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Year 3- Repro > Hormonal Control of Labour > Flashcards

Hormonal Control of Labour Flashcards

1
Q

Antenatal means

A

period before woman is in labour

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2
Q

During the antenatal phase…

A

Myometrium (the smooth muscle of the uterus) = Quiescent
It must not contract until time of birth. If it contracts before it is called preterm labour. If it remains quiescent then it leads to post term labour. Labour must happen at term = 40 weeks. (37-42 weeks)
Cervix (neck of the womb) = Closed
Membranes (which surround the baby, the amniotic sac) = Intact

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3
Q

Interpartum means..

A

period when labour begins

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4
Q

During the interpartum phase..

A

Myometrium = Contractile
If the myometrium contracts and relaxes the baby will never be born, if the uterus contracts and then relaxes the baby will go back in as the volume has to remain constant. So what must happen is that there has to be a permanent shortening of the muscle fibre length, this is called retraction. So, when the myometrium contracts it shortens, but it does not come back to its original length when it relaxes, it retracts. So there is contraction and retraction.
Cervix = Open
This is a passive process, the cervix is yielding to uterine contractions. But changes must happen in the cervix to facilitate this. So the cervix opens as a result of contractions from the uterus.
Membranes = Ruptured
They are ruptured as the process of labour is enhanced by breaking of the membranes. It is the most effective way of starting labour. BUT there is a problem that it is non reversable once the membrane is broken.

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5
Q

actin/myosin interactions

A

There is coupling of actin and myosin which leads to binding, bending of the head, so the muscle fibre length decreases. This is dependant of intracellular calcium. The calcium is then taken back for the muscles to relax, its an energy dependant process.

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6
Q

When the uterus is contracting in labour there is progressive effacement of the cervix:

A

The cervix has an internal os and an external os, there is a length to the cervical canal (left)
Nearer labour there is no length of the cervix, you cannot differentiate the internal os from the external os.
Percentage decrease in the length of the cervix = EFFACEMENT -the cervix stretches and gets thinner.
This often happens before labour begins. As labour nears, the cervix may start to thin or stretch (efface) and open (dilate). This prepares the cervix for the baby to pass through the birth canal.
SO… Once the cervix becomes very thin it will start to open in response to contractions of the uterus.

this happens under the control of several hormones

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7
Q

Why is a gradient of contraction important?

A

If the uterus contracts from all sides equally, the baby will never be born. So there as to be a gradient of contraction. The top of the uterus must contract first and stronger and for a longer period of time in order for the baby to be pushed down. This is called a triple descending gradient.

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8
Q

Quiescence phase- antepartum phase

What is responsible for keeping the uterus in a quiescence phase?

A

Progesterone
PGI2 – Prostacyclin (a prostaglandin)
Relaxin – relaxes the uterus
Parathyroid hormone-related peptide(PTHrP)
Calcitonin gene-related peptide, vaso-active intestinal peptide
Nitric oxide (NO) – smooth muscle relaxant, also acts in blood vessels.

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9
Q

How do the factors responsible for keeping the uterus in a quiescence phase work?

A

All these lead to increased intracellular (cAMP) or (cGMP) which inhibit the release of intracellular calcium for myometrial contractility.
So by inhibiting the intracellular release of calcium it will downregulate the contractile properties of the myometrium.

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10
Q

Activation Phase

A

When it is time to go into labour there is an activation/preparatory phase. Before actual labour starts, the environment must be right.

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11
Q
A

Duration of human pregnancy is 40 weeks from the last menstrual period.
Gestational age = menstrual age
It is NOT the age of conception. We do not know when this occurred, so all calculations are from the first day of the last menstrual period.

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12
Q

What ensures the right environment for activation phase?

A

Rise in estrogen and CRH (corticotropin releasing hormone – secreted by the brain)
Mechanical stretch
One theory is that when there is enough stretch in the uterus, then it is time to give birth. We know that when the stretching is too much, then labour starts to come early eg with twins.
There is up-regulation of a panel of genes required for contractions: Connexin 43, prostaglandin and oxytocin receptors (OTRs)
These genes control the synthesis of prostaglandins – prostaglandisn are stimulants of the uterus and oxytocin receptors.
Oxytocin is a hormone secreted by the pituitary, its function is to stimulate contractions of the uterus.

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13
Q

Stimulation Phase

A

When the process of preparation is completed, actual labour begins

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14
Q

Hormones involved in stimulation phase?

A

Prostaglandins
Prostaglandins form the final common pathway for labour.
Oxytocin
Hormone produced by the posterior pituitary that stimulate uterine contractions.
CRH
Increased synthesis of cytokines
Cytokines are proinflammatory substances, many processes of labour are similar to inflammation.]

