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
What do relaxants (Tocolytic agents) do?
Reduce freq & force of contractions
What are the 2 types of relaxants (Tocolytic agents)?
- β2-adrenoreceptor agonists
- Magnesium ions
When are β2-adrenoreceptor agonists used as relaxants (tocolytic agents)?
- No evidence for differences between agonists
- Contraindicated in women with heart disease and eclampsia and use with caution in diabetic mothers
When are Magnesium ions agonists used as relaxants (tocolytic agents)?
Used in pre-eclampsia to alter cerebral blood flow and lower incidence and severity of condition
What are the clinical uses of relaxants (tocolytic agents)?
- Delay or prevent premature parturition –> up to 7 days
- Slow or arrest delivery to undertake therapeutic measures
What is used to inhibit lactation?
- Estrogen
- Progesterone
What is used to stimulate lactation?
- Prolactin
- Oxytocin
What are the 2 components of lactation?
- Colostrum
- Later milk
What is colostrum?
- Watery milk produced 1st few days after birth
- Proteins, few nutrients
What is later milk?
Nutrients, growth factors, hormones & antibodies
Defo worth looking at the mammary glands diagram
Thanks
What does prolactin stimulate?
Stimulates milk synthesis
What does oxytocin stimulate?
Stimulates the milk ejection reflex
Control of lactation diagram pls
Too complex to write on here
What are the advantaegs of breast feeding for the mother?
- Oxytocin release hastens uterine involution (around 4 weeks in lactating mother, 6 weeks otherwise)
- Suckling surpresses menstrual cycle by inhibitn LH & FSH secretion
How does suckling surpessing the mestrual cycle benefit the mother?
- Acts as natural contraceptive (though not reliably!)
- Directs mothers resources to newborn
How does the cessation (stopping) of milk production at weaning happen?
- Absence of suckling, prolactin secretion is not stimulated
- No suckling leads to no oxytocin release –> therefore no milk letdown
- Milk production does not immediately shut down, so pressure builds in alveoli (further stimulus to suppress milk production)
How does the absence of suckling, leading to no stimulation for prolactin secretion cease milk production?
Removes the main stimulus for continued milk synthesis & secretion
