A

Pacemaker cells present in myometrium(ICCs)
-These initiate and coordinate contractions
Electrical communications in myometrium via gap junctions made of connection proteins

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5
Q

What are gap junctions present between?

A

Between:

  • ICCs
  • ICCs and smooth muscle cells
  • Smooth muscle cells
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6
Q

What do the gap junctions function as in the myometrium?

A

Function as a syncytium

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7
Q

How do the waves of electrical activity lead to contraction?

A

ICC periodic activation of inwards currents –> Depolarisations –>Ca2+ entry through VGCCs –>increase {ca2+]i –> Contraction

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8
Q

What are slow waves of ICCs and smooth muscle responses modulated by?

A

Slow waves of ICCs and smooth muscle responses are . modulated by neurotransmitters and hormones

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9
Q

What is the cellular mechanism of smooth muscle contraction?

A
  • Substrate binds to receptor
  • Galphaq subunuit stimulates PIP2–>IP3+DAG
  • IP3 binds to the SR causing a release of Ca2+
  • DAG increases membrane permeability excitability increasing depolarization and activating VGCCs
  • [Ca2+]i increases and allows binding of Ca2+ calmodulin to MLCK increasing myosin light chain/actin interactions
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10
Q

What mechanisms are there for lowering [Ca2+] (Ca2+ extrusion)?

A
  • ATP Ca2+ pump on sarcoplasmic reticulum causes active uptake of Ca2+ into the SR
  • ATP Ca2+ pump on membrane causes active release of Ca2+ out of cell
  • Na+/K+ ATP pump drives the Ca2+/Na+ pump to release Ca2+ out of cell
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11
Q

What do low concentrations of stimulants on ICCs cause?

A

Cause increase in slow wave frequency, increasing frequency of contractions

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12
Q

What does a higher concentration of stimulants on ICC cause?

A

Causes increase in frequency of action potentials on top of slow waves leading to increased frequency and force of contractions

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13
Q

What does a higher concentration still of stimulants on ICC cause?

A

Cause increased plateau of slow waves, producing prolonged sustained contractions

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14
Q

What does a large concentration of stimulant on ICC cause?

A

Causes:

  • Hypertonus(Incomplete relaxation)
  • The Ca2+ extrusion becomes ineffective
  • Interference with blood flow
  • Fetal distress
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15
Q

What type of innervation does the myometrium have?

A

Sympathetic innervation

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16
Q

What does an alpha adrenoceptor agonist cause in the myometrium?

A

Causes contraction

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17
Q

What does a beta2 adrenoceptor agonist cause in the myometrium?

A

Causes relaxation

18
Q

What do oestrogen and progesterone do to contraction?

A

Progesterone inhibits contraction

Oestrogen increases contraction

19
Q

When do weak and strong contractions occur in a non-pregnant uterus?

A
  • Weak contraction occurs early in the cycle(high progesterone)
  • Strong contraction during menstruation (decreased progesterone and increased prostaglandins)
20
Q

When do weak and strong contractions occur in a pregnant uterus?

A
  • Weak contractions occur early in the cycle

- Strong and coordinated at parturition(increased oestrogen)

21
Q

What happens to the estrogen/progesterone ratio during parturition?

A

Ratio increases

-Oestrogen increases while progesterone decreases gap junction expression in myometrium

22
Q

Are oestrogen and progesterone receptors found on ICCs?

A

Oestrogen and progesterone receptors found on ICCs

23
Q

What prostaglandins to the myometrium and endometrium synthesise and what do they induce?

A

Myometrium and endometrium synthesise PGE2 and PGF2alpha

-both these prostaglandins induce myometrial contraction

24
Q

What do prostaglandins have a role in?

A

Have a role in dysmenorrhoea, menorrhagia, pain after parturitions

25
Q

What are effective against pains caused by prostaglandins?

A

NSAIDS are effective against pain as they reduce contraction and pain

26
Q

What do prostaglandins act together to do?

A

Act together to:

  • Coordinate and increase frequency/force of contractions
  • Increase gap junctions
  • Soften cervix
27
Q

What are the uses of prostaglandins?

A

Uses:

  • Induction of labour before term
  • Induce abortion
  • Post partum bleeding
  • Softening the cervix
28
Q

What are concerns of prostaglandins?

A

Concerns:

  • Dinoprostone can cause systemic vasodilation
  • Potential for cardiovascular collapse
29
Q

What is oxytocin and where is it synthesized and released?

A

Oxytocin is a non-peptide hormone synthesized in the hypothalamus and released from the posterior pituitary gland?

30
Q

What is oxytocin released in the response to?

A

Its released in response to suckling and cervical dilation

31
Q

Effect of oestrogen on oxytocin?

A

Oestrogen causes:

  • Increased oxytocin release
  • Increased oxytocin receptors
  • Increased gap junctions
32
Q

What does oxytocin increase the synthesis of?

A

Increases the synthesis of prostaglandins

33
Q

What is Ergot?

A

Is a fungus

34
Q

What does the action of Ergot cause?

A

Its action causes powerful and prolonged uterine contractions, but, only when myometrium is relaxed

35
Q

What is the mechanism of ergot?

A

Its mechanism is by the stimulation of alpha adrenoreceptors and 5-HT receptors

36
Q

What is Ergot used for?

A

Used for postpartum bleeding

37
Q

What can myometrial relaxants be used in?

A

Used in premature labour

38
Q

What does myometrial relaxant ,beta2 adrenoceptor, do?

A
  • Relaxes uterine contractions by direct action on the myometrium
  • Used to reduce strength of contractions in premature labour
39
Q

What does myometrial relaxant, COX inhibitors, do?

A

-Decreases prostaglandin levels

40
Q

What are the side effects of COX inhibitors?

A

May cause fetal renal dysfunction

41
Q

How do we measure uterine contractions?

A

Isometric tension recording:

-Measure tension generated with diameter of the muscle ring remains constant

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