1. 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

2. 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.

3. 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?

4. fetal membranes and placentation - complex endpoint …
… but really arises from a series of simple steps, like origami

5. 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

6. Formation of extra-embryonic membranes
pro-amniotic cavity
extra-embryonic coelom
pro-embryonic disc
yolk sac cavity
EssRep7 13.1

7. 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

8. 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

9. 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

10. Major placenta types zonary, discoid, eg dog eg. human, mouse diffuse
eg. pig,
horse,
camel
cotyledonary,
eg sheep,
cow
see J&E

11. Grosser’s classification: placental types
Fetal
horse
sheep
dog
human
epithelio-
chorial
synepithelio-
chorial
endothelio-
chorial
haemo-
chorial
Maternal
see J&E6 – 10.6

12. Placental blood flow -- human
haemochorial
EssRep7 13.4

13. basal decidua
EssRep7 13.3

14. Cast of fetal placental capillary bed
see EssRep7 13.5

15. Placenta of sheep
synepithelio-chorial
EssRep7 13.3

16. EssRep7 13.3 fetal chorionic epithelium binucleate cell
microvillus junctional zone
maternal syncytium
maternal capillary
EssRep7 13.3

17. 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

18. placental oestrogens
testosterone
oestrone
oestradiol
oestriol

19. placental steroidogenesis – e2
steroidogenesis in pregnancy is a combination of maternal, placental and fetal activity
placental steroidogenesis – e2
Johnson & Everitt 6, Fig 11.3

20. consumes 30% of O2 supplied pH 7.4 pH 7.4 pH 7.2 pH 7.3
see Johnson & Everitt Table 12.1

21. 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

22. 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

23. 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.

24. 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

25. indicator of lung surfactant production
Johnson & Everitt Fig 12.5

26. 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

27. 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