BIOL30001 Reproductive Physiology

PlacentationGeoff Shaw

Reading:EssRep7 Ch 13 (+ Ch 14,15)Johnson & Everitt 6 Chapter 10, 11, 12Stevens 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

euth

erian

s

mar

supia

ls

mon

otre

mes

rept

iles

amph

ibian

s

fish

multiple evolution

inver

teb.

Role of placenta• Nutritive exchange

– 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)

trophectoderm

trophectoderm chorionic ectoderm

extraembryonic ectoderm

extraembryonic mesoderminner cell mass extraembryonic endoderm (pluriblast) embryonicectoderm

mesoderm

endoderm

chorion and placenta

amnion

yolk sac and allantois

embryo and fetus

also see EssRep7 13.1

mesoderm

epiblast

hypoblast

Formation of extra-embryonic membranes

EssRep7 13.1

extra-embryonic coelom

pro-amniotic cavity

pro-embryonic disc

yolk sac cavity

Formation of extra-embryonic membranes

extra-embryoniccoelom

embryonic disc(embryonic ecto-, meso- and endo-derm

amniotic cavity

amnion

chorion

developing chorio-vitelline placenta

yolk sac

EssRep7 13.1

Formation of extra-embryonic membranes

J&E – 10.8

chorio-allantois

allantoisallantoic mesoderm

chorion

regressing yolk sac

primitive umbilical cordextra-embryoniccoelom

amnioticcavity

embryo

EssRep7 13.1

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

discoid,eg. human, mouse

zonary,eg dog

cotyledonary,eg sheep, cow

diffuseeg. pig, horse, camel

see J&E6 - 10.5

Grosser’s classification: placental typesFetal

Maternal

epithelio-chorial

synepithelio-chorial

endothelio-chorial

haemo-chorial

humandoghorse sheep

see J&E6 – 10.6

Placental blood flow -- human

EssRep7 13.4

haemochorial

EssRep7 13.3

basal decidua

Cast of fetal placental capillary bed

see EssRep7 13.5

Placenta of sheep

EssRep7 13.3

synepithelio-chorial

EssRep7 13.3

fetal chorionic epithelium

binucleate cellmicrovillus junctional zonematernal syncytium

maternal capillary

Placental Hormones• hCG

– 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

oestrone

oestradiol

oestriol

testosterone

placental steroidogenesis – e2

Johnson & Everitt 6, Fig 11.3

steroidogenesis in pregnancy is a combination of maternal, placental and fetal activity

see Johnson & Everitt Table 12.1

pH 7.4

pH 7.3 pH 7.2

pH 7.4

consumes 30% of O2 supplied

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

EssRep7 14.5

Ut Art

Ut Vein

Umb Vein

Umb Art

pH 7.43

pH 7.2 pH 7.26

pH 7.35

• Fetal haemoglobin• Bohr effect – pH

change as CO2 ex-changed increases O2 transfer

note: placenta highly metabolically active – uses 30% of O2 supplied

BODY

FO

LUNG

PLACENTA

DA

Lung is fluid filled and has low O2. It has constricted arterioles restricting blood flow

Most blood shunts through foramen ovale and ductus arteriosus.

oxygenated blood draining from placenta mixes with depleted blood from body

Circulation before birth

BODY

FO closes

LUNG

DA closes

Oxygen opens capillaries in lung increasing blood flow

increased oxygenation of blood in ductus arteriosus causes contraction and closure

increased flow into Left Atrium closes flap over Foramen ovale

Circulation after birth

Johnson & Everitt Fig 12.5

indicator of lung surfactant production

Actions of fetal adrenal glucocorticoids

lung surfactant; water resorptioncentral respiratory mechanisms

metabolism glucose storage and gluconeogenesis

endocrine induced insulin secretioninduced adrenaline secretionconversion of T3 to T4placental steroidogenesis

blood switch from fetal to adult haemoglobinswitch 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