Reproductive Endocrinology 2 Flashcards
Where does fertilisation occur?
Within the fallopian tubes
What happens to the egg post-fertilisation?
Becomes a zygote, the a morula, then a blastocyst. The blastocyst implants between days 5-9 (it ‘bounces’ around the womb for a while)
Implantation
Blastocyst edge with inner cell mass closest to endometrium begins to grow into uterine lining
Trophoblast cells start dividing rapidly and form syncytiotrophoblast and cytrotrophoblast
Syncytiotrophoblasts
Secrete hCG (human choronicgonadotrophin), which acts like LH and maintains the corpus luteum -> corpus luteum secretes progesterone and oestrogen until placenta takes over -> endometrial lining is maintained; no menstruation
hCG
This is the hormone tested for in pregnancy tests
It’s responsible for morning sickness
Main roles of the placenta
Endocrine organ of pregnancy
Major hormonal contributor of the 1st trimester
Takes over from corpus luteum at week 10 to produce hCG, progesterone, and oestrogen
Other roles of the placenta
Site of active and passive exchanges of gases, nutrients, and waste between maternal and foetal bloodstreams
Maternal and foetal blood interaction
Don’t actually come into contact with
Can be different blood groups without one having a reaction to the other
HIV isn’t usually passed on maternally
Progesterone
“Pro-gestation” -> pregnancy hormone
Suppresses uterine contractions
Maintains endometria lining
Develops ducts in mammary glands for milk ejection
Production proportional to placental weight
Oestrogen
Placenta lacks enzymes for de-novo oestrogen synthesis so relies of DHEA from foetus -> converts DHEA into oestrogen
Causes growth of the myometrium (for labour contractions)
Development of ducts in mammary glands
Other placental hormones
Placental Lactogen (stimulates mammary glands & supplies energy to foetus)
Parathyroid hormone RP (Increases blood Ca2+)
Relaxin (softens cervix and weakens pubic symphysis)
Corticotropin releasing hormone (pressure, blood glucose, stimulates parturition)
Pelvis
Made of 3 bones usually tied tightly together, but loosened in pregnancy to help baby’s head through -> can cause abdominal and lower back pain for pregnant people
What is parturition?
Labour
3 stages of parturition
Dilation
Expulsion
Placental
Dilation stage
Onset of labour
Cervix is dilating & thinning
Membrane rupturing -> water breaking
Expulsion stage
Cervix dilates to 10cm
Contractions reach maximum
Baby is delivered
Placental stage
Uterine contractions detach the placenta from the endometrium and placenta is expelled
Initiation of labour - CRH
Corticotrophin releasing hormone (CRH) is produced in the placenta and released into materna blood, levels rise exponentially towards term -> in the foetus, acts on foetal adrenal gland to release DHEA, which is the precursor for placental oestrogen
This may be a placental clock?
Initiation of labour - oestrogen
Promotes increased sensitivity of the myometrium to oxytocin and increases its excitability via gap junctions
Allows coordinated contraction of smooth muscles of myometrium
Initiation of labour - progesterone
No decrease in P4 levels in humans until after birth
BUT there is potentially a ‘functional’ progesterone withdrawal involving changes in receptor expression
Labour and uterine contractions
At first contractions last about 30 seconds and happen every half hour, and towards the end are last 1-2 minutes and happening every 2-3 minutes -> +ve feedback loop with oxytocin
Neroendocrine (Ferguson) reflex
Stretching of the cervix causes nerve impulses sent to brain stimulating posterior pituitary production of oxytocin, further stimulating contraction and enabling labour to progress.
Labour positive feedback loop
Oxytocin causes uterine smooth muscle to contract -? Baby pushes against cervix causing it to stretch -> stretching of cervix causes nerve impulses to be sent to the brain -> brain stimulates posterior pituitary to release oxytocin
Breast anatomy
Pectoris major
Fat pad
Suspensory ligaments
Glandular tissue
Milk duct
Nipple
Areola
Breast anatomy - glandular tissue
Epithelial alveoli -> milk-secreting cells
Mypepithelial cells
Lactation
Prolactin -> milk production and secretion
Oxytocin -> milk ejection
Lactation - prolactin
Produced by anterior pituitary lactotropes
Induces lobuloaveolar growth of the mammary gland -> Alveoli secrete milk
Stimulates lactogenesis (milk production)
Targeted deletions of PRL gene in mice cause failure to lactate after pregnancy
High levels supresses FSH and LH release -> (natural contraceptive?)
Progesterone also inhibits lactogenesis
Lactation - oxytocin
Induces milk let down (ejection) from the aveolar and ductal lumen
Contracts myoepithelial cells
Released from posterior pituitary in response to suckling at the nipple -> Neuroendocrine reflex
Targeted deletions of OXT or OTR gene in mice causes failure to lactate after pregnancy
(but they still successfully deliver their offspring AND on time!)
What hormone could be used to help labour is it is to progressing well; contactions are infrequent, weak, and lacking coordination?
Oxytocin (Synthetic oxytocin = syntocinon)
What could be administered for a preterm birth where contractions appear too early in pregnancy and there is a risk to life?
oxytocin receptor antagonist (tractocile)
Nb -> might not actually work for more than a few days, but can give time to get pregnant person to the right specialist place to give birth early