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15
Q

Hormonal changes during initiation of labour?

A

Functional Progesterone withdrawal
If you measure progesterone levels during pregnancy they increase and the plateau. When somone goes into labour, the level of progesterone does onot change before labour begins.
Increased Estrogen bio-availability
Estrogen and progesterone are competing hormones, the antagonise each other, they reverse the action of each other. So there will be increased estrogen bio-availability, reducing the effects of prostaglandins on the body.
CRH and neuro-endocrine mediators
Increased responsiveness of the myometrium to prostaglandins and oxytocin
So not only is ocytocin secreted, but the responsiveness is also increased by increasing the concentration of receptors

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16
Q

Exact mechanisms of the initiation of labour is uncertain but believed to involve:

A

Progesterone
As it keeps the uterus quiescent
Oestrogen
It is antagonistic to progesterone action
Oxytocin
Is used to start contraction, if someone is not contracting well can give oxytocin
Relaxin
Corticotrophin-releasing hormone / fetal cortisol
Nitric oxide
As it keeps the uterus quiescent
Prostaglandins
Are also used as medicines to start labour
Inflammatory cytokines

Sheep are used to study pregnancy, found that infusing sheep with corticosteroids it starts labour off. But this did not work in humans

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17
Q

Progesterone profile

A

Progesterone is one of the main hormones of pregnancy
Produced by corpus luteum in early pregnancy and the placenta later on
Cholesterol is converted to Progesterone by the action of P450scc and 3βHSD

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18
Q

Wha happens to prog levels during myometrial contractility?

A

decreases

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19
Q

effect of prog on gap junction formation

A

Inhibits myometrial gap junction formation

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20
Q

effect of prog on NO synthetase?

A

Stimulates uterine NO synthetase

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21
Q

effect of prof on contractility

A

Stimulates cAMP and sequesters intracellular calcium in the sarcoplasmic reticulum (SR)
This inhibits contractility

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22
Q

effect of prog on prostaglandin production

A

Down-regulates prostaglandin production, development of calcium channels and oxytocin receptors, stopping the uterus from contracting.

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23
Q

effect of prog on cervix

A

inhibits collagenolysis in the cervix by increasing tissue inhibitor of matrix metalloproteinase-1 (TIMP-1)
The cervix becomes shorter, but is should also become softer and more pliable for opening up. Progesterone stops this from happening.

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24
Q

inhibitory effects of progesterone

A

Prostaglandins synthesis
CRF secretion
Interleukin synthesis
Estrogen receptor expression
Oxytocin receptors affinity

