Reproduction 4 Flashcards
How long does pregnancy last?
40 weeks
What is parturition?
Birth
What is lactation?
Milk production in mammary glands
What are the stages of parturition?
Positioning of the fetus:
* Head-first on the cervix
At 37 weeks only 5% are still in feet-first position (breech):
* Half of these will ‘kick’ themselves around once labour start
How long does the first stage of labour last?
Up to 24 hours
What are the 2 main steps in the first stage of labour?
- Dilation of the cervial canal to accomodate fetus
- Inc myometrial contractions to exel the fetus - 30 min interval & 30s duration
What happens during dilation of the cervical canal to accomodate fetus (first stage of labour)?
- 10 cm dilation of the cervix required to accommodate the head
- As the fetus ‘bears down’ head-first on the cervix, amniotic sac is ruptured
- ‘waters breaking’
- serves to lubricate the cervical canal
What happens during the increasing myometrial contractions to expel the fetus (first stage of labour)?
(30 min interval and 30s duration)
- Braxton-Hicks contractions increase in frequency and force during 3rd trimester
- in 1st stage of labour the contractions become more coordinated and stronger
What happens in the second stage of labour?
- 30-90 minutes duration
- Cervical dilation is complete
- Head of fetus activates cervical stretch receptors to synchronise abdominal and uterine contractions –>3 minute intervals, 60s duration
- Baby is delivered connected to umbilical cord –> Cord is tied, then severed
What happens in the third stage of labour?
- (30 min post-partum)
- Second series of myometrial contractions expel the placenta - the ‘afterbirth’ —> continued contraction of the myometrium prevents excessive haemorrhage
- loss of the placenta causes a major fall in maternal progesterone and estrogen levels
What is the main fetal response to parturition?
Inspiration of air following delivery, it has 2 concequences;
- Elevated levels O2 in fetal circulation
- Fetal supply of O2 to placental cirulation
What happens when levels of O2 in fetal circulation elevate in the fetal response to partuiton?
Increased production of vasoconstrictor prostanoids leads to closure of the ductus arteriosus
What happens to fetal supply of O2 to placental cirulation in the fetal response to partuition?
Induces prostanoid vasoconstriction of placental blood vessels - contributes to third stage of labour
What are the stages of parturition?
1 - End of pregnancy - cervix ripens
2 - Beginning of partuition –> cervix dilates, labour (uterine contractions)
3 - Babies head wedges cervix open - baby born head first
4 - Expulsion of placenta = afterbirth
Please look at the diagram on the regulation of partuition
It is a +ive feedback loop
What is known about the trigger for partuition?
Unkown, but current throty suggests signal comes from fetus
What are the triggers for partuition that are known?
- Fetal placenta = CRH –> fetal ACTH –> DHEA
- DHEA -> estrogens = Enters maternal blood stream
- Estrogen -> parturition
What is the role placental Cortiotophin Releasing Hormone (CRH)?
- Regulate fetal adrenal production of DHEA sulphate and increases estrogen levels
- Evidence for CRH receptors regulating sensitivity of myometrium to other agents
When do placental levels of Cortiotophin Releasing Hormone (CRH) increase?
Placental levels increase during the pregnancy and levels at 16 weeks predicts duration
The placenta (and not the hypothalamus) is the principal source
Descibre the pharmacology of pregnancy:
- Uterine muscle characterised by high degree of spontaneous electrical and contractile activity
- can be modified by humoral and neuronal factors
- spread of excitation occurs via low resistance contacts (gap junctions) between cells - creates a functional syncitium
- Therapeutic agents either increase intracellular calcium (spasmogen) or cyclic AMP (tocolytics)
What is the role of spasmogens?
In force & frequency of contractions
What are the spasmogens involved in birth & what do they do?
Oxytocin
* Given by slow infusion to titrate dose - intense contractions are sometimes precipitated which requires fetal monitoring
Prostaglandins F2∝ and E2
* Intravaginal tablets produce localised action which limits side effects - also used to ‘ripen’ cervix
What are the slincal uses of spasmogens?
- Induce or augment labour
- Control post-partum uterine haemorrhage
- Induce therapeutic abortion
What sort of pregnancies are spasmogens used to induce?
Post-term pregnancies, near-term pre-eclampsia, active management of labour
