reproductive physiology Flashcards
The placenta in materno-foetal exchange
- development & structure of placenta
- modes of transport across the placenta
- transport of O2/CO2 Na+, Ca+, glucose, amino acids, proteins
Functions of the placenta
- protection from the mothers immune system
- nutrition, gas exchange, excretion organ of homeostasis – maintains the foetus
- hormone secretion maintains HCG levels
Communication between conceptus and mother
- implantation: physical and nutritional contactmust be established to nourish embryo
- presence of foetus signalled to maternal pituitary-ovarian axis
^ to prevent more follicles being stimulated, if corpus luteum dies before placenta is ready then this could result in menstruation/miscarriage - placenta takes over at 6-12 weeks - hence communication is essential to maintain pregnancy
Development of placenta
(see diagram)
- Day 1-3 Zygote moves down fallopian tube to uterus
- Day 3-6 Blastocyst formation in uterine fluid
- Day 7 Implantation of blastocyst in endometrium, changes at site of implantation
- Day 7 onwards placenta forms– Must be completely self-sufficient by week 12
Blastocyst parts:
* trophoblast– outer mass becomes placenta
Syncytiotrophoblast: invades endometrium
Cytotrophoblast: stem cell lining of syncy
* pluriblast – inner mass, becomes embryo
Implantation:
Syncytiotrophoblast invades endometrium
Embryo capillaries persist in this region
No mixing of maternal and foetal blood
At week 10 near complete appearance of foetus
Early umbilical present
* syncytiotrophoblast becomes chorion
* chorionic villi project into pools of maternal blood
* chorionic villi contain capillaries supplied by umbilical artery
* placental sinuses receive blood from uterine artery
* there is no mixing of maternal & fetal blood
Transport across the placenta
*simple diffusion – lipophilic low molecular weight
*facilitated diffusion – carrier system required on both sides
*active transport – requires energy
*endocytosis, exocytosis – collected from mother (endo) released to foetus (exo)
see diagram:
1) hydrophillic substance – almost none crosses syncy
2) lipophillic substance – crosses relatively easily syncy
Oxygen is moved from mother to foetus and CO2 back to mother.
Gas exchange: oxygen and carbon dioxide
gas exchange: oxygen
Oxygen is moved from mother to foetus and CO2 back to mother.
*Diffusion down concentration gradient from mother to foetus
*Aided by
–different O2-hb dissociation curves
–effects of CO2
–Bohr effect
*Oxygen transfer will always favour direction to foetus
Gas exchange: Carbon dioxide
*CO2 transported in blood
*diffuses across placenta from foetus to mother
*diffusion aided by
–improved ability of deoxy hb (haemoglobin) to form carbamino compounds
–improved ability of deoxy hb to take up H+
Water transport mother-foetus
Water transport
*Normally net movement is 20-25ml mother-foetus
*mother and foetus in osmotic balance
*physiology of control poorly understood – but not osmosis
–haemolytic disease of foetus leads to inc feotal venous
pressure and hyponatraemia
–no net loss of fluid from foetus generally
Hydrops fetalis condition causes foetus to absorb water indefinitely and swell up with water – a foetus with this condition usually will not carry to term – new research has found surgical introduction of drainage tubes into the foetus allow it to carry to term Find name in recording
Transport of sodium mother-foetus
*membrane limited passive diffusion
*some active transport
*maternal venous plasma slightly lower Na+ than foetal
*Na/K ATPase especially on foetal surface of placental membrane
(no electrical gradient across placenta)
*Na+/H+ exchange and Na+/aa co-transport
Ca transferred by carrier mediated transport
Transport of glucose mother-foetus
*Facilitated diffusion:
–2 carriers
–Na+ independent
–maximal rate of transport exceeds foetal requirement (baby always gets enough glucose)
–net transfer dependent on materno-foetal concentration difference
–importance of maintaining high maternal glucose
Gestational diabetes can cause macrosomia (very large baby)
Late stage of pregnancy insulin tolerance develops
Transport of immunoglobulins mother-foetus
Any small lipophillic molecule can be transferred to the foetus impacting development long-term – including chemicals from alcohol, smoking recreational and prescribed drugs.
*transport from maternal to foetal blood
*receptor mediated endocytosis on maternal side
*exocytosis on foetal side
*e.g. immunoglobulin G important for passive immunity (added benefit comes from breast feeding)
Events leading to parturition
10cm dilation of cervix required for delivery
Estimated delivery date is 40 weeks from last missed period
Labour overview:
*Stage 1: increased uterine contraction, cervical dilation
*Stage 2: complete dilation of the cervix to delivery of infant
*Stage 3: delivery of placenta
Ferguson reflex: Cervix dilation due to foetal distension triggers neuroendecrine response resulting in oxytocin production – positive feeling
Changes associated with parturition
*Softening and dilation of the cervix – to allow for dilation
*Marked increase in uterine contractions
Incompetent cervix can occur – the cervix stays open slightly leaving the internal environment open to infection and can cause loss of pregnancy
*Cervical ripening: Softening and shortening
*Achieved by cervical recomposition: breakdown of collagen, increase in water content
*Regulation of changes: prostaglandins (local inflammatory), leukotrienes, oestrogen, relaxin (relaxes collagen
Changes leading up to labour (pre-labour)
*increase in uterine activity, contractions and sensitivity to oxytocin
*increasing number of gap junctions between myometrial cells – means more facility for contraction
The uterus is a smooth muscle which always contracts (you don’t notice it)
At 28 weeks braxton hicks contractions begin approx. 0.3 contractions per hr at 40 weeks 2.3 contractions per hour – check in recording
Factors stimulating uterine contractions
(see diagram)
*Increased uterine activity: increase in electrical activity
*PgE2, PgF2a, oestrogen
*Source of prostaglandins: amnion and endometrium, inc pgE2 receptors in myometrium
*Oxytocin: increases force and frequency of contraction of uteri which are already contracting, drives parturition once started
Just before baby is born levels of progestrone drops for increased responsiveness to oxytocin (and oestrogen increases no. Of oxytocin receptors)
Removing CRH ends pregnancy in sheep
In humans anencephalic (without skull) baby can result – can carry to term
