Flashcards in Parturition &lactation Deck (28)
- Process of giving birth 'to be in labour'
-Involves softening & effacement of the cervix and development of uterine contractions( rupture of membranes not essential)
Outline the stages of labour
1.) INITIAL (LATENT) PHASE: Contractions develop, cervix softens &effaces (days)
2.)ACTIVE PHASE: Regular contractions (~3 every 10mins) & steady dilation of the cervix (~3-4cm to 10cm)
3.)STAGE 2: cervix fully dilated-10cm; strong propulsive contractions 1-2hours
4.) STAGE 3: placenta delivered (oxytocin important)
What else may be given to a woman if oxytocin is insufficient in delivering the placenta
-Clinically women may be given ergotocin & oxytocin mix to allow artificial contraction of the uterus in case the oxytocin is insufficient
Describe the quiescent stage of pregnancy
-During this stage the cervix &membranes are intact
-Closed cervix maintains pregnancy and acts as a barrier to ascending infection
-The cervix is elastic tissue with some smooth muscle; collagen fibres in a proteoglycan matrix
-There is also epithelia cell lining and a mucous plug
Outline the preparation of the cervix& fetal membranes for labour (activation and stimulation)
-PGE2 is used for induction. This causes membrane weakening and rupure, causing cervix ripening to begin and allowing the cervix to dilate
-iNOS, COX-2, prostaglandin production (PGE2), matrix metalloproteinases 2&9(these break down the collagen), cytokines and immune cells
-Cervix softens and more likely to dilate/efface; ready for labour
What instigates the inflammatory process?
Hormone changes: functional progesterone withdrawal---> inflammation &influx of immune cells,increased corticotrophin releasing hormone & oestrogen, plus cervical distension ---> oxytocin--->PGR (Ferguson reflex)
How is the myometrium prepared for pregnancy?
-At the quiescent stage the myometrium is dense smooth muscle cells embedded in connective tissue & well vascularised. It is sparsely innervated in pregnancy
-To get to the activation / stimuation stage....
-There's induction of 'contraction associated proteins; prostaglandin receptor COX-2, oxyotcin receptor, gap junctions (connexins), calcium signalling proteins & ion channels
-Myometrium primed for contraction
-activation with some uterine activity
powerful effective contractions stimulate it
What causes preparation of the myometrium for pregnancy?
-function progesterone withdrawal-inflammation &influx of immune cells
-prostaglandins from the fetal membranes
What is Nifedipine used for in labour
-used to treat pre-term labour
-It is an L-type ca2+ channel blocker so targets the voltage gated ca2+ channels to stop contraction
How does the contractile interval change during pregnancy?
-Decreases as the woman comes to term
How does the resting membrane potential change during pregnancy?
-Gets less negative so it's more likely to be excited and more likely to contract at the end of pregnancy
What is the clinical application of PGE2?
-Used to ripen the cervix
Outline the functions of gap junctions& connexins in pregnancy
-Gap junctions made from connexin proteins(Cx)
-Cx43 & Cx26 up-regulated during labour---> allows for better transmission of signals between cells
Increased gap junctions results in:
-More powerful contractions
Outline the role of oxytocin in labour
-Important uterotonin in labour
-Increased uterine sensitivity to oxytocin at term
-Increased expression of oxytocin receptor mRNA & protein towards term and peak after onset of labour
Which hormone is thought to be the placental clock?
-As the placenta matures it starts pumping out CRH
Why must time of delivery be relatively tightly controlled?
-Babies need to be born at the right time as if not the mother will no longer be able to provide adequate support
-The placenta ages over time so there will be a risk of insufficient nutrients
-All the babies are delivered by 42 weeks, as if not then medical intervention would result
What initiates/times labour in humans ?
-Fetal HPA axis involvement, but progesterone drop not apparent. Evidence for 'functional' progesterone withdrawal
-Increasing oestrogen concentrations
-Anecephaly& fetal adrenal gland hypoplasia association with prolonged gestation
Describe the circulating placental steroid hormone levels during pregnancy in humans
-Steady rise in Estradiol (E2) across gestation
-Steady rise with plateau at term in progesterone
-Steady rise in human placental lactogen
-No decrease in progesterone at term
Outline the Ferguson reflex(PGR)
-A neuro-endocrine reflex
-A +ve feedback mechanism involving oxytocin
-Estrogen from ovaries--> Induces oytocin receptors on uterus---> stimulates placenta to make---> prostaglandins which stimulate more contractions of uterus---> positive feedback causing oxytocin release
-Oxytocin from fetus and mother's posterior pituitary stimulates the uterus to contract
-Initiated by pressure at the cervix or vaginal walls
List the important signals in human parturition
-Fetal hypothalamus activity increases--> increased CRH production--> increased ACTH production
-Fetal adrenal gland increases cortisol & dehydroepiandrosterone sulphate (DHEAS)
-Increased placental CRH & Estrogens
-Reduced progesterone responsiveness ( increased PRA:PRB ratio)
-Fetal membranes increase COX-2 and increase prostaglandin production
What is the function of DHEAS?
-Can get over to the placenta
-Gets converted to oestrogen
When do the lobules/alveoli grow for milk production
-They grow during early pregnancy to make more milk-producing cells
-Human alveoli adequately differentiated to produce milk from 16 weeks gestation & prolactin is being produced
-But full lactation doesn't occur until post partum period
Outline how milk is pushed to the nipple
Milk production--- Baby suckles--- contraction of myoepithelial cells around the alveoli--- pushes the milk to the nipple
Describe the hormonal changes that occur at the onset of lactation
-Prolactin is secreted from 16 weeks but breast tissue is unresponsive due to a steroid block
-Withdrawal of oestrogen & progesterone are essential
-Prolactin also drops (suppressed by oestrogen & progesterone) but a steady production maintained (if no suckling-small amount of milk produced 3-4weeks)
-Suckling ensures prolactin secretion; full lactogenesis
What is the link between prolactin & VIP
VIP is a prolactin releasing factor
What is the link between prolactin & dopamine?
Dopamine is a prolactin inhibitory factor
How does suckling ensure milk production?
1.) Neuroendocrine reflex
-Stimulates production of Vasoactive Intestinal Peptide
-Reduces dopamine release
3.) Strength &duration of suckling determines amount of prolactin released from the anterior pituitary
-This determines amount of milk made to be available for subsequent feeds