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Repro > Uterus Pharmacology > Flashcards

Uterus Pharmacology Flashcards

1
Q

name an important property of the myometrium

A

it is myogenic, self stimulating, produces regular contractions without the need for hormonal or nervous input

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2
Q

what is the importance of the myometrium producing rhythmic contractions over sustained contractions?

A

sustained contractions are more dangerous as they can restrict blood flow, leading to foetal distress

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3
Q

what is a contraction and its role?

A

it is an an increase in uterine pressure

  • forces content towards the cervix
  • also acts as a prevention for blood loss
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4
Q

how does these synchronous contractions come about?

A

pacemaker cells in the myometrium intimate and coordinate contractions
-these cells are called the Interstitial Cells of Cajal (ICC’s)

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5
Q

how does electrical communication occur?

A

via gap junctions made of connexion proteins

Between ICCs
Between ICCs and SM cells
Between SM cells

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6
Q

how do the gap junctions function and what do they allow?

A

as a syncytium, integrated and functioning as a whole

depolarisations can be transmitted to neighbouring cells via gap junctions
-allow electrical coupling between the ICC and SM cells

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7
Q

the electrical activity of ICC’s leads to activation of what?

A
  • inward currents that pass the threshold

- causes depolarisation and Ca2+ entry via VGCC’s and contraction

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8
Q

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

A

neurotransmitters and hormones

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9
Q

explain the cellular mechanisms of SM contractions?

A

depolarisation of cells, VGCC’s, ca2+ levels increase, binds to IP3 receptors on intracellular calcium store. release of calcium into cytosol, binds to calmodulin and activates MLCK. Myosin light chain/actin interactions and contraction
-oxytocin acts this way, increasing calcium and therefore causing contractions

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10
Q

relationship between calcium levels and contraction

A

Graded response

increases in intracellular ca2+ concentration = increases in force of contraction

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11
Q

mechanisms for lowering Ca2+

A

increase Ca2+ into SR, increase ca2+ out of cell via Na+/Ca2+ channel and Ca2+ ATPase channel

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12
Q

too high concentrations of calcium can produce what?

A

prolonged sustained contractions

-useful for preventing blood loss, but can cause foetal distress

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13
Q

what is hypertonus?

A

incomplete relaxation, occurs with large concentrations of calcium

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14
Q

how can myometrial contractions be regulated?

A
  • neurotransmitters
  • sex hormones
  • prostaglandins
  • oxytocin
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15
Q

explain how contractions can be regulated by neurotransmitters?

A
  • sympathetic innvervation

- alpha receptors and beta 2 receptors

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16
Q

alpha adrenoceptor agonist binding causes what?

A

contraction

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17
Q

beta-2 adrenoceptor agonist binding causes what?

A

relaxation

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18
Q

explain how contractions can be regulated by sex hormones?

A
  • progesterone inhibits contraction

- oestrogen increases contraction

19
Q

why is the ratio of oestrogen and progesterone carefully controlled?

A

imbalance could lead to early labour

20
Q

what is a non-pregnant uterus like?

A
  • weak contractions early in cycle

- strong contractions during menstruation due to progesterone and prostaglandins

21
Q

what is a pregnant uterus like?

A
  • weak and uncoordinated in early pregnancy due to high progesterone
  • strong and co-ordinated at parturition due to oestrogen
22
Q

how does the oestrogen / progesterone ratio change during parturition?

A

increases

-oestrogen increases

23
Q

where are oestrogen and progesterone receptors also found

A

on ICCs

24
Q

what can oestrogen modulate?

A
  • activate the oxytocin receptors
  • modulate prostaglandin and oxytocin levels at uterine SM cells
  • increase gap junctions in myometrium
25
Q

explain how contractions can be regulated by prostaglandins?

A
  • contractile agents
  • oestrogen promotes the synthesis of PGE2 and PGF2α from the endometrium and myometrium
  • both of these induce myometrial contraction
  • increase expression of gap junctions
  • coordinate increased frequency/force of contractions
  • soften cervix
26
Q

does PGE2 have the same function in every past of the body?

A

no, PGE2 is a relaxant in other types of SM – dilates blood vessels

27
Q

what role do prostaglandins play in menstrual pain?

A
  • dysmenorrhoea (severe menstrual pain)
  • menorrhagia (severe menstrual blood loss)
  • pain after parturition
28
Q

what can be used to reduce contraction and pain?

A

NSAIDs

29
Q

when are prostaglandins effective?

A

early and middle pregnancy

30
Q

why do prostaglandins soften the cervix?

A

so its easier to push out the baby

31
Q

name some prostaglandin analogues

A

Dinoprostone (PGE2), Carboprost (PGF2α), Mistoprotol (PGE1) analogues

32
Q

uses of prostaglandin analogues

A
  • Induction of labour – before term
  • Induce abortion
  • Postpartum bleeding
  • Softening the cervix
33
Q

concerns of prostaglandin analogues

A
  • Dinoprostone can cause systemic vasodilatation
  • Potential for cardiovascular collapse (given as cervical gel/vaginal insert)
  • PGs – hypertonus and foetal distress
34
Q

where is oxytocin synthesised and released from?

A

synthesised in hypothalamus, released from posterior pituitary gland

35
Q

what causes oxytocin release?

A
  • suckling and cervical dilatation

- oestrogen

36
Q

how does oestrogen, released at later stages of parturition, affect oxytocin?

A
  • increased oxytocin release and oxytocin receptor expression
  • increased gap junctions
37
Q

why is oxytocin only effective at term?

A

requires oestrogen-induced oxytocin receptor expression

38
Q

uses of oxytocin?

A
  • Induction of labour at term – does not soften cervix

- Treat / prevent post-partum haemorrhage

39
Q

low vs high oxytocin concentrations

A

Low concentrations of oxytocin increase frequency and force of contractions

High concentrations cause hypertonus – may cause fetal distress

40
Q

name 2 synthetic versions of oxytocin

A

Syntocinon and Pitocin

41
Q

Ergot to ergometrine

A
  • fungus that grows on some cereals
  • powerful and prolonged uterine contraction, only when myometrium is relaxed
  • stimulation of alpha adrenoceptors
  • use in stopping post-partum bleeding - NOT induction
42
Q

when might myometrial relaxants be used?

A

in premature labour
-Important: Delay delivery by 48 hrs, so mother can be transferred to specialist unit, and given antenatal corticosteroids to aid foetal lung maturation and increase survival

43
Q

name some myometrial relaxants

A

beta 2-adrenoceptor stimulants e.g. Salbutamol

  • relax uterine contractions by a direct action on the myometrium
  • reduce strength of contractions in premature labour
  • may occur as a side effect of drugs used in asthma

Ca2+ channel antagonists e.g. Mg sulphate

Oxytocin receptor antagonists e.g. Retosiban

COX inhibitors e.g. NSAIDs, decrease prostaglandin levels, but may cause fetal renal dysfunction

44
Q

Stimulation of beta 2-adrenoceptors on SM (vascular, airway, myometrial) produces relaxation - explain the mechanism

A

agonist eg. adrenaline binds to beta-2 receptor, activates PKA

  1. increase in Ca2+ ATPase activity, so Ca2+ enters SR or leaves the SM cell
  2. increase in K+ channel activity, causing hyperpolarisation and decreased Ca2+ entry via VGCCs
  3. decreased MLCK

Repro (11 decks)

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