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25
Stimulatory effects of progesterone
Prostaglandins degradation PTH-rp synthesis (Parathyroid hormone-related protein) CGRP secretion - Calcitonin Gene-Related Peptide (is a vasodilator) CGRP and AM (Adrenomedullin) receptor expression
26
what causes changes in prog activity?
In most species, progesterone levels fall pre-labour This does not occur in humans However there is changes to different progesterone receptors: upregulation of PR-A (pro-inflammatory receptor), and suppression of PR-B (anti-inflammatory receptor) receptor activity, This results resulting in "functional" progesterone withdrawal. So levels of progesterone remain the same but receptors change.
27
how does prog make contractility conditions suitable?
Increased PR-A/PR-B ratio is linked with activation of nuclear factor kappaB (NF-kB) in the myometrium NF-kB increases expression of COX-2 and various pro- inflammatory cytokines (e.g. IL-8 and IL-1b), which cause cervical ripening and up-regulate oxytocin receptor expression in the myometrium SO… it is making the environment favourable for action of substances that will contract the uterus.
28
oestrogen
Estrogen is essential for uterine development & function The placenta is the primary source
29
Placenta relies on DHEAS from...
fetal & maternal adrenal glands for the supply of precursor for estrogen synthesis So in some ways the fetus can regulate the onset of labour as it contributes to the DHEAS supply to the placenta.
30
Both oestrogen & progesterone increase
towards term but the ratio of estrogen to progesterone begins to favour estrogen
31
This occurs in the mother. Mothers adrenal glands make DHEA-S and the babys adrenal glands also Hormones act on DHEA to produce different estrogens
32
Oestrogen induced myometrial changes?
Increase in the number of PG and OCT receptors. (prostaglandin and oxytocin) It causes Up-regulation of the enzymes responsible for muscle contractions (myosin light chain kinase, calmodulin) Estrogen causes Increase in connexin-43 synthesis & gap junction formation in the myometrium Also causes Induction of collagenase & elastase: Cervical ripening It breaks down the connective tissue in the cervix, and makes the cervix go from hard to soft, so it is less resistant to actions of contractions.
33
summary of oestrogen effects
An increase in uterine contractility (of the myometrium) by: Increase in gap junction formation Increase in oxytocin responsiveness Increase in prostaglandin synthesis and release Estrogen also causes an increase in cervical dilatation This is by collagenase and elastase induction
34
oxytocin effects
Oxytocin is synthesised in hypothalamus and released from posterior pituitary gland of mother, also produced by myometrium, decidua, placenta and membranes. It acts on smooth muscles of the uterus and also serval other The levels of oxytocin increase even after the mother has given birth to cause the release of breast milk as there are also smooth muscles in the breast. It also causes the uterus to contract preventing postpartum haemorrhage. Nipple stimulation is also another way of initiating labour as it leads to oxytocin release.
35
myometrium and oxytocin
Myometrial sensitivity to oxytocin increases near to term due to changes in density (up to 200-300 fold) and affinity of oxytocin receptors Receptor concentration greatest in the fundus (top) and minimal in the lower segment and cervix If everything contracted the baby will not come out. It has to be maximum in the fundus and as you go down it decreases.
36
Oxytocin receptor upregulation is promoted by...
is promoted by oestrogen and mechanical stretch Stretching the cervix is another way to initiate labour
37
oxytocin and intracellular Ca
There is an increase in inositol 1,4,5-triphosphate and intracellular Ca
38
Oxytocin effect on myometrium
Causes an increase in intracellular calcium levels This causes an increase in myosin phosphorylation This causes an increase in myosin actin binding
39
Oxytocin effects on decidua?
Causes an increase in PGF2a synthesis This causes an increased secretion of PFG2a
40
Relaxin is..
an insulin-like hormone produced by placenta and myometrium (corpus luteum in early pregnancy) It promotes myometrial quiescence in pregnancy
41
Role of relaxin in labour
Induces vasodilatation, skeletal muscle relaxation and renal adaptation to pregnancy Increases cAMP, inhibits calcium release in myocytes, decreases affinity of MLCK for calmodulin and myosin and activates K channels, thus hyperpolarising the muscle cell membrane. So it is supressing the contractions Suppresses oxytocin release Enhances cervical ripening – one of the most important functions.
42
Inflammatory cytokines...
play a major role in enhancement of uterine contractility and cervical ripening There are several types including: IL-1, IL-6, IL-8, TNF-α, interferon and TGF-β
43
Inflammatory cytokines- role in labour
They all stimulate prostaglandin (PG) production in the myometrium, placenta and fetal membranes IL-8 also induces neutrophil chemotaxis/activation and production of matrix metalloproteinase (MMP). This therefore causes the ripening of the cervix Inflammation away from the uterus can also trigger labour e.g. surgical procedures, appendicitis, UTI
44
NO origin
NO is produced by decidua, membranes, fetoplacental vascular endothelium and the syncytiotrophoblast
45
Role of NO in labour
Regulates vascular tone via release of prostacyclin Maintains myometrial quiescence Activates guanylate cyclase pathway, increases cGMP, decreases intracellular Ca concentrations Levels are elevated in myometrium (but not cervix) during pregnancy and decreases prior to onset of labour Cervical NO increases at term, thus implicated in ripening. NO donors is used as agents to increase ripening of cervix.
46
Corticotropin Releasing Hormone (CRH) and Cortisol
Extra CRH is produced by placenta and myometrium and levels increase 50–100 fold by late gestation CRH binding proteins fall towards term, increasing free (active) levels of CRH CRH inhibits PGE2, increases cAMP and upregulates NO synthase, promoting quiescence antenatally At term, however, CRH enhances the myometrial contractile response to PGF2α, PGE2 and oxytocin CRH stimulates the fetal adrenal gland to produce cortisol, which triggers conversion of progesterone to oestrogen – also promotes fetal lung maturation
