Session 10 Flashcards
Normal anatomy of the uterus?
Hollow pear shaped organ
Situated in pelvic cavity Anteverted, anteflexed
Non-pregnant measures Length = 7.5cm Width = 5cm Depth = 2.5cm
Weighs 60gms
Consists of corpus and cervix
Uterine muscle fibres
3 layers - use panopto
Define labour and its stages
oLabour is the process where the fetus, placenta and membranes are expelled through the birth canal.
oNormal labour is spontaneous in onset at term (37-42 weeks), with the fetus presenting by the vertex and is usually completed within 18 hours with no complications arising.
oLabour is divided into three stages:
o1st Stage is the onset of regular contractions until the cervix is fully dilated (latent and active).
o2nd Stage begins when the cervix is fully dilated to the birth of the baby.
o3rd Stage is from the birth of the baby to the delivery of the placenta and membranes and bleeding is controlled.
No abrupt change between sages. all three overlap slightly.
Define latent phase of labour, established/active labour and transition
oLatent phase: a period of time, not necessarily continuous when there are painful contractions and cervical effacement and dilatation up to 4cms.
oEstablished/Active labour: is when there are regular painful contractions and progressive dilatation from 4cms.
oTransition: usually from 8cm to 10cm.
What is Pre-labour?
• Lightening occurs 2-3 weeks prior to the onset of labour
• Expansion of the lower segment • Fetal head engages • Symphysis pubis widens, sacro-iliac joints relax • Pelvic floor relaxes • Increased vaginal secretions • Frequency of micturition • Braxton Hicks contractions • Taking up of the cervix
oFrom 24 weeks cervical cells gradually change in collagen content Take up more water
oGap junctions formed between cells act as electro-chemical signalling systems between cells Facilitates coordinated contractions
oUp regulation of oxytocin receptors in each myometrial cell Myometrium more sensitive Fergusons reflex: contractions fetal head presses on the cervix release of oxytocin from posterior pituitary gland contractions (positive feedback loop)
Theories of how labour is initiated
- Theories:
* Mechanical • Hormonal • Prostaglandins • Neurological • Other
Mechanical initiation of labour
- Uterus grows and stretches detected by stretch receptors in the wall of the uterus critical degree of stretch contractions
- Contractions are caused by stimulation of the cervix – pressure from presenting part
Hormonal initiation of labour
oJust before labour level of progesterone decreases and oestrogen levels rise Stimulates production of prostaglandins from the placenta Decidua and membranes also produce prostaglandins
oOxytocin is released from the posterior pituitary gland
oCombined action of oxytocin and prostaglandins brings about uterine contractions.
Placental Oestrogen levels increase in the last few weeks (Jackson, Marshall & Brydon 2014) Oestrogen thought to stimulate:• An increase in oxytocic receptors in myometrium • An increase in gap junctions in myometrium • Placenta to release prostaglandins leading to production of collagenases –digest collagen in cervix-help to soften (Tortora & Grabowski 2011) Balance between oestrogen and progesterone facilitates myometrial activity Fetal membranes Involved in the synthesis of Prostaglandins Decidua Gustavvi theory (1977) . Decidual cells responsible for production of prostaglandin
Prostaglandin initiation of labour
- Reduction of prostaglandins inhibiting substances prior to term
- Facilitates liberation of calcium ions from intracellular stores in myometrium – increases cell contractile activity
- In cervix facilitates production of enzymes reduce collagen by digestion glycoaminolcans increases cervical ripening
Other theories of how labour is initiated
oNeurological element- maybe determined by the 1st trimester
oOestrogen synthesis may be mediated by fetal adrenal gland activity
Cortex – produces different hormones at different stages of pregnancy 3rd trimester produces cortisol – associated with the maturation process (fetal lungs)
Fetal theory–Hypothalamus/pituitary /adrenal axis
?Onset due to ACTH from fetal pituitary leading to:
1. Increase in fetal cortisol from the fetal adrenal glands. Converts progesterone to oestrogen. Increases uterine sensitivity to prostaglandins and oxytocin Stimulates release of prostaglandins from placenta and myometrium
2. High concentrations of oxytocin found in umbilical circulation. Thought to arise from the fetus and transferred to maternal circulation to induce labour.
