MFWB_A - Mammal Reproduction - Viviparity, Placentation and Pregnancy

oviparous

lay eggs

viviparous

give birth/internal eggs

patrotrophy

males take eggs in brood pouch, cost usually higher for females so male investment offsets, mostly in seahorses, maybe Darwins frog in vocal sack

dolphin pregnancy cost

increase body girth, increases drag, therefore slower swimming

elephant seals cost of pregnancy

spend their gestational period in ocean, duration of foraging dives decrease, due to high foetal oxygen demand

prototheria

monotremes, 5, oviparous, no placenta

metatheria

marsupials, 335, viviparous, chorio-vitelline placenta

eutheria

placental mammals, ~6000, viviparous, mostly chorio-allantoic placenta, loss of many egg-linked genes

diversification of eutherian mammals

linked with increase in oxygen levels ~50 mya, driven by diversification of diatoms

cleidoic eggs

protective shell, membranes develop into placenta - vitellus (nutrients) and allantoic (gas exchange and waste storage), amnion protective fluid, chorion protects amnion

chorio-allantoic placenta

fusion of chorion, allantoic and uterus

chorio-vitelline placenta

large yolk, attaches to chorion then uterus, offspring born altricial, external gestation continues, unable to provide enough nutrients for entire pregnancy

how is maternal blood shared with the foetus

via intervillus space

epitheliochorial placenta

horse, cow, dolphin, blood vessel in mother and foetus, interface across epithelium and trophoblast walls

endotheliochorial placenta

fox, cat, aardvark, outer layer of uterus removed, still enclosed blood vessels

haemochoral placenta

primates and rodents, maternal blood vessels open to chorion, cytotrophoblast (super cell with many shared nuclei), ancestral state, only kind able to transfer antibodies to foetus

early microaerobic life

spinal arteries blocked until second trimester, oxygen to foetus is low, conversion of maternal spinal arteries to low pressure, high capacity flaccid conduits, foetus requires strong anti-oxidant defences to deal with strong increase in blood oxygen

placental functions

transfer glucose from mother to foetus as gluconeogenesis inactive until birth, almost impermeable to lipids, long chain fatty acids transferred during last ten weeks of pregancy

trans-placental gas exchange

maternal pulmonary ventilation increases by 40%, CO2 decreases by 25%, oxygen diffused across placenta, production sites of metal erythrocytes change (yolk sac, liver, spleen then bone marrow), composition of haemoglobin subunits change

trans-placental immunoglobulin

only with haemochorial placenta, IgG, small amount of antibodies produced at birth, 60% of adult levels at 12 months

immune tolerance

placenta release chemicals to prevent killing from immune system of mother, trophoblast cells display limited MHC, sanction prevents migration of immune cells from mother to foetus