Cervix, vagina, uterus, stages of labour
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From where does the vagina receive its main blood supply?
Uterine arteries & veins
What are the 3 main functions of the vagina?
- Passageway for elimination of menses
- Receives penis during sexual intercourse and holds semen prior to its passage into uterus
- Forms inferior part of birth canal
What separates the vagina from the anal canal?
How long is the vagina?
7.5 - 9cm long
What is the vaginal space surrounding the cervical protrusion called?
How big is the uterus?
- 7.5cm long
- 5cm wide
- 2.5 cm deep
Name the ligaments of the uterus.
- Uterosacral ligaments
- Broad ligaments
- Round ligaments
- Lateral cervical ligaments
- Suspensory ligaments
Name the three layers of the uterus.
- Endometrium - glandular inner layer next to uterine cavity
- Myometrium - bigger middle layer containing muscles needed to contract
- Perimetrium - membranous outer layer
From where does the uterus get its blood supply?
Uterine arteries which rise from branches of internal iliac arteries
What are the four main functions of the uterus?
- To prepare to receive fertilised ovum
- To provide a suitable environment for growth and development of the embryo and fetus
- To assist in explusion of fetus, placenta and membranes at birth
- For involution following birth, preventing haemorrhage
How does the uterus grow during pregnancy?
Initially by hyperplasia (cell division) then subsequently by hypertrophy (cell growth) stimulated by uterine distension. Walls of the uterus thin to accommodate contractile proteins
What are the two segments of the uterus called?
- Upper (formed of body and fundus)
- Lower (formed by ithsmus & cervix)
What are the factors that govern uterine contractions?
- Fundal dominance/polarity - upper segment of uterus contracting longer than lower segment
- Contraction/retraction - when contracting, uterine cells never completely return to pre-contraction phase
What are the actions of the uterus during pregnancy & labour?
- Exhibits spontaneous contractility, inhibited by progesterone during early stages of pregnancy
- From around 7 weeks of pregnancy, contractions are unsynchronized and irregular with low frequency and low intensity
- From around 20 weeks of pregnancy, contractions increase gradually until around 6 weeks pre-term when intensity increases more markedly, causing Braxton Hicks, which are strong but irregular and not normally painful as cervix remains closed
- During labour, contractions are synchronized, regular and increase in frequency and intensity as it progresses
What is the cervix?
'Neck of the uterus' made up of connective tissue and collagen fibres which resists dilatation during pregnancy
What is the length of the cervical canal?
- 3-5cms in early pregnancy
- 2-3cms in late pregnancy
What is the portion of the cervix that protrudes into the vagina called?
What is the passage between the internal and external os called?
What is the portion of the cervix exterior to the external os called?
What percentage of the cervix is smooth muscle?
What are the functions of the cervix?
- Provides lubrication for vagina
- Produces mucus to help sperm movement
- Protects uterus & contents from infection
- Retains fetus in uterus throughout pregnancy
- Dilates & effaces to permit passage of fetus through birth canal at term
Which hormones promote ripening of the cervix towards at term?
Oestrogen & relaxin
What two proteins interact to cause contractions?
Actin & myosin
What regulates the action of actin and myosin?
Calcium ions released from sarcoplasmic reticulum into intracellular space in myometrial cells
How do contractions work?
- Oxytocin stimulates release of calcium from sarcoplasmic reticulum into intra cellular space
- Calcium activates actin and myosin crossbridges to pull against each other
- Cell shrinks (contracts)
- Calcium pumped back into sarcoplasmic reticulum
- Muscle relaxes
Where are contractions the strongest?
At top of fundus and electrical activity spreads to bottom of uterus
What two membranes make up the amnotic sac?
- Amnion (fetal side)
- Chorion (maternal side)
What are the functions of the amniotic sac?
- To aid cervical dilatation & effacement
- To create equal pressure on fetus during contractions
- Prevents cord compression
- Maintains constant temperature for fetus
How long following a spontaneous membrane rupture (breaking waters) should intervention be considered?
What are the responses of the fetus during labour?
Continuing pressure on head causes fetal heart rate to drop. A healthy baby should bring its heart rate back to normal following a contraction
What is the 'Ferguson reflex'?
The urge to bear down/push due to continued pressure of baby on cervix
What happens to the pelvic organs during the second stage of labour?
- Bladder is pushed up into abdominal cavity
- Rectum is compressed causing bowels to empty
- Levator ani muscles are separated and thinned
- Perineal body is flattened and elongated
What is the second stage of labour defined as?
Begins at full dilatation and ends with the birth of the baby
What is the 'Rhombus of Michaelis'?
The kite shaped area consisting of three lower lumbar vertebrae and sacrum being pushed out by the descent of the fetus to increase space. This may or may not be visible during second stage
What is the normal blood flow through the placenta during pregnancy?
500-800mls per minute
Describe the stages of placental separation during the third stage of labour.
- Retraction of the uterus causes clamping of maternal blood vessels
- Veins in decidua become tense and burst
- Villi collapse as blood is released
- 'Living ligatures' retract and seal off vessels
- Blood vessels collapse & blood tracks between decidua & placenta, completing separation
What signs do you look for to indicate successful separation of the placenta from the uterine wall?
- Lengthening of the umbilical cord
- Trickle of fresh blood
- Fundus becomes rounder and more mobile
What are the consequences of early cord clamping?
- Lower bilirubin level - cause jaundice in newborn
- Reduction of oxygen flowing from placenta to baby
- Reduction of baby blood volume
What is the Schulze method of the third stage of labour?
When placental separation occurs centrally forming retro-placental clot which aids in the separation of lateral borders of placenta
What is the Matthews Duncan method of the third stage of labour?
When placental separation occurs at the lateral borders of the placenta first, causing ragged membranes and a higher blood loss. This is uncommon.
How is the third stage of labour actively managed?
- Syntometrine (5IU synto, 0.5IU ergo)
- Syntocinon (10IU)
- Ergometrine (usually given with Synto)
- Controlled cord traction (CCT)
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