However fetal death/ brain /adrenal malformation does not prevent labour
oTime of onset of labour may be determined by the release of corticotrophin-releasing hormones (CRH) CRH is released from the hypothalamus and produced by the placenta
oMaternal levels of CRH begin to rise before the onset of labour CRH stimulates production of prostaglandins by the placenta and potentiates the effect of oxytocin and prostaglandins
oImmune response
oPlacenta produces: Cytokines- cells of immune system communicate Interleukin 8 (IL8) – inflammatory mediator attracts neutrophils to local areas local inflammation
oImmune rejection theory Placenta rejected like a donated organ During pregnancy progesterone facilitates a degree of immunosuppression
oNitric Oxide
Placenta produces nitric oxide Nitric Oxide maintains relaxation of uterus during pregnancy Reduction of Nitric Oxide at term increases the excitability of the uterus.
Hormones involved in labour
Progesterone Oestrogen Prostaglandins Oxytocin Endorphins Adrenaline/ Noradrenaline
How long does labour normally last?
• The duration of established labour varies from woman to woman, and is influenced by parity. • Progress is not necessarily linear. • In established labour, most women in their first labour will reach the second stage within 18 hours without intervention. • In their second and subsequent labours, most women will reach the second stage within 12 hours without intervention.
Working together?
slide 28
How does uterine activity give the pushing power aspect of labour?
oMyometrial tone must change to allow co-ordinated contractions of the myometrial body
oWeak, irregular contractions build up to 3-4 contractions every 10mins. They become strong and last around 1min.
oFundal dominance – contractions begin at the cornua and remain strongest at this point. They spread out and down towards the lower segment in waves.
Polarity in labour
- Upper and lower poles of the uterus work in unison.
- The upper pole contracts and retracts whilst the lower pole dilates allowing expulsion of the fetus.
- The upper segment of the uterus thickens and shortens propelling the fetus downwards.
Normal muscle contraction vs uterine/myometrial muscle contraction
Normal muscle
Contracts and relaxes Returns to the original size E.g. biceps in the arm
Uterine/myometrial muscle
Contracts and retracts Does not return to its original size Permanent partial shortening of muscle fibres Remain shorter than they were originally Resting tone 4-10mmHg
Effacement
oThe gradual merging of the cervix into the lower uterine segment convert the cervix from a function of support into the function of a birth canal.
o Effacement usually occurs before dilatation on a primigravida. oProstaglandins implicated- change the collagen content of the cervix.
effacement in primigravida compared to effacement in a multigravida
slide 37/38 use panopto
Dilatation during labour
oIncreased pressure from the presenting part is said to aid dilatation Ferguson’s Reflex
oCrucial that regular contractions are co-ordinated with cervical dilatation
o10cms is considered to be ‘full dilatation’ when the largest diameter of the presenting part can pass through.
Fergusons reflex
slide 40
What happens to the mucus plug during dilation of the cervix?
- As the cervix dilates the plug of mucus (Operculum) comes away.
- This may be streaked with blood.
- Not always indicative of the imminent onset of labour
Factors hat affect dilatation of the cervix during labour?
oAs the lower uterine segment stretches, the chorion becomes detached.
oThe well flexed head fits snuggly against the cervix trapping a small pocket of fluid = forewaters.
oThe remaining fluid remains behind the fetus = hindwaters.
oFetal axis pressure is exerted down the long axis of the fetus from the fundus ensuring flexion.
o The smallest circumference is evenly applied to the cervical os.
possible include slide 43
Spare
spare
What might be the effects of labour on the mothers physiology?
slide 47