lecture 16: placentation Flashcards Preview

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Flashcards in lecture 16: placentation Deck (17):

What is viviparity?

  • birth of live-young 
  • advantages – foetal development and survival 
  • requires specialised maternal-foetal interface – placenta 
    • foetal and maternal components 
    • exchange of gases, nutrients, and wastes 
    • hormones 
    • limits foetal invasion 
    • immunological interface 


What is the role of placenta?

  • nutritive exchange 
    • histotrophic vs haemotrophic (cells or blood)
    • gas: O2 and CO2
    • sugars, amino acids, lipids etc 
    • waste products, e.g. urea 
  • hormones 
    • maternal recognition of pregnancy 
    • uterine contractility and secretion 
    • modulation of maternal and foetal physiology 
  • immunological interface 
    • foetus has "foreign" paternal genes → MHC etc so foetus is an allograft. why isn't it rejected by an immune response?


How do we get formation of extra-embryonic membranes (mouse/human)?

  • trophectoderm → chorionic ectoderm →  chorion and placenta 
  • inner cell mass:
    • embryonic ectoderm, mesoderm, endoderm → embryo and foetus
    • extraembryonic ectoderm → amnion, chorion and placenta   
    • extraembryonic mesoderm → yolk sac and allantois, amnion 
    • extraembryonic endoderm → yolk sac and allantois 
  • endoderm surrounding a cavity - (yolk sac cavity) 
  • mesoderm spread all the way around 
  • pro-amniotic cavity 
  • extra-embryonic coelom 
  • in most eutherian mammals the yolk sac will regress, lose its main function, come away from the coelom 
  • formation of allantois → forms about the time when the mesonephric kidney starts to function 
  • embryo inside amniotic cavity 
  • connected via primitive umbilical cord to chorio-allantois (future placenta) 


What is the classification of placentation?

  • tissues 
    • chorio-vitelline
    • chorio-allantoic 
  • macroscopic structure 
  • microscopic relationship between foetal and maternal tissues – invasiveness 
    • non-invasive e.g. pig, horse, sheep, cow 
    • invasive - eccentric e.g. dog, rat, rabbit
    • invasive - interstitial e.g. human 
  • placentation evolved in lots of different types of mammals at lots of different times 


What are the major placenta types?

  • discoid, e.g. human, mouse 
    • single disc in which the foetal and maternal blood come together 
  • zonary, e.g. dog 
    • donut around the uterus 
  • cotyledonary e.g. sheep, cow 
    • lots scattered over the uterine placenta 
    • sub placentas 
    • in each one is foetal and maternal tissue 
    • interdigitate 
  • diffuse e.g. pig, horse, camel 
    • interactions all over the surface 


What is Grosser's classification of placental types?

  • horse: epithelio-chorial 
    • non-invasive 
  • sheep: synepithelio-chorial 
    • slightly invasive - part of maternal tissue lining has been eroded 
  • dog: endothelio-chorial 
    • syncytial structures forming 
  • human: haemo-chorial 
    • very invasive 
    • syncytium 
    • pool of blood 
    • large blood sinuses with foetal villi dangling in them


What is the placental blood flow in the human?

  •  blood flow is clearly vital to the functioning of the placenta 
  • maternal blood spaces → foetal tissue going into that → connected via umbilicus to the embryo 
  • maternal spiral arteries: blood vessels that supply the placental surface, very distinctive anatomical structures 


What is seen when you make a cast of foetal placental capillary bed?

  • very dilated capillaries 
  • drive blood at reasonably high speed, high pressure into these capillaries which are close to the maternal system 
  • hits this big space 
  • blood goes slowly, spends time there, exchange
  • gets carried back by narrow vessels 


What is the placenta of sheep?

  • synepithelio-chorial
  • maternal tissue forming a cup around the foetal tissue 
  • tissue with maternal blood vessels interdigitating with tissue with foetal blood vessels 
  • counter-current exchange 
    • maternal and foetal flow going in opposite directions


What are placental hormones?

  • hCG
    • LH activity - maintains CL
    • immune suppression 
  • hPL (hCS)
    • prolactin/growth hormone activity 
    • increased breakdown of adipose tissues 
  • progesterone and oestrogen 
    • modulates endometrium: MRP; implantation; secretory activity; immunological modulation; etc 
    • suppresses gonadotrophins 
    • myometrium; mammary development 
    • maternal amino acid metabolism 


What are placental oestrogens?

  • oestrone
  • oestradiol 
  • oestriol 
  • converted from androgens e.g. testosterone via aromatase 
  • different number of alcohol or ketone groups 
  • oestradiol is potent 
  • oestrone and oestriol are weak but present in large amounts so that balances up 


In what way is steroidogenesis in pregnancy a combination of maternal, placental and foetal activity?

  •  production of progesterone in the placenta which goes through the maternal system 
  • DHA - a weak androgen from the maternal adrenals → androgens → testosterone 
  • oestradiol, oestrone, progesterone → acting on mother 
  • some of progesterone and pregnenolone goes in the foetal system 
  • foetal liver making oestriol  → placenta → maternal circulation 
  • urinary tests for oestrogens can tell you a lot
  • if oestriol levels are lower than normal often a sign that the foetal liver is not forming as it should → sign the foetus is not doing well 


What is the placental exchange membrane?

  • consumes 30% of O2 supplied 
  • uterine artery supplying freshly oxygenated blood 
  • in through placental exchange 
  • loses oxygen, picks up CO2 
  • coming out with reduced oxygen and increased CO2 
  • umbilical artery supplying deoxygenated blood to the placenta
  • picking up oxygen 
  • not very high percentage oxygen 
  • it works
  • placenta is highly metabolic so it requires a lot of the oxygen 
  • foetuses have a form of haemoglobin that can grab oxygen from the maternal system 
  • haemoglobin in the face of acid tends to release oxygen 


What is the metabolism of the placenta?

  • placental transfer
    • main energy from glucose and lactate in humans 
    • active transfer of specific materials – amino acids, lipids, vitamins, etc 
  • placental metabolism 
    • uses 30% of glucose and oxygen supplied by mother 
    • highly active in protein synthesis 
    • conjugation and inactivation of maternal hormones 
  • foetal haemoglobin 
  • bohr effect - pH change as CO2 exchanged increased O2 transfer 
  • note: placenta highly metabolically active - uses 30% of oxygen supplied 


What is circulation before birth?

  • lung is fluid filled and has low oxygen 
  • it has constricted arterioles restricting blood flow 
  • oxygenated blood draining from placenta mixes with depleted blood from body 
  • most blood shunts through foramen ovale and ductus arteriosus 
  • functionally running on a two chambered heart 


What is circulation after birth?

  • oxygen opens capillaries in lung increasing blood flow 
  • increased flow into Left Atrium closes flap over Foramen ovale 
  • increased oxygenation of blood in ductus arteriosus causes contraction and closure 
  • standard four chambered heart : left and right side
  • placenta gone 


What are the actions of foetal adrenal glucocorticoids?

  • lung: surfactant; water resorption, central respiratory mechanisms 
  • metabolism: glucose storage and gluconeogenesis 
  • endocrine: 
    • induced insulin secretion
    • induced adrenaline secretion 
    • conversion of T3 to T4 
    • placental steroidogenesis 
  • blood
    • switch from foetal to adult haemoglobin 
    • switch haematopoiesis to bone marrow
  • salt balance: stimulation of GFR and Na+ resorption, ? activation of ANF
  • lactogenesis: ductal-lobule-alveolar growth in pregnancy