BIOL30001 Reproductive Physiology Placentation Geoff Shaw Reading: EssRep7 Ch 13 (+ Ch 14,15) Johnson & Everitt 6 Chapter 10, 11, 12 Stevens DH (1975) “Comparative Placentation” Renfree MB (1982) Implantation and placentation. In Austin & Short: Reproduction in mammals, Book 2. Mossmann HW (1987) “Vertebrate fetal membranes” This illustration was made by Luc Viatour http://commons.wikimedia.org/wiki/File:Da_Vinci_Studies_of_Embryos_Luc_Viatour.jpg
Viviparity - birth of live-young advantages - fetal development & survival requires specialised maternal-fetal interface - placenta fetal and maternal components exchange of gases, nutrients & wastes hormones limits fetal invasion immunological interface multiple evolution marsupials monotremes amphibians eutherians reptiles fish inverteb.
Role of placenta Nutritive exchange Hormones Immunological interface histotrophic vs haemotrophic gas: O2 and CO2 sugars, amino acids, lipids etc waste products, eg. urea Hormones maternal recognition of pregnancy uterine contractility and secretion modulation of maternal and fetal physiology Immunological interface fetus has “foreign” paternal genes MHC etc so fetus is an allograft. Why isn’t it rejected by an immune response?
fetal membranes and placentation - complex endpoint … … but really arises from a series of simple steps, like origami
Formation of extra-embryonic membranes (mouse/human) epiblast hypoblast mesoderm trophectoderm trophectoderm chorionic ectoderm extraembryonic ectoderm extraembryonic mesoderm inner cell mass extraembryonic endoderm (pluriblast) embryonic ectoderm mesoderm endoderm chorion and placenta amnion yolk sac and allantois embryo and fetus also see EssRep7 13.1
Formation of extra-embryonic membranes pro-amniotic cavity extra-embryonic coelom pro-embryonic disc yolk sac cavity EssRep7 13.1
Formation of extra-embryonic membranes amniotic cavity embryonic disc (embryonic ecto-, meso- and endo-derm amnion chorion extra-embryonic coelom yolk sac developing chorio-vitelline placenta EssRep7 13.1
Formation of extra-embryonic membranes chorio-allantois chorion amniotic cavity allantois allantoic mesoderm primitive umbilical cord extra-embryonic coelom regressing yolk sac EssRep7 13.1 J&E – 10.8
Classification of placentation Tissues chorio-vitelline chorio-allantoic macroscopic structure microscopic relationship between fetal and maternal tissues - invasiveness non-invasive eg pig, horse, sheep, cow invasive - eccentric eg. dog, rat, rabbit invasive - interstitial eg. human
Major placenta types zonary, discoid, eg dog eg. human, mouse diffuse eg. pig, horse, camel cotyledonary, eg sheep, cow see J&E6 - 10.5
Grosser’s classification: placental types Fetal horse sheep dog human epithelio- chorial synepithelio- chorial endothelio- chorial haemo- chorial Maternal see J&E6 – 10.6
Placental blood flow -- human haemochorial EssRep7 13.4
basal decidua EssRep7 13.3
Cast of fetal placental capillary bed see EssRep7 13.5
Placenta of sheep synepithelio-chorial EssRep7 13.3
EssRep7 13.3 fetal chorionic epithelium binucleate cell microvillus junctional zone maternal syncytium maternal capillary EssRep7 13.3
Placental Hormones hCG hPL (hCS) Progesterone & oestrogen- LH activity - maintains CL immune suppression hPL (hCS) prolactin / growth hormone activity increased breakdown of adipose tissues Progesterone & oestrogen- modulates endometrium: MRP; implantation; secretory activity; immunological modulation; etc. suppresses gonadotrophins myometrium; mammary development maternal amino acid metabolism see also EssRep7 13.7
placental oestrogens testosterone oestrone oestradiol oestriol
placental steroidogenesis – e2 steroidogenesis in pregnancy is a combination of maternal, placental and fetal activity placental steroidogenesis – e2 Johnson & Everitt 6, Fig 11.3
consumes 30% of O2 supplied pH 7.4 pH 7.4 pH 7.2 pH 7.3 see Johnson & Everitt Table 12.1
Placenta Placental transfer placental metabolism 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
Umb Art Ut Art Umb Vein Ut Vein Fetal haemoglobin pH 7.43 pH 7.35 Umb Art pH 7.2 pH 7.26 Fetal haemoglobin Bohr effect – pH change as CO2 ex-changed increases O2 transfer note: placenta highly metabolically active – uses 30% of O2 supplied Ut Art Umb Vein Ut Vein EssRep7 14.5
Circulation before birth oxygenated blood draining from placenta mixes with depleted blood from body Lung is fluid filled and has low O2. It has constricted arterioles restricting blood flow FO LUNG BODY PLACENTA DA Most blood shunts through foramen ovale and ductus arteriosus.
Circulation after birth increased flow into Left Atrium closes flap over Foramen ovale Oxygen opens capillaries in lung increasing blood flow FO closes LUNG BODY DA closes increased oxygenation of blood in ductus arteriosus causes contraction and closure
indicator of lung surfactant production Johnson & Everitt Fig 12.5
Actions of fetal 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 fetal 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
Summary – Placenta structure and function nutrition, gas exchange, hormones, immune control folding and budding yolk sac (choriovitelline) allantois (chorioallantoic) morphology: discoid, zonary, cotyledonary, diffuse Grosser’s classification by degree of invasion: epitheliochorial haemochorial sophisticated countercurrent blood flow mechanisms hormones – gonadotrophins, lactogens, progesterone, oestrogens fetal gas exchange – fetal haemoglobin shift of circulation at birth from placental to lung gas exchange role of glucocorticoids in fetal ot neonatal transition