08. Pregnancy and Lactation

• the embryo produces hcg at implantation - analogue of lh
• hcg acts on lh receptors to maintain corpus luteum (progesterone) and stimulates DHEA production in the fetus
• progesterone is initially produced by the corpus luteum but this is taken over by the syncytiotrophoblast at 6-8 weeks
• progesterone maintains the decidua and decreases myometrial contractility

  • inhibits lactogenic effect - inhibits lactation during pregnancy
• progesterone is conjugated to sulphate and so is inactive in the fetus
• oestrogens increase throughout pregnancy and are produced cooperatively by placenta and fetus
• oestriol production predominates during pregnancy
• oestrogen stimulates release of prolactin

  • reduces peripheral glucose uptake to leave more available for the fetus
• hpl is produced by the syncytiotrophoblast and rises as hcg falls

  • development of mammary glands
  • suppresses insulin - increases blood glucose levels for fetus
• glucose is metabolised to lactate which is used as an energy source for the fetus
• prolactin rises linearly during pregnancy

  • oestrogen stimulates release from lactotroph cells
• parturition = birth
• parturition:

  • increase in oestrogen and decrease in progesterone
  • oxytocin -> contractions
  • prostaglandins

  requires initiating signal, coordinated muscle contraction and cervical softening and dilation
• progesterone suppresses myometrial contractions during pregnancy, but this decreases at birth

  • increasing oestrogen:progesterone -> oxytocin receptor levels increaSE
• at birth there is an increase in prA and prC receptors and a decrease in prB receptors
• cortisol leads to lung maturation in the fetus -> synthesis of surfactants

  • dexamethasone given in pre-term labour to increase this
• fetal glucocorticoids and CRH increase at term
• CRH and increasing oestrogen:progesterone at birth leads to arachidonic acid release -> prostaglandins

  • cause cervical remodelling
  • keratin sulphate replaces dermatan sulphate, this doesn't bind to collagen causing softening
  • increased MMP production
• oestrogens are the main stimulators of oxytocin synthesis

  • oxytocin is released in response to tactile stimulation of the cervix -> babies head pushing on cervix -> oxytocin -> more contractions -> more pressure -> more oxytocin
• oestrogen increases the size and number of ducts in the breast
• progesterone increases the number of alveolar cells in the breast
• prolactin levels increase with gestation and promote milk production

  • decrease shortly after birth so lose ability to breastfeed if you don't
• suckling increases prolactin and oxytocin release