47
CRH and ucorotins (NO NEED TO KNOW)
Uro-cortins (Ucn,Ucn2,Ucn3) are structurally similar to CRH and show similar biological effects Are synthesized and secreted by placenta and fetal membranes Ucn levels remain relatively constant during gestation and increase only after onset of parturition Augment matrix metalloproteinase, ACTH and prostaglandin secretion Act as pro-inflammatory agents
48
Prostaglandins
Final common pathway in labour onset mechanisms Produced in decidua and fetal membranes
49
Role of prostaglandins in labour
Stimulatory PGs (PGF2α, thromboxane, PGE1, PGE2) bind to the myocyte cell membrane, increase action potential frequency and stimulate contraction PGE2 plays a central role in cervical ripening – is a drug used for cervical ripening PGF2α increases intracellular calcium / contractility – is a drug used as treatment for postpartum haemorrhage. Inhibitory PGs (PGD2 and PGI2) repress contraction PG levels are low and receptors down-regulated during pregnancy, and increase towards term. So the reactivity to PGs increases nearer term. Synthesis is upregulated by NF-κB / COX-2 activation
50
Other factors involved in labour
Epidermal growth factor Increases PG levels, promotes uterine contraction by increasing intracellular Ca Parathyroid hormone related peptide (PTHrP) Has relaxant effect on myometrium (decreases levels at term), also relaxes blood vessels and plays a role in placental calcium transport Magnesium competes with calcium for calmodulin binding, reduces MLCK Endothelin enhances myometrial contractility by increasing intracellular Ca / MLC phosphorylation, modulates fetoplacental circulation Oestrogen to progesterone ratio Engagement and descent of fetal head (placing pressure on cervix) – leads to release of hormones Neuroendocrine effects of cervical stretch, leading to increase oxytocine release (“Ferguson’s reflex”) Altered uterine wall tension (myometrial stretch) Parasympathetic to sympathetic balance Hyaluronic acid levels – leads to ripening of the cervix Cervical stimulation (sexual intercourse / “sweep”)
51
Major changes in the myometrium
Increased coupling Increased Ion channels Increased receptors Reduction in NO-system This leads to: Increased conductivity Increased Excitability Decreased relaxation This leads to: Reinforcement of contractions.
52
Major changes in the cervix
Increased inflammatory response Increased collagenase = reduction in collagen This leads to: Cervical ripening This leads to: Dilatation
53
Major changes in the membrane
Increased ECM (extracellular matrix) degradation This leads to: Decreased tissue integrity This leads to: Rupture
54
Phase 0 hormones
Phase 0 = Quiescence Progesterone Relaxin NO
55
Phase 1 hormones
Phase 1 = Activation Estrogens Progesterone PGs CRH
56
Phase 2 hormones
Phase 2 = Stimulation PGs Oxytocin CRH Ucn/Ucn2
57
Phase 3 hormones
Phase 3 = Involution Oxytocin – The uterus has to reduce in size
58
Labour- definition?
Labour is: Regular painful contractions associated with cervical change (± spontaneous rupture of fetal membranes) End result is delivery i.e. expulsion of the fetus(es), placenta and membranes) – also called “parturition”
59
Stages of labour
First stage = onset to full cervical dilatation (10cm). This is broken into two: latent phase = 0–3cm active phase = from 4cm Second stage = full dilatation to delivery of the fetus Third stage = delivery of fetus to delivery of placenta
60
Preterm birth
Delivery prior to 37 completed weeks gestation Affects between 7 to 11% pregnancies worldwide Predictive tests perform poorly but may be used in high risk groups: Ultrasound cervical length – The shorter the cervix the higher the chances of preterm birth fetal fibronectin – Degradation from the decidua. the higher the chances of preterm birth
61
Causes of preterm birth
Causative/associated factors: Infection Inflammation Maternal stress Intrauterine haemorrhage Uteroplacental insufficiency (e.g. pre-eclampsia and fetal growth restriction)
62
Maternal stress
There is activation of the HPA axis Cortisol formation This acts on CRH This increases prostaglandin formation This leads to: contractions, cervical changes and rupture of membranes Foetal stress can also lead to the same outcomes as foetal cortisol is a precursor to estrogen formation by the placenta. This can also lead to preterm birth
63
Inflammation
Inflammation anywhere is very similar to labour (labour causing factors), this will lead to the same changes that occur in labour:
64
Haemorrhage
Leads to decidual activation with release of clotting factors including factor VIIa/tissue factor This ultimately leads to extracellular matrix (ECM) degradation This will lead to: contractions, cervical change and rupture of membranes.
65
Summary
Labour is a complex physiologic process involving fetal, placental, and maternal signals. A variety of endocrine systems play a role in the maintenance of uterine quiescence and the onset of labour (increase in uterine contractility and cervical ripening). There are many factors that can tip the balance between quiescence & contractile
66
Define effacement of cervix (progressive)
when the cervix softens, thins and shortens
67
Activation vs Stimulation
activation- starting to induce contractions Stimulation- actual phase?
68
what is the triple descending gradient- Caldeyro-Barcia?
wave-like contraction which starts at the fundus, spreads down the uterus, and decreases in strength and duration as it progresses
69
Why is inflammation elsewhere in the body dangerous during pregnancy?
May induce early labour at any stage of the pregnancy
70
Exogenous use of NO and PGE2
artificially ripens cervix- induces labour?
71
Postpartum haemorrhage treatment
PGF2a
72
First way of inducing labour artificially and disadvantage
Breaking waters as this increases prostaglandin production- IRREVERSIBLE

Year 3- Repro (34 decks)

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